Sediment Source for Melt-Water Deposits

Abstract

A question is posed regarding the source of melt-water sediment. Does stagnant ice, functionally separated from active ice and gradually melting in place, contain enough rock debris to account for the volume of melt-water deposits known to exist in deglaciated areas, or does the volume of these deposits require a sediment source in close association with active ice from which the supply of rock debris is continually replenished?Differing opinions on this question are implied in two contrasting models for deglaciation in the north-eastern United States. One, involving regional stagnation, assumes a sediment source in stagnant glacier ice; the other, involving stagnation-zone retreat, considers active ice the principal sediment source. This paper presents reported values of debris content in glacier ice and uses these values to calculate theoretical sediment volumes for a small drainage basin (1 300 km2) in northeastern U.S.A.A typical value for the amount of rock debris in temperate glacier ice is 25% (volume) debris content in a 400 mm-thick basal debrisrich zone. This value gives a calculated sediment volume of 0.13 km3, about 6% of the estimated actual volume of melt-Hater sediment in the test basin. Comparison of calculated theoretical sediment volume with the estimated actual sediment volume in the basin indicates that stagnant ice is an inadequate sediment source, and that active ice, rather than stagnant ice, is probably the principal sediment source for melt-water deposits.