NASA has devised a plan to predict sinkholes via specialized radar satellites. Scans of areas prone to sinkholes can provide up to a month of warning by recording subtle shifts in the ground that gradually add up to noticeable movement. The idea came to researcher Cathleen Jones after the Bayou Corne sinkhole opened up in Louisiana in 2012. It appeared suddenly and caused major damage, forcing 350 people out of their homes. It is estimated that it will cover an area of 25 acres by 2014, and is still expanding and devouring surrounding ground at a steady rate.
After the sinkhole appeared, Ms. Jones went back and reviewed satellite images of the area where the sinkhole first appeared. She noticed that when she went back a month before the appearance and moved forward until the emergence of the hole, the ground could be seen moving slowly inward toward the center of the affected area. Reviewing footage of other sinkholes revealed the same movement, despite previous hypotheses saying that horizontal movement in the earth was not indicative of future sinkholes.
The type of radar needed to track these small, slowly occurring changes is called interferometric synthetic aperture radar, or iSAR. The devices are currently found on several reconnaissance planes that see frequent use, but due to the long period of tracking time needed to see the movement, the task is better suited to satellites. Scans in several different wavelengths are carried out over a defined area by the iSAR scanner, which is sensitive enough to detect ripples in the earth created by earthquakes or changes in riverbanks caused by flooding. As satellites pass over an area, the results of the scan are recorded and can be reviewed at any time in fast forward to check for changes. Playing weeks of footage at a faster rate makes the changes easier to see and means that sinkholes can now be predicted by NASA.
Sinkholes are caused by layers of rock and dirt falling into hollow pockets in the Earth’s crust. These pockets usually form when previously solid matter becomes soft, such as when liquefaction causes soil to become partially liquid. Although liquefaction most often occurs when earthquakes stir up soil that has slowly been absorbing water over a long period of time, sinkholes can develop without an initial event, which lends to their dangerous reputation. Many areas of the United States are particularly susceptible to sinkholes, including Missouri, Alabama, Florida, Kentucky, Tennessee, and Pennsylvania. Soil types, recent weather, and how built up an area is are all factors that contribute to sinkholes, so pinning down an exact area is difficult at the best of times.
Ms. Jones believes that the new surveying method would be useful for oil expeditions as well as predicting sinkholes. The iSAR scans show strain on the Earth’s surface that can be indicative of pressure in lower levels, often caused by deposits of materials of a different density than the surrounding stone and soil. Even if not applied in this way, one more fear can be buried now that sinkholes can be predicted by NASA.
By Daniel O’Brien