Landslides - 11 of 22
Landslides FAQs - 22 Found
The landslide that occurred during the 1980 eruption of Mount St. Helens, a volcano in the Cascade Mountain Range in the State of Washington, U.S. is the largest landslide that we've recorded. The volume of material was 2.8 cubic kilometers (km).
However, much larger landslides have been discovered that occurred before recorded history. Geologists can identify these by the deposits and other evidence that has been left in the geologic record and on the surface.
One is in southwestern Utah, and is named the Markagunt Gravity Slide. The landslide is located on Markagunt Plateau northeast of Cedar City, Utah, centered at about 38 degrees north latitude, and between 112 and 113 degrees west longitude. The landslide covers an area of about 5000 square kilometers, is more than 100 km long and 60 km wide, and has a travel distance of 30 km!
The other is in northwestern Wyoming and southeastern Montana. It is located between about 44:30 and 45 degrees north latitude and 109 – 110 degrees west longitude. Called the Heart Mountain gravity slide, it also has a reported area of about 5000 square kilometers and a long travel distance.
Sources of Information:
Anders, M.H., Fouke, B.W., Zerkle, A.L., Tavarnelli, Enrico, Alvarez, Walter, and Harlow, G.E., 2010, The role of calcining and basal fluidization in the long runout of carbonate slides: An example from the Heart Mountain slide block, Wyoming and Montana, U.S.A.: The Journal of Geology, Vol. 118, No. 6, p. 577-599. DOI: 10.1086/656383.
Biek, R.F., Hacker, D.B., and Rowley, P.D., 2016, Update on the Markagunt gravity slide Utah’s largest landslide just got bigger—A lot bigger: Utah Geological Survey, Survey Notes, Vol. 38, no. 1.
Hacker, D.B., Biek, R.F., and Rowley, P.D., 2014, Catastrophic emplacement of the gigantic Markagunt gravity slide, southwest Utah (USA): Implications for hazards associated with sector collapse of volcanic fields: Geology, Vol. 42; no. 11; p. 943–946. doi:10.1130/G35896.1