One of the most worrisome effects of glacial melting at Mount Rainier is the increased likelihood of outburst floods — sudden releases of water trapped inside or beneath the glaciers.
Large lakes can build up inside glaciers as they melt, and when the water bursts free, the downstream effects can be disastrous.
Big outburst floods often morph into debris flows — liquefied masses of water, rock and mud that travel rapidly downhill, destroying or burying everything in their paths.
Geologists sometimes call outburst floods jökulhlaups, the term for the phenomenon in Iceland, where some of the world’s most spectacular outburst floods have occurred.
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An outburst on Iceland’s Grimsvotn volcano in 1922 released about 1.7 cubic miles of water — more than the total volume of ice and snow on Mount Rainier — in a gusher 10 times bigger than the average flow of the Columbia River.
Outburst floods are not unusual at Mount Rainier. They’ve been recorded at four glaciers on the mountain: the Nisqually, Kautz, South Tahoma and the Winthrop.
They often initiate debris flows, and in rare cases where they’ve been witnessed, the sound has been compared to that of a freight train.
The outbursts often are accompanied by strong local wind, thick dust clouds and violent ground shaking, said Carolyn Driedger, a U.S. Geological Survey hydrologist who’s studied Rainier’s glaciers extensively.
The Nisqually, South Tahoma and Kautz glaciers are the most worrisome, because their likely paths are aimed directly at places in the park that are heavily used by visitors.
Floods from the Nisqually have wiped out, damaged or destroyed bridges over the Nisqually River four times since the 1920s. A flood in 1955 swamped the Longmire community.
An outburst flood from the Kautz Glacier in 1947 triggered a debris flow that traveled more than five miles downstream, burying the Nisqually-Longmire Road under 28 feet of mud and debris.
Park managers worry that, as climate change progresses, outburst floods will happen more often, increased by more rapidly melting ice and perhaps heavier rainstorms at especially sensitive times of the year.
Being able to predict when outburst floods will occur is the holy grail of park geologists, who say early warning would potentially save lives.
Unfortunately, there’s been little progress so far.
National Park Service geologists Paul Kennard and Scott Beason are experimenting with several theories, hoping to establish an early warning system at Longmire and farther downstream on the Nisqually River, even if it gives only a few minutes’ notice.
“It might at least give people enough time to start running,” Kennard said.
One theory, Beason said, is that water pressure before an outburst flood is so great that portions of the glacier float. By installing a sensitive GPS device in the right place on the glacier’s surface, he said, the upward movement could be detected and used to trigger alarms.
Another theory is that outburst floods might produce a distinctive seismic signature that’s distinguishable from the run-of-the-mill tremblers that constantly rattle the mountain. Seismometers on the glacier might be able to recognize the signal and relay a warning.
Evidence suggests some outburst flooding might be caused when a glacier’s terminus, or “snout,” stops moving and is cut off from the ice above – a condition geologists call “stagnant ice.”
Kennard and Beason know the lower portion of the Nisqually Glacier is moving more slowly than the upper portions, and they say it is stagnant.
Careful monitoring of the movement of the glacier could provide some warning.
“We do know that stagnant ice and, specifically, slowing ice on the lower glacier combined with faster ice on the upper glacier, has been associated with these events in the past,” Kennard said.
Also, Kennard and Beason are carefully watching a “kinematic wave” on the Nisqually Glacier, a bulge of heavy ice working its way down from the summit. They think that when the bulge reaches the bottom, it might trigger an outburst flood.
Andrew Fountain, a glaciologist and Portland State University professor who has studied and written about Mount Rainier’s glaciers, said he doesn’t think kinematic waves and outburst floods are related.
“I suppose it’s possible,” he said, “but I don’t see how.”
Fountain said he thinks finding as way to predict outburst flooding at Rainier could well be a lost cause.
Predictions are especially difficult at Rainier, he said, because the high altitude and steep slopes make analysis so difficult.
“Glaciers on Rainier are tough,” Fountain said. “They’re hard to measure, and there’s a lot of rock on top of a lot of them.”
“A lot of stuff is going on on Rainier,” he said, “but it’s very complex and difficult to draw conclusions.”
Even in the most structurally simple glaciers, Fountain said, where it’s possible to determine where hidden water is located, there’s still no way of telling what will trigger a release.
“At Mount Rainier, things get more difficult from there,” he said. “Water accumulates, but we don’t know where and we don’t know how much. It suddenly comes out, and it surprises everybody.”
“Why today, and not yesterday or tomorrow?” he asked. “We don’t know.”