Wednesday, 5 October 2016

Sinkhole swallows car in the Adelaide Hills, South Australia.

A couple escaped without serious injury after their car was swallowed by a sinkhole at Glen Osmond in the Adelaide Hills of South Australia, at about 11.30 pm local time on Tuesday 4 October 2016. The pair were in the vehicle at an overlook when the hole opened up beneath them; they were able to escape unharmed, but the car could only be removed with the help of a crane.

Vehicle trapped in a sinkhole at 4 Glen Osmond on 4 October 2016. Denny Spence/ABC.

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.

The Glen Osmond sinkhole is thought to have occured due to subsidence into an old mineshaft; the area was a center of mining from about 150 years ago up until about 40 years ago. The collapse is likely to have be related to heavy rainfall that has fallen across South Australia this summer, driven by a climatic event called a Negative Indian Ocean Dipole Phase. 

Indian Ocean Dipole Phases are similar to the El Niño/La Niña climatic oscillation that affect the Pacific Ocean. Under normal circumstances equatorial waters off the east coast of Africa and west coast of Indonesia are roughly similar in temperature, however during a Negative Indian Ocean Dipole Phase the waters off the coast of Indonesia become significantly warmer. As the prevailing currents in the area flow west to east, this warm water is then pushed onto the shallower continental shelf of north Australia, where it warms the air over the sea more rapidly, leading to increased evaporation (which fuels rain) and a drop in air pressure over the east Indian Ocean and west Pacific. This in turn drives air currents over the Indian Ocean to flow more strongly west to east, leading to higher rates of  cooling off the coast of Africa (where more water is drawn up from the cool sea depths) and more warming off the coast of Indonesia, fuelling a feedback cycle that tends to remain through the winter season in any year when it forms. This leads to a particularly wet winter across much of Australia, as well as a potentially damaging heatwave in the north, while much of East Africa is at risk of drought (during a Positive Indian Ocean Dipole Phase the reverse happens, with drought in Australia and flooding in East Africa).

 Areas of warming and cooling and air flow during a Negative Indian Ocean Dipole Phase. Australian Bureau of Meteorology.

See also... begin amid widespread flooding in South Australia.                                       The South Australian State Emergency Service has begun evacuating people from low lying areas in Old Noarlunga and other parts of the Onkaparinga River basin, as well as parts of the Adelaide Hills and... trapped by sinkhole at Cape Burney, Western Australia.                                          A car became trapped after falling into a sinkhole at Cape Burney near Geraldtown in Western Australia at about 6,40 a.m. local time on Sunday 31 July 2016. The driver of the car, Ms Naomi Suckling... flooding in southeast Australia. Widespread flooding and at least one fatality have been reported in New South Wales, Victoria and South Australia following heavy rainfall across the region on Sunday 3 and Monday 4 January 2016. Authorities are advising against driving into floodwaters and...

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