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How Catastrophic Floods May Have Carved Greenland’s ‘Grand Canyon’

For years, geologists have debated how and when a network of canyons under the Greenland ice sheet formed, especially one that is so deep and long it’s been called Greenland’s Grand Canyon. Its shape suggests it was carved by running water followed by glaciation, but until now, the genesis of this canyon, and similar features in northern Greenland, have remained unknown.

In a new study in the journal Geology, scientists at the University of Massachusetts Amherst and the University of Copenhagen have proposed a new mechanism for how the mega-canyon formed: from a series of catastrophic outburst floods that suddenly and repeatedly drained lakes of melting ice-sheet water over time. Based on ice-sheet model simulations of the early ice sheet’s history, they show that climate and bedrock topography have exerted strong controls on the ice sheet since its beginning.

First author Benjamin Keisling, now a postdoctoral fellow at Columbia University’s Lamont-Doherty Earth Observatory, did the work as a graduate student with senior author and advisor Rob DeConto at UMass.

Lead author Benjamin Keisling at the East Greenland Ice Core Project. Dome in the background is where researchers gather for meals. (Courtesy B. Keisling)

Keisling says that before now, repeated outburst floods appeared to be the mechanism by which the Columbia River and other North America canyon networks formed. But they had not been considered as having played a role in forming the tortured landscape under the Greenland ice sheet.

“If the floods we propose occurred, they could have influenced ocean circulation, causing abrupt climate changes with regional and perhaps global significance,” said Keisling. “The mega-canyon beneath northern Greenland also influences how ice and water flow in the subglacial environment today, which affects present-day ice-sheet stability.”

Keisling says that in most Greenland studies, researchers use the modern ice sheet as a starting point for understanding how it has changed over time. But Keisling and his co-authors took a different approach, investigating what Greenland looked like before widespread glaciation. “We wanted to better understand the dynamics of “glacial inception — how, where and why the ice sheet first grew on an ice-free island,” he said.

The team also wanted to gain a better understanding of how the ice sheet grew back after melting. “We know from prior work this has happened multiple times in the past and could again in the future, given enough global warming,” said Keisling.

They used coupled ice-sheet and climate models to simulate the ice sheet’s evolution over many glacial-interglacial cycles in the last few million years. They found that following long periods with stable temperatures, an exceptionally warm period could cause the ice sheet to rapidly retreat. This led to large, ice-dammed lakes forming in areas where the bedrock was still depressed from the old ice sheet’s weight.

Their simulations show the ice dams eventually giving way as large outburst floods. “Over time,” said Keisling, “it appears that the filling and draining of these lakes as the ice repeatedly retreated and advanced carved Greenland’s mega-canyons.” Similar floods have been documented at the edge of other retreating ice sheets, he said.

Comparing Greenland with modern outburst floods, the researchers estimate that as many as hundreds of floods carved its giant canyon. Results suggest testable hypotheses for future research that could settle the long-standing debate about whether the ice sheet’s stability has changed over time, they say.

“Knowing the history of Greenland’s bedrock provides context for understanding the ice sheet’s long-term behavior,” Keisling said. “This helps paint a picture of what happened during past warm periods when the melting ice sheet caused global sea levels to rise, a phenomenon we are also seeing today.”

The work was supported by NASA, the U.S. National Science Foundation, a GROW Fellowship, and the Danish National Research Foundation.

Adapted from a press release by the University of Massachusetts Amherst.

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Michael Walsh
2 years ago

The method by which this, and other canyons, formed on Greenland is an interesting geological study, and one can see how this study gets “mixed up” with climate change science. However there are other factors at play which must not be neglected, and which must be kept in context.

One of these factors is plate tectonics.

As I understand the current state of things the Greenland ice cores represent about 110,00 years of recent history.

It also appears that Greenland is part of the North American Plate which is moving at a speed of between 15-25 mm per year. Thus we can calculate fairly easily that Greenland has moved about 1.5-2.5 km during the time it took for the ice sheet, from which the core(s) were extracted, to form. In rough terms this means that Greenland is moving at a speed of about 1.5-2.5 km per 100,00 years, or 15-25 km per million years.

Now, if we look at the Grand Canyon in the USA, its age (time to be formed) has been estimated by some to be 5-6 million years old and by others to in the range of 17 million years old. Let us suppose that it took around 17 million years.

Now if we go back Greenland we can see that it can have moved 250-400 km in the the time it took for the Grand Canyon to form. Or in the (say) last 50 million years it could have moved 750 – 1,200 km from its past position.

Now, we can appreciate that a change in position of 750-1,200 km could account for a very significant change in climate, therefore it seems not just possible, but very likely, that the climate of Greenland was vastly different 50 million years ago (which is only about 1/100th of the age of the earth) compared to now but the change in climate would not have been caused by global climate change, but because Greenland has moved to a latitude where the climate is colder.

Therefore, in the mid-past (say 50 million years ago) Greenland could easily have had major rivers that were quite capable of cutting very large canyons comparable to the Grand Canyon, but the presence of these rivers might have nothing to do with global climate change.

Times and dates, climate change and the dynamics of plate tectonics all need to be kept in their proper perspective.

I am certain that the geoscientists who are studying these phenomena take these things into account but I add this perspective for the reader who might not think about the effect of plate movement when studying ancient climates.

Thank you

J R Michael Walsh

Last edited 2 years ago by Michael Walsh