Geography decides a glacier’s shape: valley, cirque, piedmont, or niche. On precipitous north-facing mountain slopes, a niche glacier (also known as a pocket glacier) forms when snow ﬁlls a cup-shaped depression in a mountainside. Over years, this snow resists melting, compacts to glacial ice, spills over the lip of its rock niche, and begins to move. This smallest glacier type takes up only the space of a gully or hollow on a steep slope and resembles a large snowﬁeld. Rarely, niche glaciers are natal forms of larger glaciers, evolving into a cirque (or corrie) glacier, which in turn may evolve into a valley glacier. More often, however, niche glaciers are remnants of cirque glaciers that have shrunk, a phenomenon more common in recent decades as a result of global warming.