Ancient ‘megafloods’ tilted the very direction of Earth’s crust, scientists find

Image credit: NASA

Ice age flooding, recreated in models.
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Earth’s last major ice age locked up gargantuan amounts of water in vast glaciers, says Science Alert.

Once they melted, it was a spectacle to behold as tremendous floods gouged channels into the face of the planet.

The remnants of one of the largest of these ancient deluges are still visible in eastern Washington, in an area now known as the Channeled Scablands.

For a long time, geologists have been struggling to understand the dynamic properties of these floods, until a recent key insight was made.

These ancient glaciers were so large and heavy, they actually tilted Earth’s crust beneath them – when weight was released due to melting, the land would have moved too, changing the course of the megaflood.

Using modeling of ancient megafloods, researchers decided to test whether glacial isostatic adjustment (GIA) – deflections in the crust as heavy chunks of ice form and melt – would affect the routing flow and erosion in two prominent Scabland tracks.

“We used relatively simple, yet plausible, numerical experiments to test whether GIA could have had a substantial impact on flood routing and erosion for two major scabland tracts, Cheney-Palouse and Telford-Crab Creek,” write the authors of the study.

“To this end, we modeled GIA to reconstruct the topography of the Channeled Scabland at different times during the period of Ice Age flooding.”

Up until now, reconstructions of ancient megaflood routing had investigated how other variables would affect them – things like erosion and the movement of sediment, the three-dimensional mechanics of the environment, or how ice dams break, for example.

But they would also base these reconstructions on present-day topography, approximating how past landscapes may have looked.

“People have been looking at high water marks and trying to reconstruct the size of these floods, but all of the estimates are based on looking at the present-day topography,” said lead author Tamara Pico, assistant professor of Earth and planetary sciences at UC Santa Cruz.

Geologists realized that the effects melting glaciers were having on Earth’s crust were also likely playing a role in the routing and behavior of these megafloods.

“GIA caused crustal deformation in the Channeled Scabland with rates up to 10 millimeters per year, orders of magnitude above regional tectonic uplift rates and, therefore, may have influenced flood routing,” note the authors.

“The course of ancient, glacial outburst floods was likely influenced by glacial isostatic adjustment (GIA), and reconstructing these events informs our understanding of how floods shape landscapes on Earth and Mars,” they added.
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The researchers believe the deformation of Earth’s crust due to the expanding and contacting of the ice sheets would have altered the elevation of the landscape by hundreds of meters over this period.

Moving forward, the researchers want to simulate past megaflood events which incorporate the multiple factors that determine their routing.

However, understanding the important role that ice age crustal deformation plays during flood routing and erosion in these ancient megafloods is a step in the right direction.

Full article here.