Sinkholes

quote [A sinkhole, also known as a sink-hole, sink, swallow hole, shakehole, swallet or doline, is a natural depression or hole in the Earth's surface which may have various causes. Some are caused by karst processes—for example, the chemical dissolution of carbonate rocks or suffosion processes in sandstone. Others are formed as a result of the collapse of old mine workings close to the surface]. [more]

Have a look also at Sinkholes: When the Earth Opens Up a great article with an amazing photo gallery! ...and thesinkhole.org, the world’s largest collection of sinkholes images and video.

[Thumbnail: Sinkhole in the neighborhood of San Antonio, north of Guatemala city, on February 23, 2007].