TRACKING THE TAHOE TSUNAMI | SierraSun.com

TRACKING THE TAHOE TSUNAMI

David Bunker
Sierra Sun
Emma Garrard/ Sierra SunJess Hersher uses a remote to look at the 3D display of Lake Tahoe at the Tahoe Environmental Research Center in Incline Village. The map shows details of the lake bottom.
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Coming off a ground-breaking Tahoe tsunami research year, scientists are planning for a new season of underwater science, one they hope will pinpoint the date of a past monster wave.

Along the way they will investigate the potential for a tsunami in Tahoe’s future, including analyzing the strength and stability of steep rock walls along the lake, which could collapse and cause another huge wave.

Last year scientists believed they found definitive proof that a huge landslide caused approximately 100-foot waves to wash over what is now Tahoe City, sometime within the last 20,000 years or so.

This summer, the clue-finding will continue, aided by a remote-controlled submarine named Triton, which has served as underwater eyes for a conglomeration of scientists.

The submersible comes from Santa Clara University, and is used from Antarctica to Japan for underwater observations.

University of Nevada, Reno Geology Professor Richard Schweickert said the team will search for remnants of ancient, underwater forests that may help date the last Tahoe wave.

Last year, researchers used the sub to video long ridges of boulders in the water along Tahoe City they believe are vestiges of a wave produced by the collapse of shoreline near Sugar Pine Point State Park on Tahoe’s west shore.

“We think we have some very profound evidence of tsunami waves sweeping up onto the Tahoe City shelf,” Schweickert said.

Tahoe’s past generates questions about a tsunami in Tahoe’s future, he said.

“One could infer from [evidence of past tsunamis] that there will be a tsunami in the future,” said Schweickert.

But Schweickert doesn’t want to scare anyone.

“These are quite rare events,” Schweickert said. “The last thing that I want to do is cause alarm.”

Despite the long-shot odds of another tsunami, the possibility is serious enough that these scientists are pushing for some planning.

“We’re trying to get the local agencies to do some coherent planning for these events,” Schweickert said.

But planning may take a more scientific approach, such as investigating if areas of shoreline are prone to collapse similar to the McKinney Bay landslide.

The problem with an emergency warning plan is a tsunami would occur so quickly there would be little or no reaction time, according to Placer County officials.

“There would be no warning,” said Jennifer Merchant, manager of the Tahoe operations of Placer County. “Or very, very little. Not enough time to get out of harm’s way.”

But the county’s plans for earthquakes and wildfires have overlapping evacuation and response strategies that would be used in the case of a tsunami.

“The impacts of an earthquake, with or without a tsunami, would be catastrophic,” said Merchant.

The county’s emergency experts have read through the scientific research done on the possibility of a Tahoe tsunami, she said. So it may be up to the scientists ” who have already calculated the height of waves in different areas of the lake that could be produced from three major earthquake faults in Tahoe ” to assess the propensity for a landslide around Tahoe.

Two tsunami sources

Inside the Tahoe Center for Environmental Studies in Incline Village, UC Davis assistant Jessie Hersher is controlling a three-dimensional video tour of the geography of Tahoe’s lake bottom.

The debris from the McKinney Bay collapse is strewn from its source near Blackwood Canyon, and stretches all the way to near the shores of Incline Village.

“They are enormous boulders,” Hersher said of the rubble littering the lake bottom.

The UC Davis imagery shows both sources of potential tsunamis ” landslides and earthquake faults.

Two parallel rifts run near Incline Village ” the Incline and Crystal Bay faults.

Another, larger convergence of plates runs along Tahoe’s west shore.

“These might displace enough water to produce tsunamis,” Schweickert said.

They also might cause strong enough quakes to cause landslides, the other tsunami-producer.

After a summer of underwater investigation, scientists hope to get a clearer picture of these tsunami threats.

As Schweickert and the other authors of an article about Tahoe tsunami research said in the November issue of Geology Magazine, a destructive lake wave is not just a figment of the imagination.

“The uncollapsed part of the sediment bench, including the Tahoe City shelf, poses a hazard because it may fail again, producing a landslide and damaging waves,” read the article.