A second massive sinkhole to appear in Guatemala City in four years may also have been caused by a combination of geological anomalies and problems with water utility pipes.
Soil mechanics experts told NCE that similarities between the 30m deep and 20m wide sinkhole that opened up last week and a deeper version that swallowed up houses in 2007, cannot be ignored.
Engineers are now convinced that the 2007 collapse was prompted by failures in the city sewer system.
The latest chasm appeared after a tropical storm, swallowing several buildings, although there have been no reported fatalities.
The unusual event echoes a similar incident just over three years ago in the same city when a 100m deep sinkhole pulled several houses and a truck into the ground (NCE 8 March 2007).
University of Leeds engineering geology course director Bill Murphy - who has worked in Central America - said that atypical geology, such as the presence of volcanic rock, was a likely factor in the appearance of sinkholes
in the area.
“Sinkholes are normally formed in soluble ground such as chalk, limestone or gypsum,” he said. “Soluble ground is then eaten by water creating a cavern that then migrates to the surface until there isn’t enough strength left to support the land.
“In Guatemala City, it is likely the cause is due to the ground in the area being dominated by volcanic rock rather than a tectonic or other geological fault.”
British Geological Survey expert Tony Cooper said that it was “very likely” the same factors were involved in both incidents, which comprised geological anomalies coupled with problem water systems.
Cooper said that much could be learned about from a 2008 report into the 2007 sinkhole by geological specialist Tony Waltham.
That report echoed other engineers who at the time said that the incident emulated karstic formations seen elsewhere that were prompted by human activity.
“With few exceptions, the ground collapses that constitute the karst geohazard in engineering activity in limestone
terrains are induced by human activity,” says Waltham’s report.
“Subsidence sinkholes, formed entirely within the soil profile, constitute the most widespread karst geohazard, but are largely induced by engineered works, either directly or accidentally.”
Cooper added that there was no doubt that a broken drainage system had a large part to play in the sinkhole of 2007. “There was a major sewer failure after a period of heavy rain and residents had heard noises from the pipes for months beforehand,” he said. At the time, Guatemala City mayor Alvaro Arzu blamed only a saturated sewer main.
Cooper said the latest sinkhole was a “man-induced removal of material” meaning the cause was “largely unnatural” because of the effect of men placing drains above the ground over many years.”