Humans are causing the Sierra to grow faster

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Humans are causing the Sierra to grow faster

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The Sierra Nevada is rising. Decades of pumping groundwater in California's Central Valley has accelerated the growth of mountains across the West Coast, according to UNR scientists.

The Sierra Nevada is rising. Decades of pumping groundwater in California's Central Valley has accelerated the growth of mountains across the West Coast, according to UNR scientists.

You wouldn't notice it if you were standing on top of Mount Rose south of Reno. Over the last ten years, the Sierra has grown a centimeter or so-about the width of your pinky. But geologically speaking, that's a big deal. It translates to a kilometer over a million years.

UNR professor Bill Hammond is one of those behind the study recently published in the journal Nature. He leans over a map with dozens of red dots clustered around the edges of the Central Valley, from Tahoe down to Southern California.

"All the little dots are colored given the vertical rate of the GPS stations, so blue is downward and red is upward."

These stations are measuring how much the earth is rising or falling.

"You can see there are contours in the valley where the greatest amount of water extraction has occurred the last century and a half."

Hammond and his colleagues have discovered the valley is sinking as humans remove groundwater for things like agriculture. As the load gets lighter there, the earth's crust reacts in the surrounding region like a bedspring.

"It's unloading the plate, like when a man gets out of bed the elastic rebound causes the ground to go up."

He also says they've identified another trend: it's possible to track the valley moving up and down each year based on the season. In summer, it sinks a bit; in winter, it rises. Hammond says they've observed that this variation changes the seismic activity around the San Andreas Fault to the west. Small earthquakes there actually correspond to the up and down movement of the valley. But this doesn't necessarily mean humans will bring about the next big quake.

"It's just slightly changing the timing of these smaller earthquakes because they are such a sensitive measure of stress in the fault region. But it's not like the rate of large earthquakes will change over time."

Taken together, these findings reflect a surprising reality-that humans are not only capable of affecting the weather, but also the very shape of the earth.