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Drought made California’s Sierra Nevada get taller, NASA scientists say

By Dale Kasler

dkasler@sacbee.com

December 14, 2017 10:25 AM

California’s drought turned lawns brown and caused crops to wither. But here’s something that actually grew a little: the Sierra Nevada.

The fabled mountain range rose nearly an inch between 2011 and 2015, according to a study released this week by scientists at NASA’s Jet Propulsion Laboratory in Pasadena. NASA’s scientists concluded that the lack of snow and rain was the reason.

The study’s co-author, NASA scientist Donald Argus, said heavy precipitation literally weighs the mountains down. When it’s dry, the mountains spring back up.

“It’s like a bathroom scale,” Argus said in an interview Thursday. “When you took the water off, it rose.”

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Scientists have long known that the Sierra has been growing because of the gradual shifting of the earth’s tectonic plates, a phenomenon known as “tectonic uplift.” The NASA study shows that only a sliver of the 1-inch gain was caused by tectonic uplift; the bulk was the result of water and snow no longer weighing down the mountains.

Besides the lack of precipitation in the mountains, the drought contributed to the growth in the Sierra in a more perverse way: The relentless groundwater pumping by farmers in the Central Valley, which caused portions of the valley floor to sink, also generated an “elastic response” that nudged the mountain range up slightly, although the effect wasn’t as great as the drying up of the mountains.

So if the drought made the Sierra grow, the drought-breaking precipitation of the past two winters should have made the mountains shrink, right? That’s exactly what happened. The NASA scientists say the Sierra has given back about half an inch of its height since 2015.

The study, published in the Journal of Geophysical Research: Solid Earth, was based on 1,300 sensors scattered in the mountains in California, Oregon and Washington. The study factored in seasonal fluctuations.

Argus said the study provides some fresh insights into how the mountains behave. In particular, the research shows that the Sierra acts more like a sponge than previously believed; during the spring snowmelt season, a lot of water stays in the mountains.

“It infiltrates, seeps into the ground,” Argus said. “There’s a lot more infiltration into the ground.”

Dale Kasler: 916-321-1066, @dakasler