Nam Nao National Park


The Caves of Nam Nao National Park,





Between December 2003 and January 2006 there have been four Shepton Mallet Caving Club expeditions to the Nam Nao National Park in Phetchabun province. A total of ten weeks have been spent in the field exploring and surveying the caves.  The longest cave in the national park, Tham Yai Nam Nao, has been surveyed to a length of 9.8km.  Several other major caves have been found including Tham Phaya Naak/Tham Wi Mahn Mek/Tham Nop Pa Krauw (1,285m, -133m), Tham Bah Dahn (655m) and Tham Monhwa (350m).  




This report is dedicated to the memory of David 'Fig' Briggs.




After three expeditions to Umphang in Tak province on the western border of Thailand with Myanmar, between 2000 and 2003, the Shepton Mallet Caving Club started looking for another area to explore.  It must be admitted that we were also looking for a more 'civilised' area with decent hotels, a variety of restaurants and a more lively night life.


John Dunkley's 'Caves of Thailand' book was consulted along with a list of Thailand's longest caves.  It was noted that Tham Yai Nam Nao in the Nam Nao National Park had not had a follow up trip since the original exploration in 1992.  We had already been caving in this region on our first Thailand expedition in February 2000 and again in February 2002.  Although Tham Yai Nam Nao had not been visited we had been to the other well-known cave in the Park, Tham Par Hong.  In addition we had stayed at the hotel in Lom Sak and knew that access to the park was fairly easy.


We had intended for our first visit, in December 2003, to be part of a reconnaissance of the whole Phetchabun Mountain range from Nam Nao National Park in the north to Khao Yai National Park (Nakhon Ratchasima province) in the south.  However, Tham Yai Nam Nao and the surrounding hills were found to be so promising that we stayed here for the duration of our visit.  This first trip was quickly followed by another visit in April 2004 and a month long expedition in January 2005.  The most recent trip has been in January 2006 and we now feel that enough work has been done to justify publishing this detailed report.


This report includes information on all the caves, stream sinks, digs, etc. that we have found on the expeditions.  General information on the Nam Nao National Park, accommodation, noodle shops, etc. is also given, but it should be remembered that this sort of 'guidebook' information soon becomes out of date.


Nam Nao National Park


The Nam Nao National Park is located in the north of Phetchabun province.  It is about 400km north of Bangkok and 75km from Laos.  The park covers 966 square kilometres and was designated on the 4 May 1972.  The park straddles the watershed between north-central Thailand (the Pa Sak River basin) and north eastern Thailand (Mekhong River basin). Its part of the Phetchabun Mountain range that runs south from Phu Luang mountain in Loei province and forms the border between Chaiyaphum and Phetchabun provinces. The park headquarters are located about 50km east of Lom Sak on the H12 road.  This has a small museum and library, administrative buildings, the usual food stalls, a campsite and there are several bungalows that can be rented. 


The National Park is part of the 5,948 square kilometre Western Isaan Forest Complex of eight contiguous protected areas.  This area stands out as being the only sizeable expanse of closed forest remaining in the region. The protected areas are the Phu Kheio, Tapo-Huay Yai, Phu Pha Daeng and Pha Phueng Wildlife Sanctuaries and the Tad Mok, Nam Nao, Phu Pha Man and Phu Kradung National Parks.


At 1,271m Khao Phu Phajit is the highest mountain in the Park. There are many rivers and streams within this important watershed area.  The Pa Sak River (which flows south through Lom Sak and Phetchabun town) is one of these and it eventually joins the Chao Phraya River in Ayutthaya before flowing into the Gulf of Thailand just south of Bangkok.  Other important rivers are the Pong and Loei rivers (which flow north from the park) and the Khon Kaen and Nam Churn rivers (which flow east into the Ubonrat Dam). All these rivers eventually join the Mekhong River which flows into the South China Sea in Vietnam.


The mountains and forests create a cooler climate in the Park, particularly during the night and early morning. The daytime temperatures are very pleasant with an average annual temperature of 25°C. The rainy season is between July and October. The cold season can be very cold (for Thailand), sometimes even with a frost and temperatures as low as 0°C. The coldest month is November.  We have experienced comfortable temperatures of 20-25°C in January, but in April it has been 30-35°C and occasionally hotter. 


The forest of Nam Nao contains many different forest types, including dipterocarp, deciduous, evergreen, hill evergreen and pine forest. The karst areas we have been exploring, in the north of the Park, are mainly open bamboo and dipterocarp forest.  In the bottom of the dolines there are often old signs of agriculture such as banana plantations.  In the past the forest has been commercially exploited.

The forest structure within Nam Nao provides good shelter for 120 mammal species, including elephant, marbled cat, Asiatic black bear, Malayan sun bear, tiger, leopard, Asian jackal, Lar gibbon, fox, porcupine, wild pig, guar, mouse deer and rabbits. These are distributed throughout the park. The last sighting of rhinoceros in Thailand was in the neighbouring Phu Kheio Wildlife Sanctuary in 1979.  The signs of elephants (dung, knocked over trees and footprints) are commonly found in the area we have been exploring.  Wild elephants have been seen twice and heard once.  The first incident was when elephants were heard in Doline 725 which was nicknamed 'Elephant' doline as a result.  The following year two people on foot got within 20m of an elephant before seeing it, but fortunately it ran away.  Finally an elephant was seen after dark beside the H12 road near the Park headquarters and it was possible to get within 5m of this animal.  The monk's campsite at Tham Nop Pa Krauw was destroyed by elephants one night in 2005 and they were also heard here by the monks in 2006.

There are 203 confirmed species of birds in the park. It is claimed that when walking the trails you are likely to see birds such as parrots, hornbills, warblers, babblers and siamese firebacks. However, we have found the forest to be very quiet and little bird life has been seen by us.  Three hundred and forty or so butterfly species are reported to have been found in the park. These have not been studied by us, but several large Troides birdwing butterflies were seen flying along the stream in the 'Elephant' doline.


The Park is under pressure from the surrounding villages. The hills to the north of the park, along the H2216 road, have been completely cleared of forest and are used for growing maize, cabbage, etc.  This clearance has been carried out by Thais rather than hilltribes such as the Hmong.  The clearance probably began in the 1970s when the road was constructed, forest was cleared and people were settled in the area to deny the region to the Communist insurgents.  The nearby Pha Luang (to the north) and Phu Hin Rong Kla and Khao Kho mountain ranges (to the west of the Pa Sak valley) were Communist strongholds until the early 1980s.  Local farmers also hunt within the park boundaries.  We have found a muzzle-loading rifle hidden amongst limestone rocks in the Park and one farmer, met at a nearby noodle shop, admitted hunting birds within the Park boundaries.  There are indications that there used to be agriculture in the Park with old banana plantations in the floors of Doline 715 and 'Banana' doline and degraded cart tracks.  The only agricultural activity we have seen are cows and buffalo being grazed at the edges of the park and in the 'Banana' doline.  In the dry season there are often fires which clear the dry bamboo leaves from the forest floor without causing too much destruction to the rest of the vegetation.  It is not known if these fires are set by villagers or are caused naturally.


Accommodation and General Information


Although Tham Yai Nam Nao is easily accessible by road it is unfortunately a long way from the nearest town.  The Shepton Mallet Caving Club expeditions have been based in Lom Sak which is a 75km (one hour) drive from the cave.  In Lom Sak there is one 3 star hotel, the Nattirat Grand Hotel, which charges 695 baht per room (January 2006). This price doubles over the New Year and Songkran holiday period and pre-booking is advised at these times.  The Nattirat is located on the road heading north towards Loei.  The hotel is a soul-less place to eat and drink, but fortunately there are good restaurants, a karaoke bar and a 'singing girls' bar ('nak rong pu ying') close by.  Be warned that an evening spent in the karaoke or singing girls bar can make the next day's caving hard work.  Lom Sak is a fairly large town with many other eating places, markets, newsagents (the English language papers arrive around 13:00), hospital, etc. There is a direct bus service to Bangkok which costs 250 baht one way.


Outside of Lom Sak there are a couple of 'resorts' on Khao Khor and one near Lom Kao, but these tend to be a lot more expensive, are remote from the town's attractions and are even further from the caves. There are hotels on the other side of the mountains in Chumphae, but these are further away than Lom Sak and the access roads are even worse.


Another option is to turn up with a cool box of food and ask in the villages near the cave if anyone has a spare room or house.  This requires some proficiency in spoken Thai, but you are almost certain of finding lodgings.  We were offered the chance to stay at a farm by someone who we met in the noodle shop.  Although staying locally would save a lot of driving it must be remembered that the accommodation will be fairly primitive (squat toilets, cold water showers), you will have to be on your best behaviour and the village is likely to be completely dead after 9 pm.


Somewhere between Tham Yai Nam Nao and Ban Nam Nao there is a 'campsite'.  This is actually a small resort with some basic bungalows available to rent. I have seen the website and have a business card for the resort, but have not managed to work out exactly where it is.  A final possible source of accommodation is the National Park headquarters on H12 where there are tents and bungalows available.  These are almost certainly going to be fully booked at busy holiday times and the Park headquarters is considerably further by road from Tham Yai Nam Nao than the hotel in Lom Sak.


To reach Tham Yai Nam Nao from Lom Sak you need to turn left out of the Nattirat Grand Hotel and head towards Loei.  This road, the H201, is a fairly fast road with perhaps half of it being dual carriageway.  A few kilometres north of the town the Lom Sak bypass road joins from the left and there is a petrol station just before the dual carriageway ends. After passing the small town of Lom Kao the road is mainly single carriageway with a lot of agricultural traffic.  About 10km north of Lom Kao a turning on the right is a quiet 'short cut' to the H2216 which goes to Tham Yai Nam Nao.  However, as this turning is hard to differentiate from the other junctions it is probably best to keep on the H201 to where it becomes a dual carraigeway again.  Here there is a large junction with the road becoming very wide. 


At this large junction the H2216 is on the right and Tham Yai Nam Nao is signposted. There are several stores at this junction including a shop selling snacks, beer and whisky and a hardware store that sells 12v 'caving' lamps, digging implements, bailer twine and wellington boots. About 5km along the H2216 there is a petrol station and this is the last proper petrol station before Tham Yai Nam Nao.  However, there are a couple of 'barrel and pump' petrol vendors in the villages along the road.  These villages also have the usual noodle stalls and small general shops.


Although some maps show a route from the H2010 near Lom Sak going almost directly to the Tham Yai Nam Nao area this road is still a dirt track that is very rough in places and takes nearly three times longer to drive compared to going via the H2216.


As you enter the village of Ban Non Chat from the Lom Sak direction the road to Tham Yai Nam Nao is on the right.  It is signposted and has a yellow, concrete filled, oil drum in the centre of the junction.  Opposite this junction there is a basic restaurant selling noodle and rice dishes, beer, etc. that we have frequently patronised after our caving trips.  On the other side of the road, beside the junction, there is another noodle shop.  At Tham Yai Nam Nao there is a car parking area and the ranger station.  The accommodation here is very basic and the rangers do not have any spare rooms.  There is a camping area down beside the stream, but apart from the toilets there are no facilities here.  During busy holiday times there are a couple of stalls selling basic food dishes and drinks. At other times there is nothing at the ranger station.  However, the rangers have frequently invited us to join them for aprés-caving drinks and food.  In return they are happy to receive a box of Chang beer or bottle of whisky.


History of Exploration


As is usual in Thailand the large, dry caves in the National Park have been known to the local inhabitants since the clearance and settlement of the area.  The caves have been used as shelters while on hunting trips in the forest, the guano is mined for use as fertiliser or as a source of saltpeter for making gunpowder and bats would have been hunted within the caves.  Tham Yai Nam Nao has a large Buddhist shrine near the entrance and several of the caves in the park have been, and still are, used by wandering 'thudong' meditation monks.  Monks still frequently camp at Tham Nop Pa Krauw and use Tham Phaya Naak for walking and sitting meditation.  The report of the 1992 expedition records that monks were living at the entrance to Tham Yai Nam Nao, but by 2003 they had moved out. As part of their meditation practices and due to natural curiosity the monks would have explored many of the caves and evidence was found which showed that they had reached the end of the 1992 Series in Tham Yai Nam Nao. The table belows shows how many of the caves had been visited and explored before our expeditions. Caving aids include bamboo ladders, bridges and poles used to help explore the caves.



