Rock glaciers in the Eastern Cascades, Washington State, USA: Impacts of selected variables on spatial distribution and landform dimensions

Recent regional-scale studies of rock glaciers have added much to our knowledge of rock glaciers and associated permafrost spatial distribution. In this study, we used Google Earth Pro imagery and selected field work to identify and classify 159 rock glaciers in the marine-influenced, continental margin, Eastern Cascades of Washington state in Western North America. Most rock glaciers are tongue-shaped, talus-derived, intact features. The majority are found in the Northeastern Cascades where temperatures are lower because of high elevations, high latitudes, and increasingly continental conditions. Most rock glaciers are also clustered around high peaks and ridges at the bases of cirque headwalls where steep, converging slopes provide ample debris. Dimensions of rock glaciers increase with increasing maximum elevation, area, relief, length, and slope of rocksheds. In comparison to other ranges, Eastern Cascades rock glaciers are generally small and low in spatial density, perhaps because of lower elevations and younger landscapes. Despite this, rock glaciers are significant components of the alpine/subalpine geomorphic continuum in the Eastern Cascades typically occupying late Pleistocene or Holocene cirques. Intact rock glaciers suggest that discontinuous permafrost currently exists down to ~1945 m elevation while relict features suggest that permafrost once extended down to ~1870 m elevation. As climate warms, slowly melting ice in rock glaciers will play a larger role in providing base flow for streams previously primarily supplied by snow and glacier melt