Tsunami research ongoing at Lake Tahoe
Special to the Sierra Sun
The past year was a wild ride with so many unexpected twists and turns that even the thought of a tsunami at Lake Tahoe probably doesn’t sound out of reason.
Several thousand years ago according to Dr. Richard Schweickert, a retired professor of geology at the University of Nevada, Reno who has spent most of his career working in the Sierra Nevada, Tahoe had a tsunami.
Whether he is mapping or studying faults around the basin, Schweickert and colleagues are dedicated to research around the basin.
Schweickert has been collecting evidence for over 15 years that have helped piece together the tsunami theory.
In 1999, the idea of one or more large tsunamis hitting Lake Tahoe first took fruition by Dr. Mary Lahren when she and Schweickert were mapping on land near Eagle Rock close to Homewood.
While a specific date is the hardest to pinpoint, it is estimated that a tsunami hit Lake Tahoe about 10,000 – 20,000 years ago after a massive earthquake shook the basin.
Over the years more evidence inspired researchers to dig deeper into what may have taken place in the region, including several faults that had never before been mapped.
In 1998, Jim Gardner at the United States Geological Survey released a detailed map. Jim Moore of USGS began a collaboration with Schweickert in 2005.
The map showed the landslide that occurred at McKinney Bay along with several other indicators that all point to the tsunami theory.
While Schweickert and other researchers had already been collecting data on land, Dr. Christopher Kitts, Associate Professor at Santa Clara University of the Mechanical Engineering Department and Director of SCU Robotics Systems Laboratory, first brought his students and equipment to Lake Tahoe to take a closer look at lies beneath the surface of the lake about 13 years ago.
“We began to realize there is underwater evidence that could also be attributed to the tsunami,” said Schweickert.
In 2005, the team which consisted of Dr. Winnie Kortemeier from Western Nevada College, Kitts, Moore, Lahren and Schweickert researched the Tahoe City Shelf where they discovered “boulder ridges” which have never been described in a lake before.
Similar to the small ripples you see on the beach when you walk along the shore, massive ripples formed due to the volume and force of gigantic waves.
Some ripples which are “boulder ridges” are as tall as 6.5 feet and extend as long as 6,562 feet on the Northwest side of the lake.
These perfectly aligned boulder ridges were found in four different locations just off the west shore, adding to the theory of “mega ripples” that would imply “mega waves.”
Schweickert says that there is no other explanation to why these boulders were perfectly lined up in a row underwater.
If you are on a boat on a relatively calm day, these boulder ridges can be seen with a naked eye at a depth of about 15-30 feet.
Large sand waves can also be found at 15 areas around the lake. They were caused by the flow of large volumes of water into the lake from onshore, some reaching almost 10 feet high.
The research team spent 40-50 days all together on the lake using robotics to take a deeper look and interpret underwater features of the lake.
Another indicator is that beneath the surface, Lake Tahoe has massive vertical canyons, some as deep as 200 feet, that have been carved into the sidewall such as in Rubicon Point.
“A mass amount of water had to have been thrown out onto the shores that poured back in carving the sidewalls,” said Schweickert. “Extremely large volumes of water were pouring into the sides of the lake.”
Some of these canyons extend to some of the deepest parts of the lake.
One of these locations is the Tahoe Keys in South Lake Tahoe, where the largest number of deep canyons are carved into the sidewall of the lake.
“The landslide generated such large waves that they flooded low areas around the sides of the lake and produced these features,” he said. “Lake Tahoe is the only lake we are aware of that has features like this, out of anywhere else in the world that has been documented.”
This earthquake not only shook the ground in Tahoe but caused approximately 3.5 cubic miles of the surrounding earth to dramatically slide 1,640 feet into the lake.
When the mass hit the lake at that force, it created a splash that caused waves that were about 300 feet high. The immense height of these waves lowered the lake’s water level by 33 feet for a period of time.
The earthquake and consequential tsunami waves altered the Tahoe Basin.
Lake sediment and glacial deposits were swept into the lake and the sheer force of the waves flattened countryside areas around the lake such as the relatively “flat” area found from Bijou to Meyers in South Lake Tahoe.
Secondary landslides also wiped out life that inhabited the edges of the lake. The most impacted areas of the lake from the massive waves were the Glenbrook and Zephyr Cove areas and Stateline to Baldwin Beach in South Lake Tahoe.
Enormous waves may have reached the upper Truckee River Canyon before pouring back into the lake.
To understand the impact, Schweickert has been researching active faults around the basin.
While evidence of several faults have been around since the 1960s, Schweickert mapped one of the faults called the North Tahoe fault that runs northeast from the lake through Incline Village and over Mount Rose and even into Reno.
The West Tahoe Dollar Point fault runs north-south along the West Shore, and the third fault, called the Tahoe Sierra, runs through the mountains just west of the lake.
“Major earthquakes on the West Shore can produce a series of potential hazards,” he said.
“As of now, it doesn’t look like something that should cause worry for those who live in the basin. “The hazard of forest fires in the basin is far greater,” said Schweickert.
With active faults and relatively “weak” sediment in some areas of the lake, he says that there is a possibility of another tsunami occurring in Lake Tahoe again.
“There is no way to predict if it’s 20,000 or 20 years from now,” he said.
Other researchers have also worked on this theory. While there is no work currently being done by the UC Davis Tahoe Environmental Research Center, they still highlight the historic tsunami in their outreach and in Lake Tahoe in Depth.
The underwater landslide that caused a destructive tsunami is recreated by computer simulation in TERC’s video, https://www.youtube.com/watch?v=q_mzGm-g9LI.
Every year, Kitts brings students to Lake Tahoe who want to use their gear. Schweickert hopes to continue future research with Kitts and his team. As technology advances, he hopes the robotics team can go even deep in the lake in the future.
“There are still a lot of places we haven’t been to,” he said.
Schweickert released an ebook last fall, “Journeys Across Nevada’s Wild Lands,” that takes readers on a geological history tour and includes portions of the south and east sides of Lake Tahoe.
Cheyanne Neuffer is a reporter for the Tahoe Daily Tribune, a sister publication of the Sierra Sun.
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