Harvey sinks Houston … temporarily
Considering all the misery that Harvey inflicted, it’s doubtful that anyone noticed that Houston also sank a bit. At least that’s the conclusion of a California geophysicist.
Chris Milliner, a postdoctoral fellow at NASA’s Jet Propulsion Laboratory at the California Institute of Technology, used observations from the Nevada Geodetic Laboratory and the University of Nevada, Reno statistics department to determine that the Houston metro area was 2 centimeters lower because of the load of the floodwaters on the Earth’s crust.
The explanation? Water is heavy. About a ton per cubic meter.
“GPS data show that (the flood) was so large it flexed Earth’s crust, pushing Houston down,” Milliner said via Twitter.
Elaborating on Tuesday, Milliner said there’s no reason to worry. It should be a passing thing.
“This should be a temporary drop,” he said. “Once floodwaters recede, we should expect a similar, but opposite elastic response of the crust, i.e., uplift. Similar to if you were to jump on-and-off your mattress.”
Milliner referred to the phenomenon as local elastic subsidence. He said it is seen in most areas that experience significant seasonal changes in water or ice.
Those commenting on Milliner’s tweet suggested the measurements could reflect compacting of the soil. He said that was unlikely, as a number of the measurements were taken where monitors rest on bedrock.
Subsidence should not be an issue after a flood, said Michael Turco, with the Harris-Galveston Subsidence District, because less groundwater is being used.
“I would not expect any short term thing like that to have any impact on overall subsidence” Turco said.