Advisor

Scott Burns

Date of Award

Fall 12-29-2015

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Geology

Department

Geology

Physical Description

1 online resource (xvii, 186 pages)

Subjects

Debris avalanches -- Washington (State) -- Mount Rainier, Lahars -- Washington (State) -- Mount Rainier, Mount Rainier (Wash.)

DOI

10.15760/etd.2650

Abstract

In November 2006 a Pineapple Express rainstorm moved through the Pacific Northwest generating record precipitation, 22 to 50 cm in the two-day event on Mt. Rainier. Copeland (2009) and Legg (2013) identified debris flows in seven drainages in 2006; Inter Fork, Kautz, Ohanapecosh, Pyramid, Tahoma, Van Trump, and West Fork of the White River. This study identified seven more drainages: Carbon, Fryingpan, Muddy Fork Cowlitz, North Puyallup, South Mowich, South Puyallup, and White Rivers. Twenty-nine characteristics, or attributes, associated with the drainages around the mountain were collected. Thirteen were used in a regression analysis in order to develop a susceptibility map for debris flows on Mt. Rainier: Percent vegetation, percent steep slopes, gradient, Melton's Ruggedness Number, height, area, percent bedrock, percent surficial, percent glacier, stream has direct connection with a glacier, average annual precipitation, event precipitation, and peak precipitation. All variables used in the regression were measured in the upper basin. Two models, both with 91% accuracy, were generated for the mountain. Model 1 determined gradient of the upper basin, upper basin area, and percent bedrock to be the most significant variables. This model predicted 10 drainages with high potential for failure: Carbon, Fryingpan, Kautz, Nisqually, North Mowich, South Mowich, South Puyallup, Tahoma, West Fork of the White, and White Rivers. Of the remaining drainages 5 are moderate, 10 are low, and 9 are very low. Model 2 found MRN (Melton's Ruggedness Number) and percent bedrock to be the most significant. This model predicted 10 drainages with high potential for failure during future similar events: Fryingpan, Kautz, Nisqually, North Mowich, Pyramid, South Mowich, South Puyallup, Tahoma, Van Trump, and White Rivers. Of the remaining drainages, 6 are moderate, 9 are low, and 9 are very low. The two models are very similar. Initiation site elevations range from 1442 m to 2448 m. Six of the thirteen initiation sites are above 2000 m. Proglacial gully erosion initiated debris flows seem to occur at all elevations. Those debris flows initiated partially by landslides occur between 1400 and about 1800 m. The combined regression analysis model for the Mt. Rainier, Mt. St. Helens, Mt. Hood, and Mt. Adams raised the predictive accuracy from 69% (Olson, 2012) to 77%. This model determined that percent glacier/ice and percent vegetation were the most significant.

Persistent Identifier

http://archives.pdx.edu/ds/psu/16472

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