A sinkhole is a natural depression or hole in the Earth’s surface caused by:
karst processes or the chemical dissolution of carbonated rocks or salt beds.
suffosion processes for example in sandstone.
Carbonated rocks such as limestone can be dissolved by water, especially acidic water.
When the carbonated rocks dissolved, there will be empty space or hole under the ground.
When there is nothing more to support the surface land, the gravity caused the surface land to suddenly collapse into the underground hole.
And that causes a sinkhole.
Suffosion processes can also cause sinkholes.
This picture will explain the suffosion processes.
Formation of a suffosion sinkhole
Sinkholes are very dangerous especially when it happens in the city under big buildings or busy highways.
In 2010, a giant sinkhole in Guatemala City caused by heavy rain from Tropical Storm Agatha swallowed at least one three-story building!
Here are photos of some sinkholes:
A sinkhole covers a street intersection in downtown Guatemala City, Wednesday, June 2, 2010. Authorities blamed heavy rains caused by tropical storm Agatha as the cause of the crater that swallowed a a three-story building but now say they will be conducting further studies to determine the cause. (AP Photo/Moises Castillo)
John Sparkman is dwarfed as he looks into a sinkhole near Picher, Okla., Saturday, April 6, 2008. (AP Photo/Charlie Riedel)
A giant sinkhole that swallowed several homes is seen in Guatemala City February 23, 2007. REUTERS/Daniel LeClair
A massive, approximately 200′ x 240′, sinkhole opens up and tears apart the pavement of Soledad Mountain Road, October 3, 2007 in the Mount Soledad neighborhood of La Jolla near San Diego, California. The landslide has damaged or destroyed reportedly 6 homes and forced the evacuation of at least 20 others. (Photo by Kent Horner/Getty Images)
A Cadillac Escalade sits at the bottom of a sinkhole in Milwaukee, Wis. on Friday, July 23, 2010, still running almost 20 hours after the driver fell in. On Thursday, powerful storms pounded southeastern Wisconsin and caused widespread flooding. (AP Photo/Mark Was)