trimline
**Definition:** A visible boundary on the wall of a glacier valley marking the maximum recent thickness of the ice — a horizontal line separating weathered rock above (which was exposed to the sky) from polished or unweathered rock below (which was covered by ice). The trimline is the glacier's high-water mark, etched into the valley wall. As glaciers thin and retreat, trimlines become increasingly visible — stark evidence of how much ice has been lost.
A visible boundary on the wall of a glacier valley marking the maximum recent thickness of the ice — a horizontal line separating weathered rock above (which was exposed to the sky) from polished or unweathered rock below (which was covered by ice). The trimline is the glacier's high-water mark, etched into the valley wall. As glaciers thin and retreat, trimlines become increasingly visible — stark evidence of how much ice has been lost.
Etymology
English compound — the line to which the glacier was trimmed, or the line that trims (marks) its former extent.
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