http://www.digitaljournal.com/news/environment/ancient-river-system-found-under-greenland-s-jakobsvahn-glacier/article/469398

Jakobsvahn glacier has been hiding a primeval river system

Posted Jul 6, 2016 by Karen Graham
A huge network of rivers was found to be hiding beneath Greenland's Jakobsvahn Isbrae glacier recently. The discovery may help to explain the location, size and velocity of the country's fastest flowing outlet glacier.
An aerial view from NASA of the retreating Jakobsvahn glacier.
An aerial view from NASA of the retreating Jakobsvahn glacier.
NASA
In a press release issued by the University of Bristol in the UK, a team of researchers made the discovery by analyzing data collected over decades using ice-penetrating radar.
Michael Cooper, along with colleagues from Bristol's School of Geographical Sciences, Cabot Institute, and Imperial College London studied Greenland's bedrock using data collected through NASA's Operation Ice Bridge, as well as data collected by researchers in the UK and Germany over several decades.
What the team found was an ancient network of channels, formed at least 2.3 million years ago, they believe, that extends through a basin covering over 173,000 square miles (448,068 square kilometers). The basin accounts for about 20 percent of Greenland's total land mass.
Mr. Cooper said: "The drainage basin we discovered shows signs of being carved by ancient rivers, prior to the extensive glaciation of Greenland, rather than being carved by the movement of the ice itself. It has been remarkably well preserved – and has not been eroded away by successive glaciations. The channel network has never been seen before by humans – it was last uncovered around 3.8 million years ago."
Actually, the channels could be more accurately called canyons, says Cooper, with depths of around 4,593 feet (1,400 meters) in some areas, and nearly 7.5 miles (12 kilometers) wide, and they are all hidden under the ice. From above, the river basin looks like a bunch of nerve fibers radiating out from a nerve cell, or the branch of a heavy tree with all its twigs intact.
More than just being an interesting discovery, it is also likely the river channels played a role in forming the location and flow of the ice when the glacier was forming in the deep interior, and after several glacier cycles, set in motion the movement we see today.
Channels cut by rivers, not the glacier
Cooper says, "Without the channels present underneath, the glacier may not exist in its current location or orientation." Cooper also points out that the glacier didn't form the river channels, but instead the channels were formed by rivers cutting the rock away over time.
"The shape of the valleys was V-shaped, rather than U-shaped; the flow network had a dendritic or tree-like structure; and the long profiles showed a smooth, concave-up shape," Cooper told Live Science. He says these are very good clues to how the channels were formed over time.
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A harbinger of changes to come?
The Jakobshavn Isbrae is one of the world's fastest moving glaciers, racing toward the sea at 11 miles (17 kilometers) per year. In the process, it dumps huge amounts of ice into the sea and is Greenland's main contribution to sea level rise, raising levels only 1 millimeter (0.04 inches) between 2000 and 2010.
Climate scientists are very interested in following Jakobshavn Isbrae's movement because it may be a harbinger of climate change in the future. It is melting very fast, and according to scientists, has lost 9,000 gigatons of ice since 1900. A gigaton is equal to one billion tons.