Depressions or holes in the ground are not necessarily the result of sinkholes. Depressions or standing water may be the result of the natural contour of the landscape, and small holes may be created by animals or insects. A variety of signs in the landscape and in buildings, however, may be the effects of sinkholes on the area around them. There are three different types of sinkholes, each with a different surface appearance.
A dissolution sinkhole occurs when rock beneath a thin layer of surface soil is dissolved and carried away by water. The resulting sinkhole often appears as a depression in the ground, and the depression may be filled with water.
A cover-subsidence sinkhole occurs when there's a thick layer of permeable soil above the dissolving rock. These sinkholes develop slowly and often imperceptibly as the soil settles into the cavity created by the dissolved rock.
A cover-collapse sinkhole occurs when a layer of heavy soil above the dissolving rock remains in place until it is eroded from below to the point that it collapses suddenly into the cavity.
Several problems in buildings may indicate that a sinkhole is forming near the building. Cracks in foundations, walls or floors can be a sign that a sinkhole is causing the building to shift, as can be doors or windows that don't close correctly.
Muddy or cloudy well water in a home's water supply may be caused by sediment flowing from a sinkhole into the well.
Signs in the Landscape
Areas of bare soil or eroded gullies may occur where water flows into a sinkhole and carries surface soil along with it. A pattern of surface cracks around a circular depression may be a sign of a sinkhole that is close to collapse.
Patches of wilting or dying grass or other vegetation may be an indication that a sinkhole is draining water away from the plants' roots.
Trees, fences or other structures that begin to lean may be undermined by a sinkhole, and foundations, walls, fence posts or other structures that were once buried but are now exposed may also be evidence of soil being carried into a sinkhole.
Depressions in the ground that appear suddenly or ponds that form in new locations may be an indication of sinkhole formation, as well.
If you suspect that a sinkhole is forming on your property, rope off and stay away from the area, and then contact your homeowner's insurance company. An insurance adjuster will assess the situation and determine if it's necessary to call in an engineer.