Grottes et karsts de Chine
Sur les traces de Xu Xiake

Bai-Mo Dong

2km North East of Po Yue the track to Bai-Mo village, running parallel to the Pan Yang river, skirts a lagoon fed by two resurgences, which then enters the main river. The Pan Yang rises only 200m away round the corner - with perhaps 5 cumecs flowing out of an inviting cave entrance in the middle of tt:e dry winter season. This major river resurgence cave was clearly a 'must'. When we finally got round to it the dinghy preparaticns were watched by a crowd of hundreds, who followed us across the dry paddy-fields to witness the launch and departure into the unknown. We paddled across the entrance lake and bumped into the rock wall on the other side. Totally sumped and still in daylight! What a fiasco. (Talk about loss of face.)

Back at the small resurgences running into the lagoon... The mountain rose directly behind, with a bay leading back to an impressive cave entrance (Figure 5). Once inside the entrance and beyond a stalactite boss a long slope leads back up to the right, lit by daylight (in the Bai-Mo caves just about everywhere is beyond giant stalagmite bosses!). Toiling up this slope one passes evidence of human occupation, and walls which were clearly of a defensive nature that enclosed the uppermost part of the daylight cave (Roberts; this volume). One wall blocked the approach up the ramp, another, at the highest point, (built partly of brick) had an entrance - with a very steep approach route leading from it down the hillside. Behind the inhabited area, which contained pottery sherds and many sloping benches, was a large and extremely well decorated passage. Bladed stalagmites, formed by the cave wind blowing the formative drips along a line, are a special feature of this area, which also contains massive stalagmite bosses, superb flowstone and the first of thousands of cave pearls which grow in unique profusion in the caves of Bai-Mo. The passage continues before finally emerging high in the side of the main cave passage below, a steep track down making the connection.

Down below, back at the stalagmite boss in the initial entrance to the cave, a path leads via a large arched passage, through a short dark zone and back into daylit cave. The path is used by the local villagers living in a deep doline valley reached by going through the cave to its second entrance, a collapsed chamber, where a vertical cleft allows them to climb out. The second entrance is reached via a vast portal, the way down from the upper passage joining before the lip of the exit. At this point the portal is over 90m high, with only a few metres of roof supporting the land surface above. Not surprisingly, the continuation of the cave on the far side of this giant skylight is obvious.

Not far inside - still in daylight - a large circular chamber is encountered, "Cloud Chamber", with a dried mud floor indicating seasonal ponding. There are two ways on. Straight ahead, a slope leads up past two enormous stalagmite sentinels and on into an even bigger chamber. (Mike Meredith, warden of the world's largest caves in Mulu, Sarawak, was heard to mutter around here, "If they get bigger, I'm going to explore myself out of a job!"). From beyond the sentinels a look back revealed a dramatic layer of cloud in the upper part of the first chamber, mysterious in the pale back-lit daylight. This was the first manifestation of the strange atmospherics of the big Bai-Mo caves. Roof domes were filled with static, humid air at around 22-23°C, while cooler air flowed along at the base of the passages, of speeds of up to 3m/s. The transition from one to the other was often abrupt - a matter of centimetres, so that it was possible to stand at the top of a rise in a passage with a cool draught blowing past your body while your head was hot, sticky motionless cloud.

The cloud layer often extended further down into the even larger chamber beyond the sentinels, obscuring the remarkable formations. One elegant stalagmite, over 30m tall, we nicknamed the 'Rocket'. At the end of this chamber, the passage is bisected by a massive stalagmite pillar. Up the left is a route which passes right through a stalagmite boss. At this point daylight can be seen and the exit is reached by climbing up a steep boulder slope, past massive dry-stone walling. This entrance, some 3m in diameter, is tiny in comparison with the cave below and is clearly just the accessible remnant of a much larger infilled arch. Directly across the valley is the imposing entrance to the continuation - Qian Dong. Returning to the chamber just inside the second entrance to Bai-Mo cave, "Cloud Chamber", one can enter a lower passage running west with clean-washed walls and roof and a mud floor which clearly carries a large stream in wet conditions. After 400m the passage divides, the right hand branch dropping down a rift after 60m to slow moving water. The left branch continues, with a mudcracked floor, until a squeeze through flowstone must be passed. A slope on the left descends to the phreas. Skidding along the muddy floor leads to an awkward blockfall which can be climbed directly or passed by an alternative route along epi-phreatic tubes of increasing size to daylight. To the right an eyehole drops around 30m to a river cave almost directly below. The slope is walled and terraced and obviously formed a living place in the not too distant past. However, even the remnant rice-mill and baskets were covered in layers of cracked mud, indicating that water fills the passage to a depth of many metres in times in flood. At the foot of the daylit slope the cave walls continue, giving the effect of a deep ampitheatre. This entrance, Ren Tung Dong, like most of the other ones, is gradual affair. It is quite clear that the caves were formed at a time when the surface relief was at least 100m higher than at present. The Fenglin karst surface of towers and dolines has evidently been corroded downwards until the Bai-Mo cave system has become truncated. In some places the truncation is relatively recent - as with the collapsed chamber forming the window between the first and second Bai-Mo caves - in others it has left gaps of nearly a kilometre, e.g. between Bai-Mo and Qian Dong.

'Round the corner' to the north east of the previous entrance, is an imposing river sink entrance. This quickly narrows to a 6m wide, 20m high canyon, with a deep canal entering the mountain below the drier cave above. The river sumps after 200m and carries the water which resurges into the lagoon at the first entrance to Bai-Mo.

Turning upstream, one can follow the stream across a wide doline, which on first aquaintance can be mistaken for a valley. Over to the west are sandstone hills rising to around IOOOm from which one stream joins this cave-river just before it enters the lowest level of Bai-Mo. At the time of our visit the stream on its sandstone bed was dry before it reached the confluence. To the east the 'valley' narrows and a descending outlet can be envisaged between the towers although in fact, the far end rises conclusively in a barrier of towers. So, back up the flowing river, past an unexpected and beautiful turquoise lake, the bed becomes increasingly walled in by jagged limestone before the rock finally arches right over the water. Not far inside this resurgence cave the way on is sumped at water level and it is necessary to search for the continuation 30m above. Half a kilometre along the doline is the entrance of Qian Dong (Figure 6), around 80m wide and high and the continuation of the main Bai-Mo passage.