Executive summary by darmansjah
Imagine if you could pick up the Greenland Ice Sheet and see what lies beneath. Surely 1.7 million square kilometers of slowly thawing ice must rest on a massive pool of melted water, right?
Unlike the ice sheet covering Antarctica that sits atop numerous lakes, the Greenland Ice Sheet blankets a giant subglacial canyon nearly twice as long as the Grand Canyon located in Arizona.
Before the land was completely glaciated at least four million years ago, melt from partial ice cover likely flowed through the bedrock canyon.
While flying over the ice sheet, scientists over the past three decades have measured the depths of the canyon using a radar system that operates at frequencies where ice is transparent to radio waves—from around 50 megahertz to 500 megahertz.
The Antarctic Ice Sheet, which is ten times as large as Greenland's, sits on a complex topography that includes bedrock and mountain ranges.
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