Lake Tahoe Tsunami simulation from Tsunami that occurred 7,000 to 15,000 years ago.

Could there ever be a damaging tsunami on Lake Tahoe? In the words of Fargo’s Sergeant Marge Gunderson “you betcha!” but such a wave wouldn’t actually be a tsunami, it would be a seiche.

What exactly is a seiche? I’ll give you two clues – it’s not exactly a tsunami, and it’s definitely not a tidal wave. A seiche is a standing wave on a freshwater lake or in a semi-enclosed harbor on the ocean. The word ‘seiche’ is often used interchangeably with ‘tsunami’ and ‘tidal wave,’ but all three refer to different phenomena.

The Japanese translation of ‘tsunami’ is literally ‘harbor wave,’ but in the modern era, ‘tsunami’ is used colloquially to refer to the devastating ocean waves and surges that crash hundreds of yards inland as a result of gigantic underwater earthquakes in places like Indonesia, Thailand, and Japan. The use of the word ‘tsunami’ in referring to damaging waves came about in ancient Japan when waves appeared seemingly out of nowhere and caused grave damage to harbors. Eventually, people started to realize that tsunami waves were caused by underwater earthquakes, and were not tidal waves, because they have nothing to do with tides. Given what happened in Japan just a few months ago, I probably don’t need to describe the horror and destructive potential of these waves since they are so fresh in all of our minds.

Weather-caused seiches are regularly observed in the Great Lakes, including Lake Erie where they occur often and are up to 5 feet in height. The National Weather Service even issues warnings for them when they cause water fluctuations of 2 feet or more. In July of 1995, a seiche on Lake Superior caused the water level to drop by 3 feet in fifteen minutes, leaving some boats dangling from docks (Korgen, 2008).

Seiches can be just as devastating as tsunami waves are in the ocean. What causes seiches? Seiches are caused by earthquakes, landslides, prolonged wind events, meteorite impacts, and gradients between large areas of high and low pressure on either side of the body of water. Anything that can establish resonation on the surface of water in a lake or harbor can cause a seiche. The relatively short cross-shore distances compared to the ocean can cause seiche waves to be reflected back and forth across lakes for hours and hours. As you might imagine, this could be very bad for things and people that call the shores of lakes home.

Lake Tahoe has suffered from these destructive waves in the past. Deep into the past as far as humans are concerned, but barely a moment ago in terms of geologic time. A 2006 USGS study led by internationally recognized tsunami expert James G. Moore found that a giant landslide in McKinney Bay on Tahoe’s west shore dropped several cubic miles of the West Shore 1,500 feet to the bottom of the lake and likely generated enormous seiche waves between 7,000 and 15,000 years ago (Moore et al., 2006).

Another group of scientists led by Graham Kent of Scripps Institute of Oceanography mapped and described several major faults running underneath Lake Tahoe in 2005 (Kent et al., 2005, see map above), and declared them capable of producing an earthquake as large as M 7.0 that could in turn cause seiches between 10 and 30 feet in height. John Anderson and Gene Ichinose of the UNR seismological laboratory studied the faults underneath the lake and they estimated that the probability of such an event would be around 2-4% in the next 50 years, or in other words, minute (Ichinose, 2000).

If Tahoe did suffer from a large earthquake that suddenly slammed up the lakebed, or angered local telemarking hippies and caused a giant chunk of Jake’s Peak to slide into the lake, the consequences would be devastating for just about everything and everyone on or a few hundred feet back from the shores of the lake. Imagine a three story wall of freezing cold water smashing ashore in Tahoe City, Incline Village, or South Lake Tahoe. Buildings would be smashed into bits, people wouldn’t stand a chance. Waves would crash around the lake for hours, ricocheting off the shores and amplifying in places like Emerald Bay and Meek’s Bay. Giant trees would be snapped like twigs, and huge volumes of water would overtop the dam in Tahoe City and rush down the Truckee River through Truckee and down into Reno.

[youtube]http://www.youtube.com/watch?v=D8Py3XgRMkk[/youtube]

The above video shows one interpretation of the giant pre-historic McKinney landslide and the ensuing seiche waves superimposed on a digital elevation model of modern Lake Tahoe.

In the end though, planning for the worst case scenario is not as important as preparing for low consequence, high-probability natural hazards up here in Tahoe, such as wildfires. Seiche waves could strike on lake Tahoe, but the chances are more on par with a meteorite falling from outer space and crashing into your house. So before you go installing a titanium-kevlar roof to protect yourself, or selling your 3,500 square foot lakeside mansions and moving to Truckee, you might be better off developing an emergency evacuation plan in case you have to drop everything and run from an approaching wildfire.

What other earth-science question or questions do you have? Post them in the comments and I’ll pick one to answer in next week’s column.

References

Ichinose, G. A., J. G. Anderson, K. Satake, R. A. Schweickert, M.L. Lahren. (2000). The potential hazard from tsunami and seiche waves generated by large earthquakes within Lake Tahoe, California-Nevada. Geophysical Research Letters 27(8):1203-1206

Kent, G.M.; J.M. Babcock, N.W. Driscoll, A.J. Harding, J.A. Dingler, G.G. Seitz, J.V. Gardner, L.A. Mayer, C.R. Goldman, A.C. Heyvaert, R.C. Richards, R. Karlin, C.W. Morgan, P.T. Gayes and L.A. Owen (May 2005). “60 k.y. record of extension across the western boundary of the Basin and Range province: Estimate of slip rates from offset shoreline terraces and a catastrophic slide beneath Lake Tahoe”. Geology 33 (5): 365–368. doi:10.1130/G21230.1

Korgen, Ben. Bonanza for Lake Superior: Seiches Do More Than Move Water.

Moore, J. G., R. A. Schweickert, J. E. Robinson, M. M. Lahren, C. A. Kitts. (2006). Tsunami-generated boulder ridges in Lake Tahoe, California-Nevada. Geology 34(11):965-968.

Schweickert, R. A.; M. M. Lahren. (2002). Glacial Geology of Blackwood Canyon, Lake Tahoe, California; Implications for Landslides and Tsunamis. Abstracts with Programs – Geological Society of America 34(6):130-131.