On the Kenai Peninsula, two lakes -- one above the Snow River and the other adjacent to Skilak Glacier -- fill up and drain every two or three years. Some call the periodic outburst floods by the Icelandic name: jokulhaup.
"I think it is a real interesting phenomenon," said Larry Rundquist, a hydrologist with the National Weather Service's Alaska River Forecast Center in Anchorage.
The lakes form because glaciers block side valleys, causing natural runoff to pool behind an ice wall. In some parts of Alaska, such as at Lake George by Knik, the lake eventually spills over the top and cuts a trench to drain, he said.
But in the Kenai glacial dam lakes, the outbursts are more subtle. They happen underneath the glacier, with the water coursing through miles of hidden tunnels.
One theory, Rundquist explained, is that the lake water undermines and partially floats the glacial ice. By the Skilak Glacier Dammed Lake, he has seen a unique feature of radial crevasses on the glacial surface showing where the growing lake is pushing beneath it. As the water thaws and lifts the glacier, it trickles into natural melt water channels under the ice. Water flow makes the tunnels expand and drain faster. Eventually, the entire lake drains away from below like water leaving a bathtub.
Scientists studying such lakes took a helicopter to the bottom of one near Valdez after it had drained dry. They found a tunnel, 20 feet in diameter, melted into the glacier there, Rundquist said.
Scientists plan to monitor the Snow Glacier Dammed Lake more closely as it nears its outburst, but the area is so remote and the environment so harsh that studying the process is difficult. The area is nearly inaccessible by land, so they rely on aerial views.
"Weather permitting, we will probably try to fly over it periodically and get some still photos," he said.
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