http://news.yahoo.com/blogs/lookout/five-facts-sinkholes-214013987.htmlFive facts about sinkholes3/5/13
A gaping, 50-foot sinkhole that took the life of a Florida man, Jeff Bush, whose bedroom was swallowed up, made for scary headlines worldwide. But sinkholes, it turns out, are not as rare you would think.
The phenomena, for instance, are common in Florida, if only occasionally deadly. Here, with help from sources including the Florida Department of Environmental Protection and the U.S. Geological Survey, sinkholes explained:
How does a sinkhole form? "Cover-collapse" sinkholes occur when groundwater causes underground gaps that grow so big the ground above can’t support them. These can be dramatic events, since the holes can grow big enough to swallow a house, a road, a field or a swimming pool, even as those above ground go about their lives completely oblivious to the growing danger.
Are there other types of sinkholes? There are two other kinds:
"solution" and "subsidence" sinkholes, which don't make the nightly news.
That's because the changes to the topography happen slowly over time without catastrophic results.
Which states have sinkholes? The entire state of Florida is prone to sinkholes since it sits on top of a layer of limestone rock known as karst, which can be dissolved by acidic groundwater, according to the Florida Department of Environmental Protection.
According to the U.S. Geological Survey (USGS), other vulnerable states include Texas, Kentucky, Alabama, Missouri, Tennessee and Pennsylvania.
Are sinkholes common? Unlike hurricanes or earthquakes,
sinkholes aren’t tracked. But CNN reports that from 2006 to 2010 in Florida alone, there were 24,671 insurance claims for sinkhole damage, totaling a whopping $1.4 billion.
Can humans cause sinkholes? Yes. According to an interview with Randall Orndorff a U.S. Geological Survey supervisory geologist, human activities like drilling for a well or mining, which lower water levels underground, can cause sinkholes. So can putting up buildings and parking lots, he added, which changes where water drains. “Instead of the water naturally soaking into the ground, it's now running off and being concentrated—being put into the ground at one point," he said.
The massive sinkhole in Guatemala that was created in June 2010 is an example of one that was probably caused by human activity.
