Mountain Landforms and Geomorphic Processes - Mountain Geography: Physical and Human Dimensions - page 261

FIGURE 5.14 Debris from a landslide in the Andes. Note the road cutting across the toe of the land-
form. (Photo by J. R. Janke.)
Among the better-known mountain landslides are the great slide in 1881 at Elm,
Switzerland, and the ancient Saidmarreh landslide in the Zagros Mountains of south-
western Iran. The latter was apparently the largest in the world: The side of a mountain
broke loose, descended 1,500 m, traveled horizontally some 14 km, and eventually as-
cended 500 m over an intervening obstacle! The fallen rock covered 274 km 2 with a
thickness of over 100 m. The material ranged in size from dust particles to huge blocks
18 m in diameter (Watson and Wright 1969).
In North America, the most famous slides have been the Turtle Mountain landslide
that destroyed the small mining town of Frank, Alberta, in 1903; the Gros Ventre slide,
Wyoming, in 1925; and the Sherman landslide, which came to rest atop the Sherman
Glacier during the Alaska earthquake of 1964 (Cruden 1976; Fig. 5.15). An ancient slide
that temporarily blocked the Columbia River midway through the Cascades and gave
rise to the “Bridge of the Gods” of the Native American legend is now the site of Bon-
neville Dam (Waters 1973).
The most destructive landslide of the twentieth century took place in the Peruvian
Andes during a great earthquake in 1970. Over 50,000 people were killed, 18,000 of
them buried in the landslide that originated on Huascarán, a volcanic peak with an el-
evation of 6,768 m, about 350 km north of Lima. The earthquake caused a huge mass
of overhanging snow and ice to break loose from the summit and fall 1,000 m, until it
crashed into the mountain and pulverized. The impact dislodged unconsolidated slope
material and caused massive slope failure. Frictional heat created from the collision
also caused melting, so that vast amounts of water were available to saturate and lubric-
ate the mass (Clapperton and Hamilton 1971; Browning 1973). The slide swiftly descen-
ded the mountain, going from an elevation of 5,500 m to 2,500 m in less than 3 minutes,
traveling at speeds of up to 480 km h −1 . The survival of delicate moraine ridges and
vegetation in its path suggests that the slide rode on a cushion of air for parts of its