Phong Nha - Ke Bang national park
Phong Nha - Ke Bang National Park is a huge national park located in Bo Trach and Minh Hoa Districts of central Quang Binh Province, in north-central Vietnam. The National Park is about 500 kilometers south of the nation's capital, Hanoi. The park was created to protect one of the world's two largest karst regions with around 300 caves and grottoes, and the ecosystem of limestone forest of the Annamite Range. The core zone of this national park covers 85,754 hectares, which are divided into three zones, a "strictly protected zone" (64,894 km²), an "ecological recovery zone" (17,449 km²), and an "administrative service zone" (3,411 km²). The plateau is probably one of the finest and most distinctive examples of a complex karst landform in Southeast Asia.
The karst landscape is an extremely complex and ancient one, with high geodiversity and some geomorphic features of considerable significance. It has an Earth crust development history from the Ordovician period (464 million years ago).
The karst formation process has resulted in many features such as underground rivers, dry caves, terraced caves, suspended caves, dendritic caves and intersecting caves. The active river caves are divided into the nine caves of the Phong Nha system discharging to the Son River, and the eight caves of the Vom system discharging to the Chay River. The Phong Nha Cave is the most famous in the entire system, with a currently surveyed length of 44.5 km. Its entrance is the last part of an underground river that connects with the Son River and tour boats can penetrate inside to a distance of 1,500 m. Other extensive caves include the Vom cave at 15 km in length and the Hang Khe Rhy cave with a length of 18,902 m.
The Phong Nha–Ke Bang karst has evolved since the Paleozoic (some 400 million years ago) and so is the oldest major karst area in Asia. Like much of Vietnam, it has been subject to extensive tectonic changes, thus the limestones of Phong Nha are inter-bedded with a number of other rocks. There is also strong evidence that sulphurous solution and hydrothermal action have played an important role in shaping the broad-scale landscape and the caves.