Why sinkholes open up
An estimated 35 guests escaped unharmed as the 50-foot (15-meter) wide, 15-foot (4.5-meter) deep crater broke glass, snuffed lights, and shook the ground at the Summer Bay Resort in Clermont, about ten miles west of Walt Disney World.
It's the second time this year a major sinkhole has roiled the region. In late February a mouth 20 feet (6 meters) wide swallowed 37-year-old Jeff Bush as he slept in Seffner, Florida, inhaling his entire bedroom. Five others in the house escaped without injury, including Jeremy Bush, who tried in vain to save his brother.
That tragedy left the community shaken and full of questions. To find out more about how and why sinkholes happen, National Geographic sat down earlier this year with Randall Orndorff of the U.S. Geological Survey.
What is a sinkhole?
A sinkhole is basically any collapsed or bowl-shaped feature that's formed when a void under the ground creates a depression into which everything around it drains, Kazinform cites National Geographic.
How many types of sinkholes are there?
There are two basic kinds. One is called a cover-subsidence sinkhole. You find these in places like the Shenandoah Valley, or in sandier soils where you've got a void underground. As the soil above transports itself into that cave in the rock, the ground slowly subsides. So it's not catastrophic. It subsides over time. It could be over years; it could be over hundreds of thousands of years.
The other kind is what we call a cover-collapse sinkhole. This is the one that makes the news. It tends to occur in clay, because clay holds soil together like glue. As with cover subsidence, soil is leaching into a cave below, but it creates a void in the soil that moves upward. You can't see it on the surface. Then, all of a sudden, the bridge over top of that void can't hold anymore and it collapses-just like we saw in Florida last week.
Do any human activities induce sinkholes?
Sure. Sometimes in karst areas [irregular landscapes formed when soluble rocks like limestone dissolve], when you drill a well-looking for water or for mining purposes-as you're pulling water out of the ground, you're lowering the groundwater table. That creates almost a toilet-flushing effect. You're lowering that groundwater level, and the soil that was sitting above just falls out. That's one way.
We also induce sinkholes when we start putting up parking lots and buildings and changing what we call the hydrologic regime. 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.
Full interview