Krabi Geology


Karst, Rock Climbing, & Birds' Nests

Krabi's spectacular land and seascapes are defined by its geology.

The karst landscape in Krabi has been formed from limestone (originally coral reefs hundreds of millions of years ago) where mildly acidic water, created from carbon dioxide in rain, has dissolved the soluble bedrock along cracks and crevices. It may look like the hills have been sculpted by wind and water erosion, but the process is mostly a chemical one, acting over thousands of years.

Where the sea meets a karst tower, the resulting overhand is caused by a combination of physical and chemical erosion.

Karst exists throughout the world, and many of the more famous cave systems are located in karst areas. Krabi is only one of three spots (with Haolong Bay in Vietnam and Dalmatian Coast of Croatia) where the karst hills and towers extend into the adjacent seas and the only fully tropical location.

The Krabi caves have been the sites of most its most important archeological discoveries. (See History page)

Karst formations are usually dotted with caves and underground streams. In the area around Nai Sa in Krabi, there are deep ponds that connect through underground passages, up to 7 kilometers apart. Some record-breaking, high-tech dives have been made here. At Than Bok Khorani Park at Ao Luek, a subterranean river flows from the base of a karst tower into a deep-green pond and a stream with shallow cascades.

The coastal caves are home to the small, sea swiftets whose delicate nests are harvested and used to make the expensive birds-nest desserts prized by Chinese gourmets. The most high-producing caves are closely guarded with visitors prohibited from entering. The nest is made from the bird's saliva, forming a gel-like nest that hardens. The swiftlets only use the nest once, so harvesting does not disrupt the breeding cycle.

The karst cliffs and towers create some of the world's most accessible and best rock climbing locations. Railay and Phi Phi are rock climbing centers. Most of the climbs are mapped, rated (European system), and bolted, with makes climbing quicker and safer. (Most countries prohibit installing bolts in natural formations.) New climbing locations on the mainland and the nearby Yao Islands (Phang Nga Province) are slowly developing also.

Photo by Thomas© : Karst at Railay, Krabi
One of the Hundreds
of Karst Towers in Krabi

Swiftlet Edible Bird's Nest