Q: I am from Singapore and during my recent trip to Pulau Ubin (a remote island located north of Singapore), I come across this intriguing phenomenon on the ground on a hot sunny afternoon, where there are little holes on the ground with paddle of water on it, then there are bubbles coming out from the holes.
I wasn't sure if there are any living organisms living in them or it was a geological phenomenon, can you please let me know what is this exactly?
From Seth Wang (April 2010)
Reply by Dr Ted Nield
Thank you for your intriguing picture. There are occasions where simple sediment can – on beaches especially – produce trains of bubbles at surface. These are usually due to tidal movements, which suck air into sand when on the retreat, and then push it out when the tides re-advance. Usually the tide comes in before the air has all managed to escape, and so in shallow water you see trains of bubbles emanating from escape structures in the sand.
Your picture could represent something of the sort. The substrate however looks rather like a crumpet, which is a baked analogy rather interesting in this case. Crumpets form their bubbled structure as carbon dioxide escapes from the batter mix during baking, and the batter then sets, preserving the escape structures in “fossil form”. This appearance however is unusual in unconsolidated sand, and the clear definition of the holes from which the bubbles are emerging suggests to me that the substrate is bound together. So – I have a felling this is not a simple case of air escape, but may be complicated by a bound substrate – perhaps there are algae or bacteria holding it together.