Hang Sung Sot is a beautiful cave located in Ha Long Bay, northern Vietnam. It was discovered in 1901 by the French, named in 1938 by the French (Cave of Surprises) and welcomed its first visitors in 1993. In 1994, Ha Long Bay, where the cave is located, was inscripted as a UNESCO World Heritage area. The entrance is high above the bay on Bo Hòn Island, one of the 1,969 limestone monolithic islands that are topped with thick jungle vegetation.
Ha Long Bay has experienced at least 500 million years in the various geological states of orogeny (mountain building), marine transgression (where the sea level rises and covers land masses) and marine regression (where the sea floor is exposed above sea level). All of these phases contributed to the development of Cave of Surprises and the other caves in the area.
From 570-420 million BC, the Ha Long Bay area endured severe rains and flooding. In addition, the area was subjected to constant activity of the tectonic plates that created mountains deep under the water. After this period and until 240 million BC, the region was subjected to a very hot and dry climate along with the powerful forces of erosion and the Ha Long area emerged from under the sea and a limestone layer more than 3000 feet thick was formed.
During the period from 67 million to 9,000 BC, a mountain forming and erosion phase produced the mountains and the Ha Long depression that is seen in the area today. During this phase, 68,000-9,000 BC, the caves of the area were formed. Water seeped through cracks and eroded holes in the limestone. These holes allowed more water in, the erosion increased and the caves grew bigger. As some of the water seeped down to the cave ceiling, it slowly dripped and deposited sediment creating stalactites (formations that hang from the ceiling) and stalagmites (formations that rise from the floor) and other formations in the caves. From 9,000-1,000 BC, the sea advanced and its effects can be seen on the ceiling of the caves in the form of an interesting ‘wave’ effect.
The most remarkable geological events of Ha Long Bay’s history in the last 1,000 years include the advance of the sea, the raising of the bay area and the strong erosion that has formed coral and pure blue and heavily salted water.
A cave or cavern is a natural underground void large enough for a human to enter. The formation and development of caves is known as speleogenesis. Caves are formed by various geologic processes. These may involve a combination of chemical processes, erosion from water, tectonic forces, microorganisms, pressure, atmospheric influences, and even digging. Most caves are formed in limestone by dissolution.