Mt. Rainier's retreating glaciers are making a mess
Washington rivers are choking on debris left unstable by Rainier's receding glacier.
The fallout from Mt. Rainier's shrinking glaciers is beginning to roll downhill, and nowhere is the impact more striking than on the volcano's west side.Skip to next paragraph
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"This is it in spades," says Park Service geologist Paul Kennard, scrambling up a 10-foot-tall mass of dirt and boulders bulldozed back just enough to clear the road.
As receding glaciers expose crumbly slopes, vast amounts of gravel and sediment are being sluiced into the rivers that flow from the Northwest's tallest peak. Much of the material sweeps down in rain-driven slurries called debris flows, like those that repeatedly have slammed Mt. Rainier National Park's Westside Road.
"The rivers are filling up with stuff," Mr. Kennard says from his vantage point atop the pile. He pointed out ancient stands of fir and cedar now up to their knees in water.
Inside park boundaries, rivers choked with gravel are threatening to spill across roads, bump up against the bottom of bridges and flood the historic complex at Longmire.
Downstream, communities in King and Pierce counties are casting a wary eye at the volcano in their backyard. There are already signs that riverbeds near Auburn and Puyallup are rising. As glaciers continue to pull back, the result could be increased flood danger across the Puget Sound lowlands for decades.
"There is significant evidence that things are changing dramatically at Mt. Rainier," says Tim Abbe, of the environmental consulting firm ENTRIX. "We need to start planning for it now," added Mr. Abbe, who helps analyze Mt. Rainier's river systems.
Similar dynamics are playing out at all the region's major glaciated peaks, from Mt. Jefferson to Mt. Baker, says research hydrologist Gordon Grant, of the US Forest Service Pacific Northwest Research Station in Corvallis, Ore.
Climate experts blame global warming, triggered by emissions from industries and cars, for much of the ongoing retreat of glaciers worldwide.
North Cascades National Park has lost half of its ice area in the past century. Mt. Rainier's glaciers have shrunk by more than a quarter. "Every year it's been either bad or really bad," Kennard says. "This year it was really, really bad."
Glaciers buttress immense moraines and stabilize steep slopes. As they pull back, the vulnerable terrain is exposed to weather and tugged by gravity. All recent debris flows on Mt. Rainier have occurred in recently deglaciated areas, Mr. Grant says.
"The whole mountain is covered with unstable debris, it's steep — and then you put a lot of water on it," he says.
Most debris flows are triggered by heavy rain. Climate scientists disagree on whether the entire Northwest is being hit by significantly stronger storms than in the past, but there's no doubt that's the case at Mt. Rainier, Kennard says.
Precipitation records show more intense rainfall. According to stream-flow data, what was once a 100-year flood on the Nisqually River now occurs every 14 years. In 2006, a November storm dumped 18 inches of rain on the park in 36 hours, sweeping away a campground and closing the park for more than six months.