A NASA geophysicist released a series of tweets showing the massive weight of the floodwaters from Hurricane Harvey actually caused some parts of Houston to sink by nearly an inch.
Chris Milliner, a postdoctoral fellow at NASA’s Jet Propulsion Laboratory at the California Institute of Technology in Pasadena, California, tweeted that the weight of the water “was so large it flexed Earth’s crust, pushing #Houston down by ~2cm!”
To put this staggering amount of water weight into perspective, a gallon of water weighs about 8.34 pounds. Meteorologists estimate that southeast Texas experienced more than 20 trillion gallons of rainfall during Hurricane Harvey, which comes out to 170 trillion pounds of water across the area.
Milliner tweeted an image showing the relative amounts of sinkage in surface soil and bedrock after the rainfall ceased. Some areas showed sinkage amounts of up to two centimeters, or about eight-tenths of an inch.
The flood-related sinkage also came in addition to the normal amount of sinkage the area sees due to soil composition, urban development, and other natural and man-made events.
Milliner also said that the sinking phenomenon was related to “local elastic subsidence” of the Earth’s crust. The event, which occurs in several parts of the world experiencing seasonal changes in precipitation, causes the Earth’s crust to sink under heavy rains or ice, then rebound back to its previous state when the water melts and flows away.
Although the phenomenon is not unusual, it is highly remarkable for such an event to occur over the space of a week or less.
Scientists who have observed the sinkage are not sure when the soil will return to its previous levels, or if the weight of the water compacted the sediment to such a point that it will never rebound.