Zhong Lu – Page 3

Satellite radar images reveal ground movement of infamous sinkholes near Wink, Texas; suggest the two existing holes are expanding, and new ones are forming as nearby subsidence occurs at an alarming rate.

Residents of Wink and neighboring Kermit have grown accustomed to the two giant sinkholes that sit between their small West Texas towns.

But now radar images taken of the sinkholes by an orbiting space satellite reveal big changes may be on the horizon.

A new study by geophysicists at Southern Methodist University, Dallas, finds the massive sinkholes are unstable, with the ground around them subsiding, suggesting the holes could pose a bigger hazard sometime in the future.

The two sinkholes — about a mile apart — appear to be expanding. Additionally, areas around the existing sinkholes are unstable, with large areas of subsidence detected via satellite radar remote sensing.

That leaves the possibility that new sinkholes, or one giant sinkhole, may form, said geophysicists and study co-authors Zhong Lu, professor, Shuler-Foscue Chair, and Jin-Woo Kim research scientist, in the Roy M. Huffington Department of Earth Sciences at SMU.

“This area is heavily populated with oil and gas production equipment and installations, hazardous liquid pipelines, as well as two communities. The intrusion of freshwater to underground can dissolve the interbedded salt layers and accelerate the sinkhole collapse,” said Kim, who leads the SMU geophysical team reporting the findings. “A collapse could be catastrophic. Following our study, we are collecting more high-resolution satellite data over the sinkholes and neighboring regions to monitor further development and collapse.”

Lu and Kim reported the findings in the scientific journal Remote Sensing, in the article “Ongoing deformation of sinkholes in Wink, Texas, observed by time-series Sentinel-1A SAR Interferometry.”

The research was supported by the U.S. Geological Survey Land Remote Sensing Program, the NASA Earth Surface & Interior Program, and the Shuler-Foscue Endowment at Southern Methodist University.

Unstable ground linked to rising, falling groundwater
The sinkholes were originally caused by the area’s prolific oil and gas extraction, which peaked from 1926 to 1964. Wink Sink No. 1, near the Hendricks oil well 10-A, opened in 1980. Wink Sink No. 2, near Gulf WS-8 supply well, opened 22 years later in 2002.

It appears the area’s unstable ground now is linked to changing groundwater levels and dissolving minerals, say the scientists. A deep-seated salt bed underlies the area, part of the massive oil-rich Permian Basin of West Texas and southeastern New Mexico.

With the new data, the SMU geophysicists found a high correlation between groundwater level in the underlying aquifer and further sinking of the surface area during the summer months, influenced by successive roof failures in underlying cavities.

Satellite images and groundwater records indicate that when groundwater levels rise, the ground lifts. But the presence of that same groundwater then speeds the dissolving of the underground salt, which then causes the ground surface to subside.

Everything’s bigger in Texas, and the Wink sinkholes are no exception
Officials have fenced off the two sinkholes near Wink, a town of about 940 people, and Kermit, a town of about 6,000 people. The giant holes are notable features on the area’s vast plains, which are dotted mostly with oil pump jacks, storage facilities, occasional brush and mesquite trees.

Based on modeling of satellite image datasets, SMU’s researchers report that Wink Sink No. 1, which is closer to the town of Kermit, appears to be the most unstable. The smaller hole of the two, it has grown to 361 feet (110 meters) across — the length of a football field.

“Even though Wink No. 1 collapsed in 1980, its neighboring areas are still subsiding,” say the authors, “and the sinkhole continues to expand.” An oval-shaped deformation circling the sinkhole measures three-tenths of a mile (500 meters) wide and is subsiding up to 1.6 inches (4 centimeters) a year.

Wink Sink No. 2, which is nine-tenths of a mile south of No. 1 and which sits closer to the town of Wink, is the larger of the sinkholes. It varies from 670 feet to 900 feet across.

