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Date Permissions Signed

11-20-2017

Date of Award

Winter 2018

Document Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Clark, Douglas H., 1961-

Second Advisor

Linneman, Scott

Third Advisor

Mitchell, Robert J. (Geologist)

Fourth Advisor

Wiser, Andrew P. (Andrew Paul)

Abstract

Geomorphic mapping based on high-resolution lidar data indicates that the Van Zandt Landslide Complex (VZLC) has multiple crosscutting debris lobes (up to 51.4 x 106 m3) with long runouts (H/L= 0.14; 0.21) typical of catastrophic rock avalanches. AMS 14C dates from in situ logs and lake sediment cores yield overlapping ages for emplacement of Debris Lobe 2 (1330-1285 cal. yrs. B.P) and Debris Lobe 3 (1300-1285 cal. yrs. B.P.) Although Debris Lobe 3 overlies a portion of Debris Lobe 2, it is possible that emplacement of the two deposits was nearly synchronous or in rapid succession. The debris lobes are not contemporaneous with any known paleoseismic events from local shallow-crustal faults but do overlap with a known Cascadia megaquake (event T4). Abundant transverse surface fractures, a distal “splash zone,” as well as debris exposures showing basal mixing, soft-sediment deformation, and substrate injection features provide evidence for significant rock avalanche-substrate interaction and mobility-enhancing liquefaction. To evaluate ongoing retrogressive block sliding in the headwall region, we installed wire extensometers in three prominent tension gaps and tracked their movement over an 18-month period between 10/15 and 4/17; all three sites experienced measurable displacement (up to 5.7 cm total), with progressive movement largely accelerating and decelerating in response to short- and long-term precipitation conditions. Although recorded strain rates were relatively slow during this period, incipient detachment scarps across the headwall involve slabs with a total volume of ~35.2 x 106 m3, the potential release of which could pose a serious hazard to people and property in the valley below.

Type

Text

DOI

https://doi.org/10.25710/0wgq-5j78

Publisher

Western Washington University

OCLC Number

1026388445

Subject – LCSH

Geomorphological mapping--Washington (State)--Whatcom County; Slopes (Soil mechanics)-Washington (State)--Whatcom County; Landslides-Washington (State)--Whatcom County; Geology-Washington (State)--Whatcom County

Geographic Coverage

Whatcom County (Wash.)

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.

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