Caving aids


Meditation walkway



Tham Yai Nam Nao






Tham Pha Rai






Tham Phaya Naak






Tham Nop Pa Krauw






Tham Wim Mahn Mek






Tham Bah Dahn






Tham Monhwa






Than Song Hong






Tham Par Hong






Tham Pha Pai






Tham Pak Now






Tham Pha Ruag






Tham Pha Hok






Cave 1






Cave 2






Cave 7






Cave 10






Cave 12






Cave 17






Cave 23






Cave 24






Cave 26








Prior to the Shepton Mallet Caving Club's first visit in December 2003 there had been one recorded visit by cavers to the Nam Nao National Park.  This was by a group of six British students from Sheffield and Manchester Universities in April 1992.  They had explored Tham Yai Nam Nao, Tham Pha Rai, Tham Phaya Naak and several other caves. However, their unpublished report did not give any detailed location descriptions or grid references. This was because they did not have detailed maps and were led into the jungle by guides.  After our visit in April 2004 we contacted Nick Standing who was on this 1992 expedition.  Nick supplied further unpublished information and some photographs which were very helpful in deciphering the 1992 report.


On the first Shepton Mallet Caving Club Thailand expedition in February 2000 we had stayed at the Nattirat Grand Hotel in Lom Sak on our way to Khon San in Chaiyaphum province.  The first cave we ever explored in Thailand was Tham Par Hong in Nam Nao National Park just off the H12.  On this first expedition we visited caves in Pha Phueng Wildlife Sanctuary and Phu Pha Man National Park, but didn't explore any more caves in Nam Nao National Park.


Tham Yai Nam Nao attracted our attention in 2003.  Thorough research did not reveal any speleological investigations since the 1992 British expedition apart from a paper in 2001 by Fontaine and Salyapongse which mentioned geological research on the limestones found on Khao Tham Yai. The basic information on Tham Yai Nam Nao in 'The Caves of Thailand' was intriguing and we sensed that there could be a lot more cave in this area.  At the very least we intended to obtain accurate location data for the caves and if possible to resurvey the caves.


The first visit was from 27 December 2003 to 12 January 2004.  Although we went straight to ThamYai Nam Nao our explorations were stopped by high carbon dioxide levels just past the show cave.  We then focused our attentions on the western edge of the Park.  Several walks resulted in us finding and exploring Tham Pha Rai, Tham Pha Hok, Tham Pha Pai, Tham Pak Now and various small caves.  By hiring a couple of rangers we were guided to Tham Song Hong and Tham Pha Ruag. Four days before the end of the expedition a return to Tham Yai Nam Nao revealed that the carbon dioxide level had dropped enough for us to access the rest of the cave.  In the last three trips we surveyed Tham Yai Nam Nao as far as the 'Y Junction' and the 2004 Series was explored to the upstream sump adding an estimated 2.5km to the length of the cave.


This expedition proved the potential of the Tham Yai Nam Nao area so it wasn't long before we were back and on 7 April 2004 two cavers were in Lom Sak.  Between 8 and 17 April the survey in Tham Yai Nam Nao was extended to 700m up the 2004 Series and the 1992 Series was explored to the ducks beyond the Boulder Chamber, rangers guided us to Tham Monhwa and some surface exploration was carried out.


The next major expedition was between 27 December 2004 and 27 January 2005 and a lot of work was carried out.  In Tham Yai Nam Nao the link to Tham Pha Rai was made, the survey of the 2004 Series was completed, the end of the 1992 Series was extended below the large gour to a chamber and the 1992 Series Inlet was pushed to a small entrance.  To the south of Tham Yai Nam Nao the complex of caves which includes Tham Bah Dahn, Tham Nop Pa Krauw, Tham Mi Mahn Mek and Tham Phaya Naak were explored and surveyed.  In addition Tham Monhwa was surveyed and there were numerous surface walks which discovered various stream sinks and small caves.


During the rainy season there was a solo trip to the Tham Yai Nam Nao streamway on 5 July 2005 to check on the water level.  The stream was of a similar size to that observed in January despite recent thunderstorms.  However, this was early in the rainy season and a visit in September or October would be needed to observe what would most likely be an impressive amount of water resurging from the cave.


The third expedition was in the Nam Nao National Park from 28 December 2005 to 5 January 2006.  Unfortunately high carbon dioxide levels prevented access to Tham Yai Nam Nao beyond the show cave.  Despite this set back the Tham Phaya Naak system was linked together via a series of pitches, Cave 14 was connected to Tham Yai Nam Nao and two stream caves were found, but not explored.





To explore caves in national parks in Thailand you should have permission from the Royal Forest Department in Bangkok.  When in the national parks it is illegal to collect specimens (including geological specimens) without specific permission and a full report and surveys should be sent to the Royal Forest Department and the national park headquarters as soon as possible after your visit. However, when in the field we have found that the local rangers have not asked for any written permits and have been very helpful.


We entered the Nam Nao National Park from four car parking places on the northern edge of the park.  The easiest starting point to find is the car park at Tham Yai Nam Nao.  The cave is well signposted, both from the H201 (Lom Sak – Loei road) onto the H2216 and from the other end at the junction between the H12 (Lom Sak – Chumphae road) and the H2216.  The turning to Tham Yai Nam Nao is about 60km from either end of the H2216 and is signposted.  From the H2216 road, by following the only surfaced road through the village of Ban Huai Lat, you soon reach the ranger station complete with picnic tables, toilets, etc.  From here Tham Yai Nam Nao and Tham Yai Nam Nao Resurgence are a short walk away.  We also walked from here to Tham Pha Ruag, Tham Song Hong and Tham Monhwa.


The second parking spot we used was halfway along a rough dirt track to the left (east) of the surfaced road.  This track turns off about 200m before the Tham Yai Nam Nao car park and has a large green sign at the start.  This car parking place is the most convenient one for the path to Tham Song Hong and Tham Monhwa.  The third car park is at the end of the track, turning right at the only junction to end up at an irrigated field which often has a crop of cabbages, hence our nick-name of ‘cabbage patch car park’.  From here a couple of good paths lead southwards into the forest.  This was the starting point for all the long walks into the jungle, the Tham Phaya Naak area and for Tham Pha Rai which is about 20 minutes walk away.  It is also possible to walk to Tham Song Hong and Tham Monhwa from here via Tham Pha Hok.


The parking place for Tham Pak Now is reached by taking the unsurfaced track to the right at the T-junction in Ban Huai Lat, turning left in the village to cross the concrete bridge and then follow the track through the fields.  The track skirts the western edge of the limestone hills and ends after about 1.5km.  It is then necessary to walk southwards into the forest along a good path which follows the stream.  By following the path past Tham Pak Now and ascending the hills to the east you reach the dolines with the 1992 Inlet entrance to Tham Yai Nam Nao and the 1992 Sink.


To get to Cave 1 and Cave 2 you need to turn left at the T-junction in Ban Huai Lat and then go straight on along a dirt track when the sealed road turns right towards Tham Yai Nam Nao. This dirt track is followed through the fields and over the rolling sandy hills towards the obvious limestone outcrops.  The car was parked at the closest point to the cliff.


Tham Par Hong and Cave 12 are in the central part of the national park.  They are very easy to find as there is a well signed car park on the H12 and a good track can be followed for the 200m to the cave.


Topography of the Tham Yai Nam Nao Area


We are fortunate in that we have 1:50,000 maps which cover the Tham Yai Nam Nao area, both the American Military series from 1969 and the Royal Thai Survey Department series from 1992. Unfortunately these 1:50,000 maps do not name many of the topographical features so we have had to give some of them our own nick-names.


There are seven large dolines in the area. In the list below the number is the lowest altitude in the doline as marked on the 1:50,000 map.


Doline 715 – The doline behind the cliff with the entrance to Tham Yai Nam Nao.

Doline 735a – 'Banana' doline. This is the doline with Tham Pha Rai.

Doline 735b – 'Elephant' doline. Tham Bah Dahn and Cave 25 are in this doline.

Doline 728 – This is a very large doline which curves around the hill with Tham Phaya Naak.

Doline 806 – The doline below Cave 11.

Doline 748 – 1992 Inlet entrance doline.

Doline 771 – 1992 Series sink doline.


The limestone forms only one massif in which the seven dolines are formed.  This massif has several peaks with the highest point being the 955m high Khao Tham Yai.  'Banana' and 'Elephant' Dolines and Doline 728 form the eastern edge of the massif with the eastern boundary of there dolines being sandstone hills.  The other dolines appear to be formed within the limestone. 


Between the dolines there are a series of steep sided ridges.  The only ridge that has been explored anywhere near completely is that running south-east from above Tham Yai Nam Nao to the Tham Phaya Naak area and which marks the eastern edge of the massif.  A few high level caves have been found near the top of this ridge such as Tham Pha Ruag, Tham Song Hong and Tham Pha Pai.  This 'Tham Pha Pai' ridge ascends to a summit and then splits with one ridge running south-west towards Khao Tham Yai and Tham Monhwa as well as continuing south-east.


The presence of dry stream beds which meander through the surrounding fields indicate that in the wet season several streams resurge along the north edge of the limestone massif. However, we have found only two perennial streams flowing north out of the limestone massif which are the Tham Yai Nam Nao resurgence and the stream which flows north past Tham Pak Now on the western edge of the hills.


Although not shown on the 1:50,000 maps there are seasonal and perennial streams sinking in all seven of the dolines.  The only perennial streams are those which flow off the high sandstone hills to the east of the park into 'Banana' and 'Elephant' dolines and Doline 728.  The streams sinking in the other dolines flow over limestone and have either no flow or very low flow in the dry season.


The Caves


Tham Yai Nam Nao System


Tham Yai Nam Nao ถ้ำใหญ่น้ ำหนาว

Tourist entrance: 47Q 0767316 1874832  Alt.: 693m

Second entrance: 47Q 0767329 1874822 Alt.: 711m

Bat entrance: 47Q 0767332 1874774                   Alt.: 729m

Cave 14 entrance: 47Q 0767954 1873736 Alt.: 740m

1992 Inlet entrance: 47Q 0767459 1872603          Alt.: 750m

Tham Pha Rai  ถ้ำป่ใร่

Stream entrance: 47Q 0768798 1874006  Alt.: 730m

Upper entrance: 47Q 0768805 1874000                Alt.: 738m

Other names: Wet Sink [1992 expedition]


Length: 9,817m (800m unsurveyed)  VR: 76m


This is the longest cave that has been found in the National Park and is now the third longest known cave in Thailand.  It is a popular tourist attraction and is clearly signposted from the H2216 in Ban Non Chat.  At busy holiday times there are stalls selling food and beer, but at other times there are just three or four rangers who are there to guide tourists into the cave.  The charge is 20 baht for a tour.  To just have the lights turned on for an unguided tour costs 10 baht. These rangers are also willing, for a suitable fee, to guide you to other nearby caves. We have paid 200 baht per man for guiding and have also donated boxes of Chang beer to the ranger station.  In return we have been encouraged to explore the caves and occasionally invited to join the rangers for post-caving drinks and food.  The rangers have been very interested in our explorations.


From the car park the path descends to and then crosses the stream which resurges from the cave.  The path then ascends to a shrine (note the cloth 'tungs' hanging from the cliff and the fortune telling sticks) and then up metal stairs to the 'Tourist' entrance.


