Glacier Disappearance in the High Alpine of Oregon, U.S.A.

Abstract:

The U.S. Geological Survey mapped and named 35 glaciers in Oregon during the mid 20th century, which was the last inventory of Oregon’s glaciers. All of Oregon’s glaciers reside in the high alpine zone of the Cascade and Wallowa Mountain ranges and serve as a buffer to provide a supply of water to mountain streams during low snow years. In recent years, local observations indicate many of the glaciers in Oregon are shrinking, but these glaciers are not included in major glacier inventories. Here we present an updated assessment of the number of glaciers in Oregon. First, we identify potential threshold glaciers using a power law that relates glacier area to glacier thickness from 1981 measurements of 19 glaciers in Pacific Northwest. We find that a glacier area threshold of ~0.1 km2 corresponds to a maximum ice thickness of ~29 m; we consequently use 0.1 km2 as an initial threshold for defining active versus stagnant glaciers. Preliminary findings using satellite imagery from 2011-2013 and 2013-2015 indicates 14 of Oregon’s 35 glaciers have receded to an area of <0.1 km2, meaning ~40% of Oregon’s glaciers are no longer glaciers. We are currently conducting fieldwork to verify if these glaciers are indeed no longer active glaciers by refining estimates of glacier area and assessing the remaining ice for the presence of crevasses and glacial ‘flour’ in the outwash streams. We will combine our field observations with the satellite-based assessment to provide a long overdue update for the inventory of Oregon’s glaciers.