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.

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

June 27, 2011 – NEVADA – Lake Tahoe may be one of the most beautiful serene lakes in the world but beneath the sparkling, placid blue water lurks a monster. Three major faults lie under the lake and if a series of them are activated by a large magnitude quake, landslides and lake-floor buckling could generate a tsunami with waves as high as 10 to 100 meters.

Scientists think all three faults could be linked to one another deep inside the Earth, but it’s hard to test that theory until one becomes active. “The problem with the big faults is they are completely dormant between earthquakes,” said geologist Gordon Seitz of San Diego State University. “They are like sleeping giants, and then they suddenly awaken.” Seitz and a team of geologists and seismologists dug into the Incline Village fault in 2004 and discovered that it becomes active about every 10,000 to 15,000 years, and its last earthquake was about 500 years ago. “The Incline Village earthquakes are relatively rare,” Seitz said. Because the three faults are so close to one another, they could be linked deep underground and could set off one another like dominos, Seitz said. One piece of evidence that supports this theory is how much the fault line moved in the last earthquake, said Robert Karlin, a professor at the University of Nevada, Reno, who studies earthquake activity. The fault moved about 13 feet 500 years ago, which is more than expected for a fault line only 10 miles long. –Standeyo

When most people in northern California think of “the big one” they imagine a 1906 type earthquake rocking San Francisco; but it turns out that the Lake Tahoe region is also capable of having large earthquakes and even deadlier tsunami’s. Seismologist Graham Kent said, “We’re heading right for the largest fault in the basin, the west Tahoe fault ruptures about every four to five thousand years. Its last rupture was 4500 years ago. So obviously there’s some concern because we’re at the end of that earthquake cycle. Doesn’t mean it’s gonna happen tomorrow; but it wouldn’t be a surprise if it did.” At least three faults run underneath the lake: the Stateline, the Incline Village and the West Tahoe. Now it looks like there is one more. For instance, Kent says we now know that that the faults sometimes erupt together, creating earthquakes as large as 7.0-7.5 and a quake that big would mean a potentially deadly tsunami up to thirty feet high. Graham Kent: ”Since I also run the Nevada Seismological laboratory, I would be remiss to remind people that the biggest story in Japan is the fact that the number of people that didn’t die, and it’s because of preparedness. Ultimately, preparedness trumps everything else. If you know anything about Japan, they prepared for this day, even though the tsunami was larger than they thought, they prepared for that day, and you can see it in the YouTube videos – people by and large were on a move in a way that wouldn’t happen in the U.S. today.” So what should you do if your Tahoe summer vacation gets interrupted by an earthquake on Lake Tahoe? Kent recommends you duck and take cover waiting out the shaking and then, in a reasoned way get as high as you can. –Capital Public Radio