Internal composition, structure, and hydrological significance of rock glaciers in the Eastern Cascades, Washington
Date of Degree Completion
Master of Science (MS)
Cultural and Environmental Resource Management
Karl D. Lillquist
Second Committee Member
Third Committee Member
Low summer river base flow places a strain on natural and economic resources of the Eastern Cascades. A major contributor to stream flow in this region is snow pack which has declined over the past few decades because of a warming climate. In addition, glacial runoff, which contributes significantly to base flow in summer dry periods, will diminish from glacial recession. However, rock glaciers, because their internal ice (i.e., permafrost) is insulated by an outer debris layer, react slowly to climate change, thus acting as sinks for ice and liquid water storage in mountain environments. This study utilized ground penetrating radar (GPR) to investigate the internal structure, composition, and hydrological significance of a sample of nine Eastern Cascade rock glaciers. Analysis reveals that active layer thickness for all active rock glaciers are similar with an average of 3.4 meters (m). In addition, linear reflectors deeper in the profiles indicate bedrock and accurately depict the overall rock glacier depth. Other internal stratigraphic features show thrust planes throughout different sections of the profile which are closely tied to slope angle. Further, GPR shows the presence of massive (i.e., solid) or interstitial internal permafrost indicating glaciogenic or talus origins. Through measurements of rock glacier base depth and the active layer, this study was able to improve on previous research for estimating the total volume of ice-rich permafrost in these features. Results show a 64 percent over-estimation of permafrost-rich layer thickness using methods from previous studies. These show that previous studies over-estimate the hydrological significance of rock glaciers in comparison to ice glaciers. Results indicate a ratio of volume of rock glacier to ice glacier ice-water equivalence of 1:46 in the Eastern Cascades. In turn, results indicate Eastern Cascade rock glaciers rank similarly in terms of hydrological significance to other mountain ranges around the globe. While rock glaciers in this region will continue to contribute to base flow, they will not totally compensate for the inevitable loss of ice glaciers. This research provides insight for water management for the Eastern Cascades experiencing shifting water resources due to a warming climate.
Riffle, Adam, "Internal composition, structure, and hydrological significance of rock glaciers in the Eastern Cascades, Washington" (2018). All Master's Theses. 1010.
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