There are three major fault lines running across the bottom of Lake Tahoe. In the event of major quake, portions of the lake floor may shift physically and cause a massive, underwater landslide. Water displaced by the slide can generate a powerful tsunami wave.


For example, the scientists developed a computer model that takes into account the steep, underwater banks on the west shore near one of the larger fault lines. They believe that a 7.1-magnitude trembler could trigger a 20-foot-high tidal wave that would race northeast across the lake's surface and inundated portions of the beaches and lakeside homes along the North Shore from Carnelian Bay to Incline Village.

Geologists have warned Tahoe residents since 1999 that underwater surveys revealed continued, small movement in the under-lake faults. 'It's only a matter of time," one commented off the record. In 1999 they discovered evidence of a prehistoric landslide that moved huge blocks of material hundreds of feet across, south of Tahoe City. "The blocks were tossed around like toys."

One other factor was mentioned for the first time in the new report: A major quake could dislodge the plug at the bottom of the lake. Were this to happen, the lake would drain over a period of about two years; most of the water would end up in the Reno area and flood it. The elevation of Reno (4,490 ft) is about 100 ft. less than the elevation of the bottom of Lake Tahoe (4,584 ft.). The draining water would seep downhill through the maze of rock fractures and occasional mine shafts that perforate the ground east of Lake Tahoe.