Rivers sometimes follow paths that appear strangely out of place in the landscape. Instead of flowing around mountain ridges or following the easiest path through softer rock, some rivers cut directly across resistant rock formations and mountain ranges, producing spectacular water gaps and gorges.
Geologists call some of these systems discordant drainage because the course of the river does not correspond to the present geological structure or topography of the land.
Conventional geology generally explains these features in one of two ways. An antecedent river is proposed to have existed before the surrounding land was uplifted, cutting downward rapidly enough to maintain its original course as mountains slowly rose around it. A superimposed river is thought to have established its course upon rock or sediment that once covered the present landscape. After that overlying material eroded away, the river supposedly retained its original course and cut into the harder formations beneath.
These explanations may be reasonable reconstructions, but they necessarily depend upon geological conditions and landscapes that are no longer present. The existing gorge alone does not tell us how quickly it was excavated.
CANYONS DO NOT NECESSARILY REQUIRE VAST AGES
One lesson of modern geology is particularly important: large erosional features can sometimes form extraordinarily quickly when sufficient water, sediment and energy are available.
Your view likely depends on your worldview and not actual evidence.
Mount St. Helens provided a dramatic modern example.
The May 18, 1980 eruption deposited enormous quantities of loose volcanic material throughout the North Fork Toutle River drainage basin. Water, mudflows and subsequent runoff then began cutting through these deposits.
The U.S. Geological Survey documented extensive channel erosion and described sediment yields following the eruption as among the largest ever measured. New channels developed across the debris-avalanche deposits, while existing channels were dramatically deepened and widened.¹ ²
A particularly intense erosional event occurred on March 19, 1982, when volcanic activity melted snow and generated powerful water and mudflows. Researchers studying the area reported that substantial portions of the newly developing drainage network were excavated during this catastrophic event. Some channels eventually exceeded 100 feet in depth.³
The resulting landscape included steep-sided gorges and branching drainage channels that superficially resemble much larger canyon systems.
THE LESSON OF MOUNT ST. HELENS
Mount St. Helens does not demonstrate that every major canyon on Earth formed in a single event, nor are its loose volcanic deposits identical to every type of consolidated bedrock.
It does demonstrate something extremely important:
The size or depth of an erosional feature by itself cannot tell us how long erosion required.
Erosion rates depend upon water volume, velocity, sediment load, rock strength, gradient and the magnitude of catastrophic events.
Processes occurring under ordinary river conditions today therefore should not automatically be projected backward as though erosion always proceeded at comparable rates.
Where enormous quantities of moving water are involved, landscapes can change with remarkable speed.
CATASTROPHIC EROSION DESERVES CONSIDERATION
Discordant rivers, water gaps and gorges are commonly explained through long histories of uplift, denudation and river incision. Those models should be evaluated on their evidence.
But modern catastrophes give us something equally important: direct observation.
Mount St. Helens demonstrated that powerful water and sediment flows can establish drainage networks, excavate valleys and produce deep gorges within years, with some major erosional episodes occurring much faster.
For anyone considering catastrophic models of Earth’s geological history, including massive post-Flood runoff and drainage, such observations deserve serious consideration.
They remind us that large geological formations do not necessarily require slow geological processes.
Sources
Austin, S. A., Rapid Erosion at Mount St. Helens, describing rapid gorge development following the March 19, 1982 mudflow and subsequent erosion.
https://www.icr.org/research/index/researchp_sa_r04/
Meyer, D. F., Nolan, K. M., and Dodge, J. E., Post-Eruption Changes in Channel Geometry of Streams in the Toutle River Drainage Basin, 1980–82, Mount St. Helens, Washington, U.S. Geological Survey Open-File Report 85-412.
https://doi.org/10.3133/ofr85412
Major, J. J., and others, Rates and Processes of Channel Development and Recovery Following the 1980 Eruption of Mount St. Helens, Washington. U.S. Geological Survey.