Inside the cave a metal ladder and walkway soon leads to the 'Second' entrance.  By exiting the cave via this entrance it is possible to ascend the cliff past an unexplored cave entrance (which almost certainly links back into the main cave) and up to the 'Bat' entrance. Beyond the Second entrance the subtly lit 'Tourist Cave' follows a large fossil passage.  There is a bat colony in the big chamber where the 'Bat' entrance enters from high on the right. Beyond the bat chamber the cave has a few formations and then reaches a breakdown area with a series of high level passages ascending up on the right.  This area has not been fully explored or surveyed (there is perhaps 100m of passage up here), but daylight has been seen high up above a climb and a strong, cool draught comes down into the cave from up here.  After the breakdown area there is a mud floored chamber that funnels down to the left.  By descending this it is possible to go through a low, squalid, occasionally wet section to reach the bottom of the 6m ladder.  However, it is easier to follow the lit cave which ends at the top of the solidly constructed 6m metal ladder.  Descending the ladder leads to a series of smaller, muddy passages.  The main way on, marked with white paint arrows, is a short crawl on the right followed by some smaller passages with a second crawl.  Finally there is a flat out crawl of about 10m over mud which breaks out into a large passage with a mud and silt floor.


This large passage ends by descending a mud slope to a stooping and crawling height passage.  This area occasionally has a pool of water and can be prone to carbon dioxide build up – we recorded over 5% here on our first visit and this section was impassable. In January 2006 this section again had a pool of water and very high carbon dioxide levels making the rest of the cave inaccessible.  However, once past this low section you regain the large passage, named 'Main Passage' by the 1992 expedition, which meanders gently to the junction with the streamway.  The passage is floored with sand and dry mud which has created some large mudbanks.


At the streamway it is possible to climb down the 3m bank of cobbles and mud fill. It is also possible to reach the stream via the network of small passages on the left just before the climb.  Downstream enters a small passage with many cascades and deep pools, a couple of which can require swimming to cross in high water conditions, to end at a sump.  Upstream is a magnificently large streamway with a lot of cemented cobble fill on the walls and floor.  After 275m the passage makes a 90° turn to the south.  The passage changes character as the gradient is lower and more wading is required, often at stooping height.  It is possible to bypass one particularly low and wet section by taking a high level route on the left hand side.


Before reaching this high level bypass there is a small, insignificant inlet on the left hand (eastern) wall of the passage.  This starts as a flat out crawl over cobbles to a small chamber.  More crawling leads to a stream which disappears into a very small hole in the left hand wall.  The stream way continues as mostly crawling for a total of 300m to a wide pool with very limited airspace.  A gravel bank was dug out and the water level lowered.  Crawling through the duck for 50m leads into a high rift passage which is the end of Tham Pha Rai.  This cave is described after the Tham Yai Nam Nao description.


After the Tham Pha Rai inlet and high level passage you reach the 'Y Junction'.  The main stream comes in from under the left (eastern) wall and can be difficult to spot – it wasn't found by the 1992 expedition and the 2003 expedition walked past it twice before finding the duck under into the streamway.  This junction is clearly marked with a painted 'Y'.


This streamway, named the '2004 Series', was first explored by the Shepton Mallet Caving Club in January 2004. At the 'Y Junction' a short, wet crawl leads into larger passage where there is a short section of wading in deep water. The stream meanders across the floor of a fairly straight passage and there are extensive deposits of sand and mud. After 450m from the junction the roof lowers and more wading is required. The water gets steadily deeper until at 700m from the junction you are in water over 1.5m deep with only 20cm of airspace. The water soon gets shallower, but the low, wet crawling continues for another 200m until you reach larger passage and can stand up out of the water. This series of wet crawls ends in a very high rift passage. The passage is now easy going for about 400m to a dry oxbow on the left which is followed for 100m back to the streamway.  After the  oxbow the streamway continues for about 1.5km to the upstream sump and no side passages or inlets have been found (only two groups have been to the sump).  The going is mainly wading with varying water depths and one short swim.  In one section just before the sump the passage is up to 20m wide and 45m high and there are a couple of places where it is necessary to scramble over a boulder floor with the stream flowing below. Large numbers of medium sized bats have been seen in a couple of places in the 2004 Series suggesting that there are other entrances into this section of the cave.


The 2004 Series heads in a south-easterly direction and is a fairly straight passage with few meanders.  This trend follows the alignment of ridge of the mountain above the cave and is following the strike of the limestone's bedding.  The upstream sump is 300m from the stream in Cave 25 and the downstream sump in Tham Bah Dahn.


From the 'Y Junction' the other branch of the cave leads southwards and has been named the '1992 Series' as it was first explored by the student expedition.  In the dry season it does not have a stream for most of its length until you reach the 'Boulder Chamber'. After about 200m it is necessary to crawl through a low, muddy, sometimes wet, passage for about 100m.  Above this section there is a series of dry, boulder-filled chambers. Cave 14 was connected to Tham Yai Nam Nao just before this crawling section and is described below.  After the crawl the large passage is regained and it is mainly easy going for 500m to the 'Boulder Chamber' with just some crawls under boulders and flowstone to negotiate.  About 100m before reaching the Boulder Chamber there is a small series of side passages that has been used as a campsite by previous explorers, probably monks.


The Boulder Chamber is the second largest chamber in the cave (after the Bat Chamber in the Tourist Cave) and is a collapse feature on the left (eastern) side of the stream passage.  It is possible, with great care, to ascend the slope of boulders and debris to reach the back wall of the chamber, but the rock is heavily corroded and friable.  There didn't appear to be a passage entering into the roof of the chamber. There might have been a high level passage heading downstream, but access would have been via a very exposed traverse.


After the Boulder Chamber the stream passage becomes smaller and passes through a couple of small, decorated chambers.  Eventually you reach a duck.  This duck, and the three following ducks, are easily passed and the large main passage is rejoined. This 200m of passage is quickly traversed to end at a large gour that fills the passage.


About 50m before the gour there is a tall, vadose inlet passage on the right (western) side, named the '1992 Series Inlet'. The inlet passage is followed for about 400m to a boulder choke. The stream is regained beyond the choke and can be followed upstream to a 5m climb up a waterfall. This is free climbable, but a handline is advised. The water is then followed to a second boulder choke. The path of least resistance leads to a duck which may need bailing. Beyond the duck a crawl of 10m goes straight on and then sharp left to a squeeze. After the squeeze a slot up to the left leads to the surface. However, only the thinnest member of the expedition was able to pass through the slot.  Above the first boulder choke there is a chamber where evidence of a camp and bats was found.  Noodle packets were found at this camp which had a sell by date of 2530 BE (1987 AD), which is five years before the student expedition in 1992!


The 1992 expedition had failed to pass the large gour that blocks the main stream passage in the 1992 Series. They had looked for a route over the top and had pushed the wet crawl underneath for about 2m.  In January 2005 concerted canal digging lowered the water level by 20cm.  A wet crawl lead to the left while the stream came in from the right. Continuing to the left went through a flat out crawl in a pool. Beyond the pool a small chamber was reached.  The way on was to crawl through another pool and head right to a dry crawl.  Finally bearing left and following the crawl over cobbles allowed the very large passage to be regained.  By ascending the boulder floored passage a pool is reached at the base of a 10m aven. The stream enters at the top of this aven which has not been climbed and is currently the end of exploration in this section of the cave.


Cave 14 was found on a walk from Tham Yai Nam Nao via the very steep path which goes to Tham Pha Ruag.  From this col access was gained to the bottom of Doline 715 and when ascending back out of this doline towards Tham Song Hong the 20m deep entrance shaft was found.  The entrance is the sink for a seasonal stream.  The shaft was descended in January 2006 and linked to the 1992 series by 80m of muddy crawls.


Tham Pha Rai is an active swallet and was known as Wet Sink to the 1992 expedition. The entrance is located in the first doline, 'Banana' doline, to the south-east of the 'cabbage patch' parking place.  After descending into the doline the path flattens out as it goes through an old banana plantation.  After about 100m the stream channel is 30m to your right.  If you can't find the stream keep following the path as this soon crosses the stream which can then be followed down to the cave.


There are two entrances, but there is little point scrambling up to the dry entrance as you will soon get wet inside the cave.  Going in the wet entrance and across a 0.5m deep pool brings you to a 7m pitch.  At the bottom of this the stream descends a couple of short drops and after crossing a pool a crawl leads to the main streamway.  Upstream the passage can be followed for 100m through a couple of ducks to a sump.  Downstream the cave goes for about 500m through varied passage.  In places the passage is large and triangular in cross-section where it has formed along the strike.  In other places it is necessary to crawl under flowstone blockages.  Eventually the stream disappears into a low passage and then sumps.  Just before the stream enters the low section there is a small hole on the right which leads up into a boulder choke above the sump. A route through the boulder choke was found (it has been marked with string!) which leads back to the stream.  This stream passage is generally small and it is often necessary to crawl round low sections, over boulders, wade a short canal, etc. to eventually reach the high inclined rift passage which has already been described from the Tham Yai Nam Nao end.  The through trip from Tham Pha Rai to Tham Yai Nam Nao is recommended.


Although the two upstream ends of Tham Yai Nam Nao have been found there is still potential to extend the system.  The Shepton Mallet Caving Club survey currently ends at the first duck upstream of the Boulder Chamber so the 1992 Series Inlet and extension beyond the gour have not been surveyed (and have only been visited once).  Other possible extensions are by diving the resurgence or downstream sumps; high level entrances to the Tourist cave, Tham Pha Rai Inlet, the 1992 Series or 2004 Series; various oxbows and unclimbed avens; joining the Cave 25/Tham Bah Dahn/Tham Phaya Naak area caves to upstream 2004 Series which would add over 2km to the length; linking caves high on the mountain above, such as Tham Monhwa where exploration of a shaft system was stopped due to high carbon dioxide. 


Tham Yai Nam Nao Resurgence 

Main entrance: 47Q 0767346 1874950                 Alt.: 676m

Upper entrance: 47Q 0767360 1874943                Alt.: 690m

Length: 130m                            VR: 11m


The stream resurges from amongst boulders on the left hand side of the path to Tham Yai Nam Nao.  A 1.5m high entrance to the right allows dry access into the streamway which can be followed for a few metres, past a small second entrance on the right and across a pool to reach the base of a rift.  This rift is a third entrance, but the steeply sloping rubble bank is tricky to descend.  Beyond this rift entrance the water can be followed along 80m of canal (up to 1.2m deep) to reach a deep upstream sump.  White fish were seen in the sump pool and if they are found to be cave adapted they are most probably a new species as no other cave fish are known from this hydrological basin.


A dive at the upstream sump has plenty of potential to reach several hundred metres of air filled passage.  The sump is formed by a steeply dipping chert bed in the roof and thus it is likely to be a short sump.


Cave 27

Approx. 47Q 0767950 1873900               Alt.: 750m

Length: ~10m                            VR: ~10m


From the col above Cave 14 take the path southwards towards Cave 14.  When you reach a gulley follow it down for about 200m to the cave.  Cave 27 is a seasonal stream sink in a limestone outcrop.  The entrance pitch is estimated to be 10m and has not been descended.

1992 Series Sink

47Q 0767786 1872218                Alt.: 770m

Length: ~3m                              VR: ~3m


Walking via Tham Pak Now a large stream sink was found at the bottom of Doline 771, but was not investigated properly because of a lack of kit.  The stream sinks into boulders and can be seen to descend 3m and then go 3m horizontally.  The sink is approximately 150m south of the aven at the end of the 1992 Series in Tham Yai Nam Nao.


High Level Fossil Caves


Cave 13

47Q 0767727 1874364                Alt.: 810m


This entrance was found when ascending from the bottom of Doline 715 towards Tham Pha Pai.  The hole will need digging, but was draughting out in January 2005.


Tham Pha Ruag  ถ้ำป่รวก

47Q 0767936 1874604                Alt.: 860m

Length: 59m                              VR: 11m


Tham Pha Ruag is a very short remnant of a high level fossil system.  The cave is located to the east of the col above Tham Yai Nam Nao and is reached by a very steep path up the side of the hill just to the east of the ranger station. From the Tham Yai Nam Nao car park walk down the surfaced road for a few metres and then follow the first track on the right (east) which leads to some fields.  The path heads north into the forest about 100m past a bamboo shack, but is difficult to find.  Alternatively it is possible to reach this area via the path that goes to Tham Song Hong and then ascend to the ridge and head north.


The entrance is a small hole about 1.5m in diameter and opens onto a 4m pitch. This was already "rigged" with a bamboo pole, but we installed our own lifeline (belayed to a fresh bamboo pole over the entrance).  The pitch drops into a small chamber with some formations and a passage on the left leads to a smaller second chamber.


