Geologic Publications for Mount Rainier

Rivers gone wild: Mountain river response to a warming climate in the Pacific Northwest

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Author(s): Timothy B. Abbe, Scott R. Beason, Paul M. Kennard, Jim Park

Category: PUBLICATION
Document Type:
Publisher: Freshwater
Published Year: 2010
Volume: 2
Number: 2
Pages: 10 to 13
DOI Identifier:
ISBN Identifier:
Keywords:

Abstract:
Rivers move. They change course, jump banks, move trees and carve canyons. In balance, rivers generally do these things on geological timelines, over decades and centuries. Climate change disrupts this balance by violently accelerating changes in river architecture.

In November 2006, an intense storm dumped 17.9 inches of rain in 36 hours on Mount Rainier National Park in southwest Washington state. The deluge carried massive amounts of sediment down the heavilyglaciered mountain, overwhelming stream capacity and washing away trails and roads park-wide. The extensive damage to Mount Rainier closed the park for an unprecedented six months and cost tens of millions of dollars to repair.

In December 2007, a similar storm slammed Southwest Washington, shutting down Interstate 5 for four days and causing millions of dollars in damages. Sadly, the dangerous flooding conditions also took the lives of five people. The increase in large storms is a trend - six of the largest storms on record have occurred in the last 25 years.

Because the Pacific Northwest is an important climatic region, home to an abundance of natural resources and hundreds of glaciers that are critical to freshwater supplies, geologists and scientists are studying recent, catastrophic flood events and asking important questions. Are floods getting worse in the Pacific Northwest, and, if so, is it linked to climate change? Is the sediment being released by receding glaciers contributing to flooding? Was the damage on Mount Rainier in 2006 a warning of things to come?

Rivers convey not only water, but also sediment and debris, like wood. The form of a river is a balance between the supply of sediment to the river and the river's ability to move it. The primary variables driving a river's transport capacity are the quantity of water it conveys and the steepness (slope) of its channel. When these variables are not balanced, a river will respond by changing its shape. Rivers that suddenly change their character after long periods of relative stability indicate some sort of disturbance in a river's delicate balance.

As an almost three-mile high obstruction to Pacific Ocean storms, Mount Rainier receives prodigious amounts of rain and snow. Because the volcano's steep mountain slopes are comprised of very weak rock (ask the climbers!), the high amounts of precipitation send large amount of sediment into the eight rivers that drain Mount Rainier. As a result, there is a constant battle as to which prevails at any given time - too much sediment means the river channel fills in (aggrades), too much water means the river channel gets deeper (degrades).

Another factor that comes into play on most glacier-sourced rivers is "braiding." During floods, enormous amounts of sediment and wood are moved downstream. As the floods subside, much of this load is unceremoniously dumped in-place, forcing the river to flow around the obstacles, creating a braided channel morphology. Historically, Mount Rainier's rivers have been unruly, but in recent years it appears the balance has been seriously disrupted. Consuming ancient forests and posing new historic threats to park infrastructure, the volcano's rivers have truly gone wild.

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Suggested Citations:
In Text Citation:
Abbe and others (2010) or (Abbe et al., 2010)

References Citation:
Abbe, T.B., S.R. Beason, P.M. Kennard, and J. Park, 2010, Rivers gone wild: Mountain river response to a warming climate in the Pacific Northwest: Freshwater, Vol. 2, No. 2, pp. 10-13.