From our friends at the
Northwest Geological Society, a topic of interest to the North Cascades generally:
October 9th Speaker Program
Speakers: Paul Kennard, Regional Geomorphologist, Mt. Rainier National Park, and Chris Magirl, Research Hydrologist, U.S. Geological Survey, Tacoma
Title: Goats to geoducks: Landscape response to climate change from the summit of Mount Rainier to Puget Sound
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| This debris flow is in lower Colonial Creek |
Abstract: Mount Rainier is an active volcano, and is considered the most dangerous mountain in the United States, because of its proximity to major cities. However, it is the more “everyday” risks such as floods, debris flows, and river aggradation (or filling) that are posing unprecedented challenges to people and roads at Mount Rainier National Park, and to the downstream communities.
Because of vast amounts of sediment sloughing off the mountain, Mount Rainier’s rivers are aggrading - that is, the river beds, on average, are rising by natural processes. Recent aggradation has more than doubled in the last 10 years (to over 3 feet/decade). This means that for the same size storms, the flood potential is ever increasing, since the “capacity” of the river channel is reduced, as the channels fill in.
Ongoing glacial recession has exposed large volumes of oversteepened and very unstable sediment, promoting increased numbers of debris flows, compounding the flooding problems. Debris flows are destructive, sediment-laden slurries that move downhill by gravity. In areas affected by debris flows, large rivers near developed areas have aggraded an astounding
38 feet since 1910, and almost 6 feet in a single year. The park has had at least 16 debris flows since 2001, and there were multiple debris flows in 3 streams that had not had debris flows in hundreds of years. In 2006, there were 10 debris flows in two days, resulting in extensive damage to park roads and campgrounds, and closing the Park for 6 months.
To add insult to injury, climate change is expected to increase storminess, and further escalate debris flows and flooding.
Stream flow records at Mount Rainier show a striking rise in the occurrence of large floods. Specialists predict further increases, as glaciers continue their rapid retreat due to global warming, making this a major management concern at Mount Rainier National Park.
Location: Talaris Conference Center, 4000 NE 41st St., Seattle, WA
Oct 9, 2012
5:30pm: No-host social hour
6:30pm: Buffet dinner
7:30pm: Speaker program
All are welcome to attend —
reservations are required
if coming for dinner.
►Reservations here
1 comment:
Was a really interesting presentation. Rainier Park is a prime test-case of what the N. Cascades are in for as climate warms and glaciers recede. Glacier mass balance on Rainier is closely monitored and the story is not good: 10 years of huge losses, followed by last 2 years modest gains, all of which was more than lost this very summer. Meanwhile the lower part of most of the Rainier glaciers is going stagnant and that's a very bad sign - usually this is followed by very rapid ablation. All of this yields unprecedented debris load for glacial-fed rivers, with riverbeds aggrading (filling with sediment) forcing the river to find new courses across its floodplain, impacting roads build along hitoric channels. The roads become the new riverbeds in flood events following storms. The road to Paradise has 5 or 6 'hot spots' any one of which will potentially take the road out of commission in any one storm. Budgets may not exist to rebuild many very popular roads from the likely recurrent storm events of the future. All the fuss about "access" on existing roads is likely to seem superfluous in the near future.
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