Author: Douglas Fox / Source: Science News for Students
Martin Sharp vividly recalls his first slush flow.
He spent that June, in 2007, camping on the Devon Ice Cap. This gently curving dome of ice is 140 kilometers (87 miles) across and rises to a height of 1,900 meters (6,200 feet). It sits atop an island in the Canadian high Arctic.Sharp was riding a snowmobile when he heard a roar. It sounded like the rumble of a subway train. The entire snow slope in front of him was moving: A slow-motion river of waterlogged slush was slurping down the mountainside. A spate of hot, sunny days had melted so much snow that the slope could no longer support itself.
Slush flows didn’t used to happen here. The summers weren’t warm enough, notes this glaciologist at the University of Alberta in Canada. But by the time he saw this one in 2007, he had been hearing about them more and more. In one memorable case, a lake of melt water sitting on top an ice cap suddenly drained. This sent a flood of water, slush and ice rampaging 10 kilometers (6 miles) down a valley. It nearly wiped out a camp where scientists had been staying.
For Sharp, it prompted a decision. He and his colleagues had visited Devon Ice Cap nearly every summer for the last few years. Going forward, they would now come in April or May, when the days were still cool enough to avoid such dangers. “The world has changed,” he says.
Devon is one of thousands of glacial ice masses that dot the world. Some are narrow streams of ice, called glaciers. These ooze down mountain canyons. Others, like Devon, are broad, blobby ice caps that cover entire islands, spreading outward at the edges.
These icy areas are tiny compared to the world’s three great ice sheets, which cover Greenland, and East and West Antarctica. Altogether, these smaller icy areas hold only a hundredth of the world’s ice. But because they occupy parts of the Earth that are warmer than the ice sheets, they are melting much more quickly. For now, they also are a major source of sea-level rise. Collectively, they are losing some 230 cubic kilometers (55 cubic miles) of ice per year. Dump all of that ice into one big pile, and it could form its own mountain range.
Slithering winds
It started when a belt of strong winds shifted that year. Called the polar jet stream, it bent northward like a slithering snake. Its winds carried warm air from the Atlantic Ocean up along the west side of Greenland, into the islands of Arctic Canada.
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