Many people love to go Canyoneering with its challenge of hiking through some of the most amazing patterns of reflected light that captives photographers all over the world. Each year hikers observe a change in-depth, which is caused by reoccurring flash floods. In the evolutionary time frame it is assumed to take eons of time for them to be formed.
It peaked much interest in a team of geologists who wanted to find out how about long it would take. They tested for erosion rates by observing an actual incipient canyon starting during floods in the Henry Mountains, Utah. Going by “a well-constrained initial geometry of a steep, unchannelized bedrock slope” and discovered a remarkable amount of cutting – half a meter – in just 23 days of flooding from seasonal snowmelt. If this was the actual rate, it would take only 200 years to cut 100 meters.
This was surprising for geologists who were submitting themselves to the evolutionary time frame. If the slot canyons are millions of years old then why do we still see sandstone left after all that time? The authors recognize the issue…
“Rates of fluvial bedrock incision mimic rates of external landscape forcing (e.g., tectonic uplift and eustacy [sic]) when averaged over geological time scales, but local rates of channel downcutting into bedrock can be fast during the individual floods that actually drive bedrock incision: we measured up to 1/2 m of local vertical incision into bedrock over 23 days of snowmelt runoff (Fig.9). Local channel morphology and high but not overwhelming rates of sediment transport enabled such a high local erosion rate.”
“The local thalweg2 slope was high (~20%, Fig. 8), and the cross-sectional morphology of an inner channel focused flow and sediment transport over a narrow zone where almost all erosion occurred. While poorly constrained, field measurements demonstrated high rates of coarse-sediment transport.”
“Additionally, preexisting inner-channel alluvium was entrained during this snowmelt runoff event, and so alluvial cover was not consistently present to mantle the inner-channel bed and inhibit bedrock erosion. Field observations also suggest that thresholds of detachment for abrading the local sandstone are negligible (Fig. 6).”
Now let’s take cosmogenic radionuclide dating for the sake of argument with the slowest rate mentioned in the paper which would make the Navajo sandstone about 190 million years old. Using calculation from the slowest rate which is (0.4mm/year), divide by 4 to get a tenth of a millimeter per year. This would make the canyon 19 km deep which is well over fifteen times (95,000 kilometers deep) compared to the actual depth of the Grand Canyon!
By contrast, let’s take the most conservative value measured at 10mm in a year, then you could get a decently deep canyon 50 meters deep (similar to many observed) in just 5,000 years! Using the Biblical time frame keeps the slot canyons rate within reason of what is being observed!