In a press release, Jonathan Bamber of Bristol's School of Geographical Sciences, lead author of the study, said: "With Google Street View available for many cities around the world and digital maps for everything from population density to happiness one might assume that the landscape of the Earth has been fully explored and mapped. Our research shows there's still a lot left to discover."
The scientists know the canyon formed before Greenland was covered in ice 3.5 million years ago. Without additional information about the type of rocks around the canyon, they can't be more specific about its age. Thankfully, they know where to look.
"One of the only ways to get information about what was there before is to look at what is deposited offshore," Stuart Thomson says. Thompson, a geologist from the University of Arizona, has studied glaciers and glacial erosion in Antarctica but was not involved with this study.
Over centuries, a river carves a giant canyon through dramatic erosion, carrying away a huge amount of soil and rock. All that material has to go somewhere. It usually ends up deposited at the end of the line, where the canyon's river meets the sea.
In the example of the Grand Canyon, the sediments carried by the Colorado River eventually end up in the Gulf of California. In the case of the newly discovered Greenland canyon, any sediments would likely end up in the Arctic Ocean or the Nares Strait. One potential area for future research would be to find the exact location of these sediments and figure out what types of rocks the canyon is carved into.
Although the researchers don't know when the canyon was formed or what rocked it was carved from, they were able to determine how it was made by looking at the shape. The profile of the canyon has a distinct V shape, which indicates to geologists that it was formed by a river and not by ice, which tends to erode U-shaped valleys. The long and winding nature of the canyon was a big clue too. "Rivers have meanders or bends in them, whereas ice tends to move in straight lines," Thomson says.
Water still flows through the canyon today. The weight of the ice sheet that sits on top of it creates enormous pressure at the bottom, so much so that the ice at the base melts. This meltwater takes the same path that the ancient river carved millions of years before, flowing from the south to the north as it drains the water from the base of the ice.
This newly discovered drainage system also provides an answer as to why this area of Greenland has so many fewer subglacial lakes than similar ice-covered areas, like Antarctica. Because of the topography beneath the ice, the meltwater never has the opportunity to pool up under it.
This water, which flows into the sea under the massive Petermann Glacier, may be responsible for one of the glacier's more bizarre features. Scientists had known about strange channels carved upward into the portion of the Petermann Glacier floating on the Arctic Ocean. These channels—0.6 to 1.2 miles long and 650 to 1300 feet deep—were long assumed to be the result of ocean currents, but the canyon's discovery means they might have a different origin: carved not by seawater but by streams of melted glacier water flowing out from the canyon.