First Advisor

Scott F. Burns

Date of Publication

Fall 12-1-2016

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Geology

Department

Geology

Language

English

Subjects

Debris avalanches -- Oregon -- Mount Hood, Lahars, Sedimentation and deposition

DOI

10.15760/etd.5267

Physical Description

1 online resource (xiv, 193 pages)

Abstract

Over a span of six days from November 2-7, 2006 approximately 43 cm of precipitation fell over the Hood River Basin in Oregon. A lahar was initiated on the Eliot Branch of the Middle Fork Hood River by two or more landslides that occurred on the lateral moraines of the Eliot Glacier on the early part of November 7th, 2006. The Eliot Branch lahar was embedded within the larger regional flood that was occurring in the Hood River Basin and traveled a total of 48 km from the initiation points on the north flank of Mount Hood to the Hood Rivers confluence with the Columbia River.

The initiating landslides abruptly transformed into a debris flow upon mixing with flood waters of the Eliot Branch. The debris flow traveled a distance of ~28 km at which point it was transformed first to a hyperconcentrated flow and then to water flow via selective deposition of coarse sediment and progressive dilution by channel flow waters from the East and West Fork Hood Rivers. The transformation from debris flow to hyperconcentrated streamflow was recorded by a thickening wedge of hyperconcentrated streamflow sediments found above and below progressively fining debris flow sediments over a reach of 22 km. Finally, the hyperconcentrated-flow phase of the lahar transformed to water flow and then traveled an additional 20 km to the Hood River delta. Upon reaching the apex of the Hood River delta, depositing sediments led to an expansion of the delta. Debris-flow sediments were predominantly gravel (36.0-69.7% by wt.) with sand (22.1-55.9% by wt.) and fines (4.7-7.8% by wt.). Hyperconcentrated flow deposits contained a larger sand fraction of (66.8-99.2% by wt.) with few gravel clasts (0-26.0% by wt.) and fines (0-8.8% by wt.). Water flow deposits averaged 90.5% (wt.) sand with 6.0% (wt.) gravel and 3.0% (wt.) fines. Sorting was a key factor in flow identification and showed progressive improvement downstream from the initiation point. Sorting values for the flow types are as follows: debris flow deposits ranged from 3.3Φ (very poorly sorted) to 1.8Φ (poorly sorted), hyperconcentrated flow deposits ranged from 2.4Φ (very poorly sorted) to 0.8Φ (moderately sorted), and water flood deposits ranged between 1.4Φ (poorly sorted) to 0.6Φ (moderately sorted).

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Persistent Identifier

http://archives.pdx.edu/ds/psu/19175

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