Sinkholes: get the facts
Sinkholes often take thousands of years to form and vary in size from small to extremely large. Sinkholes are found all over the world. In the U.S., sinkholes are especially common in Texas, Alabama, Missouri, Kentucky, Tennessee, Pennsylvania and Florida, according to the U.S. Geological Survey. Causes of sinkholes: According to the PA DEP, some of the causes of a sinkhole are:
- Water dissolved minerals in the rock, leaving residue and open spaces within the rock. (This is called "weathering".)
- Water washes away the soil and residue from the voids in the rock.
- Lowering of groundwater levels can cause a loss of support for the soft material in the rock spaces that can lead to collapse.
- Changing groundwater gradients (due to removing or introducing water to the system) can cause loose material to flush out quicker from the voids and the surface to collapse in response.
- Any change to the hydrologic system (putting more water in or taking it out) causes the system to become at least temporarily unstable and can lead to sinkholes.
- Sinkholes can result from seasonal changes in the groundwater table, freeze and thaw of the ground, and extremes in precipitation (drought vs heavy rain).
What to watch for:
- slumping or sagging or slanting fence posts
- buildings or trees that start to lean
- doors and windows that don't close properly
- foundations begin to slant
- new ponding of water after rain
- wilting of circular areas of vegetation
- dips, depressions and slopes that appear in a yard
- ground, wall, floor and pavement cracking (different from hairline cracks)
- sudden drainage of a pond
- rapid appearance of a hole in the ground
Sinkholes can be stopped:
If a sinkhole is caught early grout can be injected into the hole to rebuild a foundation over the degrading bedrock.