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The karst formation of Phong Nha-Ke Bang National Park has evolved since the Palaeozoic and so is the oldest major karst area in Asia. Subject to massive tectonic changes, the park's karst landscape is extremely complex with many features of geologic significance, and many cave formations such as stalactites and stalagmites. The vast area, extending to the border of the Lao People's Democratic Republic, contains spectacular formations including 65 km of caves and underground rivers. The Phong Nha caves are reached through a pleasant river journey starting in the village of San Trach. The visits include one cave that is reached through an underwater river, and one cave that is reached after climbing many steps into one of the karstic hills. Phong Nha is part of a larger dissected plateau, which also encompasses the Ke Bang and Hin Namno karsts. The limestone is not continuous and demonstrates complex interbedding with shales and sandstones. This, together with the capping of schists and apparent granites has led to a particularly distinctive topography Situated about 50 km northwest of Dong Hoi township, Phong Nha - Ke Bang National Park was recognised as a world natural heritage site by UNESCO at its 27th general assembly session in Paris in July this year. Phong Nha-Ke Bang covers 85,000 hectares, including the most ancient limestone mountain range in Asia. The park has a system of nearly 300 caves, particularly the Phong Nha Cave, which boasts many fascinating rock formations, long underground rivers and wide pristine sand banks. Its tropical forest is home to 36 of the over 750 rare plant species listed in Viet Nam's Red Book as endangered, with some species listed as becoming extinct in the world. The park also boasts dozens of unexplored mountain peaks standing at more than 1,000 metres The caves demonstrate discrete episodic sequences of events, leaving behind various levels of fossil passages, formerly buried and now uncovered palaeokarst (karst from previous, perhaps very ancient, periods of solution); evidence of major changes in the routes of underground rivers; changes in the solutional regime; deposition and later re-solution of giant speleothems and unusual features such as sub-aerial stromatolites. The location and form of the caves suggests that they might owe much of their size and morphology to some as yet undetermined implications of the schists and granites which overlay the limestone. On the surface, there is a striking series of landscapes, ranging from deeply dissected ranges and plateaux to an immense polje. There is evidence of at least one period of hydrothermal activity in the evolution of this ancient mature karst system. The plateau is probably one of the finest and most distinctive examples of a complex karst landform in SE Asia. In summary, Phong Nha displays an impressive amount of evidence of earth’s history. It is a site of very great importance for increasing our understanding of the geologic, geomorphic and geo-chronological history of the region. |
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