The Editor,

The Journal of Glaciology

Sir,

A project undertaken from the Base Camp of the Sierra Club, high on the east slope of the Sierra Nevada, in California, will have interest for glaciologists. This work is summarized in a report describing studies of run-off from a small isolated snow bank at 12,200 ft. (3718 m.) elevation on Middle Bishop Creek (lat. 37° 10′ N., long. 118° 38′ W.), authored by Gene Serr II, Gene Serr III, and Oliver Kehrlein, members of the Sierra Club. The work was assisted by other members of that organization.

It was desired to test Matthes’ earlier statement to the effect that almost all of the snow above 12,000 feet in the Sierra Nevada evaporates so there is little run-off from snow melt at and above this elevation. On 19 July and again on 2 August 1950 the amount of water represented by a selected snow bank was determined by careful survey of its size and density. The amount of run-off was measured over this period through a weir set on bedrock below the snow bank. These measurements showed that approximately 99 per cent of the wastage ran off through the weir, leaving about 1 per cent for evaporation and other losses. These run-off figures were checked and confirmed by measuring the amount of water derived from melting of snow blocks of known size and density under natural conditions. These blocks gave a 97.3 per cent yield on melting.

It is recognized that considerable condensation may have occurred and that for this reason the total run-off is not an exact measure of the amount of melting. Nonetheless, the conclusion appears justified that evaporation was a relatively minor factor in the wastage of this snow bank, for evaporation certainly could not occur while vapor was condensing on the snow, and the total amount of water supplied by condensation need be only a small fraction of that produced by melting. These results strongly suggest that evaporation occupies a relatively minor part in the ablation of snow in areas above 12,000 feet in the Sierra Nevada. This, of course, is in keeping with the relatively insignificant rôle of evaporation in ablation previously determined by Sverdrup and Wallén.

19 January 1951