Sponsor
Portland State University. Department of Geography
First Advisor
Larry W. Price
Term of Graduation
Summer 1987
Date of Publication
8-7-1987
Document Type
Thesis
Degree Name
Master of Science (M.S.) in Geography
Department
Geography
Language
English
Subjects
Rock glaciers -- Washington (State) -- Olympic Mountains
DOI
10.15760/etd.5440
Physical Description
1 online resource (3, ix, 126 pages)
Abstract
Rock glaciers are tongue-shaped or lobate masses of rock debris which occur below cliffs and talus in many alpine regions. They are best developed in continental alpine climates where it is cold enough to preserve a core or matrix of ice within the rock mass but insufficiently snowy to produce true glaciers. Previous reports have identified and briefly described several rock glaciers in the Olympic Mountains, Washington, but no detailed integrative study has been made regarding the geomorphic character, age, and distribution of these features.
The purpose of this study is two-fold. First, surface sediment fabric analysis and relative and absolute dating methods are used to determine the geomorphic character and age of Akela rock glacier. Secondly, the distribution of rock glaciers in the northeast Olympics is analyzed in terms of topoclimatic and geologic factors in order to understand the environmental conditions under which they formed. In addition, the distribution of rock glaciers is compared to that of past and present glaciers.
Radiocarbon dates indicate that Akela rock glacier formed within the past 10,000 years, most likely about 3,000 to 5,000 years ago. The rock glacier has clearly not been active for at least 200 to 300 years. Relative age data indicate that the surface of the rock glacier is variably-aged; boulders at the head of the rock glacier have been most recently deposited and have been least influenced by rock glacier flow. In contrast, boulders at the rock glacier toe display signs of being inactive for many years. Boulders at the rock glacier toe and upper lobe face display a preferred orientation, which is attributed to past rock glacier activity. The lateral ridges of the rock glacier were the first areas to stabilize, probably more than 1000 years ago. In addition to a warming climate, the lack of a continued supply of debris from the headwall above Akela rock glacier was a factor in its becoming inactive. These results indicate that both fabric analysis and relative dating methods can be used to better understand the geomorphic character and age of rock glaciers.
Rock glaciers in the Olympic Mountains occur entirely within the more continental northeastern section of the Olympics. Within this area, they are preferentially located to the lee of the Needles Ridge and Mt. Constance Massif, where precipitation is most limited. These rock glaciers may be composed of either sandstones or basalts, but are restricted to areas where their debris supply is coarse and blocky. The surface character of the eight rock glaciers surveyed suggests that at least seven of them are inactive.
The rock glaciers occupy an elevational zone distinct from present or past glaciers as a result of their formation in areas of limited snow accumulation. Also, their downslope elevation may be restrained by lack of debris from the cliffs above them. The mean rock glacier toe elevation of about 1700 m suggests an approximate lower limit for discontinuous Neoglacial permafrost.
Rights
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Persistent Identifier
https://archives.pdx.edu/ds/psu/20182
Recommended Citation
Welter, Steven Paul, "Geomorphic Character, Age and Distribution of Rock Glaciers in the Olympic Mountains, Washington" (1987). Dissertations and Theses. Paper 3558.
https://doi.org/10.15760/etd.5440
Comments
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