Geography Reference
In-Depth Information
Figure 7-2:
Talus
cones have
formed at the
base of the cliffs.
Going with the flow: Water
Flowing water is far and away the principal agent of erosion and deposition. The extent to
which it can rearrange the landscape is largely dependent on three things that vary widely.
The amount of water.
Thisisano-brainer.Thelargerariverorwave,thegreateritsability
to move surface materials.
Velocity.
The faster water travels, the greater its ability to pick up and move surface mater-
ial. On land,
gradient
(the steepness of a slope) is a major determinant of speed. The steeper
the inclination, the faster water travels. Similarly, storms at sea greatly increase the size and
velocity of waves, and therefore greatly increase their impact on coasts.
Surface cover.
Generally, the more open or bare a landscape, the greater is the likelihood
of its alteration by flowing water. Vegetation inhibits erosion by slowing down flow speed and
by generating root systems that hold soil in place. Bare ground, in contrast, is rather at the
mercy of water and velocity. Thus, one of the great geographical ironies is that flowing water
is the principal agent of landscape change in dry areas, where bare ground is very common.
Rain and streams may be scanty in arid and semi-arid regions, but it doesn't take lots of flow-
ing waters to make major impressions on the land in those areas. Witness the Grand Canyon,
for instance.
Any volume of water that interacts with earth's surface can produce mass wasting. That includes
small-scale phenomena like raindrops and rivulets. Thus, run-off on exposed soil in an agricultural
field or even a backyard garden may erode soil and result in
gullying
that produces very miniature
