Florida Karst Sinkhole Tragedy


Patrik Jonsson of the Christian Science Monitor, writes “one of the most heavily developed states is also one of the most geologically hazardous – two facts that are not mutually exclusive in creating dangerous sinkholes.” He is referring to the news of a man being swallowed up by the earth as he slept in his Seffner, Florida, a victim of a sinkhole in a karst-based environment.

[. . .The] tragic series of events that began [. . .] as a 30-foot hole that swallowed Jeff Bush as he slept [. . .] also highlights just how geologically hazardous the Sunshine State is, and how human activities have likely increased the number of sinkholes – essentially geological plumbing breaks as the ceilings of carved-out limestone caverns buckle. Within a mile of Mr. Bush’s home, which apparently sits atop a 100-foot-wide cavern, are 16 verified sinkholes, compared to over 15,000 known sinkholes throughout the state.

Known as a “karst” landscape, Florida, which was once part of the seafloor, sits on a vast limestone bed cratered with caverns dug out over eons of tidal and chemical weathering. About 10 percent of the earth’s landmass is karst, meaning land shaped by eroding bedrock. “What feels capricious to those above is the toll of an active planet, one of those improbable collisions of a human timescale and a geological one,” writes the Atlantic’s Rebecca Rosen on Friday.

[. . .] Sinkholes usually collapse in slow motion. Walls crack, strain, and complain as the earth begins to slowly give way under a house. In the vast majority of cases, residents have enough time to gather valuables and evacuate the premises. “Losing a house to a sinkhole is very common, losing life is uncommon,” says retired University of Florida geologist Tony Randazzo. “Most people will have some warning of the pending doom or catastrophic collapse. But there apparently were no warning signs of what happened at the Bush house. That would be very scary.”

[. . .] Changes in drainage due to construction or agricultural irrigation have been known to activate mass outbreaks of sinkholes, where dozens of sinkholes can suddenly appear next to drainage wells and farm fields. Drought followed by heavy rains can also instigate sinkholes as heavy, water-logged earth presses down on limestone caves suddenly devoid of buoyant water. The two previous deaths attributed to sinkholes both involved professional well drillers whose activities cracked the top of limestone caverns, causing collapse. “Humans can [destabilize karst landscapes] by drawing down water tables or irrigate too much, increasing the weight of the mass of materials that sits on top of the void,” says Jonathan Martin, a geologist at the University of Florida, in Gainesville. “Humans can modify the environment” enough to cause sinkholes. [. . .]

For full article, see http://news.yahoo.com/cause-florida-sinkhole-tragedy-human-activity-revenge-karst-140923625.html

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