AREA 3: Bom Bay

BY10 Ban Ai

This cave acts as the main sinkhole of the Nam La River. The cave entrance is located behind a dam construction.
The entrance is a boulder choke. About 5m lower, between blocks, the water is reached. A passage of 30m gives way to a chamber with big blocks. At the right side there is a muddy slope, but no continuation was found. The cave continues with a passage of 30m. From there on two ways can be followed: the first along small joints and the second through the water. A bigger room (10m wide) with big blocks on the bottom is reached. 60m further the room becomes lower and smaller. At the end of the cave the joints become too narrow to continue.

BY11 Ban Mon

The entrance of this cave is one of the dolines in a large polje about 2 km westwards from the Ban Ai village. The polje is situated at a lower altitude compared to the base of the Nam La river (-40m). According to local people the polje is submerged two or three months a year, constituting a big and deep lake.
The cave starts as a series of little pitches between boulders which  lead to a nice underground water course (discharge estimated at 10l/sec) at a depth of 80m. Upstream, a sump is met after a few meters. It is possible to progress over the sump through a fossil passage which becomes too narrow a little further. Downstream, the water goes through a narrow gully, which can be avoided by another passage leading to a nice 15m pitch. Another little descent leads towards a sump at 101m depth. It should be noted that the existence of this underground river at an altitude which is about 140m lower than the Nam La river and streaming in an north-east direction,  shows that there are severed underground water courses and there is probably no real aquifer near the surface of the area between the Nam La and Suoi Muoi river bassins. Moreover it raises even in a more prominent way the question about the underground course of the Nam La river.

BY12 Bum Hau

Starting from the polje of the Ban Mon cave, one can walk further to the north where a similar polje starts immediatly after a small ridge. This polje looks different of the polje of the Ban Mon cave: since, the forest hasn’t been removed. It’s a difficult walk through this dense forest. An interesting point is that there hasn’t been so much erosion as in the previous polje. One can distinguish several dolines with a lot of small entrances. A gunmen told us we could find over 80 of these dolines here, and during raining season water is rising that high that all those dolines are submerged. He claimed that at that time big fish can be caught in these small lakes.

We explored several of these dolines, of which one gave way to a cave. Bum Hau starts chaotic: several entrances can be distinguished. The cave starts with some good pitches (an R2,5 and a P5 to be rigged with a rope of 4 and 8 m.) untill the cave is chocked with boulders. After a smart desobstruction we opened a squeeze to a pitch of 6 m. (8 m. rope) that became very narrow and chocked with boulders.