There are several different types of mass wasting and these types are listed in
Table 5. The types are differentiated by their speed and degree of lubrication as
moderated by the type of material being mass wasted. Some of the types happen
so quickly that they are deadly to anything in the way. For instance, rockfalls,
landslides, and avalanches can have speeds in excess of 160 kph. They are usually
quite localized. Soil creep is universal on soil-covered landscapes and averages a
fraction of a centimeter per year. It is imperceptible except for traces such as lean-
ing fence posts and cracked concrete walls.
Some of the terms in the table need elaboration. The familiar avalanche is a
form of landslide with much snow accompanying the rock and soils. Earthflows
are quite slow and generally over slopes with no connection to the drainage net-
work; mudflows are much faster and confined to valley bottoms. Soil creep is a
general form of exceedingly slow downslope movement in all latitudes, while sol-
ifluction is a specialized form of soil creep in the active layer of permafrost in tun-
dra environments and is manifest as parallel arcuate lobes of soil material pointed
in the downhill direction.Wind Erosion and Deposition
Air is a form of fluid, albeit much less dense than water, and undergoes significant
flow when heated and cooled. It readily expands, contracts, and moves horizontally
and vertically. Despite the seeming ease through which we move through the air, it
is composed of molecules and the molecules exert force when they are in motion.
The force is enough to erode, transport, and deposit considerable amounts of mate-
rials. Thelandscapedevelopments related to wind are corporately known as aeolian
processes (derived from Aeolius, the mythical Greek keeper of the winds).
The force exerted by air depends on the air’s velocity and the force exerted is
proportional to the square of the velocity. This means that as velocity increases,364 Wind Erosion and Deposition
Table 5. Classification of Mass Wasting
Type Material Speed Lubricating water
Rockfall Rock Fast Dry
Landslide Rock and soil Fast Moderately wet
Slump Soil and Rock Moderately slow Moderately wet
Mudflow Soil Moderately fast Wet
Earthflow Soil Moderately slow Wet
Creep Soil Slow Dry
Solifluction Soil Slow Wet