Tsunami! At Lake Tahoe? Author/s: Kathryn Brown
Issue: June 10, 2000
Surprised tourists could catch the ultimate wave
Postcards from Lake Tahoe all flaunt a peaceful, brilliant-blue stretch of mountain water. But geologists have been snapping a very different picture of the lake lately. Far beneath Lake Tahoe's gentle surface, they say, several hidden earthquake faults snake across the lake's flat bottom. These faults put the lake at a bizarre risk for an inland body of water.
If the researchers are right, Lake Tahoe tourists could one day feel the ground tremble and, just minutes later, face a tsunami. Roiling waves of water would crest to 10 meters at the shore and criss-cross the lake for hours.
Tsunamis typically emerge in oceans, usually after a quake drops or lifts part of the seafloor. Undersea landslides--alone or following a quake--can also trigger these giant waves. In 1998, for instance, a tsunami devastated Papua New Guinea, sweeping away more than 2,000 people living on the country's northern coast (SN: 8/1/98, p. 69). And in the past decade, tsunamis have lashed the coasts of Japan, Nicaragua, and Indonesia, as well. But Lake Tahoe?
While it may seem improbable, Lake Tahoe holds just the right blend of ingredients to brew a tsunami. For one thing, it has plenty of water. As the world's 10th-largest lake, Lake Tahoe stretches 35 kilometers long, 19 km wide, and, in some spots, 500 m deep. What's more, the lake sits smack in the middle of earthquake country, nestled in a fault-riddled basin that straddles California and Nevada. Dozens of minor or moderate quakes erupt along faults in the region every week, and the Lake Tahoe area is no exception. All it would take, scientists say, is a strong quake directly beneath the lake to send the waters spewing, tsunami-style.
To get a better grip on Lake Tahoe's tsunami potential, University of Nevada, Reno geologists have been modeling different quake scenarios. According to their calculations, if a magnitude 7 quake struck either of two major faults under the lake, the bottom could open like a trapdoor, with a chunk of it suddenly dropping as much as 4 m. Just behind it would fall a huge, sinking slosh of water--generating a giant wave that would reach the surface, gather strength, and come barreling to shore as a tsunami.
And that's just the beginning. The scientists think the tsunami, in turn, would create so-called seiche waves, mountainous waves that lurch from shore to shore for hours on end. "Think of the lake like a pan full of water. When you knock one end way down, the water surges and then sloshes back and forth for some time," says Gene A. Ichinose, a geophysics graduate student at Nevada-Reno and lead author of the group's study, which appeared in the April 15 GEOPHYSICAL RESEARCH LETTERS. As in a jostled pan of water, some waves would likely splash past their usual borders--right into the homes and hotels that dot the Lake Tahoe shoreline.
As Ichinose puts it, "If you feel the earth shaking for 5 or 10 seconds, get to high ground."
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