Snow, Ice, Avalanches, and Glaciers - Mountain Geography: Physical and Human Dimensions - page 205

FIGURE 4.42 Cirques and glacial lakes in the Wind River Mountains, Wyoming. The glacial features
may be cut into an older erosional surface composed of subdued and gently rolling uplands, al-
though there are other interpretations of this relationship. (Austin Post, U.S. Geological Survey.)
Since cirques require a glacier for their full expression, the presence of cirques in
areas not now glaciated indicates the former existence of glacial ice. It is generally es-
timated that the level of cirque floors roughly approximates the annual snowline that
existed when the cirques were made (Trenhaile 1976). Plots of the elevation and ori-
entation of cirques in different regions have provided a great deal of information about
past climatic conditions. As with all natural phenomena, however, caution must be used
in their interpretation. For example, the formation of cirques may take a long time, and
most areas have experienced more than one glaciation. Also, cirques may have been oc-
cupied and reoccupied during several glacial periods. Once a depression is formed, it
provides a greater reservoir for snow collection and greater protection from melting, so
that more snow will accumulate and less will melt than on surrounding slopes. When
one cirque sits above the other, the two may coalesce to form one large cirque. This may
be the reason why a single cirque exists at the head of many mountain valleys. In other
cases, cirques are simply enlarged with each glaciation, so their present level is not a
true representation of the most recent snowline but is, instead, a composite feature res-
ulting from a combination of events. Despite these problems, cirques can provide excel-