Workers from the Des Moines Public Works Department are carrying out emergency work on a sinkhole which opened up in the garden of a home on the morning of Wednesday 13 April 2016, swallowing a tree about 15 m in height. The hole abruptly following a series of loud noises, causing the tree to sink vertically into the ground and cutting the power to nearby properties. The house closest to the home has been evacuated as a precaution, while power has been restored to other properties.
The 13 April 2016 Des Moines sinkhole. Des Moines Register.
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.
On this occasion the hole has been linked to a former mineshaft in the area, one of a number of such mines dug in the nineteenth and early twentieth centuries. Such old mines can be a serious problem in central Iowa (and other areas with old mineworkings), as the roofs of the mines, and any overlying strata, are supported only by wooden support beams, which eventually give way as they deteriorate. If sufficient solid rock formations overly the mineshaft, then this is not usually noticed at the surface, but if overlying sediments are poorly consolidated then sinkholes can develop at the surface. Iowa suffers a number of sinkholes every year, though not all occur in residential areas, with most of these being linked to old mineworkings in the central part of the state or soft limestone deposits in the northeast of the state.
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