Growing mountain a scientific marvel
August 5, 2004
Magma moving deep in the earth may have triggered an earthquake swarm near Lake Tahoe that caused Slide Mountain to rise slightly higher, according to a report released Thursday in the online version of the journal Science.
The migration of the molten rock material 20 miles beneath the surface of the Sierra Nevada over an eight month stretch last year also likely caused the mountain beneath Mt. Rose Ski resort east of Incline Village to rise 8 millimeters, or about 3/8 of an inch, researchers said.
“We’ve been watching earthquakes for 30 years in the Tahoe area and have never witnessed an earthquake swarm anything like this,” said Ken Smith, a research seismologist for the Nevada Seismological Laboratory at the University of Nevada, Reno.
“The magma itself is the force breaking the rock and that’s what we see the earthquakes associated with,” he told The Associated Press on Thursday.
“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 the Geological Survey. “The most recent instances of magma reaching the surface in the Lake Tahoe area occurred about a million years ago.”
Darryl Young, director of the California Department of Conservation, concurs.
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“The chances of us seeing a volcanic eruption the Tahoe region in our lifetime are practically nil,” Young said.
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 the swarm of 1,600 tiny earthquakes coincided with the slight horizontal and vertical shift of a Global Positioning System station on Slide Mountain, about 10 miles northeast of the swarm’s center.
The earthquakes were usually below magnitude 2 and were not noticeable.
“They were very deep,” Reichle said.
That information was shared with CGS, which tracks seismic activity in California, since most of the earthquakes occurred on the California side of the Lake Tahoe Basin.
“The finding is pretty exciting because it gives us a picture of what the Earth is doing. It is the kind of thing that not too may years ago we would not have seen because we didn’t have the instrumentation,” Reichle said.
“With this new information, we’ll be keeping a close eye on future seismic activity in the Tahoe area,” Reichle said pointing to the Slide Mountain finding. “From a layman’s point of view it takes a lot of energy to move that amount of mass and it happened all within that (7-month) window.”
The swarm and other recent temblors are a reminder that residents of the Lake Tahoe-Reno region, like other Californians, should prepare for earthquakes, Reichle said.
“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 state capitol in Carson City, 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.
-Associated Press writer Scott Sonner contributed to this report.