Blue holes

Blue holes along low-lying coastlines are the remnants of sinkholes formed during past ice ages when the sea level was 300 to 400 feet lower than today. As sea levels rose, the sinkholes became flooded, forming vertical caves. Noticeably high depths of the sinkholes impart it a dark blue colour and hence the name is derived.

Sinkholes after rain

Heavy rains can trigger the collapse of a sinkhole that had been slowly forming earlier. When rainfall collects in an area where water previously did not collect, that is another sign that the land is subsiding.

Sinkholes: warning signs

Sinkholes form when water dissolves minerals in the bedrock leaving the structures on top of the ground sitting precariously on loose soil that can quickly wash away. If a sinkhole is in the process of forming, the structures on top of it can give a hint to its existence: for example, slumping or sagging fence posts, and trees that start to lean. Subtler signs can include doors and windows that don’t close properly.

Artificial sinkholes

Artificial sinkholes get created due to human activities like mining, salt cavern storage, leaking of old sewerage pipes, drain pipes and water pipes. Sinkholes also get created due to over pumping and extraction of groundwater and subsurface fluids. The construction of sub surface industrial storage ponds creates substantial weight and finally results in the collapse of supporting material causing a sinkhole.

Published in Dawn, Young World, September 3rd, 2022