Rainier's rocks are filling riverbeds
enigma
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 sdou...@seattletimes.com
http://seattletimes.nwsource.com/html/localnews/2010689013_rainiergravel04m.html
tunderbar
>
> http://seattletimes.nwsource.com/html/localnews/2010689013_rainiergra...
One of over 100 thousand glaciers.
Marvin the Martian
< absolutely nothing, just a copyright violation about rocks in a
riverbed >
So, pointing out that people all over the world are freezing their asses
off is "weather" and not climate change, but a glacier melt that began
25,000 years ago is presumed to be "man made". So says the bimbo passed
off as a "science reporter" at the commie rag.
Ouroboros Rex
As usual, you have nothing. lol
Monkey Clumps
How about "sorry, not global?"