April 2, 2009 -- In the Pacific Northwest, majestic volcanoes loom ominously close to major populations centers. Though quiescent now, a major eruption could take huge tolls in life and property. But their snowy peaks hold more than just the threat of eruption.
According to a new study, the glaciers on Mt. Hood in Oregon and Mt. Rainier in Washington are melting, and regional rain storms are getting bigger. The change in climate appears to be increasing the risk of large debris flows and massive flooding on rivers that drain the mountains.
"Since 2000, Rainier has lost 15 square kilometers (5.8 square miles) of its glaciers," Anne Nolin of Oregon State University said. Nolin is lead author on a study, which was presented last week at the American Association of Geographers meeting in Las Vegas. "That leaves a lot of loose, unconsolidated material that can be washed away," she said.
A slurry of mud and boulders sometimes as big as cars, the debris rolls like a freight train down the steep mountain slopes, tearing at narrow canyon walls and uprooting huge stands of forest in its path.
Related Content:
"It's hard to fathom the degree of impact without seeing it," Nolin said. "It's so huge."
This was in stark display in November of 2006, when a massive rainstorm rolled through the region. Filled with warm moisture, the storm dropped heavy rain instead of snow, initiating massive debris flows on Hood and Rainier that caused $30 million in damages to roads, bridges, and farming infrastructure.
This is increasingly common. So-called "pineapple express" storms that develop in the tropics are hammering the region. Their warmth means rock-scouring rain falls instead of snow, which would normally pile peacefully on top of the glaciers.
Nolin said it's still too soon to say for sure whether or not climate change is leading to more -- and more intense -- debris flows. And for now the Rainier events only affect areas within the national park that surrounds the volcano.
But Paul Kennard of Mt. Rainier National Park said that there is historic precedent for hugely destructive flows that coursed 30 to 40 miles down local waterways. If such an event happened today it could devastate the town of Orting, Wash. and even threaten the rapidly developing outskirts of the city of Tacoma.
"These sorts of flows can happen without a volcanic eruption," Kennard said. "There are probably tens of thousands of people living directly along the rivers the drain Rainier. Potentially up to 200,000 people could be affected."
Inside the park, Kennard said that debris flows have raised a portion of the Nisqually River bed 38 feet since 1910. It's is an extreme exampling of river infilling, but the process has made what was once a 100-year flood far more common: They now occur every 14 years. The Carbon, White and Puyallup Rivers are also infilling steadily, increasing the flood risks to populated areas downstream.
Related Links:
Go to Discovery Earth for slide shows, quizzes, interviews and more.
our sites
video
mobile
shop
stay connected
corporate
