Regional Modeling of Volume Change of glaciers in the North Cascades, Washington
Glaciers are important sources of water for their surrounding localities. Because of their dependence on temperature and precipitation, they also are good indicators of climate (Bennett and Glasser, 2009).
This study will apply the Regional Glaciation Model (RGM) to the North Cascades to observe how glaciers with different topographic features, such as headwall elevation, slope, and aspect, affect response to climate and their projected extents in the future. The RGM is a distributed 2-dimensional model that incorporates a Positive Day Degree (PDD) melt model and calculates the thickness, area, and volume change of the glacier at time steps of one year Clarke et a., 2015; Menounos, personal communication). The model will be calibrated with climate data from two different sources to ensure the efficiency of the model.
Using future climate projections, the extent of the 2100 glaciers will then be estimated. It is expected that glaciers with higher headwall elevations, steeper slopes, and northern aspects are expected to react less to climate warming than glaciers with lower headwall elevation, gentle slopes, and southern aspects, and therefore lose more volume compared to other glaciers.
Modeling of the Sensitivity of Glaciers in the Pacific Northwest and their Response to Climate Change
Glacial melt rivers feed into local drainage basins and power hydroelectric energy. Melted ice will feed into the local water supply, so as glaciers retreat the glacial discharge will increase. However after an initial surge in melt water the amount of glacier ice will lessen, as will the amount of water available for consumption, making it important to understand how glaciers respond to climate warming to understand the future of water for the nearby localities (Bennett and Glasser, 2009).
To do this a model can be used to observe how physical factors such as width variations, slope, and headwall elevation are related to a glacier’s sensitivity to climate change. A steady state, width-varying flow line model will be used to model glaciers on Mount Rainier and in the North Cascades National Park and observe how different characteristics cause some glaciers to have lower mass balances than others (Huybers, personal communication).
Higher headwall elevations, larger lapse rates, steeper slopes, and glaciers that end in a narrow tongue are related to glaciers that are less sensitive to climate, whereas lower headwall elevations, gentler slopes, and channel like width variation are related to more sensitive glaciers. Since glaciers in the North Cascades are lower altitude with gentler bed slopes than Mount Rainier glaciers and have weaker width variations or variations that open up, they are more likely to respond strongly to climate change.
Modeling Pacific Northwest Glaciers with Differential Equations
Glaciers are extremely dependent on climate, and small increases in temperature can cause changes in glacier size. Understanding what physical characteristics of glaciers, such as headwall elevation, slope, and width variations affect how a glacier's size changes in response to climate change is important since the localities around these glaciers rely on them for water, as well as hydroelectric energy (Bennett and Glasser, 2009).
In this study a model based on equations from the shallow ice approximation (Huybers, personal communication) was used to describe changes in glacier size for glaciers in the North Cascades and Mount Rainier National Parks. From the model we can see that higher headwall elevations, steeper bed slopes, and narrowing width variations contribute to lessening glacier sensitivity, potentially explaining why the Mount Rainier glaciers are less sensitive than North Cascade glaciers.
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Bennett M., and N. Glasser, (2009) Glacial Geology: Ice sheets and landforms, 2nd ed. Wiley-Blackwell, Chichester, UK
Clarke, G., Jarosch, H., Anslow F., Radic V., and B. Menounos, (2015), Projected deglaciation of western Canada in the twenty-first century, Nature Geoscience (8), 373-377, doi: 10.1038/ngeo2407
Huybers, K. (2016), personal communication
Menounos, B. (2017), personal communication