Today's photo is a vertical framing taken inside a hong. I think it better demonstrates the scale of the space.
The islands in Phang Nga Bay are a karst limestone formation. This name refers to a landscape where a mildly acidic water has acted on a weakly soluble rock – such as limestone. Over time as more of the rock dissolves, large caves are formed. Eventually, more and more of the rock is dissolved leaving isolated towers behind.
Thus, the hong might be a collapsed cave, a sinkhole or simply where the rock has dissolved within a bedrock tower.
Over time these remaining towers will themselves dissolve as rain attacks the exposed sides, and the rock cleaves along the fissures in the natural weathering process. Maybe we should have been wearing hard hats!
