The story of the Grand Canyon began 30 to 70 million years
ago when plate tectonics led to the uplift of the Colorado Plateau. This uplift
left a high and flat rock formation that allowed the Colorado River to carve
downward beginning 5 to 6 million years ago. As the river began to carve out
the canyon, the processes of weathering and erosion came along contributing to
the 18 mile wide, one mile deep canyon. Looking into the future for the canyon,
downcutting, erosion, weathering, and faulting will continue to have the
largest impact on the landscape and will cause widening and deepening of
the canyon.
Within the next 1,000 to 10,000 years, the canyon will look
much as it does today because carving out noticeable changes is too lengthy a
process to see anything considerable within the time frame. Nevertheless, the appearance
of the canyon will change because downcutting by the river, weathering and erosion
will continue to expose new rock. The process of mass wasting will lead to most
of the carried off rock particles, but weathering in different forms will lead to erosion
as well. At the canyon, mass wasting can be seen in the form of falls and
flows. Falls occur when rocks become detached usually because of a steep slope
or undercutting. Undercutting occurs when
the bottom portion of a rock is eroded to the point where the top of the rock becomes
too heavy to stand and eventually detaches and falls off.
The canyon pictures provide examples of mass
wasting in the form of falls and talus (rock particles) that accumulate. An example of undercutting is also displayed.
This YouTube video beautifually captures an actual debris flow. Towards
the middle of the 4 minute clip you see a highly thixotropic consistency in the
flow. http://youtu.be/TDtBby7lJX0
Sources