Cave 18

47Q 0768009 1874348                Alt.: 830m

Length: ~5m                              VR: ~2m


From Tham Song Hong the ridge was followed north towards Tham Pha Ruag.  At the base of the summit outcrop, on the eastern side, there is an inclined area of exposed limestone.


A 5m long vadose canyon was found near the southern edge of the exposed limestone. Much of the canyon is unroofed and there are numerous other holes in this area.


Tham Song Hong  ถ้ำสองห้อง

Lower entrance: 47Q 0768150 1874261                Alt.: 820m

Upper entrance: 47Q 0768183 1874172                Alt.: 836m

Length: 215m                            VR: 23m


This is a large, truncated fossil cave on the limestone ridge above Tham Pha Rai.  The cave can be reached from either the Tham Yai Nam Nao car park or from the 'cabbage patch' car park. The cave has been used as a retreat by monks.


The wide lower entrance opens into a big fossil passage with many large formations.  A route between the formations climbs up to a ledge where there is a short passage off to the right.  To the left the passage closes down for a short distance before opening up again.  The smaller upper entrance is soon reached.  Another smaller passage leads steeply down from the upper entrance.  This appears to take a small stream in the wet season, but is solidly choked with mud. 


Tham Pha Pai  ถ้ำป่ใผ่

47Q 0768307 1874020                Alt.: 860m

Length: 84m                              VR: 7m


This is another remnant of the old high level system.  It is located only a few metres below the ridgeline between Doline 715 and 'Banana' doline on the eastern side of the mountain.  From the 'cabbage patch' car park take the path up the valley to the col where the main path goes to the left towards Tham Pha Rai and Tham Phaya Naak. Take the path which turns off to the right, past Tham Pha Hok, and ascends towards the ridge.  The cave is to the right of the path and is not particularly obvious despite the large entrance.  Alternatively go past Tham Song Hong and follow the ridge south.  However, the path goes over the top of the cave and the entrance cannot be seen.


The entrance has been used as a retreat by monks.  To the right a small passage soon closes down. To the left the passage leads to a second chamber which has been mined for guano.  At the back of the chamber the passage is completely choked with clastic fill and a small oxbow in this fill has been crawled through.


Tham Pha Hok  ถ้ำป่หก

Main entrance: 47Q 0768482 1874257                 Alt.: 760m

Second entrance: 47Q 0768495 1874248 Alt.: 759m

Pitch entrance: 47Q 0768465 1874257                 Alt.: 770m

Length: 51m                              VR: 13m


Tham Pha Hok is a short fossil cave located above a flood sink at the northern end of the 'Banana' doline.  It is in a cliff only a few metres uphill and to the right from the first col reached from the 'cabbage patch' car park.  The cave has four entrances, one of which is small and another is a 7m pitch.


Cave 7

47Q 0768404 1874234                Alt.: 780m

Length: ~20m                            VR: ~5m


Just beyond Tham Pha Hok there is an outcrop of limestone on the right of the path.  The cave in this outcrop has a couple of entrances rigged with old bamboo ladders, but the cave has not yet been surveyed and this area needs to be looked at more closely.


Cave 8

47Q 0768408 1874263                Alt.: 770m

Length: ~10m                            VR: ~5m


A few metres downhill from Cave 7, but further away from the path, Cave 8 is a short phreatic tube descending at a 45° angle.


Draughting holes amongst boulders

47Q 0768453 1874218                Alt.: 775m


Opposite Cave 7, on the left of the path and a few metres uphill from Tham Pha Hok, there is a limestone outcrop and a jumble of boulders.  A draught has been detected blowing out from between these boulders.


This area with Tham Pha Hok, Cave 7, Cave 8 and the draughting holes is of interest as it is above the Tham Pha Rai Inlet in Tham Yai Nam Nao.


Cave 15

47Q 0768372 1873545                Alt.: 820m

This cave is located on the side of Doline 715 as you descend from the path which follows the ridge between Tham Pha Pai and Tham Monhwa. This hole will need digging, but was draughting out in January 2005.


Tham Monhwa  ถ้ำมอนว้า

Main entrance: 47Q 0768555 1873314                 Alt.: 952m

Second entrance: 47Q 0768529 1873376 Alt.: 947m

Length: 365m                VR: 55m

Other names: Tree Forest Cave [1992 expedition]


Tham Monhwa is in an interesting location high on Khao Tham Yai.  The easiest access is the path via Tham Song Hong.  Follow this path south-east, past Tham Pha Pai to the limestone outcrops at the top of the hill.  The path then bears left and descends and contours round the southern edge of Doline 715.  The path then ascends passing Cave 21 and Cave 22.  The Second entrance is a few metres above the path before you reach these two shafts, but can be hard to find.  The main entrance is on the other side of this hill and is best reached by contouring round to the left.


The main entrance to Tham Monhwa is a spectacular, large collapsed passage.  To the right (east) a short passage crosses a bamboo bridge to a 5m pitch down into a large passage.  This passage ends at a slippery climb up (which wasn’t ascended) with an aven above which was draughting inwards.  On the left hand side (west) of the main entrance there is a series of pitches, but unfortunately high carbon dioxide levels (a cigarette lighter wouldn’t work) stopped exploration.  The way on down another pitch could be seen.


The 1992 expedition reported another cave, Miserly Spirit Cave, with a large entrance close to Tham Monhwa, but this has not been found.


Cave 21

47Q 0768481 1873364                Alt.: 948m

Length: ~20m                            VR: ~15m


The path to Tham Monhwa ascends a limestone outcrop and two shafts are found beside the path, just past the second entrance to Tham Monhwa.  Cave 21 is a 15 m pitch into a blind rift heading towards the nearby Cave 22.


Cave 22

47Q 0768490 1873372                Alt.: 931 m


This shaft is located close to and on the same joint as Cave 21. It has not been descended, but is almost certainly another blind shaft.


Cave 11

47Q 0768765 1873158                Alt: 922m

Length: 45m                              VR: 18m

Other names: Cliff Cut Path Cave [1992 expedition]


While crossing the flat floor of 'Banana' doline, after crossing the stream which sinks at Tham Pha Rai, the path forks.  Left leads up to the far end of the doline and on to Tham Phaya Naak.  However, the right hand fork ascends the steep side of the doline to a col between 'Banana' doline and Doline 806. The easiest path goes right (north) and ascends a ridge before heading left and decsending gently around the northern side of the doline (for a short distance it appears to follow an old track cut into the side of the hill).  A limestone outcrop is seen above the path and the entrance is at the base of this outcrop.


The 12m entrance shaft lands in a chamber 10m by 10m with a blind rift at one end and no way on.  The cave is located a couple of hundred metres to the south-east of the end of Tham Monhwa.  The 1992 expedition report described Cliff Cut Path Cave as being "on the side of a rocky knoll, a small entrance leads to a 10m by 10m chamber containing weathered calcite.  An 8m pitch was descended to another chamber with a pool, and no obvious way on."  This description is close enough to what we saw in Cave 11 to be confident they are the same cave.


The ridge to the north-east of Cave 11 has been descended from Tham Monhwa to the col down to 'Banana' doline (not recommended as it is steep and overgrown with no paths).  However, the rest of this doline has not been explored.


Tham Phaya Naak Area


These caves are a brisk 1½ hour's walk from the 'cabbage patch' parking area.  Follow the path up the valley to where the path to Tham Pha Hok, Tham Song Hong and Tham Monhwa forks off to the right.  Take the track left, over the crest and descend into the 'Banana' plantation.  After passing Tham Pha Rai the path crosses the flat floor of the doline through an old banana plantation.  It then ascends steeply to a col at the south-eastern end of the doline.  The path contours round to the right and crosses a gully (this gully has been descended into the 'Elephant' doline, but this route can be best described as hard) before gently ascending to a second col.  The path than narrows and traverses round to the right, going across the steep mountainside.  This path is also used by elephants.  The far end of the traverse is marked by a limestone outcrop and the path descends.  Head left and go round the left hand side of the limestone hill.  At the next col you can either follow a path right which descends to Cave 5 or take the path that goes left and then ascends round to the right to Tham Nop Pa Krauw.  At Tham Nop Pa Krauw there is a camp used by forest monks and the southern entrance to Tham Phaya Naak is reached by continuing along for about 50m and then dropping down by about 30m in altitude.  A path from Tham Nop Pa Krauw heads up the hill to Tham Wi Mahn Mek.


Tham Phaya Naak, Tham Wi Mahn Mek and Tham Nop Pa Krauw have been connected via a large pitch. This connection has created a system which is 1.2 km long and 133 m deep.  The 650m long Tham Bah Dahn, near the bottom of Doline 725 ('Elephant' doline), runs below the Tham Phaya Naak system.  There is a tall rift passage in Tham Bah Dahn below the shaft that links up the Tham Phaya Naak system.  Cave 25 is downstream of Tham Bah Dahn and has an open streamway that has not yet been explored.


Tham Phaya Naak System

Tham Wi Mahn Mek ถ้ำวิมานเมฃ

Main entrance: 47Q 0769746 1872034                 Alt: 875m

Eastern entrance: 47Q 0769819 1872059 Alt.: 874m

Tham Nop Pa Krauw  ถ้ำนพเก้า

47Q 0769664 1872010                                        Alt.: 848m

Tham Phaya Naak  ถ้ำพญานาึค

North entrance: 47Q 0769838 1872159                Alt.: 801m

South entrance: 47Q 0769648 1871890                Alt.: 812m

Other names: Tham Pa Pha Rai [Caves of Thailand], Bamboo Cave [1992 expedition]


Length: 1,285m (80m unsurveyed)           VR: 133m


Tham Phaya Naak had been explored and surveyed by the 1992 expedition.  Their survey showed a large passage that linked two smaller entrances.  The cave looked impressive and we had hoped to be able to relocate the cave on our first expedition to Nam Nao.  We didn’t find it on this first trip although we were very close when exploring Cave 5 and Tham Nop Pa Krauw.  However, we did manage to find it in 2005 because some forest monks were in residence at Tham Nop Pa Krauw and they guided us to the southern entrance.


Tham Wi Mahn Mek has one entrance at the base of the limestone outcrop at the top of the hill.  The main passage of Tham Wi Mahn Mek has several skylights and goes through the hill to a second entrance. A passage to the right inside the main entrance leads to a large chamber in the floor of which there is a very large pitch that has been aurally connected with the pitch in Tham Nop Pa Krauw, but the pitch has not been descended.  The total depth of this pitch is around 70m.


The entrance to Tham Nop Pa Krauw is located lower down the hill than Tham Wi Mahn Mek.  The first visit was in January 2004 and exploration was soon stopped by a crawl after 90m. This crawl was dug out a year later to reach about 40m of passage ending at a pitch.  This pitch was descended into a big chamber where the connection to Tham Wi Mahn Mek was above and to the right.  In January 2006 the pitches linking this cave to Tham Phaya Naak were descended and surveyed.


The southern entrance to Tham Phaya Naak is small, but a very strong draught blows out of the cave.  A 3m bamboo ladder lands in a narrow passage that gradually gets larger as you follow it to the north-east. Another 3m bamboo ladder allows access to the large main passage.  A high level oxbow goes from above this second ladder round into the main passage.  There is a shrine in front of a large calcite column and the cave is also used by the monks for walking meditation.  The large passage descends gently to a junction with a passage on the right.  The right hand passage soon reaches a T junction and the pitch in from Tham Nop Pa Krauw lands at the junction. To the left leads steeply up a mud slope to end at the foot of an aven.  This pitch is stal covered and appears to be about 20m high. To the right the passage soon ends at a grotto.  A pit in the floor has been descended for 4m and was found to be blind.  This blind pit is above the high rift passage in Tham Bah Dahn.  Before the grotto an inclined, mud floored passage on the right can be followed for about 30m.


Back at the junction the main passage continues, but soon reduces in size.  The monks have constructed various bamboo ladders and bridges which allow you to ascend through several small chambers and climb up to the small northern entrance which is in the other side of the hill to where you went in.  This area near the northern entrance appears to take a small stream in the wet season.


