AREA 21: Ban Hon

The Dong Pao system

Near the village of Dong Pao, a very interesting karst landscape can be observed, where the Nam Hon river disappears several times underground, sometimes for less than 50 m, sometimes for several hunderds of meters, where it is conducted by huge caves.

In fact, the Nam Hon river once flew from the south-west tot the east, in the direction of the Dong Pao village, where it turned with a very sharp bend to the north-west.  This curve was the result of  the geological situation: the Nui Mo mountain (1149 m) is still the witness of the hard rocks that caused the bend in the Nam Hon river. Due to erosion, the Nam Hon river cutted the valley deeper into the rocks until it reached the limestone. From then on, the water dissappeared in the Dong Pao cave under the Nui Mo mountain and the bend in the Nam Hon river became a fossil valley. Erosion continued and the active Nam Hon fiver cutted a deeper valley, but the fossil riverbend near the Dong  Pao village didn’t change anymore en became a higher situated valley.

BH1 Dong Pao 1

Dong Pao 1 is the first cave where the Nam Hon river disappears. The entrance is impressive: about 25 m wide and 5 m high.  A fossil passage of 125 m long and about 20 m wide gives way to a slope consisting of huge blocks. Before this slope there is a low and wide passage at the left side, but it becomes to low and muddy to follow. At the base of the boulder slope the active river is reached.

Downstream: The river is about 10 m wide and becomes too deep to walk. At the left side, the river can be followed over large blocks.  The passage is about 40 wide.  After 150 m, a very large formation is reached (diameter 30 m and 10 m high).  Here the passage becomes smaller and lower. The river gets a meandering course. The banks of the river consist of fine sand and clay.  After 300 m a large room, with a diameter of 60m, is reached.  At the left side, we climb the boulder slope up to 50m above the river.  At the right side, a gently climbing fossil passage could be followed for 150 m.  At the end, the passage was closed with huge formations.  A strong draft could be felt.
From the big room the passage changed in a siphon like muddy passage.  After a very low passage a siphon lake was reached. Above the lake, we tried to find continuation in a boulder choke.  There is a strong cold draft between the blocks. A connection with the surface is very likely. On the survey, one can see that this boulder choke is nearby the fossil passage.

The river has a meandering course. The banks of the river consist of fine sand and clay. After 400 m the river appears between blocks and could not be followed anymore.

BH2 Dong Pao 2

Dong Pao is the cave where the Nam Hon river appears from under the Nui Mo mountain.

BH3 Dong Pao 3

Dong Pao 3 is a semi-cave: here the Nam Hon river disappears under the valley, but sometimes it can still be observerd through highly eroded blocks.

BH4 Dong Pao 4

Some 120 m. further the Nam Hon river disappears again under a very huge porch for 40 m. Once can swim under this beautiful arch of  15 m. high.

NH5 Dong Pao 5

Again, 120 m. further, the Nam Hon river disappears underground. Now it follows a cave of 500 m. long through a large gallery of 15 m. high. Sometimes the roof of this gallery has collapsed, so the blue sky and an amazing tropical forest can be observed. The swim through this cave was a wonderful experience.

This area with all the beautiful karst phenomena is a very interesting opportunity to be developed for tourism.