NR 2004-25
August 5, 2004

Contact: Anita Gore
Ed Wilson
Mark Oldfield
Don Drysdale
(916) 323-1886


SACRAMENTO -- Magma moving deep in the Earth may have been behind a recent earthquake swarm near Lake Tahoe and may also have caused Slide Mountain the Sierra Nevada to grow slightly taller, according to a report in the online version of the journal Science.

But that does not mean there’s an imminent danger of a volcanic eruption, according to the California Geological Survey (CGS).

“This is a very interesting scientific discovery, but there’s no cause for the public to be alarmed,” said Michael Reichle, acting California State Geologist and head of CGS. “The most recent instances of magma reaching the surface in the Lake Tahoe area occurred about a million years ago.”

Added Darryl Young, director of the California Department of Conservation, which includes CGS: “The chances of us seeing a volcanic eruption the Tahoe region in our lifetime are practically nil.”

Research conducted by the Nevada Seismological Laboratory, Nevada Bureau of Mines and Geology, the California Institute of Technology, and the Harvard-Smithsonian Center for Astrophysics showed that a swarm of 1,600 tiny earthquakes coincided with the slight horizontal and vertical shift of a Global Positioning System station on Slide Mountain in Nevada, about 10½ miles northeast of the swarm’s center.

The full text of the report is available on the Web at the following address:

That information was shared with CGS, which tracks seismic activity in California, since most of the earthquakes occurred in California.

“With this new information, we’ll be keeping a close eye on future seismic activity in the Tahoe area,” Reichle said.

According to Reichle, the swarm and other recent temblors are a reminder that residents of the Lake Tahoe-Reno region, like other Californians, should prepare for future earthquakes.

“When someone says `earthquake,’ most people probably think of San Francisco or Los Angeles,” Reichle said. “But there’s an appreciable earthquake hazard in the Reno-Tahoe region, too, as well as other locations, such as Eureka and the Mojave Desert.”

Nearly 90 earthquakes of magnitude 3 or larger have struck the Reno-Tahoe area since 1943. A 1966 magnitude 6.0 temblor in the Donner Pass area damaged the dome of the Nevada state capitol in Carson, cracked dams on the Truckee River and was felt as far away as San Francisco. The largest known earthquake to strike the area was a magnitude 6.5 in 1887.

In addition to studying and mapping earthquakes and other geologic phenomena, the Department of Conservation regulates oil, gas and geothermal wells; ensures reclamation of land used for mining; administers agricultural and open-space land conservation programs; and promotes beverage container recycling.