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Ethan Welty, a doctoral student in environmental studies at CU-Boulder, took this shot of Kevin Steffa walking across the Sulphide Glacier below the summit of Mount Shuksan on Sept. 2 in Washington’s North Cascades. The 9,131-foot mountain is a sprawling massif of sheer rock faces, tree-drenched valleys and lofty alpine basins. It’s home to most of the glaciers in the lower 48.

Photo by Aurora photosÌý