Equilibrium line/zone

The line or zone on a glacier’s surface where a year’s ablation balances a year’s accumulation (cf. Firn line). It is determined at the end of the ablation season, and commonly occurs at the boundary between superimposed ice (q.v.) and glacier ice.

The arrow in this photo actually points out the firn line. However, as the photo was taken near the end of the ablation season, the firn line more-or-less coincides with the equilibrium line. Aerial photo J. Alean.

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