Around 70 people have been evacuated from their homes after a large sinkhole opened up in the Virac District of Itogon Municipality on Luzon Island, the Philippines on Thursday 22 October 2015, swallowing several houses. All of the evacuated persons are from homes directly affected by the incident or close to it, but there fears that the sinkhole may grow, affecting as many as 500 houses in the densely populated area. Despite the alarming nature of the incident there are no reports of any injuries associated with this event.
Aerial photograph of the Itogon Municipality sinkhole. Office of Civil Defense-Cordillera Administrative Region.
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. Potash, a potassium salt, is readily soluble and can be dissolved quickly if water gains access to deposits, leading to the rapid formation of sinkholes.
The approximate location of the Itogon Municipality sinkhole. Google Maps.
The Itogon Municipality sinkhole is thought to be directly above a tunnel that forms part of a former gold mine. The area is economically dependent on gold mining and many former mine tunnels underly the area, causing fears that a tunnel mat have collapsed in the aftermath of Typhoon Koppu, which brought the heaviest rainfall experienced in the area for a decade on Sunday-Monday this week, causing widespread flooding, and potentially weakening mineworkings and unstable sediments. The incident is being investigated by the Mines and Geosciences Bureau.
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