Seakayaking in Thailand - Phuket, Phang Nga, Krabi, Khao Sok and South Thailand : Original Sea Kayak Tour Operator Since 1989

Hongs, Caves, Lagoons

How did the hongs form ?

Nobody knows for certain, though there are a few theories.

75 Million years ago Today

The significant amount of limestone found in the islands suggests that they were once coral reefs. The most likely theory is that the cave systems have probably been in existence since the formation of the coral reef. Underwater caves in reefs are common today and coral often grows upwards with large depressions and gaps. As the coral died and regrew upon itself en masse, large mounds of coral reef took shape. The gaps between the layers of coral were filled by deposits of clay and sand. Over time, these deposits hardened and adhered to the limestone. Approximately 75 million years ago, shifts in the earth's crust caused many of these mounds of coral reef to be pushed up through the surface of the water. Over time, rain and tidal currents eroded away a good portion of the softer deposits around the limestone, forming numerous caves throughout the islands

There may have been a roof over the top of the caverns that collapsed many years ago, perhaps as a result of an earthquake. If that is the case, then why are there so many hongs? Why did all the roofs collapse? How did the huge cavern below the roof get there? Why are there so many caverns?

Some theories compare the islands to coral atolls or coral islands- where coral grows up on the rim of an underwater dead volcano. A circular island is formed that often encloses a lagoon.

This theory is probably untrue since there are so many lagoons on Koh Panak alone. There were certainly not so many volcanoes so close together .

The formation of the lagoons was probably similar in nature to the way the caves were likely formed. When the rock was pushed out of the ground, the depressions would have collected water from rain. This rain water, being pure, could have dissolved minerals in the rock at weak points and formed a basin of water. As the tides worked in combination with the rain water to erode the sediment away, the caves and basins of water lying in the interior of the islands were connected.

koh hong