I think the Pleistocene flash flooding of Oregon and Washington State is a cool read, those ice dams at Lake Missoula must have been huge.
Posted on 07/20/2002 4:00:28 PM PDT by gcruse
Catastrophic floods built Grand Canyon
UPI Environment News
Science & Technology
Desk
Published 7/20/2002 6:00 AM
GRAND CANYON NATIONAL PARK, Ariz., July 20 (UPI) -- Dams of volcanic rock laid across the Grand Canyon have burst repeatedly and catastrophically over the past million years -- most recently about 165,000 years ago -- carrying enormous onrushing floods and carving out much of the great landmark in the blink of a geologic eye, new research by U.S. Geological Survey and University of Utah geologists suggests.
The findings tend to support other new data indicating the canyon's Inner Gorge may be no more than 700,000 years old, much younger than earlier estimates of 3 million to 5 million years, said Robert Webb, a research geologist with USGS.
"The newer interpretation is that there was a basalt dike that crossed the Grand Canyon that's been dated at 770,000 year ago," Webb told United Press International. "So the Inner Gorge wasn't there then. It's been downcut since then."
Downcutting refers to the phenomenon that occurs when enormous volumes of water are unleashed by sudden removal or failure of natural barriers such as lava dams. In the case of the Grand Canyon, downcutting means the Colorado River did not form the canyon through gradual erosion over millions of years. Instead, intermittent dam failures unleashed massive flash floods, in at least one case carrying many times more water than the largest Mississippi River overflow ever recorded.
"Large sustained floods can cause rapid downcutting in bedrock," Webb said. A similar event on a smaller scale occurred in 1976 when Idaho's Teton Dam failed. The water flow left a distinctive profile in soils and on canyon walls, he said. The water level dropped extremely rapidly in a phenomenon called a decay curve.
"We have that curve preserved from a lava dam that failed in the Grand Canyon 165,000 years ago," Webb said.
The lava was deposited by a chain of volcanoes that runs across the Grand Canyon. Periodic eruptions created the dams, which blocked the river's flow. Over time, enormous quantities of water backed up, eventually breaching the dams and continuing the downcutting process.
Webb, who collaborated with University of Utah researcher Cassandra Fenton, said, "There's a big volcanic field that straddles the Grand Canyon" and was active relatively recently. A minor eruption probably occurred there around 1,300 years ago, he said.
The most recent basalt dam probably occurred between 100,000 and 120,000 years ago, Webb said. However, "The one we've worked on most was there 165,000 years ago." When the natural lava dam failed, it unleashed 15 million cubic feet of water per second -- 37 times larger than the biggest Mississippi River flood -- helping to carve the lower canyon.
"These were some high dams," Webb said. "We estimate some were more than 1,500 feet tall."
The lava dams also were inherently unstable. The researchers explained when the molten basalt lava met cold river water, it cooled almost instantly, forming fragile walls of glass. "When basalt hits water, it shatters into glass, and there is just glass all over the place in these deposits," Webb said.
Another piece of evidence is the short life spans of the lakes building up behind the dams. Webb said the lakes filled quickly under pressure from large snowmelts in the Pleistocene era, which lasted from about 2 million years ago to the end of the last ice age -- around 9,000 B.C. The lakes did not have enough time to form deltas, he said.
USGS geologist George Billingsley, one of the leading experts on the age of the Grand Canyon, said although Webb and Fenton's work adds more data, he still regards the age issue as unresolved.
"We don't have enough hard-core evidence to prove it one way or the other," Billingsley told UPI. "All we're saying is that there has been a lot of Grand Canyon cutting in the last million years."
Other geologists share the skepticism, he said. "There are still a lot of holes to fill in. We need more data. That's why I'm hesitating to say 2,000 feet (of canyon depth) was cut in a million years." But some work, like the Webb-Fenton work, is supporting the hypothesis, he said.
One theory the catastrophic flood work does not support is the biblical flood story in Genesis. Some creationists have taken evidence of a "young Grand Canyon" as grounds for biblical literalism. One company, Another Viewpoint, offers trips through the canyon explaining its features as the result of Noah's flood.
"It isn't directly relevant to something like the Noachian flood because in this case we know what the source of the flood is," Webb said. "It is not like a rainfall flood that happened over an entire watershed. This is a river being blocked."
He added, "But it is a nice parallel to make. We do have in the geologic record where sometimes we can tell if they are rainfall related ... It's important to stress that a lot of the biggest floods worldwide have not been the result of unusual climatic events. They have been the result of the failure of a natural dam."
(Reported by Dan Whipple, UPI Science News, in Broomfield, Colo.)
Copyright © 2002 United Press International
My suggestion is that we should find which ancient deep-pockets republican corporation is responsible for all that sediment and force them to remediate: FILL IT IN! </sarcasm>
So I guess there's nothing unusual about Lake Powell. Somebody should tell the Sierra Club.
I think the Pleistocene flash flooding of Oregon and Washington State is a cool read, those ice dams at Lake Missoula must have been huge.
The feds are just pissed because people have fun there.
According to geologists, Lake Bonneville was formed from an ice dam during the last major Ice Age on this planet. As the glaciers receded, the dam probably melted and gave way about 15,500 years ago, resulting in a huge torrent of water that craved out the Snake River Canyon and much of the canyons of the Columbia River basin.
It's been speculated that many of the human legends of a Great Flood may be based on humans witnessing the collapse of ice dams at the end of the last great Ice Age causing massive land flooding; the stories got passed down through oral tradition. Oceanographer Robert Ballard (of Titanic rediscovery fame) said in National Geographic magazine that the Black Sea around 9,000 BC rose quite rapidly because of the combination of water coming from the north from glacial melting and the sudden rush of water from the south through the Bosphorus Straits.
The ice dam formed and burst some 40 times.
I don't buy this Grand Canyon formation theory though. There should be some heavy evidence of a flood of such magnitude many miles below the dam location such as plunge pools and ripples.
Also assuming that the elevation of the river bed above and below the dam would be about the same you would think that there would be a waterfall where the escaping water first gouged the river bed below the breech.
They don't really know squat, except they are SURE it wasn't Noah's flood. Another example of our tax dollars at waste.
Like you, I am skeptical of this theory. The Mississippi River flood of the late sixties covered much of Miss., La. and some other states. I remember seeing water as far as the eye could see from 35,00 ft. A lake with 37 times that much water would have covered quite and area, too much IMO to be contained by a dam at one end.
Talking to myself I say it was lake Missoula that formed some 40 times.
Lake Bonneville had nothing to do with an ice dam. Appx 17,000 years ago the lake reached the level of Red Rock Pass (5,220') in S. Idaho and wore it down about 375 feet in 1 year.
The leftover is the Great Salt Lake and given enough rain Lake Bonneville could form again.
Why not? It doesn't matter how much water is in there, just how deep it is and how wide the chokepoint is.
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