Why are sinkholes round
A sinkhole is defined as a depression on the surface of the earth’s crust formed due to the disintegration of carbonate rocks like sandstone or limestone through chemical processes called karst processes. A sinkhole is known by other names like shake hole, swallow hole or doline as well. It is a natural phenomenon found to occur all over the world. What we are talking about in this article however, is a typical round sinkhole, otherwise known as a “dropout”.
For a dropout sinkhole to appear, the soil needs to be fine grained like volcanic ash or a karst bedrock formation. A fine example of such geographical conditions is of course of that of the famous Guatemala sinkhole. Heavy rainfall has a huge part to play in the formation of such sinkholes as it is this accumulated rainwater that runs right through the fine grained soil in channels, eroding it over time. The continuous eroding action of the underground water sometimes creates voids under the sediment into the shape of an arch. Once the arch formation is made, the rest is only a matter of time until the passing water pushes the arch up enough for it to reach the surface. When it collapses on reaching the surface, the arch naturally leaves a round depression on the surface, therefore creating a round sinkhole or a “cover collapse”.
The most amazing thing is that although most people believe that sinkholes are largely round, it is a misconception to begin with. There is no hard and fast rule that all sinkholes must be round, a sink hole usually takes the shape of the eroded underlying layer of earth, which can be anything from being an oval formation or just a random crack formation.
It is to be noted that some believe the Guatemala sinkhole, which is probably the most perfectly round sinkhole is not a sinkhole at all. “Piping Feature” is the name that is given to the phenomenon by a school of thought and in this school of thought it is believed that unlike the original sinkholes, which are natural in occurrence, this one is manmade.