Mountain Landforms and Geomorphic Processes - Mountain Geography: Physical and Human Dimensions - page 262

journey. The mass caromed back and forth from one side of the valley to the other in its
descent, like a great sloshing liquid. Before the slide came to rest on the far flanks of
the valley, it had traveled more than 16 km and had destroyed two villages in its path,
Yungay and Ranrahirca. Ridges as high as 140 m were overridden, and blocks up to 6
m in diameter were scattered about like pebbles. The slide was preceded by a turbulent
blast of air that demolished buildings even before the rock debris struck, and a dense
dust cloud hung over the area for three days (Clapperton and Hamilton 1971).
These landslides were exceptionally large and involved millions of cubic meters of
material, but most landslides are smaller and more frequent. Their effectiveness in
transporting material downslope and in changing the face of the landscape is tremend-
ous. It is difficult to spend much time in mountains without seeing landslide scars and
deposits. Like many other processes in mountains, the landslide is a low-frequency,
high-energy event capable of accomplishing more geomorphic work in a few seconds
than day-today processes accomplish in centuries. It is important to realize, however,
that although the landslide is a sudden and intense event, it depends on the less spec-
tacular processes which have been slowly preparing the way for its eventual release.
FIGURE 5.15 Landslide on the Sherman Glacier, Alaska, that was released during the great Alaska
earthquake in 1964. Rock debris has since been transported to the terminus. (Photo by Austin
Post, 27 March 1964, U.S. Geological Survey.)