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1995
PNW Project Overview 1995
Geologic Mapping and Landslide Inventory of the West-central Portion of the Olympic Peninsula, Washington
Principal
Investigator:
Wendy
Gerstel, Washington Department of Natural Resources
Awarded: $38,400
Project
Description:
This
project will compile an inventory of deep-seated landslides, accompanied
by geologic maps, in the following drainages and their associated
tributaries on the west slope of the Olympic Peninsula: Queets, Hoh,
Bogachiel, Calawah, and lower Soleduc (the last three combining to form
the Quillayute). Differentiating quaternary deposits is particularly
critical to this project as glacial deposits commonly control landslide
type and failure mechanisms. Existing map coverage of deep-seated
landslides is spotty and at present there is no comprehensive inventory;
however, the need for such an inventory is pointed out by Dr. Susan Shaw
in her recommendations for a riparian management plan for the Olympic
Experimental State Forest. Furthermore, geologic maps detailing the
glacial stratigraphy provide a basis for identifying sediment sources and
stream characteristics and support continuing studies by David Montgomery
and others characterizing stream gradients and sediment supply.
Project Status:
ONRC
received a hard copy of the geologic inventory map and associated
digital data.
Two final reports have been completed.
Report
1. Gerstel, Wendy.
1999. Landslide inventory of the West Central Olympic Peninsula,
Washington Division of Geology and Earth Resources. Open File Report 99-2
Olympia, WA.
Abstract:
Deep-seated landslides on the west side of the Olympic Peninsula fall into
two broad categories; those that occur in bedrock, and those that occur in
valley-bottom glaciofluvial terrace deposits.
Landslides in both categories are affected by climatic conditions
and by land-use activities. Most deep-seated landslides on the western Olympic Peninsula
are probably several hundred to several thousand years old and may be
dormant. However, events of
1996-1998 in many western Washington counties demonstrate that wetter
climatic conditions and the effects of human activities can reactivate
these “ancient” landslides.
Because deep-seated landslides are difficult to model with existing analytical tools, landslide hazard maps are essential tools for the land manager, land-use planner, and scientist. The most reliable method of mapping deep-seated landslides is by field observations in combination with air photo interpretation, reaffirming the fact that existing landslides are the best indicators of the potential for future landslide activity.
Report
2. Gerstel, Wendy. 2000.
Geologic Map of the Forks 1:100,000 Quadrangle, Washington,
Washington Division of Geology and Earth Sciences. Open File Report
2000-4. Olympia, WA.
Abstract:
The report describes a compilation of geologic mapping of the Forks
1:100,000 quadrangle, which covers the lower western slopes of the Olympic
Mountains and extends westward to the Pacific Ocean.
Using zircon fission-track minimum ages, scientists confirmed the
contacts of the three major structural sheets on the Olympic Peninsula.
Principal investigators used standard nomenclature outlined in
Schuster, 1994 to describe quaternary and tertiary units.
The report also outlines the major faults, cleavage, folds and
lithologic layering within the Forks quadrangle.