Monday, March 10, 2014

Nasa can now forecast sinkholes

But probably couldn't have saved the Corvettes in Bowling Green, Kentucky.


Two years ago, a giant sinkhole swallowed trees whole in a Louisiana bayou. This year, Nasa says it could have predicted it.

It might sound like too little too late, but with five-to-ten times more sinkholes occurring in this country because of the wet weather this year, any potential tool for mapping precarious landmasses will be most welcome.

The sinkhole Nasa is basing its study on, near Bayou Corne, was a monster measuring 10.1 hectares. It was 229m (751ft) deep by the time it ceased swallowing everything in sight. In a paper published in the journal Geology, Cathleen Jones and Ron Blom, from the Jet Propulsion Laboratory, have shown how radar data captured by Nasa's Uninhabited Airborne Vehicle Synthetic Aperture Radar (UAVSAR) between 2011 and 2012 could have been used to predict the natural catastrophe.

The UAVSAR captures interferometric synthetic aperture radar (InSAR) data—the returning waves the aircraft captures are used to generate digital surface elevation and deformation maps. It's the same technique used to assess fault lines, or even glaciers, capturing incremental changes at the centimeter scale over the course of years.

Although it would seem impossible to predict sinkholes, which happen so suddenly (at least the cover-collapse kind), the groundwork that causes them is being laid over some time. They can occur when rainwater and all the acids it carries permeate the soil to reach soluble rockbeds that are vulnerable, often made from limestone, gypsum, or salts. Over time, chunks begin to erode to create holes and break the connections between the layers. Loose soil layers from above then fill those gaps to create an unstable replacement. Eventually, when these holes and gaps grow too great, this "cover" of soil will collapse. In the case of Bayou Corne, there was also an existing hole to contend with—an underground storage space 914m (2,998ft) below the surface connected to a well—and often sinkholes occur when a natural underground cave already exists.

Those loose soil particles trickling down to the earth below to fill the gaps before the collapse, however, could be a possible sign of danger. And this is essentially what the radar captured—incremental movements in soil particles that over time represent an indicative shift.

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