Portland State University. Environmental Sciences and Resources Ph. D. Program
Date of Award
Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources
Environmental Sciences and Resources
1 online resource (x, 147 pages)
Rock glaciers -- United States, Glaciers -- United States, Glaciology, Meltwater, Riparian plants
Continental-scale inventories of glaciers are available, but no analogous rock glacier inventories exist. We present the Portland State University Rock Glacier Inventory (n = 10,343) for the contiguous United States, then compare it to an existing inventory of contiguous United States glaciers (n = 853), identifying geographic and climatic factors affecting the spatial distributions observed. At least one rock glacier is identified in each of the 11 westernmost states, but nearly 90% are found in just five; Colorado (n = 3889), Idaho (n = 1723), Montana (n = 1780), Utah (n = 834), and Wyoming (n = 849). Glaciers are concentrated in relatively humid mountain ranges, while rock glaciers are concentrated in relatively arid mountain ranges. Mean glacier area (0.60 ± 0.073 km2) is significantly greater than mean rock glacier area (0.10 ± 0.002 km2), though total glacier area (507.70 km2) is lower than total rock glacier area (1008.91 km2). Glacier and rock glacier areas, as a percent of small watersheds containing them, are modeled using geographically weighted regression. Glacier percent area (R2 = 0.55) is best explained by elevation range and mean fall snowfall, while rock glacier percent area (R2 = 0.42) is best explained by mean spring dewpoint temperature and slope standard deviation. Finally, we compare riparian vegetation along meltwater streams draining glaciers and rock glaciers. Initial 500 m long meltwater stream reaches emanating from a total of 35 pairs of collocated glaciers and rock glaciers were delineated, allowing estimation of riparian vegetation cover and density. Rock glacier meltwater stream riparian vegetation cover (mean cover = 86.2% ± 9.3%) and density (mean NDVI = 0.30 ± 0.02) are significantly greater (p-value < 0.05) than glacier meltwater stream riparian vegetation cover (mean cover = 64.5% ± 10.9%) and density (mean NDVI = 0.13 ± 0.01). This study shows that while the spatial distributions of glaciers and rock glaciers are both generally influenced by a combination of geographic and climatic variables, the specific forcings and local magnitudes are distinct for each cryospheric feature type, and processes inherent to rock glacier cryospheric meltwater sourcing positively influence first-order meltwater stream vegetation patterns.
Johnson, Gunnar Forrest, "Rock Glaciers of the Contiguous United States: Spatial Distribution, Cryospheric Context, and Riparian Vegetation" (2018). Dissertations and Theses. Paper 4507.