AREA 20: Tam Duong

TD1 Duy Phong Cave (2000 Expedition)

The entrance is located about 1km east of Duy Phong village where the limestone and the granit meet. A small river drops (20m pitch) into a rather large gallery (3x4m) where it can be followed down between blocks, descending a long waterfall into a nice and high chamber towards a large sump. Huge granite blocks can be found throughout this gallery. There are no mud or clay deposits. This river is supposed to be part of the ‘Sin Cau’ cave system which develops from the north to the south over a (supposed) distance of over 10km. Some other fossil caves and active dolines were visited in the same area, without much promising results.

TD2 Sin Cau 1 (2000 Expedition)

As well as Duy Phong Cave this entrance is situated at the contact between limestone and granit. The river which flows from the east over the granite disappears underground once it reaches the limestone. The direction of the flow also changes towards North-South. The entrance is a large porche with many different departures of galleries. Following the water over  blocks in a nice gallery one quickly reaches a sump. Swimming over the sump pool leads to some additional passages however without real continuation. At the pool it is possible to climb up (7m) between formations to a fossil gallery which in one direction leads back to the entrance and in the other other direction to an second exit about 100m. further. In this gallery, which probably acts as an overflow there are a lot of deposits. There are signs of different stages of cave formation (including old deposits which are partly removed again). The water in this cave is supposed to go to the collector of the Sin Cau master cave.

TD3 Sin Cau 2 (2000 Expedition)

The entrance of this cave is between blocks at the eastern end of the doline which can be found at the exit of Sin Cau 1. A little climb down leads directly into a large and muddy gallery where one can hear the river. The gallery is about 5 to 6 m wide and 7 to 8m high and offers indeed an acces to what we suppose to be the master cave of the whole Sin Cau system. After 100m the fossil gallery gives way to the streamway which can be reached by climbing down a steep wall. Downstream the river (4 to 5m large and deep) can be followed by climbing along the wall on the left bank for about 50m. A side passage then leads back after another 50m to the point where the river sumps. Upstream a big metro gallery can be accessed, developing about 6 to 10m above the waterway. This beautifully shaped gallery (4 to 5m wide and 10 to 15/20m high) can be followed to a crossing where an inlet joins the main river. At this crossing a nice lake (10mx 15m) is met. It can be crossed by a fine climb along the leftbank. A climb over blocks at the other side gives access to the continuation of the metro gallery, which still appears to function as overflow in the flood period. This gallery can be followed for another hundred meters where it leads back to the level of the water. At this point one enters a 800m long gallery with the aspect of a real master cave. The water is streaming through a very high ellips shaped meandering gallery (3 to 5m width with sometimes an enlargement) with clean floor and walls. This fantastic underground river can be followed for about 800m upto a large sump which can be shunted to a second final sump. It is only at this point that large sand and mud deposits are present showing indeed that the water flows very slowly here. A few inlets to this gallery were explored without giving way to real important extensions. A thorough search could reveal further galleries.

TD 4 Sin Cau 4 and 5

The entrance is a large porch a few meters above a small disappearing river. The cave starts with a very large (20m width and up to 15m high) and dry gallery (dry at least during the winter season), where one progresses over big blocks and large rounded stones. After about 80m the gallery narrows considerably and through a small passage which will certainly form a sump during the rainy season one enters a beautifully shaped gallery of smaller dimensions (2m large, 4 to 5m high). This gallery, with flowstone and small steps down, dips in an angle of about 60°. A first small pitch (6m) is soon followed by a slippery and delicate step to another little pitch (7m) which lands in a nice active streamway. We first thought that this streamway was the same as the one which disappeared in the entrance. However, as the map shows, it could well be that this water is coming from other sinkholes more to the north of Sin Cau 4. During this expedition we didn’t find the time to follow the river upstream (to be continued). Downstream, the river meanders first through a low but large gallery (4 to 5m large, 1m high) which then opens up (5 to 6m large, 2 to 4m high). Sometimes the river fills the whole width of the gallery, sometimes it meanders nicely around sand and stone deposits. Progress is easy either through the water or on the banks. On the left bank inlets occur at three points. We followed two of them for some hundred meters upstream through nice galleries without reaching the end (not surveyed, to be continued). The river in the main gallery can be followed for about 500m to where it enters a much larger and very important streamway. This stream is supposed to be the down end of the master cave of the Sin Cau water system. It can be followed downstream through a sometimes huge (20m width, 30m high) and very beautifully decorated gallery by progressing mainly on the right bank. Some side galleries were noticed but not explored. The river comes in to the open by an impressive porch. Upstream of the intersection the river can be followed, mainly on the left bank, for another 400m to a large boulder choke where the river flows out as a cascade through the blocks. An intensive search could not reveal any passage through. Allthough it seems rather unrealistic to find an easy acces to the upstream part of the master cave by remaining near the river, it is certainly worthwhile to futher investigate the important inlets and the upstream part of the first smal streamway. It will for sure deliver important extensions and it is might access to the fossil master cave. Signs of the existance of this fossil master cave have been noticed and maybe it will enable us to find another access to the upstream part).

TD4 Sin Cau 4 & 5 (2001 Expedition)

Development: 2080, Denivelation :    -47

The cave exploration was continued. Starting from the P6, the rope ends in a pool. Walking upstream in a wide gallery the river meanders through rounded pebbles and boulders. At the far end we find a very narrow gallery, which is too small to pass.

Walking downstream from the bottom of the P6 we found a first inlet on our right side. A small river meanders through a muddy wide gallery (often more than 10m wide). Half way this gallery we found an important gallery with high boulders and pebbles. At the end of this inlet gallery we found different smaller inlets.

There is also a second inlet downstream. A low but wide rectangular shaped side gallery, 50m long.