Cave 23

47Q 0769838 1872087                Alt.: 894m

Length: ~10m


From the eastern entrance to Tham Wi Mahn Mek turning left brings you to Cave 23.  It is a small shelter cave with a couple of beds.


Cave 24

47Q 0769858 1872052                Alt.: 875m

Length: ~20m


From the eastern entrance to Tham Wi Mahn Mek turning right brings you to Cave 24.  This cave is about 20m wide and deep and is also used by monks.  There is a skylight entrance to the right and the cave has some fossil calcite bosses.


Cave 10

47Q 0769673 1871887                Alt.: 825m

Length: 35m                              VR: 2m


From the southern entrance to Tham Phaya Naak a large cave entrance can be seen in the cliff above.  After climbing the 20m to the entrance the cave is found to consist of a 10m entrance chamber with a small crawl leading off from the back of the cave.  The crawl was not draughting in January 2005.


Cave 5

47Q 0769664 1871759                Alt.: 776m

Length: ~100m                          VR: ~35m


Cave 5 is located below and about 100m from the southern entrance to Tham Phaya Naak.  Due to its location and nature (a boulder choke) there was a hope that it might have connected with the streamway between the stream sink in Doline 728 and the upstream end of Tham Bah Dahn.


The cave had been found in January 2004, but had not been explored to a conclusion. The small entrance opens into a chamber.  From here it is possible either to descend the steep, dry streamway which has a couple of climbs in it or to descend the chamber to the left.  At the bottom the way on is down through a boulder choke.  This was looked at by two groups in January 2005, one of which used a ladder to descend the choke, but due to time constraints a definite conclusion was still not found.  In January 2006 there were two visits to Cave 5 when more determined and better equipped explorers pushed down through the boulders until it became too tight.


Tham Bah Dahn  ถ้ำบาดาล

47Q 0769885 1872279                Alt.: 760 m

Length: 655 m                           VR: 29 m


This stream cave is located in 'Elephant' doline to the north of Tham Phaya Naak. Although this is likely to be the stream seen in the 2004 Series of Tham Yai Nam Nao it runs in a south-west to north-east direction which is at 90° to the 2004 Series.  It runs below the Tham Phaya Naak system, but no indications have been seen that the caves are connected.  The streamway appears to be the link between the stream sinking in Doline 728 below Cave 5 and the 2004 Series streamway.  Cave 25 is between the known ends of Tham Bah Dahn and the 2004 Series and the stream sinking in 'Elephant' doline probably joins this cave.


The entrance passage is rigged with rotten bamboo ladders on the drops and leads down to a streamway that quickly sumps going downstream.  Heading upstream there is a muddy slope and chamber on the left which ascends to a possible second entrance.  After the chamber there is over 500m of passage to a sump.  This stream passage is very high in places.  With a lot of work it might be possible to dig away the sandbanks at the upstream end and lower the sump.


Cave 25

47Q 0769928 1872305                Alt.: 750m

Length: 25m+                            VR: ~5m


The entrance to Cave 25 is, according to the GPS fixes, 50m north-east of Tham Bah Dahn and a few metres lower.  To enter the cave you climb down an old dry waterfall for about 10m.  The stream comes in from ahead of you (from Tham Bah Dahn?) into a clean cut passage heading downwards at about 60°.  It is possible to climb down the slope for about 5m to where a ladder or handline is required.  Falling water could be heard at the bottom.


The following two sinks and three caves were originally reached by walking from the 'cabbage patch' car park along the path that traverses the sandstone hills on the eastern flanks of the 'Banana' doline and 'Elephant' doline.  These sites are in the third doline along, Doline 728, but a long way upstream from the bottom of the doline which is below Cave 5. Easier and quicker access to these sites is to continue along the path that goes to Tham Phaya Naak, turning left to Sinks 1 and 2 and Caves 19 and 20 or continuing straight on to reach Cave 26.


Sink 1

47Q 0770114 1871638                Alt.: 755m


This sink was thought to be the sink for the stream seen in the 2004 Series in Tham Yai Nam Nao. However, the exploration of Tham Bah Dahn has cast doubt on this hypothesis. A stream was sinking here in January 2005. The sink is choked with wood and bamboo which will have to be removed to allow exploration. A rope or ladder might also be useful to gain entry.


Sink 2

47Q 0770233 1871587                Alt.: 755m


An overflow sink for Sink 1 which has a small stream sinking in it.


Cave 19

47Q 0770214 1871540                Alt.: 755m

Length: ~2m                                          VR: ~2m


There are two shakeholes at this location.  The larger hole needs kit to descend the 2m deep drop between boulders. Not explored.


Cave 20

47Q 0770062 1871551                Alt.: 755 m

Length: ~5m                                          VR: ~5 m


Cave 20 consists of a 5m drop in two steps leading to a crawling sized cave that hasn't been explored.  There are several other shakeholes in this area.


Cave 26

47Q 0770376 1871080                Alt.: 790m

Length: ~65m                            VR: ~2m


To reach Cave 26 follow the path beyond Tham Phaya Naak down to the floor of doline on the right (west).  The two small entrances are in an outcrop next to open area.  The larger entrance has a camp inside.  Climbing over the bed leads to a fossil passage with the other entrance immediately on the left.  After 15m a 2m climb down leads to a further 50m of walking passage to a large static pool which has a strong draught flowing out and appears to be a duck with water about 0.5m deep.  However, the cave was not properly explored and has great potential as it is over 1km from the upstream sump in Tham Bah Dahn.


Cave 17

47Q 0771387 1871712                Alt.: 900m

Length: ~10m


This cave was found on the longest walk so far made by the Shepton Mallet Caving Club into the forests of the Nam Nao National Park.  The good path follows the edge of the sandstone hills just outside the eastern boundary of the park past the 'Banana' and 'Elephant' dolines and nearly past Doline 728.


This cave is located in the line of limestone cliffs that are on the eastern edge of the national park. This is an old relict cave used as a camp by hunters. A bamboo ladder leads up to the 10m long, 5m wide by 30m high cave.


Western Caves


Apart from the 1992 Inlet entrance to Tham Yai Nam Nao and the 1992 Series Sink (which have been described above) only one cave is known from the limestone hills on the western edge of the massif.  However, very little exploration work has been done in this area. 


Tham Pak Now  ถ้ำพัคเน่า

47Q 0766600 1872899                Alt.: 757m

Length: 75m                              VR: 15m


See the Access section for the car parking spot for Tham Pak Now.  From here take the path that follows the valley floor until some limestone cliffs are seen on the right.


Tham Pak Now is a short relict cave with a large chamber about 30m across.  Some small passages and crawls were not explored. It has been used extensively by monks in the past. The cave is in a limestone outlier on the western edge of the mountain. This area needs to be looked at more closely on future expeditions.



Tham Par Hong Area


The caves here are in an isolated limestone outlier about 20km south of Tham Yai Nam Nao.  Access is easy via the H12 and Tham Par Hong is signposted from the road.  We walked south-west round the hill from Tham Par Hong, down into the dry valley and back up to the road. There does not appear to be any major caves here, but more limestone outcrops may be present to the north.


Tham Par Hong  ถ้ำผาหงษ์

Upper entrance: 47Q 0767755 1854078                Alt.: 885m

Small entrance: 47Q 0767755 1854078                Alt.: 878m

Lower entrance: 47Q 0767755 1854082                Alt.: 879m

Length: 105m                            VR: 11m


This cave is very well known and is sign posted off the H12.  A metal ladder leads up to a shrine formed in a short bit of passage.  Below this shrine two smaller entrances lead into a more extensive cave.  To the left a 3m deep rift has been descended and apart from an oxbow in the western wall was found to be blind.  The passage to the right was followed to where crawling was necessary.


Cave 12

47Q 0767824 1853906                Alt.: 855m

Length: ~10m


By following the base of the limestone hill for about 100m past Tham Par Hong this cave is reached.  The cave consists of a couple of short phreatic tubes with bamboo structures built by monks.


Caves Outside The National Park


Whilst exploring the eastern edge of the limestone massif a couple of small caves were found in one of the limestone cliffs.  These limestone cliffs are outside the park boundaries.


The vehicle access to these caves is described in the Access section.  From the end of the track head down across the field to the bottom of the small valley and follow the path up through the forest to the large main entrance to Cave 1.  To reach Cave 2 continue to follow the path up the stream bed, past the upper entrance to Cave 1 and then continue round to the other side of the limestone cliff.


Cave 1

Main entrance: 47Q 0769310 1875793                 Alt.: 830m

Upper entrance: 47Q 0769357 1875767                Alt.: 841m

Length: 90m                              VR: 14m


The large main entrance, which is 15m wide by 5m high, appears to be considerably older than the small seasonal stream passage which leads to the upper entrance.  This main entrance is heavily choked with calcite and clastic deposits. and is used occasionally by monks.  The streamway is only 1m to 1.5m high and about 1m wide.  After 70m the cave opens out into a small chamber.  The upper entrance enters the far end of this chamber as a rift and has a small climb.  There is a possible high level passage leading off from this chamber.  There are a couple of bamboo poles which have been brought into the cave to enable one to reach the top of the chamber, but we didn’t attempt the ascent.


Cave 2

47Q 0769402 1875587                Alt.: 860m

Length: 43m                              VR: 4m


This is a short cave located on the same limestone outcrop as Cave 1.  It is used by monks as a retreat.  The passage soon chokes and the floor has been excavated in a couple of places, probably for guano.


It is of interest to note that Cave 1 and Cave 2 are at the same altitude as the old fossil system above Tham Yai Nam Nao, but are 2km to the north-east.


Caves Visited By The 1992 Expedition


The caves described below have not been found by the SMCC expeditions.  The descriptions are taken from Standing (1992) and Dunkley (1995).  These descriptions are repeated here as the 1992 report is not widely available (there are now copies in the National Caving Library and the Shepton Mallet Caving Club library).  Tham Yai Nam Nao, Tham Yai Nam Nao Resurgence, Tham Pha Rai (Wet Sink), Tham Phaya Naak (Bamboo Cave), Tham Monhwa (Tree Forest Cave) and Cave 11 (Cliff Cut Path Cave) which were visited in 1992 have also been explored by the SMCC and are described above.


Note:  In the 1992 report the phrase "south-west" was found to be a typographical error for "south-east" in the Tham Pha Rai description.


Tham Phra

Other names: The Monk's Cave

Length: ~30m

"On our second trip into the forest, our guides led us to a fascinating group of caves situated about 50m up a cliff.  A lack of suitable maps coupled with the dense forest cover prevents any precise description of the location, but the place is obviously well known by the locals, and the entrances are visible from some distance away.

A series of wooden ladders and walkways lead up from the base of the cliff, held together with rusty nails and bamboo lashings.  Rotten sections had obviously been patched up and the whole thing appeared relatively safe.  About 50m up, the level of the series of entrances is reached, and precarious bamboo platforms tied into nearby tree trunks head off around the cliff, allowing access to all the caves.

The main cave is about 5m high, 10m wide and extends back into the cliff for about 10 or 12m, providing one of the most perfect rock shelters imaginable.  According to the guides, the cave was inhabited by the monks in the rainy season.

The monks had obviously been using the cave for a long period of time and had transformed it into a comfortable dwelling place.  The floor had been leveled and neatly covered with bamboo slats.  At one side was a fireplace and the cave contained numerous ladles and other utensils as well as a small cupboard of pots and pans.  Growing out of the floor near the front was a small tree (which we were told was an apple tree), and right on the edge, growing out over the drop, were three other trees which had obviously been cultivated there.  These bore paw-paws which the guides cut down and cooked.  The view out across the forest was very impressive as we were well above the level of the tree-tops.

Other chambers connected to the main cave contained sleeping platforms and blankets, with space for 6 or 8 people to live quite comfortably."


Tham Pha Phrik

Other names: Chilli Cliff Cave

Length: ~150m

"A stream sink through boulders about 500m from the base of the cliff containing Tham Phra.  A climb down through boulders leads into a series of small chambers with a tight wet passage at the bottom.  A feeling of breathlessness, together with noticing our carbide lamps burning very yellow and frequently extinguishing suggested foul air, so we explored no further.  Another small passage containing the stream was followed for about 100m."


