Wednesday 20 November 2013

Homes destroyed by Florida sinkhole.

Two homes have been destroyed and a further four evacuated after a sinkhole opened up in Dunedin in Pinellas County, Florida on Thursday 14 November 2013. The hole first appeared early in the morning, and by noon had reached 20 m wide and 15 m deep. The next morning it was 27 m wide and had begun to swallow houses on either side, prompting local authorities to order an evacuation.

Homes damaged by the Dunedin Sinkhole. Luke Johnson/Getty Images.

Sinkholes are generally caused by water eroding soft limestone or unconsolidated deposits from beneath, causing a hole that works its way upwards and eventually opening spectacularly at the surface. Where there are unconsolidated deposits at the surface they can infill from the sides, apparently swallowing objects at the surface, including people, without trace.

Southwest Florida is particularly prone to sinkholes, due to the porous limestone that underlies much of the area. This is eroded over time by acid in rainwater (most rainwater is slightly acidic, though pollution can make this worse), and can collapse suddenly, causing overlying sediments to collapse into the hole and a sinkhole to open up. This can be triggered by human activity, such as pumping water out (which causes the water to flow, facilitating acid dissolution of the limestone), but is essentially a natural process. 

The approximate location of the Dunedin sinkhole. Google Maps.

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