Grand Canyon began by natural erosion & continues to do so; how long before it completely erodes?

Answer 1

Erosion is a process that will always occur if the land surface is above sea level and there is precipitation to supply water for runoff erosion and wind for wind blown sand erosion.
If it were not for continuous uplift of the plateau that the grand canyon resides in it could have been completely eroded eons ago.
The answer therefore is that eorsion will never stop and the grand canyon will only disappear long after the rate of uplift either halts or decreases to less than the rate of erosion.
The ongoing process is that the Colorado River is actively eroding a narrow path through a continuosly rising continental crust while the higher land is worn back by a combination of minor runoff, mass wasting as land drops off the cliffs into the river below, and some wind blown sand erosion. The high rates riverbed erosion in an arid region have been driven by widespread rain and snow far upstream in the rocky mountains. The first thing you will see when uplift stops and the river bed erosion has brought the river down to sea level will be a flooded estuatry within the meandering river system surrounded by gradually eroding highlands. At that point only the local rain driven runoff and wind erosion will continue on the highland and the rate of land erosion will be much lower. The remaining higher elevations of the canyon will gradually be brought down to sea level over an incredibly long period of time. In that case uplift may recur, ocean levels may even change and cover the land. Subsidence of the continental crust (which would bring the entire plateau down towards sea level without the aid of erosion) is also possible. If you visit the canyon you will see that many the rocks making up the canyon walls contain seabed fossils indicating that the plateau was at one time below sea level prior to the uplift.
In any case remember that the Uplift of the continental crust in combination with the eroding action of the Colorado River is responsible for the great depth of the canyon we see today. Erosion does very little without uplift.

Answer 2

That's kind of difficult to answer, because climate and tectonics are factors needed to answer your question. Here is how the Grand Canyon formed. The ancestral Colorado River drained a large part of the southwestern US. The Kaibab Plateau began a slow upward movement, but there was sufficient energy in the river to keep up with the uplift. As uplift continued the river stayed about the same place, but the land rose around it. Currently the Colorado River is dammed in a couple of places, so it's energy is diminished, and I doubt seriously if the amount of erosion going on now is comparable to before the damming of the river. Also, if the climate becomes drier or wetter, things will change, and if uplift begins anew, that will add time to the answer. Net result? Don't know. All I do know is if a coal mining company had built the canyon in search of coal it would be considered an eyesore.

Answer 3

It erodes very little now since the Glen Canyon dam cut off most of the flood waters.