Largest landslides

The largest landslides occur in the oceans.  The largest known landslide, called the Storegga slide, occurred about 8100 years ago off the coast of Norway.¹ Between 2500 and 3400 cubic kilometers of sediment moved; the resulting tsunami reached England and Greenland. In the Shetland Islands the waves reached 20 meters above sea level.

digital before and after models of Mt.St. Helens

Digital models of Mt. St. Helens before and after the May 1980 landslide.

Courtesy USGS

The largest surface landslide in recorded history was the rock slide-debris avalanche associated with the eruption of Mount St. Helens in May 1980. It contained about 2.8 cubic kilometers, which traveled as far as 22 kilometers.²

Prehistoric landslides in the same part of the world, and also associated with volcanoes, were even bigger. An eruption of Mount Rainier about 5600 years ago created the “Osceola Mudflow,” a water-saturated debris avalanche of about 3.8 cubic kilometers that covered 505 square kilometers.3 The Mount Shasta debris avalanche (300,000 - 360,000 years ago) had an estimated volume of 26 cubic kilometers.4

1. S. Bondevik, F. Lovholt, C. Harbitz, S. Stormo and G. Skjerdal.
The Storegga slide tsunami--deposits, run-up heights and radiocarbon dating of the 8000-year-old tsunami in the North Atlantic.
Eos Trans. AGU, 87(52), Fall Meeting Supplement, Abstract OS34C-01 (2006).

2. B. Voight, R. J. Janda, H. Glicken and P. M. Douglass.
Nature and mechanisms of the Mount St. Helens rock-slide avalanche of 18 May 1980.
Geotechnique, vol. 33, no. 3, pages 243-273 (1983).

3. D. R. Crandell, C. D. Miller, H. X. Glicken, R. L. Christiansen and C. G. Newhall.
Catastrophic debris avalanche from ancestral Shasta volcano, California.
Geology, vol. 12, pages 143-146 (1984).

4. D. R. Crandell.
Postglacial lahars from Mount Rainier volcano.
U.S. Geological Survey Prof. Paper 677 (1971).

J. D. Dragovich, P. T. Pringle and T. J. Walsh.
Extent and geometry of the Mid-Holocene Osceola Mudflow in the Puget Sound--implications for Holocene sedimentation and paleogeography.
Washington Geology (Wash. Div. of Geology and Earth Resources, Olympia) vol 22, no. 3, pages 3-26 (1994).

J. W. Vallance and K. M. Scott.
The Osceola Mudflow from Mount Rainier: sedimentology and hazard implications of a huge clay-rich debris flow.
Geological Society of America Bulletin, vol. 109, no. 2, pages 143-163 (1991).

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