Oregon central Cascade glaciers lost about 20 % of their area from 2018/20 to 2023

Why it matters

Oregon’s volcano glaciers have no reference glacier nearby, and remote sensing alone has missed their losses. Field-checked maps give a truer record. The results suggest many small glaciers may no longer be sustainable in the current climate. This is a preprint and has not been peer reviewed.

What they did

The team mapped 2023 glacier outlines on Broken Top, the Three Sisters and Mt. Jefferson. They traced outlines by hand on satellite images and walked the glacier edges to check them. They compared the outlines with earlier maps from 1990 and 2018/20, and added Mt. Hood data. They then tested which glacier traits go with fast area loss and compared the losses with regional temperature and precipitation records.

Key findings

• Every glacier in the Oregon central Cascades lost area between 2018/20 and 2023. Together they lost about 20 % of their area, after about 26 % lost from 1990 to 2018/20.
• Area loss rose from about 0.6-1.9 % yr-1 (1990-2018/20) to about 3.2-11.3 % yr-1 (2018/20-2023). Broken Top was fastest at 11.33 % yr-1.
• These rates are the fastest in each volcano’s record, going back to 1949 for Broken Top, 1925 for the Three Sisters and 1967 for Mt. Jefferson.
• Across 33 glaciers including Mt. Hood, smaller glaciers lost area faster. Smaller elevation span (p = 0.0005) and smaller area (p = 0.0018) both went with faster loss. Latitude, aspect, slope and mean elevation showed no significant link.
• Summers in 2014-2023 were about 0.7 °C warmer than 1985-1994 and about 1.5 °C warmer than 1975-1984. Winter precipitation did not differ significantly.

Limitations

• The 1990 and 2018/20 maps come from other studies. The 1990 mapping gave no area uncertainty, so the authors applied their own ± 7 % estimate. The 2018/20 maps used remote sensing without field checks.
• Some glaciers lacked data in one of the three inventories and were left out of the rate comparisons. These were Milk Creek, Thayer and Ruspen.
• The link to warming rests on regional climate records and a first-order estimate of how far the equilibrium line rose, not on a direct glacier mass balance model.

Glossary

• Equilibrium line altitude (ELA): The elevation on a glacier above which snow gain exceeds melt over a year.
• Elevation span: The height difference between a glacier’s headwall (top) and its terminus (lower end).
• Geodetic mass balance: A glacier’s mass change estimated from repeated satellite measurements of surface height.
• Glacier inventory: A map-based record of the outlines and areas of glaciers at a given date.