Existing comment:
The Shaping of the Canyon:
Swift water of the Gunnison River and abrasion from the sediment it carried are the chief cutting tools in the deepening of Black Canyon, but there are other forces important to the carving of the canyon. Moisture entering joints and fractures promotes weathering. As the fractures slowly widen, large rock masses are gradually weakened to the point where they slide or tumble to the canyon floor.
Look up the canyon to your right. The south rim (to your right) has eroded back farther than the north (to your left). The south rim faces north so it does not receive as much sun and does not dry out as quickly as the north rim. Since moisture is an important factor in erosion, a moist slope will tend to erode at a faster rate than a dry slope.
Thus, the canyon rims are gradually worn away. What the river can't carry away accumulates as steep piles of talus against the canyon walls or created rapids in the river.
This carving process has been slowed by the construction of dams upstream. These dams hold back most of the sediment and most of the peak spring run-off, both of which are necessary for the river to deepen its bed effectively and carry off material eroded from the canyon walls.
It took about 2 million years to shape the canyon as you see it today. If you could come back in another 2 million years, what do you think Black Canyon would look like? |