Geography Reference
In-Depth Information
there is little vegetation and frost action causes rapid breakdown and displacement
of rocks (Rapp 1960). Most active talus accumulations are bare and rocky with very
little fine material visible, but where mudflows, avalanches, and landslides feed into
to the talus, fine material may be present (Luckman 1978). Because the larger rocks
have more kinetic energy and therefore travel farther, they will be located at the bot-
tom of the slope (Rapp 1960). The downslope sorting will not be perfect, however, since
the rock size, shape, height of fall, nature of the surface, and interference from other
obstacles will affect this arrangement (Gardner 1973).
White (1981) defined three different types of talus forms that occur in the alpine en-
vironment.
Rockfall talus
is a collection of angular rocks of all sizes that form below
cliffs or steep rocky slopes. These are typically derived from falling, rolling, bouncing,
or sliding to the base feature, and have a slope of 35-45°. Rockfall talus is often referred
to as a rockfall cone, scree slope, talus cone, or talus slope.
Alluvial talus
forms from an
accumulation of rocks of any size or shape that are carried by rainwash or snow through
a gully or couloir to rest against a valley wall. Their slope is usually 35-38° with a con-
cave up profile.
Avalanche talus,
an assemblage of angular rocks of any size, is derived
from avalanched snow mixed with rock debris carried from cliffs or steep rocky slopes.
Some talus forms may resemble a
protalus rampart,
or ridge of angular block created
by rocks falling from cliffs that slide across a former snowbank or firn field. Protalus
ramparts mark the downslope edge of old snowbanks.
FIGURE 5.16
Accumulation of alluvial talus in Rocky Mountain National Park, Colorado. (Photo by J.
R. Janke.)
The status of a talus slope is determined by the supply of material, its movement
within the talus, and its removal. The rate of talus accumulation provides a gross index
Search WWH ::
Custom Search