Snow, Ice, Avalanches, and Glaciers - Mountain Geography: Physical and Human Dimensions - page 186

mountains receive so little precipitation that the contribution of rime and hoarfrost is
often greater than that of snow. At the same time, there is little or no melting. Calving-
of of icebergs when glaciers move into the sea is the principal method of depletion. At
the other extreme, tropical mountains often display a curious situation: The lower part
of the glacier receives more precipitation than the higher part (owing to the zone of
maximum precipitation), and melting may take place every day of the year rather than
just during summer. Consequently, tropical glaciers are typically quite short. There are
also major differences in environmental conditions through time.
FIGURE 4.30 Several small cirque glaciers along a northeast-facing ridge in the central Sierra
Nevada, California. The photo was taken in late September 1972, and the snowline (firn line)
shows up between the bright white tone of firn and the darker gray tone of glacial ice. The lobate
deposits represent very recent morainal material; the bare rock further downslope owes its ex-
posure to strong ice scouring in the past when glacial ice coverage was more extensive. (Austin
Post, U.S. Geological Survey.)
FIGURE 4.31 Longitudinal section of a typical valley glacier showing areas of accumulation and abla-
tion separated by the annual snowline (or equilibrium line). Long arrows within the glacier rep-
resent flow streamlines. (After Sharp 1960: 9 and Flint 1971: 36.)