Geography Reference
In-Depth Information
Deposition:
This is the putting down (or coming to rest) of eroded materials. Returning
once more to the Grand Canyon, all the eroded material that was carried away by the Colorado
River was eventually deposited either down-river or settled in the Gulf of California, into
which the Colorado empties.
The difference between erosion and deposition is rather like that between pick-up and delivery. Ma-
terial is taken from one place and put in a different place.
Changing the Landscape
Beauty, as they say, is in the eye of the beholder. You can find it in art museums throughout the land
and, as far as geography is concerned, in the land itself. Sculptures are made by removing material
that once surrounded the final forms. Compositions are achieved by bringing together materials that
were formerly separate. In a similar manner, erosion and deposition (see previous section) are creat-
ive processes. Like standard works of art, the results may inspire us or, frankly, leave us unmoved.
Either way, the creative power of gradation produces works that we live on and, in the case of soil,
cannot live without.
In the real world, nature has four means, or
agents,
at its disposal to quite literally carry out erosion
and deposition: gravity transfer, flowing water, glaciers, and wind. Although a glacier is a form of
flowing water, the gradational actions of solids (ice) and liquids is sufficiently different to merit sep-
arate treatment.
Staying grounded: Gravity transfer
Gravity is constantly “pulling down” on surface material. If not somehow restrained, therefore, par-
ticulatematterranginginsizefromsoiltobouldersmaymovedownslopeinanactof
gravity transfer.
This process can be awesome, as in the case of a landslide. Much more common, however, are the
decidedly unspectacular minute movements (
soil creep
) of small particles, and the occasional pebble
and rock that roll a bit downhill. Given enough time, however, the cumulative effect of gravity trans-
fer may be really noticeable. Uplands are eroded and reduced, while deposition creates new land-
forms, as when rock materials accumulate at the bases of mountains or cliffs to form talus cones, as
shown in Figure 7-2.
