THE PHONG NHA SYSTEM
Phong Nha Cave was first explored and surveyed in 1990. This magnificent river cave was surveyed for 3.3km and left wide open with the large streamway continuing. It was therefore one of the major objectives of the 1992 expedition. The exploration was continued for a further 4.4km to give the cave a total length of 7.729km. The majority of the cave is stream passage with some short sections of dry high level passage. The cave ended at a large boulder choke. This ties in with the surface features. At this point the water is seen on the surface. A check revealed no obvious way into Phong Nha through the boulders.
This year local people informed us of a dry entrance above Hang Phong Nha. Located 100m above the river cave this dry well decorated cave was surveyed for 982m. The passage ended at a choke, with no connection to Phong Nha cave.
Following the Phong Nha water upstream on the surface for about 4 kilometres, the cave of Hang Cha Ang is reached. The water resurges from two entrances, but inside the cave the two streams unite. In 1992 Hang Cha Ang was surveyed for 667m to a sump. Further to the south, the continuation of this cave was surveyed downstream for 197m towards Hang Cha Ang. It was not completely explored. Some of the water resurging from Hang Cha Ang is believed to flow to the west and through the caves of Hang E (probably known locally as Hang Tre) and Hang Toi, into the Chay river.
Hang Toi was explored in 1990 to a length of 4.5km. The passages are very large up to 50m wide and have obviously been formed by a large river, although the present stream is quite small. The cave was explored from the Chay river to it’s exit in an enclosed doline. In 1992 it was extended by 758m and the continuation Hang E was explored in 1992 and 1994. We believe that Hang Toi will be a flood overflow for the Phong Nha system in the wet season. Hang E was surveyed for 736m all of it by swimming to a sump.
Upstream of Hang Cha Ang, the river is again seen on the surface flowing from the catchment area in the south. After about 1 kilometre, the entrance of Hang Thung is reached. The entrance is located at the head of a large collapse doline. Two entrances unite after 30m, where a climb up into a high level passage is necessary to regain the main streamway. The majority of Hang Thung is very active river cave. There are many long swims, fast flowing rapids and several large collapses. The cave was explored and surveyed in 1994 to a total length of 3.351km, before ending in a sump in all directions.
In 1994 Hang En was also explored. Known by many local woodcutters and obvious from the map to be the next possible entrance to the Phong Nha system. Walking from the village of Son Trach, the team took two days to reach the entrance. The size or beauty of the cave did not disappoint them , but unfortunately this section of cave was only 1.645km long and exited into an enclosed valley. Hoping for a further continuation, the team followed the river downstream. Sadly the water disappeared into a massive tree and boulder choke, with no possible access. Hang En contains a large river, probably the majority of the Phong Nah river and is in places 120m wide. Many expedition members have now visited Hang En and described it as one of the most spectacular cave entrances they have seen.
According to the maps of the area, the water resurging from Phong Nha cave comes from a series of sinks located to the east of the village of Ban Banat kilometre 44 on the Ho Chi Minh road. It was not practical to reach these on foot from Son Trach via Hang Cha Ang, Hang Thung , Hang En etc, so our main objective in 1997 was to get to Ban Ban and attempt exploration from there.
Luckily for the team many vehicles were using the Ho Chi Minh road to collect rattan from Laos. We were able to arrange transport on one of the six wheel drive vehicles to Ban Ban. At Ban Ban we arranged local guides to take us to each of the sinks on the map.
The first sink to the east of Ban Ban known as Khe Rung. The stream sank over a wide area at the foot of a limestone cliff. Unfortunately no entrance was found as the water sank in a mixture of boulders and rotting vegetation. A short dry cave in the cliff was explored with no way on. En route to the next sink Khe Rhy, a small stream is crossed, which sinks into a small entrance into Hang Khe Rhy.
Reaching the second stream, the water was found to sink in a very small entrance among boulders. 200m beyond the sink, following a dry streambed, a large entrance was reached. Surveying in, the main river passage from Khe Rung was reached after 700m.
The upstream passage led to a sump after 700m. Downstream, the main river passage was followed for about three kilometres, at which point there are two inlets fairly close together. The first is the water from Khe Rhy sink, and the second the water from Khe Thy sink. There is no way in at Khe Thy. The entrance being a sump. A further four kilometres was surveyed in the available time, leaving the stream passage continuing. The total length of Hang Khe Rhy was 13.817km in 1997.
One team made the difficult journey overland from Khe Rhy to Khe Tien. A dry entrance was explored and surveyed for 520m to a sump. At this point due to rainfall somewhere in the catchment area, the entrance was also sumped, so it is possible that in dry conditions the cave may go further.
The main objective of the 1999 expedition was the full exploration of Hang Khe Rhy. A team of seven, took enough food and equipment into the cave for a four-day camp.
Due to the length of the cave it was not practical to reach the end continue the exploration and return to the surface in one trip. Disappointingly the cave surfaced again after a further 1.9km of streamway. The total length of the cave is now 18.902km. The cave was found to resurge into the Hang En valley, between Hang En exit and the choked sink. Khe Rhy exit is not easily visible from the Hang En valley. The water from Khe Tien has not been found in Hang Khe Rhy. Another entrance upstream of Hang En was noted, which could lead to Hang Khe Tien.
To summarise, the first sink into the system is Khe Rung, which forms the upstream section of Hang Khe Rhy. A small nameless stream then enters the system. Khe Rhy and Khe Thy waters enter fairly close together, about 7km into the system. Khe Rhy exits into the Hang En valley after 18.9 kilometres of cave. Hang En is 1.67km long and the combined waters of Hang En and Hang Khe Rhy flow throughHang Thung (3.351km), Hang Cha Ang ( 860m), and Hang Phong Nha 7.729km) to the Son river. Some of the water between Hang Cha Ang and Hang Phong Nha flows to Hang E (736m)and Hang Toi.(5.256km) to the Chay river. Thus the effects of any logging ‘pollution’ etc in the catchment area to the east of Ban Ban will be felt all the way to the Son and Chay rivers.
The length of the system including all the caves described is 40.018km.