Guatemala gigantic sinkhole

This 30 story deep hole opened beneath Guatemala City in May 2010, swallowing a three-story building and a home. Guatemala had unfortunately experienced such holes before: in 2007 three people and a dozen homes were swallowed into the earth.

While this event was commonly referred to as a sinkhole, technically it is not. Sinkholes refer to areas where bedrock is relatively solid but has been eroded by groundwater; Guatemala City is predominantly built upon pumice-fill up to 180 metres thick over a v-shaped valley of faulted bedrock.

The 2007 hole, which was 100 metres deep and opened up in a poorer neighbourhood in Guatemala City, has been classified by geologists as either a ‘piping feature’ or ‘piping pseudokarst’. It was caused by fluid from a sewer eroding the uncemented volcanic ash and pyroclastic deposits beneath the city. The hazards around this piping feature were mitigated and there are plans to rebuild over the site. The 2010 hole is also a piping feature and developed about 2 kilometres away from the 2007 one. The 2010 piping feature was at least 18 metres wide and 60 metres deep; it developed after Tropical Storm Agatha hit the region and eroded the soil.

http://news.discovery.com/earth/dont-call-the-guatemala-sinkhole-a-sinkh...