adjacent to planetary atmosphere glacial surface layer glacial summer surface 2019-04-24T20:10:03Z A glacial surface layer which is present at the point in time where any given part of a glacier reaches its minimum annual mass. Note that the glacial summer surface is diachronous. The time that the summer surface is present on a glacier can vary from point to point along the entire glacier. That is, while a high-elevation region of a glacier may have reached its minimum, lower elevation regions may still be ablating. The summer surface is the surface on which the first snow of the new balance year falls. It is easily detectable when it consists of glacier ice, which now includes superimposed ice added during the previous balance year. In the firn area it is recognizable as a well-marked crust, that is, a thin, relatively strong layer with a density near that of ice, and sometimes also (or instead) as a layer of depth hoar at the base of the current year's accumulation. The crust typically originates by recrystallization of the surface snow in late summer to form glaze. It may also be marked by an accumulation of sediment or wind-blown dust. It can be difficult to detect when melting and snowfall alternate during the transition between the ablation season and the accumulation season. In some mass-balance programmes the summer surface is 'labelled' in the vicinity of stakes with a distinctive material, such as sawdust, during a visit late in the ablation season.