Tiger Eats Pig Cave

Length: ~100m              VR: ~40m

”A small entrance up on a hillside leads to a chamber with many bats.  A short pitch through boulders in the floor was found to be choked.  Another chamber was found and a pitch in the floor of this has been descended for about 20m.  It appeared to continue for another 20m or so, but lack of rope prevented further exploration."


Hunter's Stream Cave

Length: ~30m

"A moderately large stream sink was followed in crawling sized passage for about 30m to a sump pool.”


Tham Puay

Other names: Fertilizer Cave

Length: ~50m                VR: ~15m

”A 30m long rift leads to a 15m pitch and larger passage which rapidly become blocked.  There is evidence of guano having been dug out for use as fertiliser."


Miserly Spirit Cave

Length: ~30m

"A smaller collapse entrance about 8m high, not far from Tree Forest Cave [Tham Monhwa].  Total length is about 30m." A brief attempt was made to look for this cave in January 2006, but without success.


Tham Huai Nam

Length: ~15m

"A few kilometres south or south-west of [Tham Yai Nam Nao], an active stream sink opening into a canal with diminishing air space."

There is not a Huai Nam marked on the 1:50,000 map.


Tham Huai Pong

Other names: Tham Haipong

"South or south-west of [Tham Yai Nam Nao], two streams sinking with the way on blocked by debris."

There is not a Huai Pong marked on the 1:50,000 map.


Wild Boar Cave No. 1

Length: ~15m

"A few kilometres south or south-west of [Tham Yai Nam Nao], a 15m deep shaft with no way on."


Wild Boar Cave No. 2

Length: ~5m

"Near [Tham Huai Nam] and [Wild Boar Cave No. 1], a small cave with no way on."


Cave PE36

Length: ~15m

"A few kilometres south or south-west of [Tham Yai Nam Nao], large chamber at the base of a cliff."

There is a possibility that this cave is Tham Pak Now which is at the base of a cliff to the south-west of Tham Yai Nam Nao. 


Geology and Hydrology


Various regional studies on the structural geology and lithology of the Nam Duk basin have been made, but the only paper that has been seen is the overview paper by Fontaine (2002).  However, all these papers are listed in the references. The 1:250,000 geology map has also been used in compiling this section.


The main limestone outcrop trends north-west to south-east from Tham Yai Nam Nao. This outcrop is 10km long and thins from 3km wide to 500m wide as you progress south-east from Tham Yai Nam Nao.  About 2km to the east another limestone outcrop is shown on the geological map, but it is only about 7km long and 500m wide.  In the field this second outcrop is seen as a row of isolated cliffs formed from vertically bedded limestone.  A couple of small caves were found in one of these cliffs.  The Permian limestones show significant karst features, particularly very large dolines which are up to 1km across and 200m deep.


Nam Nao National Park is located in the elongated north – south trending Nam Duk Basin which separates the Khao Khwang Platform of Central Thailand from the Pha Nok Khao Platform of Northeast Thailand.  The present geographical distribution of the different lithologies is explained by displacement, caused by a north – south trending strike-slip fault. The geology map shows the Permian limestone outcrop is the axis of an anticline. An east-west fault forms the northern edge of the outcrop and the anticline appears to plunge to the south-east with the limestone disappearing below the overlying sandstones.


The caves of the Nam Nao National Park are formed in limestones of the Pha Nok Formation which is of Lower-Middle Permian age.  Fontaine & Salyapongse (2001) report that the limestone in the northern part of the Nam Nao National Park is over 600 m thick. The limestone is very rich in diverse fossils: algae with green algae, fusulinaceans, corals in the lower part and brachiopods indicating that the limestone was formed in a shallow marine environment.  These fossils date the limestone from Murgabian to Late Midian.  The limestone is overlain by black shale and then by a relatively small body of limestone which contains foraminifera, but no fusulinaceans have been found so far and it might belong to the Triassic.


Our own observations show the limestone to be grey and massively bedded.  There are also abundant thin chert beds and these indicate a dip of between 30° and 90° towards the north-east.  The dip to the north-east has resulted in most of the surface landforms (ridges and valleys) and the major streamway in Tham Yai Nam Nao trending north-west to south-east. 


These Pha Nok Formation limestones are bordered to the east and west by the Middle Permian Nam Duk formation and to the north by the Upper Triassic Huai Hin Lat Formation.  Although the geology map describes these formations as being comprised of shales, limestones and conglomerates they appear to be mainly sandstones.


A detailed geomorphological study has not been made.  However, it was immediately seen that there is an older, fossil system overlying the more recent, active system of Tham Yai Nam Nao.  Tham Pha Ruag, Tham Song Hong, Tham Pha Pai and Tham Monhwa are all found at an altitude of 810m to 950m, which is 110m to 240m above the present day stream level which is at an altitude of 700-710m.  These caves have been truncated by the erosion of the limestone massif.  It is hoped that by finding more remnants of old caves such as these a better picture of this fossil system can be pieced together.  In the Tham Phaya Naak area fossil cave development is seen at four overlying levels: Tham Wi Mahn Mek (altitude 880m), Tham Nop Pa Krauw (altitude 835m), Tham Phaya Naak (altitude 790m) and Tham Bah Dahn (altitude 730m).


Of interest in Tham Yai Nam Nao is the capture of the stream by newer passages.  The Tourist Cave and Main Cave are the original route for the stream and the Tourist entrance is an old resurgence.  The stream was then captured by a smaller passage (the passage from the streamway junction to the downstream sump) leaving the large Main Cave dry (though the stream may overflow into this passage in the wet season).  The stream from Tham Pha Rai used to flow all the way to the Tham Yai Nam Nao streamway, but has been recently captured by a very small, immature and impassable passage. This stream certainly overflows along its old route in the wet season.


Tham Yai Nam Nao has extensive clastic deposits throughout the cave.  In the old resurgence passages of the Tourist Cave and Main Cave these are mainly mud and sand with recent roof collapse boulders nearer the entrance.  At the junction with the main streamway these floor deposits are between 3m and 4m thick.  In the main streamway there are extensive deposits of cemented sandstone cobbles, similar to those seen in the caves near Umphang in Tak province.  The 2004 Series streamway has mainly fine clastic deposits of sand, silt and mud with plenty of recent organic material which has been brought into the cave.  In the 1992 Series the deposits are of large clastics with sandstone cobbles seen along the length of the passage.  The boulder chamber towards the end of the 1992 Series is a large collapse feature.  The boulders have been heavily corroded by acidic water and are very crumbly. 


A few basic measurements have been made of the surface and underground streams.















Total hardness






Test temp


Tham Yai Nam Nao

Outside cave











Outside cave











Outside cave











Outside cave










Tham Yai Nam Nao

Junction with main cave










Tham Pha Rai

Stream at entrance











Stream at entrance











Upstream of junction











Downstream of junction










Banana doline

47Q 0769935 1874078










Elephant doline

47Q 0770086 1873625










Tham Pak Now valley

47Q 0766343 1873626











The temperature of the stream sinking at Tham Pha Rai is of particular note.  This is an exceptionally low temperature for Thailand and is probably due to the surface stream flowing under vegetation cover from the 1,000m high sandstone hills to the east.  Fortunately, from the caving point of view, this stream soon meets an inlet which is considerably warmer.  This stream must also come from the same hills as the main stream so it is odd that there is such a marked difference in temperature.


The only known resurgence in the area is the Tham Yai Nam Nao Resurgence. Along the eastern edge of the limestone outcrop perennial streams are known to run off the sandstones of the Nam Duk Formation into the 'Banana' doline, 'Elephant' doline and Doline 728 to sink into Tham Pha Rai, near Cave 26 and in Sink 1 respectively.  Another, larger, stream flowing from the south-east most probably also sinks in Doline 728 upstream of Cave 26.  The south-west of Doline 728 has not been explored, but other streams are likely to flow off the sandstone hills here to sink in this very large doline.  The water sinking in 'Elephant' doline and flowing through Tham Bah Dahn is almost certainly the source of the water in the 2004 Series in Tham Yai Nam Nao.  The water seen in Cave 26 possibly flows into the upstream end of Tham Bah Dahn and then onto the 2004 Series.


Two sinks for the Tham Yai Nam Nao 1992 Series stream have been found: the 1992 Inlet entrance and the 1992 Series Sink.  In contrast to the 2004 series feeder streams the tributaries to the 1992 Series appear to only flow for a short distance over limestone and are not sourced on non-karst rocks.


Tham Yai Nam Nao has a catchment of 32km² and an average annual rainfall of 1.18m.  In January 2004 the flow from the Tham Yai Nam Nao Resurgence was measured at 0.09m³/s.  Working on the basis of a 212 day dry season (November to May) the wet season flow at the resurgence would be approximately 2.75m³/s.  It is estimated that 15% of the total flow comes from the 'Banana' doline via Tham Pha Rai, 70% from 'Elephant' doline and Doline 728 via the 2004 Series and 15% from Doline 748 and Doline 771 via the 1992 Series.


In January 2004 the stream in Tham Yai Nam Nao was flowing all the way along the main streamway and there was no stream flowing in the 1992 Series just upstream of the junction with the 2004 Series.  However, on the 8and 9 April 2004 the water level in the main streamway was a lot lower and it was possible to reach the downstream sump without swimming.  Three days later, on the 12 April, the stream had stopped flowing at the junction with the main cave and was not flowing for a couple of hundred metres upstream of this junction.  The stream was still flowing in Tham Pha Rai and this cave’s inlet to Tham Yai Nam Nao.  At the upstream end of the 1992 Series, beyond the boulder chamber, there was a small stream flowing.  The main stream in the 2004 Series was still flowing quite strongly.  The surface stream thought to feed this branch of the cave, in the 'Elephant' doline, was seen to be flowing the day after the underground visit.  On a visit in July 2005 to the main streamway the water levels were not any higher than they had been in January despite recent thunderstorms.



This section details the casual observations made of the life in the caves.  No specimens have been taken and only a couple of animals have been identified to species level.  However, some ecological observations are reported.


A couple of pale coloured fish were seen just downstream of the sump in Tham Yai Nam Nao Resurgence.  However, no fish have been seen in the Tham Yai Nam Nao streamways. The fish were not caught or observed closely, but if they prove to be true cave adapted fish they are likely to be a new species as no other cave fish are known from this hydrological basin which feeds into the Chayo Phraya River. 


Bats are found in all the caves, but because there are an estimated 130 species of bats in Thailand they have not been identified though several distinct types can be observed. The largest number of bats have been found in the tourist section of Tham Yai Nam Nao where they roost near the third entrance on the ceiling of a large chamber. There are guano deposits here, but they are not particularly extensive and without an obvious associated fauna. In July 2005 bats were also heard above the breakdown chambers at the end of the Tourist Cave. One type of bat was found in numbers along the streamways in both Tham Pha Rai and Tham Yai Nam Nao.  They were medium sized, grey bodied and were easily disturbed.  Once disturbed they appeared to be particularly clumsy fliers and would crash into the survey tape, the water and into cavers.  They were able to take off again from the water surface or swim to the edge where they would climb up the walls.  This type of bat favoured small, low chambers over pools of water. There were occasionally found a long way into the cave, including the far end of the 2004 Series streamway in Tham Yai Nam Nao and it is thought that this indicates a possible entrance nearby.  These colonies of bats would not always be found in the same place, one group seen in January were not in the same place in April.  In Cave 1 a long eared bat was photographed.  A few individuals of a small bat species were found a long way into Tham Yai Nam Nao and we had the impression that they were hunting the small insects attracted to our lights.  This behaviour has also been observed from caves in Tak province. The chamber in Tham Pak Now was used as a roost by a few large bats.


A rat inhabited the crawl at the end of Tham Nop Pa Krauw and had a mutually scary moment when coming face to face with the first caver through. The rat has not been seen since the crawl was later enlarged considerably.


The Cave Racer snake (Orthriopus taeniurus, previously Elaphe taeniura) has not been found in any of the caves of this area, but a green snake was met in a low airspace section of the link between Tham Pha Rai and Tham Yai Nam Nao.


