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Book Chapter

Mount Baker lahars and debris flows, ancient, modern, and future

By
David S. Tucker
David S. Tucker
Geology Department, Western Washington University, 516 High Street, Bellingham, Washington 98225, USA
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Kevin M. Scott
Kevin M. Scott
Cascade Volcano Observatory, U.S. Geological Survey, 1300 Cardinal Court, Vancouver, Washington 98683, USA
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Eric E. Grossman
Eric E. Grossman
U.S. Geological Survey Pacific Coastal and Marine Science Center and Western Fisheries Research Center, 6505 NE 65th Street, Seattle, Washington 98115, USA
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Scott Linneman
Scott Linneman
Geology Department, Western Washington University, 516 High Street, Bellingham, Washington 98225, USA
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Published:
January 01, 2014

Abstract

The Middle Fork Nooksack River drains the southwestern slopes of the active Mount Baker stratovolcano in northwest Washington State. The river enters Bellingham Bay at a growing delta 98 km to the west. Various types of debris flows have descended the river, generated by volcano collapse or eruption (lahars), glacial outburst floods, and moraine landslides. Initial deposition of sediment during debris flows occurs on the order of minutes to a few hours. Long-lasting, down-valley transport of sediment, all the way to the delta, occurs over a period of decades, and affects fish habitat, flood risk, gravel mining, and drinking water.

Holocene lahars and large debris flows (>106 m3) have left recognizable deposits in the Middle Fork Nooksack valley. A debris flow in 2013 resulting from a landslide in a Little Ice Age moraine had an estimated volume of 100,000 m3, yet affected turbidity for the entire length of the river, and produced a slug of sediment that is currently being reworked and remobilized in the river system. Deposits of smaller-volume debris flows, deposited as terraces in the upper valley, may be entirely eroded within a few years. Consequently, the geologic record of small debris flows such as those that occurred in 2013 is probably very fragmentary. Small debris flows may still have significant impacts on hydrology, biology, and human uses of rivers downstream. Impacts include the addition of waves of fine sediment to stream loads, scouring or burying salmon-spawning gravels, forcing unplanned and sudden closure of municipal water intakes, damaging or destroying trail crossings, extending river deltas into estuaries, and adding to silting of harbors near river mouths.

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GSA Field Guide

Trials and Tribulations of Life on an Active Subduction Zone: Field Trips in and around Vancouver, Canada

Shahin Dashtgard
Shahin Dashtgard
Department of Earth Sciences Simon Fraser University 8888 University Drive Burnaby, British Columbia V5A 1S6, Canada
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Brent Ward
Brent Ward
Department of Earth Sciences Simon Fraser University 8888 University Drive Burnaby, British Columbia V5A 1S6, Canada
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Geological Society of America
Volume
38
ISBN electronic:
9780813756387
Publication date:
January 01, 2014

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