Wink No. 2 is not experiencing as much subsidence as Wink No. 1. However, its eastern side is collapsing and eroding westward at a rate of up to 1.2 inches (3 centimeters) a year.

“Wink No. 2 exhibits depression associated with the ongoing expansion of the underground cavity,” the authors report.

Some ground that doesn’t even border the edges of the two sinkholes is also subsiding, the scientists observed. An area more than half a mile (1 kilometer) northeast of No. 2 sank at a rate of 1.6 inches (4 centimeters) in just four months.

Ground northeast of sinkholes is subsiding, suggesting new ones forming
The largest rate of ground subsidence is not at either sinkhole, but at an area about seven-tenths of a mile (1.2 kilometers) northeast of No. 2. Ground there is subsiding at a rate of more than 5 inches (13 centimeters) a year.

It’s aerial extent, the researchers report, has also enlarged over the past eight years when a previous survey was done.

“The enlarged deformation could be an alarming precursor to the potential future development of hazards in the vicinity,” said the authors.

Additionally, ground along a road traveled by oil field vehicles, about a quarter mile (400 meters) directly north of No. 2, is subsiding about 1.2 inches (3 centimeters) a year.

Ground’s movement detected with radar technique
The satellite radar datasets were collected over five months between April 2015 and August 2015. With them, the geophysicists observed both two-dimension east-west deformation of the sinkholes, as well as vertical deformation.

The SMU scientists used a technique called interferometric synthetic aperture radar, or InSAR for short, to detect changes that aren’t visible to the naked eye.

“From 435 miles above the Earth’s surface, this InSAR technique allows us to measure inch-level subsidence on the ground. This is a monumental human achievement, and scientists will not stop endeavoring to improve this technique for more precise measurements,” said Lu, who is world-renowned for leading scientists in InSAR applications. Lu is a member of the Science Definition Team for the dedicated U.S. and Indian NASA-ISRO InSAR mission, set for launch in 2020 to study hazards and global environmental change.

InSAR accesses a series of images captured by a read-out radar instrument mounted on the orbiting satellite Sentinel-1A. Sentinel-1A was launched in April 2014 as part of the European Union’s Copernicus program.

Simply put, Sentinel-1A bounces a radar signal off the earth, then records the signal as it bounces back, delivering measurements. The measurements allow geophysicists to determine the distance from the satellite to the ground, revealing how features on the Earth’s surface change over time.

“Sinkhole formation has previously been unpredictable, but satellite remote sensing provides a great means to detect the expansion of the current sinkholes and possible development of new sinkholes,” said Kim. “Monitoring the sinkholes and modeling the rate of change can help predict potential sinkhole development.”

Sentinel-1A data were obtained from Sentinels Scientific Data Hub – Copernicus. Groundwater well data came from the Texas Water Development Board. — Margaret Allen, SMU

InSAR Image shows Volcanic uplift in the Great Rift Valley. (Credit: Study authors)

Using satellite imagery to monitor which volcanoes are deforming provides statistical evidence of their eruption potential, according to a new study in Nature Communications.

The European Space Agency’s Sentinel satellite, launched April 3, should allow scientists to test this link in greater detail and eventually develop a forecast system for all volcanoes, including those that are remote and inaccessible.

Volcano deformation and, in particular, uplift are often considered to be caused by magma moving or pressurizing underground. Magma rising towards the surface could be a sign of an imminent eruption. On the other hand, many other factors influence volcano deformation and, even if magma is rising, it may stop short, rather than erupting.

Satellite interferometric synthetic aperture radar, called InSAR for short, is a spaceborne imaging technology that will help scientists understand how volcanoes work, according to study co-author and geophysicist Zhong Lu, Southern Methodist University in Dallas.

“InSAR will aid in the prediction of future eruptions,” said Lu, a professor and Shuler-Foscue Chair of geophysics in SMU’s Roy M. Huffington Department of Earth Sciences. “At SMU, we are developing and applying this technique to track motions of volcanic activities, landslide movements, land subsidence and building stability, among other events.”

