Gorges That Were Carved Out Fast?

Comments About: Science News v. 166, 7/24/04, p. 52

"Quick Bite: Some Gorges Carved Surprisingly Fast"


This article is about the report in the July 23rd issue of Science. Scientists studied the gorges where the Potomac and Susquehanna rivers cut through "bedrock that's millions of years old" and found that "the chasms are much younger."

Of course, I have my doubts about all attempts to date things by studying their current properties (In this case "concentrations of beryllium-10, an isotope that's typically produced when oxygen-bearing minerals, such as quartz, are exposed to cosmic rays at Earth's surface."

Still, it's somewhat heartening to learn just how big a surprise the uniformitarians ran into. Their results "indicate that" the Mather Gorge (of the Potomac) "eroded downward between 37,000 and 13,000 years ago at a rate of about 80 centimeters per millennium" and the Susquehanna's Holtwood Gorge was carved at a rate of "about 50 cm per millennium.

These erosion rates are tens to hundreds of times faster than scientists had suspected."Wow, ten to hundreds of times difference? That's quite a surprise! But it still sounds too slow to me. 80 cm is a bit less than a meter, not quite 3 feet even. Rocks may be pretty hard stuff, but a thousand years is a long time. I wouldn't be surprised if rivers could cut down through 3 feet of rock in just 100 years.

Consider, too, that ordinary "abrasion of waterborne sediment" is now considered to contribute only a small part of the change. "Much of the sculpting occurs when strong floods pluck loose chunks of rock from the gorges' cracked walls and channels."

While "the Susquehanna carried meltwater from the ice sheet that invaded the northern reaches of its watershed, the Potomac had no such influx. Therefore, the scientists speculate, the boost in erosion at both locations is probably a result of other factors, such as changes in regional climate."

That might explain why the rate was greater than what they expected from their uniformitarian assumptions, but it doesn't explain why the Susquehanna didn't have a much greater rate from all that post-Ice Age glacial melt water.

Perhaps the major factor was the effect of large amounts of Flood waters draining off the continent as the still relatively soft sediments were pushed up by ongoing tectonic forces.

Until Next Time,
David Bump