Still, we can hope.
The science behind canyon erosion
By CHRIS HAYS and ALAN PAUL PRICE
This is submitted in response to a recent letter in this newspaper that contends that science ignores catastrophes when explaining the geological record. Actually, geologists frequently use catastrophic explanations to explain both large- and small-scale phenomena.
For example, a majority of geologists accept the evidence that an asteroid collision explains the extinction of the majority of dinosaurs 65 million years ago and that multiple glacial outburst floods explain the channeled scablands of eastern Washington. In fact, accelerated erosion like that caused by floods is a necessary part of geologic explanation that ranges from the slow, incremental deposition that dominates deep ocean environments to the more rapid, more changeable environments that occur on and near dry land.
The two catastrophic events that the author describes, the 1980 eruption of Mount St. Helens in Washington and the 2002 Canyon Lake flood near San Antonio, Texas, were indeed associated with rapid canyon formation. But to say they were catastrophic does not mean that they were surprising or unprecedented.
Loose, unconsolidated volcanic ash deposits like those created by Mount St. Helens are prone to rapid erosion. And though the rapid erosion of the Canyon Lake Gorge came as a shock to the local landowners, this area is known for flash floods. And, once again, the ability for high stream flows to cut through, a faulted limestone with numerous bedding planes and preexisting solution channels is not unusual.
Equating the rapid erosion of these small canyons to a canyon the size and complexity of the Grand Canyon, however, is a scientific mistake. The physical evidence does not support such a conclusion. Any flood or floods capable of cutting the Colorado in a few short years would have scoured on the Colorado plateau, left thousands of feet of recent sediments near the mouth of the canyon, and cut a gorge with vertical walls.
Moreover, geologists further substantiate the age of the canyon with each new study. As recently as March 7, 2008, a study in Science magazine used uranium-lead dating to determine that the western edge of the canyon formed around 17 million years ago. This technique and, in fact, all dating techniques used to estimate the age of geological formations, depend on fundamental principles of physics and chemistry.
This information is what can safely be said. Teachers and textbooks sometimes present this information without explaining all the research work that led to this point. Please understand, however, that these conclusions are based on the careful analysis of data using solid scientific principles and examined and re-examined by thousands of researchers over many years of work.
(Chris Hays is an associate professor of Anthropology/Sociology and Alan Paul Price is an associate professor of Geography/Geology, University of Wisconsin-Washington County.)