The weight of water can deform the Earth’s crust, if there’s enough of it. And we can measure that change with the ultraprecise global-positioning satellites humans have launched into orbit.
On Monday, Chris Milliner of the Jet Propulsion Laboratory tweeted a simple map visualizing data from the Nevada Geodetic Laboratory. It showed that the GPS data from special stations around Houston detected that the whole area had been pushed down roughly two centimeters by the weight of the water that fell during Hurricane Harvey.
Why this would happen is simpler than you might think. A gallon of water weighs about 8.34 pounds. And by one estimate, Harvey dropped 33 trillion gallons of water across the area it hit. So that’s roughly 275 trillion pounds.
And it turns out that scientists have measured the effects of loading a bunch of water onto land many times. For example, a 2012 study of the Himalayas detected a seasonal flux in the height of the mountains as water fell, and then ran off those mountains into Asia’s rivers.
A 2017 study in Science found that the Sierra Nevada exhibits “vertical surface displacement [with] peak-to-peak amplitudes” of 0.5 to one centimeter. More water is more mass. Less water is less mass. And the crust underneath that water responds to the changes.