Meltwater behavior in firn on upper Seward Glacier, St. Elias Mountains, Canada

Abstract

Studies of the volume and percolation velocity of daily meltwater flow were made in the firn of upper Seward Glacier, Canada, during the summers of 1948 and 1949 as an activity of Project Snow Cornice. The study area is situated in the heart of the St. Elias Mountains along the Alaska-Yukon border, 60° 23' N. Lat. and 139° 53' W. Long., at an elevation of 1790 meters, about 870 meters above firn limit. The data reported pertain to vertical meltwater circulation through the 1948-49 firn layer in an isothermal condition at 0° C. Attempts to measure horizontal flow were largely unsuccessful. Meltwater moves downward through this firn layer in a series of daily waves. Up to a depth of at least 2.4 meters these waves build up rapidly and then taper off more slowly after the crest has passed. At greater depth, 3 and 3.4 meters, the waves are more symmetrical in form, and the meltwater flow is more sustained, lacking the complete cessations which occur at shallower depths. The average rate of meltwater percolation downward to a depth of 3.4 meters was roughly 12 cm/hr, but it dropped to 6-7 cm/hr near the base of the 1948-49 firn layer owing to greater density and more horizontal ice bodies in the firn. Other variations in rate and volume of flow at different depths and at different times are attributed to inhomogeneities within the firn which affect meltwater circulation. The largest volume of meltwater flow recorded was 0.17 cc /cm²/hr. Various observations suggest that a large intermontane glacier, such as the upper Seward, may have a normal water-table relation. In the summer of 1948 the firn and ice of this glacier at and below a depth of 19-21 meters were seemingly saturated with water, and water stood at this level in open crevasses. In 1949, the water table lay at greater depth, somewhere below 27 meters, owing to reduced melting. This "ground water" helps sustain the year-around flow of large subglacial streams emerging from the edge of the Malaspina Glacier to which the Seward is tributary.

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