Mountain glacier mass change affects water resources, regional ecosystems and global sea level. Understanding the physical processes that control glacier mass change requires field measurements of winter snow accumulation and summer melt. Yet field measurements only capture discrete points across the glacier surface, which can result in systematic bias. Measurement stakes are not installed in locations with objective hazards, such as at the base of avalanche paths or in the middle of crevasse fields. Stereo imagery collected from airplanes or satellites captures spatially extensive glacier change that is difficult or impossible to measure from the ground. Researchers from the USGS Benchmark Glacier Project use open-source automated photogrammetry software and supercomputing resources to generate modern digital elevation models (DEMs) and orthorectified images from DigitalGlobe satellite imagery. These remote sensing products are used to quantify glacier area and elevation change across the entire glacier surface. Ongoing research collaboration with the University of Washington automates DEM generation from historical aerial photographs. DEMs from 1967–2016 (33 total), used in combination with historical field measurements collected across USGS benchmark glaciers in Alaska, Washington, and Montana, show that every studied glacier lost mass at area-averaged rates of –0.58 to –0.30 m water equivalent per year.
(A) Orthorectified image of Lemon Creek Glacier, Alaska, on 18 September 1957. Glacier outlined in blue. (B) Orthorectified image of Lemon Creek Glacier, Alaska, on 1 October 2018. Glacier outlined in blue. (C) Change in surface elevation on Lemon Creek Glacier, Alaska, from 1957 to 2018. Each image panel showing Lemon Creek Glacier is approximately 5 kilometers wide by 7 kilometers high, oriented with north to the top.
USGS researcher installing measurement stake on Wolverine Glacier in Alaska, September 2019.
Crevasses on Wolverine Glacier, September 2019. Photos by Louis Sass, USGS.