During the height of the last ice age, huge ice sheets covered much of North America. Picos group studied how the altering weight of the ice sheets throughout this duration would have tilted the topography of eastern Washington, altering how much water would stream into different channels during the floods.
Glacial Lake Missoula formed in western Montana when a lobe of the Cordilleran ice sheet dammed the Clark Fork valley in the Idaho panhandle and melt water built up behind the dam. Eventually, the water got so deep that the ice dam began to drift, resulting in a glacial outburst flood. After enough water had been launched, the ice dam transplanted and the lake refilled.
Study offers brand-new viewpoint on Washington states Channeled Scablands, carved by the Missoula megafloods at the end of the last ice age.
As ice sheets started melting at the end of the last ice age, a series of cataclysmic floods called the Missoula megafloods searched the landscape of eastern Washington, carving long, deep channels and towering cliffs through an area now referred to as the Channeled Scablands. They were among the largest recognized floods in Earths history, and geologists having a hard time to rebuild them have now identified an important element governing their flows.
In a research study released on February 14, 2022, in Proceedings of the National Academy of Sciences, scientists demonstrated how the altering weight of the ice sheets would have caused the whole landscape to tilt, altering the course of the megafloods.
” People have been looking at high water marks and attempting to reconstruct the size of these floods, but all of the estimates are based on looking at the contemporary topography,” said lead author Tamara Pico, assistant professor of Earth and planetary sciences at UC Santa Cruz. “This paper reveals that the ice age topography would have been various over broad scales due to the contortion of Earths crust by the weight of the ice sheets.”
Huge volumes of floodwater from the Missoula megafloods as soon as poured over Dry Falls, which extends 3.5 miles broad and drops 400 feet to a plunge swimming pool now fed by groundwater. Credit: Photo by Tamara Pico
During the height of the last glacial epoch, vast ice sheets covered much of North America. They began to melt after about 20,000 years back, and the Missoula megafloods took place in between 18,000 and 15,500 years back. Picos team studied how the changing weight of the ice sheets throughout this period would have tilted the topography of eastern Washington, changing just how much water would flow into different channels during the floods.
Glacial Lake Missoula formed in western Montana when a lobe of the Cordilleran ice sheet dammed the Clark Fork valley in the Idaho panhandle and melt water constructed up behind the dam. Eventually, the water got so deep that the ice dam began to drift, resulting in a glacial outburst flood.
Downstream from glacial Lake Missoula, the Columbia River was dammed by another ice lobe, forming glacial Lake Columbia. When Lake Missoulas outburst floods put into Lake Columbia, the water overflowed to the south onto the eastern Washington plateau, eroding the landscape and developing the Channeled Scablands.
Towering cliffs carved by the Missoula megafloods are found throughout the Channeled Scablands in eastern Washington. Credit: Photo by Tamara Pico
Throughout this period, the contortion of the Earths crust in action to the growing and shrinking of ice sheets would have altered the elevation of the topography by hundreds of meters, Pico said. Her group integrated these modifications into flood models to examine how the tilting of the landscape would have altered the routing of the megafloods and their erosional power in different channels.
” We utilized flood models to predict the velocity of the water and the erosional power in each channel, and compared that to what would be required to erode basalt, the kind of rock on that landscape,” Pico stated.
They focused on 2 significant channel systems, the Cheney-Palouse and Telford-Crab Creek tracts. Their results revealed that earlier floods would have eroded both systems, however that in later floods the flow would have been concentrated in the Telford-Crab Creek system.
” As the landscape tilted, it affected both where the water overflowed out of Lake Columbia and how water streamed in the channels, however the most crucial impact was on the spillover into those 2 tracts,” Pico said. “Whats intriguing is that the topography isnt static, so we cant simply take a look at the topography these days to rebuild the past.”
The findings supply a brand-new perspective on this interesting landscape, she said. Steep canyons numerous feet deep, dry falls, and huge pits and ripple marks are among the lots of amazing functions engraved into the landscape by the massive floods.
” When you exist in person, its insane to consider the scale of the floods needed to sculpt those canyons, which are now dry,” Pico stated. “There are also huge dry waterfalls– its a really striking landscape.”
She also kept in mind that the narrative histories of Native American people in this region include recommendations to huge floods. “Scientists were not the very first people to look at this,” Pico said. “People might even have been there to witness these floods.”
Recommendation: “Glacial isostatic adjustment directed incision of the Channeled Scabland by ice-age megafloods” by Tamara Pico, Scott R. David, Isaac J. Larsen, Alan C. Mix, Karin Lehnigk and Michael P. Lamb, 14 February 2022, Proceedings of the National Academy of Sciences.DOI: 10.1073/ pnas.2109502119.
In addition to Pico, the coauthors include Scott David at Utah State University; Isaac Larsen and Karin Lehnigk at the University of Massachusetts, Amherst; Alan Mix at Oregon State University; and Michael Lamb at the California Institute of Technology. This work was supported by the National Science Foundation.