Re: The Grand Canyon: "An article in the September 30, 2000 issue of Science News has shown that carving this beloved hole in the ground may not have been such a long-term project after all (Perkins, 2000).
Prior to the 1930s, geologists proposed that the Grand Canyon was about 40 million years old (p. 218). However, evidence now has come to light that indicates a much younger canyon.
Research presented at a June 1999 conference devoted to the origin of the gorge suggests that substantial portions of the eastern Grand Canyon have been eroded only within the past million years. And so, as quickly as ink dries on paper, geologists cut 39 million years off the age of the Grand Canyon, (a reduction of 97.5%)and dropped its age to 1/40 of their previous estimates." ....Apologetics Press
Slowly but surely, geologists are coming to the conclusion that the Grand Canyon and other gorges were formed in an extremely short period of time which supports the "flood model" rather than the millions/billions of years gradualism model.
Susquehanna River, by Thomas Doughty. Click and drag photo to resize.
Arlington, Va. -- In the first study to directly measure when and how quickly rivers outside of growing mountain ranges cut through rock, geologists at the University of Vermont have determined that it was about 35,000 years ago that the Susquehanna and Potomac rivers, respectively, began carving out the Great Falls of the Potomac and Holtwood Gorge.
Great Falls, located about 15 miles outside of Washington, D.C., hosts hundreds of thousands of visitors each year; Holtwood Gorge lies along the Susquehanna River, near Harrisburg, Penn.
As reported in the July 23 issue of the journal Science, the geologists analyzed rock samples collected from the gorges for 10-beryllium, a very rare isotope that is produced when cosmic rays collide with rocks and sediments at the Earth's surface.
These analyses helped them gauge when the rivers abandoned their ancient beds and, consequently, exposed bare rock surfaces, known as terraces, where people climb and hike today.
Knowing the age of each river terrace and its height above its current river bed, they were able to calculate how quickly the rivers cut through bedrock.
Their conclusions: Incision of the 10- to 20-meter-deep gorges happened at a rate far more rapid than previously thought and was prompted more by regional climate changes tied to the last ice age than by water pouring from melting glacial ice.
"The period of incision we measured correlates with a period of cold and stormy climate during the last glacial period that is also recorded in ice cores drilled into the Greenland ice sheet," said Luke Reusser, a geologist at the University of Vermont and lead author of "Rapid Late Pleistocene Incision of Atlantic Passive-Margin River Gorges."
Grand Canyon Gorge. Source: FlowerFamily Click and drag photo to resize.
"Because bedrock is hard and resistant to erosion, most incision within rivers running over rock occurs during extremely large flood events," Reusser explained.
"Changing climate, capable of increasing the number and severity of floods, appears to have sped up the rate of incision along both rivers about 35,000 years ago."
The five-year project is unique because it used many samples closely spaced to understand the spatial patterning of how and when the rivers cut into rock, according to Paul Bierman, also a geologist at the University of Vermont and co-author of the Science paper.
"Without such detail, we never would have been able to detect the link with climate, nor would we know that Great Falls, probably the most visited stretch of the Potomac, has existed there for nearly 30,000 years," Bierman said.
His group continues to take samples from the area and is completing a second paper on the Susquehanna sites.
"Scientifically, these are the first data that tell us how quickly rivers of the eastern seaboard cut into rock," said Enriqueta Barrera, director of the Geology and Paleontology Program, Division of Earth Sciences at the National Science Foundation (NSF). NSF and the U.S. Geological Survey funded the research.
"The Potomac and Susquehanna have shown they can cut nearly a meter of solid rock every thousand years, she said. "Pretty impressive for old rivers."
"There are gorges all over the world that are undated," Bierman said. "We want to work next on other East Coast rivers and streams to see how similar their histories are to the two major rivers sampled so far, the Susquehanna and Potomac."