> Rainier's rocks are filling riverbeds
> By Sandi Doughton
> Seattle Times science reporter
> Originally published January 3, 2010 at 10:00 PM | Page modified
> January 4, 2010 at 9:25 AM
> The fallout from Mount Rainier's shrinking glaciers is beginning to
> roll downhill, and nowhere is the impact more striking than on the
> volcano's west side.
> "This is it in spades," said 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 Mount Rainier National Park's Westside Road.
> "The rivers are filling up with stuff," Kennard said 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 Mount Rainier," said Tim Abbe, of the environmental consulting firm
> ENTRIX. "We need to start planning for it now," added Abbe, who helps
> analyze Mount Rainier's river systems.
> Similar dynamics are playing out at all the region's major glaciated
> peaks, from Mount Jefferson to Mount Baker, said research hydrologist
> Gordon Grant, of the U.S. 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. Mount Rainier's glaciers have shrunk by more than a quarter.
> "Every year it's been either bad or really bad," Kennard said. "This
> year it was really, really bad."
> Unstable stone
> 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 Mount Rainier have occurred in
> recently deglaciated areas, Grant said.
> "The whole mountain is covered with unstable debris, it's steep — and
> then you put a lot of water on it," he said.
> 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 Mount Rainier, Kennard said.
> 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.
> "Even without climate change, you've got to say: 'Whoa, something is
> going on here,' " Abbe said.
> Debris flows can carry boulders the size of buses and sweep staggering
> amounts of gravel and sediment into rivers. The bed of the Nisqually
> River below its namesake glacier has risen by 38 feet since 1910,
> largely as a result of debris flows from the margins of the rapidly
> retreating ice, Kennard said.
> The park visitor center at Longmire, with its stone buildings and
> National Park Inn, now sits more than 30 feet below the Nisqually
> River. The park constructed concrete-reinforced berms to keep the
> water at bay.
> Every river bed in the park is rising, or aggrading, because of the
> influx of gravel, Kennard said. The rate of buildup has increased
> nearly 10-fold over the past decade.
> The result is a constant and costly battle to keep popular recreation
> areas throughout the park open. It's a battle that's being lost in
> many places, like the Westside and Carbon River roads, which are
> partially closed.
> Like conveyor belts, the rivers move the gravel downstream toward more
> heavily populated areas. A surprise flood that hit the city of Pacific
> last January can at least partly be blamed on volume reduction in the
> White River caused by accumulation of sediment, U.S. Geological Survey
> hydrologist Chris Magirl said.
> Magirl, who has examined aggradation rates and historical records for
> downstream river stretches, sees similar buildup in several locations.
> But channels appear to be deepening in other places, including
> portions of the Puyallup and Cowlitz rivers. That type of variation is
> expected in such a complex system, Magirl said. But the longterm
> outlook for the rivers is not good.
> "The potential for glacial retreat to add new sediment is historically
> unprecedented," he said. "Clearly, water and rock are going to flow
> downhill."
> Glacial retreat may be aggravating the flow of sediment, but the basic
> process is as old as the volcano itself. Past eruptions have unleashed
> mud flows that smothered surrounding valleys and reached all the way
> to Puget Sound.
> From the 1930s through the 1980s, Pierce County dredged gravel from
> the Puyallup River system almost every year to reduce the risk of
> floods, said Lorin Reinelt, program manager for the county's flood-
> management plan.
> Most dredging ended by the early 1990s, as concern for fish habitat
> took precedence. Officials also realized that digging out gravel
> provides only a brief fix, at best, Reinelt said. "In many cases it
> just fills back up during the next event."
> Communities now are trying to figure out what rising levels of gravel
> and sediment from Mount Rainier will mean for future flood risks — and
> what they can do about it.
> Short of relocating Longmire, dredging is the only obvious way to keep
> the river from swallowing the park complex, Kennard said. Downstream,
> Reinelt said, a more effective approach might be to move levees back
> to give the rivers more room to spill their banks, meander and deposit
> gravel without impacting homes or businesses.
> "This is a pretty significant issue," he said. "It seems like we're on
> a trajectory that's not likely to reverse any time soon."
> Sandi Doughton: 206-464-2491 or sdough...@seattletimes.com
> http://seattletimes.nwsource.com/html/localnews/2010689013_rainiergra...
One of over 100 thousand glaciers.
