Water and soil instability are primary causes of sinkholes.
Sinkholes primarily occur in Karst terrain, areas that are supported by limestone, dolomite or gypsum, each of which is easily broken down by water. The effects of natural wear leave underground areas filled with rock cavities or voids, and the upper levels of earth unsupported. When these areas become disturbed by natural events or human habits, commonly earthquakes, hurricanes and construction, cave-ins and sinkholes may result. A number of factors work together to determine the risks of this occurring. Does this Spark an idea?
Common Signs
Deep cracks and large holes aren't the only indication that a sinkhole is present. Homeowners can keep a lookout for large cracks in joints, windows or door frames. These will often be an early indication that the ground is not stable and the home may be sinking.
Exterior signs may show up as cracks in the stucco, depressions in the yard or circular areas with dying plants. If homes, streets or sidewalks in the neighborhood begin showing these signs, it may be necessary to contact an environmental engineer to determine a course of action.
Declining Water Levels
In areas that are inclined towards drought conditions, sinkholes may become a serious problem. Both Florida and California are prime examples. Some areas of each state, both prone to drought conditions, have severe problems with sinkholes. This increased risk is the result of losing water from the aquifer, which provides support and some flexibility to the ground.
These qualities are especially important when builders put up large large structures --- homes, business or roadways --- over land that is already at risk. Increased groundwater pumping, usually a result of land development, increases these problems.
Soil Disturbance
The structure of soil is a fairly fragile thing. It relies heavily on a combination of factors and organisms that keep it fertile and stable, among them being the ability to filter water. When human or animal activity changes this delicate balance, it increases the risk of sinkholes.
In areas where the ground is worn and the foundation rock damaged by standing water, simple digging or drilling can cause a sinkhole. Just about any type of disturbance, even walking or biking, can compact soil, which will have negative effects on soil stability and its ability to move water.
Loam-type soils, which are ideal for gardening, are higher risk than a sand or clay-based soil, and water-saturated soils are at higher risk than dry soils. In areas where little or no freezing occurs, this compaction can be more devastating, since the frost-heaving will not recover the natural spacing needed to transport.
Vibration
Simple construction or traffic vibrations may push weakened ground to caving in. As with other causes, vibration can disturb the stability of soil, making it more likely to sink. Other problems can arise when heavy structures or roads are built over vulnerable land.
These situations can cause additional stress and weight to soil, which can increase the likelihood of sinkholes. Problems can be especially prevalent in times of excessive rain, which causes more shifting and flexibility in the soil.
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