Monday, April 18, 2016

Landslide Generated Waves: One Big Example

Trees stripped off landscape by landslide generated wave
Picture via Chris Larsen and University of Alaska Fairbanks

The University of Fairbanks has a nice write up of the massive landslide generated wave that swept through Icy Bay (http://www.gi.alaska.edu/alaska-science-forum/giant-wave-icy-bay).

Given the size of the landslide and the confines of the upper part of the bay, a big wave would be expected. The landslide was really big and early estimates are 200 million tons of rock slid in the event. If so, this puts the slide in an elite level; the UAF site suggests this might be the largest non volcanic landslide by volume in North America's written history. I like the caveat about written history as there is an excellent oral history on a not-so-old, but much larger slide.

The slide and wave generated is a reminder that landslide generated waves are a potential risk around steep slopes and water bodies. A slide off the south end of Camano Island caused a wave that led to fatalities on the nearby Hat Island to the south. This event is another oral history event and has since been verified as being relatively recent.

During recent volunteer work, I drafted some geologic hazard code language for the potential for a landslide generated wave hazard. I felt it appropriate to have specific language for landslide generated waves versus tsunami hazards or seiche hazards as the locations are different and the potential return intervals are different. The risk from tsunami, seiche waves and landslide generated waves will be unique for each county and city so simple code copying is a bad idea.

The landslide generated wave hazard is clearly no small thing in some of the very mountainous inlets of Alaska. The land shown in the image above would not be a good town site.    

3 comments:

Eric B said...

I'd like to learn more about the Camano Island slide. Do you have any sources you would recommend? The idea of including these as separate within code is a very good idea. There are several examples of dangerous landslide generated waves in Washington, including the 1949 wave generated by a landslide in the Tacoma Narrows and the numerous ones that have occurred in Lake Roosevelt.

Dan McShane said...

Eric: The Tulalip Tribe has a oral history of the event. Also this: Whitekaer, W.L., 2008. Landslide generated tsunamis: A smoking gun in Saratoga Passage, Puget Sound, Washington. School of Oceanography, University of Washington, Senior thesis.

Eric B said...

Thanks!