(ORDO NEWS) — The last major ice age on Earth locked up vast amounts of water in huge glaciers. When they melted, it was a sight worthy of contemplation: huge floods cut channels on the face of the planet.
The remains of one of the largest ancient floods are still visible in eastern Washington state, in an area known as the Canal Scablands. For a long time, geologists have been trying to understand the dynamic properties of these floods, until they recently made a key discovery.
These ancient glaciers were so large and heavy that they actually tilted the earth’s crust under them – when the weight was released due to melting, the earth also moved, changing the course of the mega-flood.
Using simulations of ancient megafloods, the researchers set out to test whether glacial isostatic adjustment (GIA)—the troughs in the Earth’s crust as heavy ice chunks formed and melted—would affect the route flow and erosion in two prominent scablands.
“We used relatively simple but plausible numerical experiments to test whether the GIA could have had a significant impact on flood routes and erosion for two major scabland tracts, Cheney Palaus and Telford Crab Creek,” the study authors write.
“To this end, we modeled the GIA to reconstruct the topography of the canal scabland at different times during the Ice Age floods.”
Until now, reconstructing the routes of ancient megafloods has studied how they are affected by other variables, such as erosion and sediment movement, three-dimensional environmental mechanics, or how ice dams collapse.
But they will also base these reconstructions on modern topography, roughly representing what landscapes may have looked like in the past.
“People look at high water marks and try to reconstruct the extent of these floods, but all estimates are based on modern topography,” said study lead author Tamara Pico, assistant professor of earth and planetary science at the University of California at Santa Cruz.
Geologists have realized that the impact of melting glaciers on the Earth’s crust likely also plays a role in the routing and behavior of these megafloods.
“GIA has caused crustal deformation in the Scubland Channel at a rate of up to 10 millimeters per year, which is orders of magnitude higher than the rate of regional tectonic uplift and therefore may have affected flood routes,” the authors note.
“The course of ancient glacial floods was likely influenced by glacial isostatic adjustment (GIA), and reconstructing these events helps us understand how floods shape landscapes on Earth and Mars,” they add.
Ice sheets covered a huge area of North America during the last ice age, but they began to melt about 20,000 years ago. The Missoula megaflood is believed to have occurred between 18,000 and 15,500 years ago.
Glacial Lake Missoula was formed when a large chunk of the Cordilleran Ice Sheet dammed up the Clark Fork Valley, and glacial melt waters accumulated behind it. Eventually, a combination of factors caused the dam to fail, resulting in the first glacial megaflood.
However, once enough water had flowed through it, the ice dam was restored and water began to accumulate again. This process probably took place several times over the next few thousand years.
The researchers believe that the deformation of the earth’s crust as a result of the expansion and contact of the ice sheets could change the height of the landscape by hundreds of meters over this period.
Going forward, the researchers want to model past megafloods with multiple factors that determine their direction. However, understanding the important role played by Ice Age crustal deformation in flooding and erosion in these ancient mega floods is a step in the right direction.
The study also points to how dynamic this landscape once was. Dotted with steep canyons hundreds of feet deep, dry waterfalls and huge ravines, the geological artifacts tell of a land that was once subject to titanic forces.
“When you’re there in person, it’s crazy to think about the amount of flooding needed to create these canyons that are now dry,” says Pico.
Pico also mentions that in the oral histories of the Native American tribes living in the region, there are references to large-scale floods.
“Scientists weren’t the first to notice this,” she says. “Perhaps people even witnessed these floods.”
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