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-- WITH PHOTO -- TO NATIONAL, AND SCIENCE EDITORS:

NASA Radar Demonstrates Ability to Foresee Sinkholes

WASHINGTON, March 6, 2014 /PRNewswire-USNewswire/ -- New analyses of

NASA airborne radar data collected in 2012 reveal the radar detected

indications of a huge sinkhole before it collapsed and forced

evacuations near Bayou Corne, La. that year.

The findings suggest such radar data, if collected routinely from

airborne systems or satellites, could at least in some cases foresee

sinkholes before they happen, decreasing danger to people and

property.

Sinkholes are depressions in the ground formed when Earth surface

layers collapse into caverns below. They usually form without warning.

The data were collected as part of an ongoing NASA campaign to monitor

sinking of the ground along the Louisiana Gulf Coast.

Researchers Cathleen Jones and Ron Blom of NASA's Jet Propulsion

Laboratory (JPL) in Pasadena, Calif., analyzed interferometric

synthetic aperture radar (InSAR) imagery of the area acquired during

flights of the agency's Uninhabited Airborne Vehicle Synthetic

Aperture Radar (UAVSAR), which uses a C-20A jet, in June 2011 and July

2012. InSAR detects and measures very subtle deformations in Earth's

surface.

Their analyses showed the ground surface layer deformed significantly

at least a month before the collapse, moving mostly horizontally up to

10.2 inches (260 millimeters) toward where the sinkhole would later

form. These precursory surface movements covered a much larger area --

about 1,640 by 1,640 feet, (500 by 500 meters) -- than that of the

initial sinkhole, which measured about 2 acres (1 hectare).

Results of the study are published in the February issue of the

journal Geology.

"While horizontal surface deformations had not previously been

considered a signature of sinkholes, the new study shows they can

precede sinkhole formation well in advance," said Jones. "This kind of

movement may be more common than previously thought, particularly in

areas with loose soil near the surface."

The Bayou Corne sinkhole formed unexpectedly Aug. 3, 2012, after weeks

of minor earthquakes and bubbling natural gas that provoked community

concern. It was caused by the collapse of a sidewall of an underground

storage cavity connected to a nearby well operated by Texas Brine

Company and owned by Occidental Petroleum. On-site investigation

revealed the storage cavity, located more than 3,000 feet (914 meters)

underground, had been mined closer to the edge of the subterranean

Napoleonville salt dome than thought. The sinkhole, which filled with

slurry --a fluid mixture of water and pulverized solids-- has

gradually expanded and now measures about 25 acres (10.1 hectares) and

is at least 750 feet (229 meters) deep. It is still growing.

"Our work shows radar remote sensing could offer a monitoring

technique for identifying at least some sinkholes before their surface

collapse, and could be of particular use to the petroleum industry for

monitoring operations in salt domes," said Blom. "Salt domes are

dome-shaped structures in sedimentary rocks that form where large

masses of salt are forced upward. By measuring strain on Earth's

surface, this capability can reduce risks and provide quantitative

information that can be used to predict a sinkhole's size and growth

rate."

Typically, sinkholes have no natural external surface drainage, and

they form through natural processes and human activities. They occur

in regions of "karst" terrain where the rock below the surface can be

dissolved by groundwater, most commonly in areas with limestone or

other carbonate rocks, gypsum, or salt beds. When the rocks dissolve,

they form spaces and caverns underground. Sinkholes vary in size from

a few feet across to hundreds of acres, and some can be very deep.

They are common hazards worldwide and are found in all regions of the

United States, with Florida, Missouri, Texas, Alabama, Kentucky,

Tennessee and Pennsylvania reporting the most sinkhole damage. While

sinkhole deaths are rare, in February 2013 a man in Tampa, Fla., was

killed when his house was swallowed by a sinkhole.

The human-produced Bayou Corne sinkhole occurred in an area not prone

to sinkholes. The Gulf Coast of Louisiana and eastern Texas sits on an

ancient ocean floor with salt layers that form domes as the

lower-density salt rises. The Napoleonville salt dome underneath Bayou

Corne extends to within 690 feet (210 meters) of the surface. Various

companies mine caverns in the dome by dissolving the salt to obtain

brine and subsequently store fuels and salt water in the caverns.

Jones and Blom say continued UAVSAR monitoring of the area as recently

as October 2013 has shown a widening area of deformation, with the

potential to affect other nearby storage cavities located near the

salt dome's outer wall. Because the Bayou Corne sinkhole is now filled

with water, it is harder to measure deformation of the area using

InSAR. However, if the deformation extends far past the sinkhole

boundaries, InSAR could continue to track surface movement caused by

changes below the surface.

Continued growth of the sinkhole threatens the community and Highway

70, so there is a pressing need for reliable estimates of how fast it

may expand and how big it may eventually get.

"This kind of data could be of great value in determining the

direction in which the sinkhole is likely to expand," said Jones. "At

Bayou Corne, it appears that material is continuing to flow into the

huge cavern that is undergoing collapse."

Blom says there are no immediate plans to fly UAVSAR over

sinkhole-prone areas.

"You could spend a lot of time flying and processing data without

capturing a sinkhole," he said. "Our discovery at Bayou Corne was

really serendipitous. But it does demonstrate one of the expected

benefits of an InSAR satellite that would image wide areas frequently,

such as the planned NASA-Indian Space Research Organisation Synthetic

Aperture Radar mission."

"Every year, unexpected ground motions from sinkholes, landslides and

levee failures cost millions of dollars and many lives," said Jones.

"When there is small movement prior to a catastrophic collapse, such

subtle precursory clues can be detected by InSAR."

NASA monitors Earth's vital signs from land, air and space with a

fleet of satellites and ambitious airborne and ground-based

observation campaigns. NASA develops new ways to observe and study

Earth's interconnected natural systems with long-term data records and

computer analysis tools to better see how our planet is changing. The

agency shares this unique knowledge with the global community and

works with institutions in the United States and around the world that

contribute to understanding and protecting our home planet.

For more information about UAVSAR, visit: http://uavsar.jpl.nasa.gov/

For more information about NASA's Earth science activities in 2014,

visit: http://www.nasa.gov/earthrightnow

For information on the latest NASA Earth science findings, visit:

http://www.nasa.gov/earth

Logo - http://photos.prnewswire.com/prnh/20081007/38461LOGO

SOURCE NASA

-0- 03/06/2014

/CONTACT: J.D. Harrington, Headquarters, Washington, 202-358-5241, j.d.harrington@nasa.gov; Alan Buis, Jet Propulsion Laboratory, Pasadena, Calif., 818-354-0474, alan.buis@jpl.nasa.gov

/Photo: http://photos.prnewswire.com/prnh/20081007/38461LOGO

PRN Photo Desk photodesk@prnewswire.com

/Web Site: http://www.nasa.gov

CO: NASA

ST: District of Columbia California Louisiana

IN: ARO ENV

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-- DC78603 --

0000 03/06/2014 20:08:00 EDT http://www.prnewswire.com

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