The longuest cave in Laos (42 km)

By its length, the Nam Don cave system is the largest in the Lao PDR, before Tham Nam Non (Khammouane, Nam Hin Boun valley) and Tham Chom Ong (Oudomxai, Northern Laos). With over 40 km already mapped, it ranks 3th among the largest South-East Asia caves.

The huge Khamsone chamber (190 x 150 m), at the Tham Houay Sai / Tham Khoun Don junction. © B. Galibert - 2011

Lao People Democratic Republic (LPDR), Khammouane, Thakhek district, near Ban Na

    Tham Khoun Dôn 48Q 486420 m E, 1941915 m N, 160 m

    Tham Houay Say  48Q 487135 m E, 1941800 m N, 165 m

From Thakhek, follow route n°12 (Nort-East). Turn left along the road heading to Tham Pha Fa, a Buddha cave famous since its discovery in 2004, but keep going straight in the north-west direction along the karst border. In Ban Nahouangoua, turn right to the north-east to reach the small Ban Na village (Ban Phondou on the map) in 3.5 km. From Thakhek, the overall distance is about 24 km.

Ban (village) Na, about forty traditional houses, nestled at the foot of the karst clifts and  surrounded by rice fields. © C. Ghommidh - 2011

On the trail, out of Ban Na, heading west, one kilometer before the clearing. © C. Ghommidh - 2011

Then turn north using a poor trail that enters the forest and narrows as an approximate track until the thalweg is reached again (1 km). Turn left, following the sandy river bed upstream, until it turns to the right. Climb the river bank. You may feel the fresh air running out of the cave. The wide Tham Houai Sai entrance is 150 m ahead, behind the tree curtain.

The discovery

In 1996, a caving expedition, led by Claude Mouret, explores the Ban Vieng polje (12 km NE of B. Na). On the polje south side, an active sink (Tham Kagnung) and a large temporary sink (Tham Houay Sai perte) are partially explored. The water destination must be somewhere in the south, along the water gradient direction imposed by the Mekong river. This hypothesis is published by C. Mouret and François Brouquisse in the CREI report (1994-1996).

The year after, during a one-day trek at the end of the 1997 expedition, the two fellows find the Nam Dôn spring (khoun) and a close-by cave (tham) (Tham Khoun Dôn), on the south side of the karst. A large temporary emergence is also found (T. Houay Saï) further east. Both caves are mapped over a few meters by CM and FB. This "discovery" (both caves have been known for a long time by the local people !) is reported in the CREI 97 report, co-signed by CM et FB.

The serious operations begin during the 1998 expedition. Tham Khoun Dôn is surveyed for over 3.5 km by F. Brouquisse, with J-F Vacquié assistance. They reach a huge chamber and establish a contact with the second survey team led by CM, entered through Tham Houay Saï. The Big Loop becomes the backbone of the Nam Dôn cave system. Without access to CM data, it is not possible to establish a clear picture of his contribution. However, a rough estimate of 1.5 - 2 km from the survey published as a vignette format in the n°84 Spelunca issue (2001, below). This was the last joint expedition of FB and CM.

Independently, a team of french cave divers (F. Auber, F. Bréhier,  A. Espinasse, D. Sablé) explores the Nam Dôn resurgence itself for about 270 m. A first sump (120 m, -10) is followed by a 90 m lake, and another sump is partially explored over 50 m (-23 m).

A few hundred meters are added in 2000 by a team led by CM, as extension of a large passage in the east of the Khamsone chamber. Unfortunately this extension was misplaced and connected to the wrong passage, several hundred meter away.

Early maps of the Nam Dôn cave system: left, Brouquisse et al., 1998 ; right, Mouret et al., Spelunca, 2001.

Five years later the team returns to THS-KD. In 2005, the topography of the maze is initiated by Bernard Giai-Checa & al. one hand, and Charles Ghommidh & al. other. To the East, the Goats Passage is followed up to two openings, a large swallow hole, the Goats Aven, and a narrow side opening : the Gypsum Gate. To the west, C. Mouret and J-F. Vacquié access an opening topped with wild hives, which evoke the local legend of the “Cave of the Honey Rock”.

In 2006, a large team is formed, still with C. Mouret as team leader. Far into T. Khoun Dôn, Maria Madrid and Florence Guillot explore a flooded passage that bypasses part of the Big Loop. A large gallery, parallel to the main route, is also mapped. A major breakthrough occurs when Helmut Steiner and Charles Ghommidh discover the Eastern Branch, beyond a complex labyrinthic path. In four sessions, they explore and map several km of passages, opening an avenue towards the sinks of the Ban Vieng polje explored in 1996. The most remote point is reached by Flo Guillot, but the progression is blocked by a sump.

A few month later, after stupid rumors spread by CM, Flo Guillot and Phil Bence decide to leave the team.

In 2007, on the eve of the 2007 Xe Bang Fai expedition, H. Steiner and J-F. Vacquié make a brief visit to Tham Khoun Dôn.

In 2010, CM and JFV, now alone after a third breakup of the Mouret team following the lamentable 2009 expedition, undertake a re-survey of the maze, adding nothing neither to the system understanding, nor to its length. Surprizingly they neglect the exploration of the Eastern Branch, from far the most promizing part of the cave. Too far ? Lost itinerary ?

In 2011, a new team, led by the former explorers François Brouquisse, Charles Ghommidh and Florence Guillot, extends the mapped area from 11 to 21 km. Connections are made to position the survey pieces scattered since 2005. A new passage network is found 40 m below the Labyrinth, the path to the Tham Houay Sai temporary river is identified and followed over nearly two kilometers of new passages, ahead of the Flibustiers Chamber, another large chamber, the eastern branch is extended to the Eastern Gate, an outlet in a remote sinkhole (Kouan Pheung - the Bees Doline) and continued on the opposite side in Tham Kouan Pheung, to a second doline.

The outlet in the Kouan Pheung sinkhole, in february 2011 (© Phil Bence - explo.fr)

Weeks later, guided by the signposts, CM and JFV, still alone, revisit the lost 2005 passages and the 2011 discoveries, and hurry to publish their "findings" in the n°122 Spelunca issue, neglecting to mention that they were merely second-hand explorers.

In february 2012, the K12 expedition extends the system in the north and east directions. Tham Kaohong, a novel cave is found in the wake of T. Kouan Pheung. The Tham Houay Saï river is discovered. The Nam Dôn system overall development is extended to 27 km.

The subsequent expeditions (K13, K14 and K15) extend the cave system to 32.5, 37, then 42 km. The No End and Houay Saï Hights sectors are explored. A continuation of the Houay Saï Grand Canal is found. Tham Phê Pha Thon Maï (the Canopee Raft cave) is added to the system.

Tham Phê Pha Thon Maï, the K14 surprise © B. Galibert, 2014

     

A more detailled map will be published after a full analysis of the results of the Khammouane 2014 expédition.