A parish in Lousiana is being swallowed by a sink hole (sometimes known as swallow holes because they swallow objects). At http://blogs.smithsonianmag.com/smartnews/2013/08/watch-this-sink-hole-s… … there is a video of the sink hole in action. It is 25 acres across and is still growing. It may have an origin in local mining or an unstable salt cavern (with some seismic activity added to the brew). The US Geological Survey people determined that the collapsing solt cavern was responsible for the earth tremors and not the other way around. Gas has also found its way up into the bayou (a large swamp or marsh) and caused the soft mud to bubble, adding tecture to the brew.
Note … swallow holes are a common geological feature around the world, including Britain. Some of these have an origin in the Ice Ages and permafrost melt and refreezing. They can be seen qite clearly in rock faces – at quarry sites for example. In chalk they tend to have a brown complexion, markedly different from the white chalk, and form a V shape. Other swallow holes exist in the modern world and are fairly common. For eample, there is one in Burnham Beeches, and branches of trees are regularly sucked up (given a helping hand by small boys). This is a tract of old wood pasture, endemic across the Chiltern plateau, purchased by the Corporation of London in the late 19th century (or early 20th) as a recreation area for its citizens. People used to ride out from the suburbs in pony and trap and pick bluebells, have a picnic and a walk, or kick a ball around with the kids, and much the same continues nowadays (but people arrive in cars).