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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
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
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
"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
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
"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,
For information on the latest NASA Earth science findings, visit:
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/Web Site: http://www.nasa.gov
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