The usual cave crickets (Rhaphidophoridae: ?Diestrammena spp.) and cave huntsman spiders (Sparassidae: ?Heteropoda spp.) were found in most of the larger caves.  Long-legged cave centipedes (Chilopoda: Scutigeramorpha) has only been seen at the end of the tourist section of Tham Yai Nam Nao. A 15cm long 'normal' centipede (Chilopoda: Scolopendromorpha: ?Scolopendra subspinpes) was seen in Tham Phaya Naak. Although the bite of these fearsome looking creatures is not usually fatal you might wish it was after  three days of excruciating pain.


Firefly beetles were an unusual find in the tourist section of Tham Yai Nam Nao, but these were accidental visitors.  Adult caddisflies or mayflies have been a nuisance in the Tham Yai Nam Nao streamway. Again these were accidental visitors which had been washed into the cave as larvae. A 4cm long, pale coloured shrimp was found in one of the pools just before the Tham Yai Nam Nao downstream sump.


Two species of moth have been found aestivating in the caves.  An impressively large noctuid moth (Noctuidae: Cataocalinae: Erebus macrops (Linmaeus, 1768)) was seen in Tham Pha Pai and a segment of wing from the same species was found in Cave 1. Erebus macrops is found throughout south, south-east and east Asia.  This behaviour of aestivating in caves has also been seen in Tham Loe Pu, Tak province and in northern Laos. A medium sized moth (?Noctuidae or ?Geometridae) was seen in Tham Pha Pai.  In January 2005 harvestmen or daddy-long-legs spiders (Opiliones) were found aestivating in the wet entrance to Tham Pha Rai and the 1992 Inlet entrance to Tham Yai Nam Nao in such large numbers that the walls of the cave appeared to be hairy.  This behaviour has recently been reported from caves in northern Laos, but has apparently not been mentioned in the literature.


Surveying and Mapping


A total of 12.50km of underground surveying and 0.25km of surface surveying has been carried out by the Shepton Mallet Caving Club in the Nam Nao National Park.


All cave entrances co-ordinates have been fixed using handheld GPS units, either an 8 channel Garmin 45XL or by 12 channel Garmin Etrex, V or 76.  In addition all the footpaths, dirt tracks and roads were tracked by GPS and have been used to draw the map in this report.  The waypoints and tracks from the GPS units were downloaded into the Fugawi moving map program.  Fugawi was used to plot these data onto a scanned map and this was used as a base for drawing the maps with Adobe Illustrator.


All the surveys and co-ordinates used in this report use the UTM grid and are on the Indian 1954 (Thailand-Vietnam) datum.  Conversions from the GPS default WGS84 datum were by the GPS unit’s internal algorithms.


The cave surveys were done using a 30m tape and handheld compass and clinometer.  In a couple of the smaller caves and in the tourist cave section of Tham Yai Nam Nao a Leica laser rangefinder was used for passage widths and ceiling heights.  The instruments were not calibrated to true or grid north, but they were calibrated with respect to each other.  The cave surveys are thus to a BCRA (1976) 3c grade.


The cave survey data was processed and managed using the Walls cave survey program.  The surveys were drawn using either Adobe Illustrator CS based on a SVG export from Walls or by the traditional pen and paper method.  The UIS (1999) symbol set has been used for the cave surveys.


Expedition Members


Tony Blick                     Dec 03/Jan 04, Dec 04/Jan 05

Dave Briggs                   Dec 05/Jan 06

Geraldine Collett            Dec 05/Jan 06

Phil Collett                    Dec 03/Jan 04, Dec 04/Jan 05, Dec 05/Jan 06

Claire Dummer               Jan 05, Dec 05/Jan 06

Paul Dummer                Jan 05, Dec 05/Jan 06

Martin Ellis                    Dec 03/Jan 04, Apr 04, Dec 04/Jan 05, Jul 05,

Dec 05/Jan 06

Glyn Francis                  Jan 05

Ivan Hollis                      Dec 03/Jan 04, Apr 04, Dec 04/Jan 05, Dec 05/Jan 06

Lee Hollis                      Dec 05/Jan 06

Sean Howe                    Dec 03/Jan 04

Dave Owen                    Dec 04/Jan 05, Dec 05/Jan 06


Expedition Diaries


Thu 27 Nov        Ivan & Martin leave UK.

Thu 25 Dec        Sean & Phil leave UK.

Fri 26 Dec         Sean & Phil arrive in Bangkok and drive to Ayutthaya to meet Tony.

Sat 27 Dec        Everyone meets up in Lom Sak.

Sun 28 Dec       Visit Nam Nao National Park HQ.

                        Tham Yai Nam Nao: survey from 6m ladder to entrance.

Mon 29 Dec       Tham Yai Nam Nao: planned long trip with guides, but stopped by bad air at                       low, wet section. Survey back to 6m ladder.

Tue 30 Dec        Look at limestone outcrop about 1 km to the NE of the park boundary.                               Survey Cave 1 and Cave 2.

Wed 31 Dec      Walk along north-east edge of national park. Survey Tham Pha Pai and Tham Pha Hok.


Thu 1 Jan          Walk along north-east edge of national park. Locate Tham Pha Rai.

Fri 2 Jan            1) Tham Pha Rai: survey and extend downstream end of cave.

                        2) Locate Cave 5 3.5 km SE of Tham Yai Nam Nao.

Sat 3 Jan          1) Tham Pha Rai: continue survey and pushing downstream.

                        2) Survey Cave 5 and find and survey Tham Nop Pa Krauw.

Sun 4 Jan          1) Survey Tham Par Hong and  Tham Phu Talor (Phu Pha Man                                          National Park, Khon Kaen).

                        2) Visit Tham Par Hong. Explore track to south of  H12.

Mon 5 Jan         1) Tham Pha Rai: survey and push upstream

                        2) Hire guides and locate Tham Song Hong and Tham Pha Ruag.

Tue 6 Jan          Hire guides and survey Tham Song Hong and Tham Pha Ruag.

Wed 7 Jan         Explore western edge of national park and find Tham Pak Now.

Thu 8 Jan          1) Tham Yai Nam Nao: discovered bad air had cleared and explore main                 streamway for 1 km. Survey Tham Yai Nam Nao Resurgence.

                        2) Plan to walk to bottom of doline beyond Tham Pha Rai doline, but meet a                       herd of elephants so turn back (‘Elephant' Doline).

Fri 9 Jan            1) Tham Yai Nam Nao: survey 850m in Main Cave and streamway.

2) Explore 2004 Series for approx. 2.5 km to sump.

Sat 10 Jan         Tham Yai Nam Nao: extend survey 950m up 2004 Series.

                        Sean, Phil & Tony leave Lom Sak.

Sun 11 Jan        Tham Pha Rai: collect rigging kit which had been left at top of pitch.

Mon 12 Jan       Ivan & Martin leave Lom Sak.


Mon 29 Mar       Ivan & Martin leave UK.

Wed 7 Apr         Ivan & Martin arrive in Lom Sak.

Thu 8 Apr          Tham Yai Nam Nao: survey downstream to sump.

Fri 9 Apr            Tham Yai Nam Nao: tourist trip to streamway.

Sat 10 Apr         Hire guides and visit Tham Song Hong, Tham Pha Pai and Tham Pha Hok.                         Shown entrance to Tham Monhwa, but stopped at pitch.

Sun 11 Apr        Visit Tham Phaya Nakarat & Tham Lai Tang (Phu Pha Man National Park,                         Khon Kaen).

Mon 12 Apr       Tham Yai Nam Nao: explore 1992 Series to duck beyond Boulder Chamber.

Tue 13 Apr        Tham Yai Nam Nao: survey Tham Pha Rai inlet.

Wed 14 Apr       Tham Yai Nam Nao: survey 700m upstream in 2004 Series.

Thu 15 Apr        Walk to 'Elephant' Doline and follow stream part way down towards                                    swallet.

Fri 16 Apr          Tham Pak Now: survey cave.

Sat 17 Apr         Martin & Ivan leave Lom Sak.


Thu 23 Dec        Martin arrives in Bangkok.

Sat 25 Dec        Dave O, Ivan & Phil leave UK.

Sun 26 Dec       Dave O, Ivan & Phil arrive in Bangkok and meet Martin. Drive to Ayutthaya to meet Tony.

Mon 27 Dec       Drive to Lom Sak.

Tue 28 Dec        Tham Yai Nam Nao: link with Tham Pha Rai. Check Main Passage and Tourist Cave for leads. Investigate between Second and Bat entrances.

Wed 29 Dec      Tham Monhwa: survey main passage

Thu 30 Dec        Tham Yai Nam Nao: survey 700m in 1992 Series.

Fri 31 Dec         1) Tham Par Hong: descend rift and explore base of limestone outcrop.

                        2) Walk through 'Elephant' Doline to the hills above Doline 728. Find Cave 17.


Sat 1 Jan          Walk to 'Elephant' Doline stream via gully down from col at head of 'Banana' Doline.

Sun 2 Jan          1) Find & explore Cave 11.

                        2) Find Tham Phaya Naak. Dig through end choke in Tham Nop Pa Krauw.

Mon 3 Jan         1) Through trip from Tham Pha Rai to Tham Yai Nam Nao surveying link.

                        2) Walk to Doline 715 from the Tham Yai Nam Nao ranger station.

Tue 4 Jan          1) Walk ridge between Tham Pha Ruag and Cave 11.

                        2) Walk to Doline 728 via 'Elephant' Doline – find Caves 19 and 20 and Sinks 1 and 2.

Wed 5 Jan         Tham Yai Nam Nao: survey 1.2 km in 2004 Series to upstream sump.

Thu 6 Jan          Surveyed Tham Phra (Phu Pha Man National Park, Khon Kaen).

Fri 7 Jan            Tham Monhwa: descend pitches and survey entrance area.

Sat 8 Jan          1) Tham Yai Nam Nao: explore 1992 Series to gour and inlet passage.

                        2) Visit Tham Erawan (Nong Bua Lam Phu) and Tham Pha Sawan (Loei)

Sun 9 Jan          Walk and find main sink for 1992 Series in Tham Yai Nam Nao.

Martin & Tony leave Lom Sak.

Mon 10 Jan       Tham Yai Nam Nao: push 1992 Series Inlet to entrance and dig below gour to find 250m passage ending at aven. 11 hr trip.

Tue 11 Jan        Walk over surface to new entrance at end of 1992 Series Inlet.

Wed 12 Jan       Dave O, Phil & Ivan leave Lom Sok.

Thu 13 Jan        Paul, Claire & Glyn leave UK.

Fri 14 Jan          Paul, Claire & Glyn arrive Bangkok. Everyone meets in Ayutthaya.

Sat 15 Jan         Dave O & Phil leave Thailand. Martin, Ivan, Paul, Claire & Glyn drive to Lom Sak.

Sun 16 Jan        Tham Yai Nam Nao: survey 700 m of the 1992 Series to the ducks beyond the boulder chamber.

Mon 17 Jan       Tham Phaya Naak: survey cave.

Tue 18 Jan        Tham Yai Nam Nao: tourist trip to showcave.

Wed 19 Jan       Walk to Doline 715 from Tham Yai Nam Nao ranger station. Find Caves 13, 14 and 15.

Thu 20 Jan        Tham Phaya Naak: finish survey and unsuccessfully attempt to find link to Tham Nop Pa Krauw. Explore Cave 5.

Fri 21 Jan          Drive to Pha Phueng Wildlide Sanctuary headquarters (Khon San, Chaiyaphum) and talk to head ranger.

Sat 22 Jan         Tham Pha Rai to Tham Yai Nam Nao through trip.

Martin leaves Lom Sak.

Sun 23 Jan        Tham Nop Pa Krauw: survey cave. Shown Tham Bah Dahn in 'Elephant' Doline.

Martin leaves Thailand.

Mon 24 Jan       Tham Bah Dahn: explore and survey cave.

Tue 25 Jan        Tham Singh Toh (Pha Phueng Wildlife Sanctuary, Chaiyaphum): survey & photograph, but didn't have tackle to fully explore the cave.

