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Conversely, if the loss of volume (from evaporation, sublimation, melting, and calving) exceeds the accumulation, the glacier shows a negative glacier mass balance and the glacier will melt back. When a glacier is experiencing an accumulation input by precipitation (snow or refreezing rain) that exceeds the output by ablation, the glacier shows a positive glacier mass balance and will advance. By early August 2017, the lake had completely drained. The river has started to carve a path through the toe of the glacier. Khurdopin glacier has dammed the Shimshal River, forming a glacial lake. Glaciers of Shimsal Valley from space, May 13, 2017. A longterm monitoring of the ELA may be used as indication to climate change. The equilibrium line altitude (ELA) and its change over the years is a key indicator of the health of a glacier. The glacier equilibrium line is the line separating the glacial accumulation area above from the ablation area below.
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Various features include large ravines called cirques and arêtes, which are ridges where the rims of two cirques meet. Alpine glaciers tend to make topography more rugged by adding and improving the scale of existing features. Alpine – ice flows down the valleys of mountainous areas and forms a tongue of ice moving towards the plains below.There are two general categories of glaciation which glaciologists distinguish: alpine glaciation, accumulations or "rivers of ice" confined to valleys and continental glaciation, unrestricted accumulations which once covered much of the northern continents.
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Glaciers can be identified by their geometry and the relationship to the surrounding topography. This mountain glacier is one of many coming down from the interior ice cap on top of the Byam Martin Mountains. A Bylot Island glacier, Sirmilik National Park, Nunavut.