Increasing glacier area loss in the Oregon central Cascades, USA

Abstract. The Oregon Cascades in the Pacific Northwest of the United States contain six glacierized volcanos. Here we document the 2023 glacier extents on five volcanos in the Oregon central Cascades: Broken Top, the Three Sisters (South, Middle, and North), and Mt. Jefferson. Using prior extent data from 2018 (Three Sisters and Broken Top) or 2020 (Mt. Jefferson) and 1990, we show that the glaciers on these summits lost ~ 20 % of their area between 2018/20 and 2023 and ~ 26 % of their area between 1990 and 2018/20. Glacier area loss thus increased 4.5- to 6.1-fold from ~ 0.6–1.9 % yr^-1 (1990–2018/20) to ~ 3.2–11.3 % yr^-1 (2018/20–2023). These rates of recent glacier area loss are unprecedented in each volcano’s recorded history. When combined with 2015/16 and 2023 glacier extents for the sixth volcano in the Oregon Cascades (Mt. Hood), we find that recent rates of glacier area loss are only correlated with measures of glacier size: glaciers with a smaller elevation span (p = 0.0005) and smaller area (p = 0.0018) are losing area faster. Because the Oregon Cascade summers of 2014–2023 were ~ 0.7 °C warmer than the 1985–1994 mean and ~ 1.5 °C warmer than the 1975–1984 mean, warming magnitudes sufficient to raise equilibrium lines above the headwalls of many of Oregon’s smaller glaciers, we attribute the increased rate of Oregon Cascade glacier area loss to this warming climate.