13 May 2020

Violent rivers of meltwater may have carved Greenland's 'Grand Canyon'

Geology

Rapid climate change and enormous amounts of ice and meltwater may have excavated a nearly 800-kilometer long canyon beneath Greenland's ice cap, the origins of which have long been the subject of discussion.

Meltwater lake at the rim of the ice cap on the northern edge of the Russell Glacier at Kangerlussuaq, West Greenland. Photo: Christine Schøtt Hvidberg.
Meltwater lake at the rim of the ice cap on the northern edge of the Russell Glacier at Kangerlussuaq, West Greenland. Photo: Christine Schøtt Hvidberg.

It is not inconceivable that a similar event could occur in the future, although in the short term, it will be on a much smaller scale.

Associate Professor Christine Schøtt Hvidberg, Niels Bohr Institute

Buried one and a half kilometers beneath Greenland’s ice cap, a network of canyons is so deep and long that it has been coined Greenland's 'Grand Canyon'. The canyons are 750 kilometers long and up to 800 meters deep. But how and when these mega-canyons were created has been the subject of debate since the 1990s, when strange depressions on the surface of the Greenland Ice Sheet began to stir wonder.

Now, researchers from the University of Copenhagen’s Niels Bohr Institute and the University of Massachusetts have proposed a new hypothesis for how these mega-canyons were carved: Repeated violent bursts of meltwater dug the canyons, emptying vast lakes into the ocean. The discovery has just been published in the scientific journal Geology.

"Our hypothesis is based upon the fact that the Greenland Ice Sheet has been formed by a series of climate fluctuations, during which its ice alternately freezes, advances, melts and finally retreats. Whenever the ice melts, huge lakes of dammed-up meltwater form, causing occasionally huge bursts of water that, over time, carve these mega-canyons," explains Associate Professor Christine Schøtt Hvidberg of the Niels Bohr Institute. Schøtt has been researching the physics behind Greenland’s ice cap for a number of years.

Even though it has long been known that enormous meltwater rivers, due to ending ice ages and sudden climatic changes, formed networks of canyons, this knowledge had yet to be coupled with the remarkable landscape beneath Greenland's ice.

"A meltwater hypothesis has never been presented before, but it provides a coherent explanation for many of the geological features apparent beneath Greenland," states Associate Professor Christine Schøtt Hvidberg.

A sudden climatic change released the meltwater

The researchers' models and simulations are unable to determine with certainty how warm it was and when precisely the ice melted. But they believe it to have been a repetitive occurrence roughly 1-2 million years ago, just as the ice cap was beginning to form. Most researchers studying the Greenland ice cap begin with a Greenland covered by ice, as we know it today.

But to better understand how ice advances and retreats, this study’s researchers sought to begin with what Greenland looked like prior to the establishment and spread of ice. By combining climate models with ice sheet data, the researchers were able to simulate the evolution of ice over the last few million years.

They discovered that after long and repeated periods of stable temperatures, periods of exceptionally warm climate occurred, which may have caused the ice cap to rapidly melt and form huge bodies of water.

"If these large meltwater rivers did occur, they may have affected ocean currents, which could have precipitated sudden global climate change. To this day, the mega-canyons beneath northern Greenland affect the flow of ice and water beneath its ice sheet, which has an impact on the development of ice in the future, and on how much meltwater the ice can release," explains Christine Schøtt Hvidberg.

The researcher believes that this is a scenario that could be repeated, as we too are in the midst of a period of rising temperatures and a melting ice cap in retreat.

"It is not inconceivable that a similar event could occur in the future, although in the short term, it will be on a much smaller scale. After all, climate change is reshaping the Greenlandic ice cap and could lead to the creation of meltwater lakes and sudden new discharges of massive amounts of meltwater," says Christine Schøtt Hvidberg. The researcher adds that those glacial lakes thought to pose a risk of flooding are monitored from around the world.


Facts:

  • Greenland's Grand Canyon is more than 750 km long and up to 800 meters deep. It is comparable in size to the Grand Canyon in North America.
  • The canyon flows from central Greenland northwards, where it ends at the large Petermann Outlet Glacier in northern Greenland.
  • The research was conducted in a collaboration between researchers from the Niels Bohr Institute at the University of Copenhagen and researchers from the University of Massachusetts.