Wed 26 Jan       Tham Nop Pa Krauw: Descend pitch, but run out of rope. Tham Wi Mahn Mek: explore and survey above pitch, aural connection to Tham Nop Pa Krauw.

Thu 27 Jan        Claire, Paul, Glyn & Ivan leave Lom Sak. Drive to Ayutthaya then onto Bangkok.

Fri 28 Jan          Day in Bangkok.

Sat 29 Jan         Claire, Paul & Glyn leave Thailand.

Sun 30 Jan        Ivan leaves Thailand.


Tue 5 Jul           Tham Yai Nam Nao: Martin on solo trip to main streamway – water level low.


Mon 26 Dec       Martin & Ivan arrive in Bangkok from New Zealand.

                        Paul, Claire, Dave O, Lee and Dave B leave UK.

Tue 27 Dec        Everyone meets up in Ayutthaya.

Wed 28 Dec      Drive to Lom Sak. Meet up with Phil & Geraldine.

Thu 29 Dec        1) Tham Yai Nam Nao: planned big surveying trip to the end of 1992 Series was stopped by high CO2 just beyond the show cave.

                        2) Phil & Geraldine on surface walk to the west of Tham Yai Nam Nao.

Fri 30 Dec         1) Cave 5: descended until it got too small.

                        2) Tham Nop Pa Krauw: pitches descended until visual connection with Tham Phaya Naak, but not enough rope to descend.

                        3) Tham Wim Mahn Mek: surveyed around the top of the pitch and aural connection with Tham Nop Pa Krauw.

Sat 31 Dec        1) Tham Phaya Naak: photography and confirm visual connection with Tham Nop Pa Krauw.


Sun 1 Jan          Look at quarry near Lom Sak.

Mon 2 Jan         1) Tham Nop Pa Krauw: rig pitch into Tham Phaya Naak and survey connection.

                        2) Find Caves 23, 24 and 25 near Tham Wim Mahn Mek and Tham Bah Dahn.

Tue 3 Jan          Long walk on the eastern path past Banana and Elephant dolines, descend following stream in the next doline to Sink 1 then join path from Tham Phaya Naak.  Follow this path south to Cave 26.  Return via path from Tham Phaya Naak to Banana doline.

Wed 4 Jan         1) Cave 14: descend pitch and connect to 1992 Series in Tham Yai Nam Nao.  Find Cave 27.

                        2) Look for caves near Tham Monhwa.

                        Geraldine leaves Thailand.

Thu 5 Jan          Leave Lom Sak and move to hotel in Chumphae.

Fri 6 Jan to        Explore caves in the Pha Phueng Wildlife Sanctuary and Phu Pha Man

Mon 9 Jan         National Park.

Tue 10 Jan to     Cha-Am: visit caves in Khao Sam Roi Yot National Park and waterfall in

Fri 13 Jan          Kaeng Krachan National Park.

Sat 14 Jan         Paul, Claire, Lee, Phil, Dave B and Dave O leave Thailand.  Martin and Ivan                         return to Lom Sak.

Sun 15 Jan to    Look for and visit various caves in Phetchabun and Loei provinces.

Fri 20 Jan

Sat 21 Jan         Martin and Ivan leave Thailand.




  1. Dunkley, John R. (1995) The Caves of Thailand Speleological Research Council Ltd., Sydney pp58-60
  2. Elliott, S. & Cubitt, G. (2001) The National Parks and other Wild Places of Thailand New Holland Publishers (UK) Ltd., London pp90-93
  3. Ellis, Martin (2003) The SMCC Expeditions to Umphang & Mae Sot, Tak Province, Thailand Shepton Mallet Caving Club Journal Series 11 No. 3 pp75-138
  4. Ellis, Martin (2004) SAM in Siam Shepton Mallet Caving Club Newsletter Vol. 40 No. 6 pp140-146
  5. Ellis, Martin & Barrett, Dave (2001) Thailand Expedition February 2000 Report Shepton Mallet Caving Club Journal Series 10 No. 8 pp247-272
  6. Fontaine, Henri (2002) Permian of Southeast Asia: An Overview Journal of Asian Earth Sciences Vol. 20 pp567-588
  7. Fontaine, Henri & Salyapongse, S. (2001) A Murgabian to Lower Triassic Sequence Exposed from Khao Tham Yai to Khao Pa Khi, Northeast Thailand: A Preliminary Report Journal of the Geological Society of Thailand Vol. 24 No. 1 pp43-47
  8. Helmcke, D. & Kraikhong, C. (1982) On the Geosynclinal and Orogenic Evolution of Central and Northeastern Thailand Journal of the Geological Society of Thailand Vol. 5 No. 1 pp52-74
  9. Helmcke, D. & Lindenberg, H.G. (1983) New Data on the Indosinian Orogeny from Central Thailand Geologische Rundschau Vol. 72 No. 1 pp317-328
  10. Helmcke, D. (1982) On The Variscan Evolution of Central Mainland Southeast Asia Earth Evolution Sciences Vol. 4 pp309-319
  11. Helmcke, D. (1994) Distribution of Permian and Triassic Syn-orogenic sediments in Central Mainland SE Asia Proceedings of the International Symposium on the Stratigraphic Correlation of Southeast Asia, Department of Mineral Resources, Bangkok. pp123-128
  12. Helmcke, D., Weber, K., Ingavat, R. & Nakornsri, N. (1985) Orogenic Evolution of NE Thailand During the Upper Paleozoic Proceedings of the Conference on Geology and Mineral Resources Development of NE Thailand, Khon Kaen, pp31-39
  13. Kononenko, Vladimir S. & Pinratana, Amnuay (2005) Moths of Thailand Vol. 3 Noctuidae Part 1 Brothers of Saint Gabriel in Thailand, Bangkok 261pp
  14. Owen, David R. (2005) On the Dating of Caving Expeditions by the Use-by Dates on Noodle Packets: A Scientific Study Shepton Mallet Caving Club Newsletter Vol. 42 No. 2 p30
  15. Standing, Nick (1992) Report of the 1992 Expedition to the Nam Nao National Park, Thailand unpublished report 11pp
  16. Steiner, Helmut (2005) Biospeleological Notes On Laos in Dreybrodt, Jeorg & Laumanns, Michael (eds.) The Unknown North of Laos (Karst and Caves of the Provinces Luang Phrabang and Luang Nam Tha) Berliner Hohlenkundliche Berichte Band 16 pp92-97
  17. Wielchowski, C.C. & Young, J.D. (1985) Regional Facies Variations in Permian Rocks of the Petchabun Fold and Thrust Belt, Thailand Conference on the Geology & Mineral Resource Development of NE Thailand, Khon Kaen University, pp41-55
  18. National Parks Department website:




1.       Phu Kradung 1:50,000, sheet 5342 IV series L7017 US Army Topographic Command (1969)

2.       Amphoe Nam Nao 1:50,000, sheet 5342 IV series L7017S, Royal Thai Survey Department, Bangkok (1992)

3.       Changwat Phetchabun 1:250,000, sheet NE 47-16 series 1501S, Royal Thai Survey Department, Bangkok (1986)

4.       Changwat Phetchabun, 1:250,000, sheet NE 47-16 series 1501S, Geological Survey Divison, Department of Mineral Resources (1976 published 1984)

5.       MapMagic CD-ROM Road Map of Thailand 2005-2006 ThinkNet Co., Ltd. (2005)




The rangers at the Tham Yai Nam Nao substation: Khun Khumpan Paichan (Head Ranger), Tiam, Manu, Bo, Pong and the rest of the guys for allowing us access to the cave, showing a lot of interest in our work and plying us with fruit wine and food after our trips.

Nopodon and the other monks living at Tham Nop Pa Krauw for encouraging our explorations, hospitality and showing us Tham Wi Mahn Mek and Tham Bah Dahn.

Ms Rattana Lakanawarakul and the Royal Forest Department for granting permission to explore and survey the caves in the national park. Thanks also to Dean Smart for helping to obtain this permission.

The Ghar Parau Foundation for £175 (2003/4) and £150 (2004/5) in grant aid.

EVA Airways for granting the 2004/5 expedition an additional 5 kg baggage allowance.

Nick Standing who was on the 1992 expedition for digging out his old notes and photographs to supply further details of the caves explored in 1992.

John Dunkley in Canberra, Australia for providing a copy of the 1992 Nam Nao expedition report.

Dave Checkley in Manchester for providing a copy of his 1989 report on the Phu Kheio Wildlife Sanctuary expedition.

Ed Waters & Mark Sims for the loan of photographic and surveying equipment.



Cave Data








Tham Yai Nam Nao




Cave 14

1992 Inlet

47Q 0767316 1874832

47Q 0767329 1874822

47Q 0767332 1874774

47Q 0767954 1873736

47Q 0767459 1872603

693 m

711 m

729 m

740 m

750 m

9,817 m

76 m

Tham Pha Rai



47Q 0768798 1874006

47Q 0768805 1874000

730 m

738 m



Tham Phaya Naak



47Q 0769802 1872166

47Q 0769611 1871896

790 m

801 m

1,285 m


Tham Wi Mahn Mek


Tham Nop Pa Krauw




47Q 0769709 1872041

47Q 0769783 1872067

47Q 0769657 1872017

880 m

880 m

835 m



Tham Bah Dahn


47Q 0769885 1872279

760 m

655 m

29 m

Tham Monhwa



47Q 0768555 1873314

47Q 0768529 1873376

952 m

947 m

365 m

55 m

Tham Song Hong



47Q 0768150 1874261

47Q 0768183 1874172

820 m

836 m

215 m

23 m

Tham Yai Nam Nao Resurgence



47Q 0767335 1874880

47Q 0767350 1874873

673 m

687 m

130 m

11 m

Tham Par Hong




47Q 0767755 1854078

47Q 0767755 1854078

47Q 0767755 1854082

885 m

878 m

879 m

105 m

11 m

Cave 5


47Q 0769664 1871759

776 m

~100 m

~35 m

Cave 1



47Q 0769310 1875793

47Q 0769357 1875797

830 m


90 m

14 m


Tham Pha Pai


47Q 0768307 1874020

860 m

84 m

7 m

Tham Pak Now


47Q 0766600 1872899

757 m

75 m

15 m

Cave 26


47Q 0770376 1871080

760 m

~65 m

~2 m

Tham Pha Ruag


47Q 0767936 1874604

860 m

59 m

11 m

Tham Pha Hok




47Q 0768482 1874257

47Q 0768495 1874248

47Q 0768465 1874257

760 m

759 m

771 m

51 m

13 m

Cave 11


47Q 0768765 1873158

922 m

~45 m

~18 m

Cave 2


47Q 0769402 1875587

860 m

43 m

4 m

Cave 10


47Q 0769673 1871887

825 m

35 m

2 m

Cave 7


47Q 0768404 1874234

780 m

~ 20 m

~ 5 m

Cave 14


47Q 0767954 1874736

740 m

~20 m

~20 m

Cave 21


47Q 0768481 1873364

948 m

~20 m

~15 m

Cave 24


47Q 0769858 1872052

875 m

~20 m


Cave 25


47Q 0769928 1872305

750 m

~20 m

~5 m

Cave 8


47Q 0768408 1874263

770 m

~ 10 m

~ 5 m

Cave 12


47Q 0767824 1853906

855 m

~10 m


Cave 17


47Q 0771387 1871712

900 m

~10 m

~0 m

Cave 23


47Q 0769838 1872087

894 m

~10 m


Cave 27


47Q 0767950 1873900

750 m

~10 m

~10 m

Cave 18


47Q 0768009 1874348

830 m

~5 m

~2 m

Cave 20


47Q 0770062 1871551

755 m

~5 m

~5 m

1992 Series Sink


47Q 0767784 1872237

770 m

 ~3 m

~3 m

Cave 19


47Q 0770214 1871540

755 m

~2 m

~2 m

Draughting holes


47Q 0768453 1874218

775 m



Cave 13


47Q 0767727 1874364

810 m



Cave 15


47Q 0768372 1873656

820 m



Cave 22


47Q 0768490 1873372

931 m



Sink 1


47Q 0770114 1871638

755 m



Sink 2


47Q 0770233 1871587

755 m