An unmanned submarine headed for Antarctica will first explore the depths of Lake Tahoe on Friday to study the blasted rocks of a seismic fault created thousands of years ago by a huge earthquake that ruptured the lake’s floor.
Gordon Seitz, an engineering geologist with the California Geological Survey and an expert on the lake’s ancient quake history, will be using the tethered sub to gather underwater images of the West Tahoe fault, which last ruptured some 2,500 years ago with a magnitude of more than 7.
The fault runs beneath the lake for some 31 miles, from south of Emerald Bay to the lake’s north shore, and underground to a point east of Tahoe City.
“We’ll be trying to get a seismic profile of the fault, and hopefully gather much sharper images of its deformed sediment layers than we’ve ever had before,” Seitz said Thursday as the sub’s crew tested the underwater vehicle and directed its first tentative dives into the lake from its mooring at Sugar Pine Point State Park.
A big question that scientists hope to resolve, Seitz said, is the relationship between the quake and a giant landslide that ripped away a huge chunk of the lake’s shoreline near what is now McKinney Bay perhaps tens of thousands of years earlier.
That slide sent masses of boulders, rocks and soil plunging across the lake bottom as far as Tahoe’s east shore, some 12 miles away.
The slide also created a tsunami, whose towering waves were reflected from shore to shore in a series of smaller waves known as seiches, Seitz said. The evidence shows that the seiches continued for days and left evidence all along the lake’s shoreline, Seitz said.
The slide along the western rim was probably triggered during the last ice age when the lake’s level dropped by more than 1,200 feet, Seitz said.
The submarine’s ability to cruise along the bottom should return images and other instrument data showing details of the rocks and canyon walls that remain from the quake, he said.
The $2 million submarine, with its array of cameras, sensing instruments and a powerful drill, will eventually be transported to the Ross Ice Shelf in Antarctica. Scientists, led by geologist Ross Powell from Northern Illinois University, plan to use it to explore a lake there that has long existed beneath the ice.
Powell and his colleagues had originally scheduled the submarine dives at Tahoe to test its equipment for Antarctica, but Seitz was invited to use the vehicle to explore the lake bottom.
The tethered submarine is only 22 inches in diameter and weighs 2,200 pounds on the surface. In Antarctica, Powell and his colleagues will lower the vehicle through a hole in the Ross Sea to examine the bottom of the shelf and seek long-buried marine life there.
Instruments aboard the submarine will also measure temperatures at the lake, where scientists say the ice above it has been melting due to global climate change.
The sub was built by DOER Marine, an Alameda firm that specializes in designing remotely operated robotic undersea vehicles known as ROVs, for specialized scientific missions.