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Worst Landslides in U.S. History

By: Christopher C. Burt, 9:08 PM GMT on March 25, 2014

Worst Landslides in U.S. History

UPDATE March 26 As Jeff Masters recently blogged the Oso, Washington landslide has taken the lives of at least 20-24 people and perhaps many more. This would make this the single deadliest event of such (excluding volcanic eruptions, earthquakes, or area-wide mudslides) in U.S. history. How does this slide compare to other such events in U.S. history?

The largest landslide in modern U.S. history (in terms of volume) was most likely one that occurred just last year in Bingham Canyon outside of Salt Lake City, Utah on April 10, 2013. It had a slide mass of 55 million cubic meters (compared to an estimated 10 million cubic meters during the Oso, Washington event). Fortunately, no one was injured or killed during the Utah slide.

The largest (in terms of volume: 55 million cubic meters) landslide in modern U.S. history occurred last year at the Kennecott Copper Mine in Utah’s Bingham Canyon. There were no injuries since the mine operators had evacuated the site days earlier. Photo by Ravell Call, Deseret News.

The 2nd largest slide was the famous Gros Ventre slide on the northern end of Sheep Mountain that overlooks Jackson Hole, Wyoming. This occurred on June 23, 1925 following one of the wettest springs on record in the region. The slide had a mass of 38 million cubic meters and formed a dam that consequently burst, flooding the tiny village of Kelly, Wyoming and killing six.

Probably the largest single landslide in modern U.S. history whose origins were completely natural was the Gros Ventre slide in Wyoming on June 23, 1925 when 38 mm cubics of rock fell. The photo above shows how it looks today. Photo from Teton County Emergency Management web site.

Prior to the Washington slide, the most recent deadly slide was that which overwhelmed La Conchita, California on January 10, 2005 killing 10. This, however, was a small slide (just 200,000 cubic meters) which unfortunately occurred in a densely populated neighborhood. The costliest slide in U.S. history was the Thistle, Utah event of April 1983 (15 million cubic meters in volume). The slide caused a lake 160-feet deep to form and the flooding wiped out the town of Thistle causing an estimated $200-400 million (1983 dollars) in damage.

The costliest landslide in U.S. history occurred in the Thistle, Utah area in April 1983. The huge lake (pictured above) caused by the landslide wiped out the town of Thistle and buried several important transportation routes. Photo from Wikicommons.

It is difficult to state what the deadliest ‘landslide’ in U.S. history has been since some were a combination of factors (sometimes of human origin like the collapse of the St. Francis Dam in California in 1928 that resulted in 500 deaths) or a series of mud and debris flows over a wide area as occurred in the Santa Cruz Mountains of California in 1982 killing 30 and in Nelson County, Virginia in 1969 when the remnants of Hurricane Camille dropped 27” of rain resulting in mudslides that killed 153. According to the USGS, landslides or mudslides/flows kill 25 in the U.S. each year.

Landslides Caused by Volcanic Eruptions and Earthquakes

Of course, the Mount St. Helens volcanic eruption on May 18, 1980 caused the largest landslide in U.S. history and its debris flows resulted in the deaths of dozens of people (57 fatalities associated with the volcanic eruption in total). The volume of the landslide caused by the collapse of the mountain is estimated at 2.9 cubic square kilometers in size.

The eruption of Mt. Saint Helens on May 18, 1980 resulted in what was obviously the largest ‘landslide’ in modern U.S. history. Some 2.9 cubic kilometers of the mountainside collapsed. Photo from USGS.

The March 27, 1964 Alaskan earthquake (9.2 on the Richter Scale) resulted in massive landslides above and below the ocean (211 mm cubic at Seward and 9.6 mm cubic in Turnagain Heights). The slides resulted in deadly tsunamis from Alaska to California and Hawaii, which contributed to the 139 fatalities associated with the earthquake. Another Alaskan earthquake, this one on July 9, 1958 caused 30 mm cubic of rock to plunge into Lituya Bay creating a wave 1,700’ tall which washed the surrounding shorelines clean of vegetation some 100 feet above the bay. Two unlucky fisherman perished. The Yellowstone earthquake in 1959 caused a landslide that killed 26 in Madison County, Montana.

The massive landslide in Lituya Bay, Alaska on July 9, 1958 caused a wave 1,700’ tall to wash away vegetation along the shores of the bay. Photo from U.S. Coast and Geodetic Survey archives.

Oso, Washington slide now deadliest in U.S. history

Late reports on the evening of March 25th indicate that the death toll from the Oso, Washington slide is at least 20 and perahps 24. Confusion reigns about this at this hour. In any case, this would make this the single deadliest single landslide/mudslide event in U.S. history excluding volcanic, earthquake, dam collapse, or multiple area-wide events such as I listed above.

Christopher C. Burt
Weather Historian

Extreme Weather Landslides

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.