California Nevada
Lake Tahoe, looking north across Fallen Leaf Lake in the foreground. The Sierra Nevada mountains are to the left, the Carson Range to the right.
Lake Tahoe is one of the deepest, clearest, bluest lakes in the world—though not quite as deep (1600 feet) as Oregon’s Crater Lake (2000 feet), or as clear. The oval shape of Lake Tahoe (and the fact that it sits in a bowl surrounded by mountains) helps perpetuate the myth that this famed lake was formed inside a collapsed volcanic crater, like Crater Lake. But Lake Tahoe, on the border between California and Nevada, is actually the result of long-term vertical faulting throughout the Great Basin region.
The Great Basin, which stretches across Nevada and into eastern California, was created by extensional forces that are pulling apart Earth’s crust. These forces create a pattern of uplifted blocks of mountains alternating with down-dropped blocks that form valleys. Lake Tahoe sits in a down-dropped valley between the uplifted blocks of the Carson Range to the east and the Sierra Nevada mountains to the west. These extensional forces are ongoing; the Sierra Nevada block continues to move at a rate of about a half-inch per year—relatively speedy in geologic terms.
One of the best ways to experience this exceptionally clean lake is by kayak. Lake Tahoe has water clarity to a depth of around seventy feet.
At least three faults lurk under Lake Tahoe, all of which are capable of producing large earthquakes. The West Tahoe Fault lines up along the west side of the lake between Emerald Bay and Tahoe City. The East Tahoe Fault follows the eastern shoreline and the North Tahoe Fault connects the two in the northern part of the lake. Of the three, the West Tahoe Fault is considered to be the most dangerous. Detailed mapping of the lake bottom and adjacent Fallen Leaf Lake has revealed that the last major quake to strike Lake Tahoe occurred between 4100 and 4500 years ago. Paleoseismic studies suggest that earthquakes tend to recur at time intervals of 3000 to 4000 years, meaning the area may be overdue for a shaking.
Because Lake Tahoe is so deep—it’s the second-deepest lake in North America and the seventeenth deepest in the world—earthquakes along the faults under the water may trigger significant tsunamis: walls of water displaced by rapid fault movement. Waves could reach heights over thirty feet, tall enough to destroy most of the marinas and homes along the shores of the lake. Shoreline residents wouldn’t have much warning to get to high ground; a tsunami could travel all the way across the lake in a matter of seconds. Evidence for past tsunamis has been found in McKinney Bay, on the west side of the lake, where an extensive collapse of a land shelf around 50,000 years ago helped shape the bay, possibly triggered by an earthquake-generated tsunami.
Look for a bright blue oval on the border of Nevada and California. Ski resorts on the north and west sides of the lake are visible from the air in winter; they capitalize on the 300 inches of snow that falls annually on the east side of the Sierras. You might see Lake Tahoe flying into Carson City or Reno, Nevada.