Juliet Biggs, the University of Bristol in England, led the study. Biggs looked at the archive of satellite data covering more than 500 volcanoes worldwide, many of which have been systematically observed for more than 18 years.

Satellite radar can provide high-resolution maps of deformation, allowing the detection of unrest at many volcanoes that might otherwise go unrecognized. Such satellite data is often the only source of information for remote or inaccessible volcanoes.

The researchers, who included scientists from Cornell University and Oxford University also, applied statistical methods more traditionally used for medical diagnostic testing and found that many deforming volcanoes also erupted (46 percent). Together with the very high proportion of non-deforming volcanoes that did not erupt (94 percent), these jointly represent a strong indicator of a volcano’s long-term eruptive potential.

“The findings suggest that satellite radar is the perfect tool to identify volcanic unrest on a regional or global scale and target ground-based monitoring,” Biggs said.

New technology may improve forecasting of volcanic eruptions
The work was co-funded by the U.K. Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics and STREVA, a research consortium aimed at finding ways to reduce the negative consequences of volcanic activity on people and their assets.

“Improving how we anticipate activity using new technology such as this is an important first step in doing better at forecasting and preparing for volcanic eruptions,” said STREVA Principal Investigator Jenni Barclay.

Global studies of volcano deformation using satellite data will increasingly play a part in assessing eruption potential at more and more volcanoes, said researcher Willy Aspinall, University of Bristol, especially in regions with short historical records or limited conventional monitoring.

However, many factors and processes, some observable, but others not, influence deformation to a greater or lesser extent. These include the type of rock that forms the volcano, its tectonic characteristics and the supply rate and storage depth of magma beneath it. Thus deformation can have different implications for different types of volcanoes.

For volcanoes with short eruption cycles the satellite record typically spans episodes that include both deformation and eruption, resulting in a high correlation between the two. For volcanoes with long eruption cycles the satellite record tends to capture either deformation or eruption but rarely both.

Seismological data indicate unrest before eruption may only be a few days
In the past, radar images of the majority of the world’s volcanoes were only acquired a few times a year, but seismological data indicate that the duration of unrest before an eruption might be as short as only a few days.

“This study demonstrates what can be achieved with global satellite coverage even with limited acquisitions,” Biggs said, “so we are looking forward to the step-change in data quantity planned for the next generation of satellites.”

The European Space Agency launched its latest radar mission, Sentinel-1, in early April. The mission is designed for global monitoring and will collect images every six to twelve days. Using this, scientists should be able to test the causal and temporal relationship with deformation on much shorter timescales.

“This study is particularly exciting because Sentinel-1 will soon give us systematic observations of the ups and downs of every volcano on the planet,” said Tim Wright, director of the U.K. Centre for Observation and Modelling of Earthquakes. “For many places, particularly in developing countries, these data could provide the only warning of an impending eruption.”

The authors reported their findings in the article “Global link between deformation and volcanic eruption quantified by satellite imagery” in Nature Communications. Besides Lu and Biggs, co-authors were S.K. Ebmeier, W.P. Aspinall and R.S.J. Sparks, all with the University of Bristol; M.E. Pritchard, Cornell University; and T.A. Mather, Oxford University. — Bristol University

Follow SMUResearch.com on Twitter.

For more information, www.smuresearch.com.

SMU is a nationally ranked private university in Dallas founded 100 years ago. Today, SMU enrolls nearly 11,000 students who benefit from the academic opportunities and international reach of seven degree-granting schools. For more information see www.smu.edu.

SMU has an uplink facility located on campus for live TV, radio, or online interviews. To speak with an SMU expert or book an SMU guest in the studio, call SMU News & Communications at 214-768-7650.

Satellite radar images reveal ground movement of infamous sinkholes near Wink, Texas; suggest the two existing holes are expanding, and new ones are forming as nearby subsidence occurs at an alarming rate.

Book a live interview

Related Links

More SMU Research news