Chemical sedimentary and carbonate rocks are responsible for sinkholes throughout the country. The U.S. consists of 35 to 40 percent chemical sedimentary rocks, such as gypsum, anhydrite and salt. Carbonate rocks are limestone and dolomite. Although the land looks steady, dramatic and catastrophic sinkholes can suddenly occur.
Meaning – A sinkhole is “a hole or depression in the ground that results from surface material moving into subsurface pathways caused by the weathering process,” according to the Pennsylvania Department of Environmental Protection.
Sinkhole Characteristics – Some sinkholes may evolve gradually as a bowl-like depression. Other sinkholes may form quickly into a deep, water-filled crater. The size of the cavity’s subsurface and the thickness of the organic or sediment matter determines the sinkholes’ shape.
Collapse Sinkholes – Collapse sinkholes occur immediately, forming deep holes in the ground. Water fluctuations trigger collapse sinkholes. When the water constantly changes, it puts pressure on the cavity’s roof, which eventually weakens.
Subsidence Sinkholes – Subsidence sinkholes form when the sediment matter thins. Sand granules replace the limestone, appearing as concave depressions. As the sand granules fill the hole, it begins to restrict the water flow from the bottom, holding water. This eventually creates a lake.
Solution Sinkholes – When the overburden or sediment matter depletes, the limestone erodes from the environment. Over time, a solution sinkhole gradually forms and the rock continues to erode.
Land Surface – Areas containing carbonate rock, limestone, rock or salt beds under the land surface are more likely to have a sinkhole. A sinkhole can occur without notice; the land is intact before it occurs.