Page 12 of 23
Phong Nha System Overview
The Phong Nha system starts about 40 kilometres south of Phong Nha Cave.
Near to the Vietnam/Lao border a series of streams and rivers enters the limestone. The area was first accessed from the village of Ban Ban at kilometre
44 on the road 20. Heading east from the village a few small streams are noted. These all enter the limestone and find their way into Hang Khe Ry. The entrance to Hang Khe Ry is a large dry entrance. A large dry passage continues and soon leads to the main streamway. This cave forms a major part of the Phong Nha system. It is almost 19 kilometres long and eventually emerges in a small valley beyond Hang En. To the east of Hang Khe Ry, Hang Khe Thi is reached. This river joins Hang Khe Ry several kilometres into the system. The final sink to the east is Hang Khe Tien. This has only been explored for about 500m, but the water is believed to eventually connect with Hang En. The next expedition plans to continue exploration of the Khe Tien area.
Hang En is the next major cave in the system. A large river enters and flows through Hang En before joining with the water from Hang Khe Ry. Upstream of Hang En, a few short caves Hang Vu Ca Tau, Hang Khanh and Hang Hong form part of the system. Water from these caves joins the river leading to Hang En. Hang En has one of the largest sections of cave passage in the system. At one point the passage is 100m wide and at least 50m high. The cave is very spectacular. Exiting from Hang En, you enter an enclosed valley. The water from Hang En and Hang Khe Ry combine, and disappear underground in a mass of enormous boulders. Attempts to pass the boulder choke have so far been unsuccessful. There are a number of high level caves above Hang En and Hang Khe Ry. Hang Long, Hang Phong, Hang Doi, and Hang Ho Nui are all very well developed caves, but are not connected with the current drainage of the Phong Nha system. Often well decorated most of them end in calcite blockages.
The next cave in the sequence is Hang Toong. This cave was explored in 1994. The water from Hang En and Khe Ry passes through an unknown section of cave before it is found in the 3 kilometre section of Hang Toong. Finding a way into this unknown section of cave is still a priority for the expedition. The water emerges from Hang Toong, and continues to Hang Tra An. Until 2007, the caves of Hang Tron and Nightmare Shaft were unexplored. The exploration of these caves completes the link between Hang Toong and Hang Tra An. Hang Tra An was first surveyed in 1992. It is about 600m long, ending in a sump. In 2001, the team explored Hang Nuoc Nut. A dry entrance leads into a very well decorated cave and a large stream passage. 2.2k long the water emerges and flows above ground to join the Tra An river. This large river flows on the surface for 4km until it enters the Phong Nha cave.
The water disappears into a large jumble of loose rocks and tree trunks. The water enters in lots of places and we have been unable to find a way into the top end of Hang Phong Nha.
Above this area is the entrance to Hang 11. This small stream cave is not yet fully explored, but must connect in some way to the Phong Nha system. At the bottom of the road 20, 3-4 kilometres before Phong Nha village, there are a number of small caves on the edge of the limestone. Hang Duc contains a
small stream, and was explored for 1.3 kilometres. It ends in a large sump pool at the down stream end. This may also feed into the Phong Nha system.
Hang Phong Nha is 7.7 kilometres long. It has long sections of deep water passed by swimming, some sections of wading and walking along sand banks, and nearer to its exit some well decorated dry sections of cave. The first full exploration and survey of the cave was completed in 1992. In 2003, whilst working on the entrance to Phong Nha, the locals uncovered a dry entrance some 100m above the river entrance, Phong Nha Kho is a large dry well decorated section of cave 980m long which ends in a 10m pitch down to a lower level and a final calcite choke. This cave has now been opened up to tourism.
To the West of Hang Phong Nha lies the Hang Toi system, comprising Hang Toi, Hang E and Hang Hung Thoc. Hang Hung Thoc lies near kilometre 14 on road 20 and is 450m long. It is in an area which obviously floods in the rainy season.
The entrance is very close to the end of Hang E. Water flows through Hang E 740m long, resurges and enters Hang Toi which is over 5 kilometres long, and is a very large impressive cave. It is believed that the Hang Toi system is formed by flood overflow from the Phong Nha system. When water levels are high, the choked upstream end of Phong Nha cannot take all the water, which is believed to overflow to the Hang Hung Thoc area where there are many places for water to sink.