Merry Thomas

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January 6, 2005
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Tsunami in Tahoe?

The deadly tsunami in Asia has brought to light recent studies by local scientists exploring the possibility of the large waves at Lake Tahoe.Although it's a possibility, the probability of a Tahoe tsunami is low, according to Rich Schweickert, professor and chairman of the Department of Geological Sciences at the University of Nevada, Reno. "It's unlikely we could see one in the foreseeable future," he said. "But it could happen tomorrow." Schweickert, along with Mary Lahren and Jim Howell, published preliminary findings recently about the potential of large earthquakes under Lake Tahoe. Researchers first realized about 18 years ago that a tsunami wave could occur in Lake Tahoe, but UNR scientists didn't announce until spring 2001 that they were studying the probability of the huge waves, caused by underwater earthquakes and landslides. About seven years ago, scientists realized that large earthquakes were possible under Lake Tahoe, and in 1999 Dr. Gene Ichinose, formerly a scientist at UNR, used data from his colleagues' work to create a computerized model of a Tahoe tsunami. "Waves could reach 10 meters high in certain parts of the basin," Schweickert said. A tsunami is much more powerful and involves a much greater quantity of water than mere tidal waves, Schweickert said. Tidal waves are nothing like the Earth's regular, tidal movement, he added. "A large tidal wave has a 30- to 40-foot trough of water," Schweickert said. "But a tsunami wave has a 1,000-foot to half a mile trough, thus carrying a lot more water behind them." Schweickert said tsunamis, such as the one that flooded Asia on Dec. 26, hits once as it comes ashore, and again as the swishing motion retreats back out to sea, in many cases carrying people along with it. Thus, people have twice the probability of drowning, a reason why there have been so many deaths from the Asian tsunami, according to Schweickert. Work done during the summer of 2004 by Gordon Seitz, paleogeologist with San Diego State University, revealed that the Incline fault line - one of three major faults that goes under the lake - is still active. He postulated that a Tahoe tsunami - the early wave action - could evolve into a seiche. A seiche is similar to the motion of water in a bathtub. The swishing from shore to shore could slop along for hours after a quake. If the seiche is high enough, it could spill over Tahoe's rim. Lahren's work with Schweickert uncovered evidence of strong wave erosion, which indicates that a large tsunami occurred on Tahoe's west shore within the past 10,000 to 20,000 years. In addition, underwater evidence analyzed by Jeff Babcock, a project scientist at the Cecil H. & Ida M. Green Institute of Geophysics and Planetary Physics, revealed the possibility of a tsunami in Tahoe's past. Tahoe's shoreline is ringed by a shallow broad shelf that abruptly transitions to a steep slope. "Sections of the shelf have collapsed in the past, causing large tsunami waves," reported Mario C. Aguilera in an online article for SDSU. McKinney Bay was formed when a massive landslide slipped into Lake Tahoe, Graham Kent, a scientist at the Scripps Institute of Oceanography told a Bonanza reporter two years ago. Kent used acoustic trenching to research the lake's topography. "This strong wave erosion is not present elsewhere (in the Basin)," Schweickert said. The water flows as far as there is flat land, he said. Low-lying areas such as South Lake Tahoe and Kings Beach would bear the brunt of this type of wave. Although scientists know there have been earthquakes of magnitude 7 or higher in the basin and it appears there might have been a Tahoe tsunami, they do not know if there is a cycle of strong earthquake activity, or - if there is - what the cycle might be. "We know the frequency for a large earthquake in the Tahoe Basin is once every 2,000 to 3,000 years," Schweickert said. In geologic time, that degree of prediction is precise; but for Tahoe residents, it isn't precise enough. The possibility of a tsunami wave in Tahoe is something to be aware of, but such an event is quite rare, Schweickert said. Research on Lake Tahoe's geology increased after former President Bill Clinton and Vice President Al Gore presided over the Lake Tahoe Basin Forum in 1997. The following year, the United States Geological Survey, led by James Gardner, mapped Lake Tahoe's topographic features. Scientific research on Lake Tahoe has been ongoing with the Tahoe Research Group of the University of California, Davis, led by Dr. Charles Goldman; the Lawrence Livermore Laboratory at the University of California, Berkeley; UNR; SDSU; the USGS; and Scripps Oceanographic Institute.

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Tahoe Daily Tribune Updated Jan 6, 2005 05:33PM Published Jan 6, 2005 12:00AM Copyright 2005 Tahoe Daily Tribune. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.