In the News

Scientists Study Submarine Geology of Lake Tahoe
date posted: December 1 2005

Lake Tahoe Report #127
Aug. 1, 2005
By John Cobourn and Heather Segale

Scientists from University of Nevada, Reno, the U.S. Geological Survey, and U.C. Davis, and engineering students and faculty from Santa Clara University have teamed up to study underwater geologic features in Lake Tahoe. In the spring of 2004 and 2005, they employed the Triton, a remotely operated vehicle designed and controlled by the students in those studies. The students have been able to operate the vehicle from aboard the UC Davis research vessel, R/V John LeConte. With a video camera on the Triton, the scientists have identified rocks on the western sidewalls of Tahoe and have gained new information about the history of the lake.

Near the west shore of Lake Tahoe, steep underwater cliffs occur around the edges of McKinney Bay and near Sugar Pine Point. These cliffs are made up of sedimentary strata that were deposited on the floor of a lake believed to have been the “ancestral” Lake Tahoe. That lake, which existed between about 2 to 3 million years ago, was probably between 1/3 and 1/2 the size of the current lake. The ancestral lake was enlarged when eruptions of basaltic lava formed a lava dam at Tahoe City about two million years ago. In places, the lava flowed over the old lake sediments.

The sediments from the ancestral lake bottom are now semi-consolidated, which means that they have become partially cemented into a relatively soft, crumbly rock.

These “lacustrine strata” are about 200 meters thick and presently form a large portion of the shoreline near McKinney Bay. These ancient sediments are now at the shoreline level due to gradual uplifting along the West Tahoe-Dollar Point Fault, discussed last week.

Dr. Richard Schweickert, the UNR geologist who has led these studies, explains, “video images show that the strata around McKinney Bay are identical with large landslide blocks in deep water on the floor of Lake Tahoe. This shows that McKinney Bay was the site of large landslides, as previously believed by scientists.”

“Previous work indicates that the underwater landslides in McKinney Bay probably have occurred over the past 100,000 years,” Schweickert says. “In multiple events during that time, as much as ten square miles of the west shore may have collapsed into the lake. Some collapse events and landslides also caused tsunamis on the lake. Such underwater landslides are relatively common in lakes that have steep underwater topography. Evidence suggests that some landslides have occurred during the past 10,000 years.”

Schweickert says research is continuing to determine when various landslides have occurred in the past, and to assess the likelihood of future landslides. Schweickert and his colleagues are grateful to the IEEE Oceanic Engineering Society for partial funding and to the students of Santa Clara University for designing, building, deploying, maintaining and piloting the Triton.

Watch for the “Lake Tahoe Report” in the Tahoe World each Thursday, and tune in to KOLO-TV News Channel 8 Tuesdays at 5 p.m. to learn more. The “Lake Tahoe Report” is a collaborative effort of the Lake Tahoe Environmental Education Coalition, University of Nevada Cooperative Extension, UC Davis Tahoe Environmental Research Center and the California State Water Resource Control Board. For more information, contact Heather Segale, UC Davis Tahoe Environmental Research Center, (530) 583-3279, or logon to www.lteec.org or www.tahoe.unr.edu.