Discharges of Turbid Water during Mini-Surges of Variegated Glacier, Alaska, U.S.A.

• Published in: Journal of Glaciology
• Main Authors: Humphrey, Neil, Raymond, Charles, Harrison, Will
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1986
• Subjects: glacier; Journal of Glaciology; Alaska
• Online Access: http://dx.doi.org/10.1017/s0022143000015513; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000015513

Abstract Discharges of water, sediment, and dissolved impurities from Variegated Glacier, Alaska, were monitored in the early summers of 1980 and 1981 during the occurrence of mini-surges. Seasonal trends, weather-related events, and diurnal variations similar to behavior of other temperate glacier streams were found. The principal effect in the stream associated with mini-surge occurrence was a brief discharge of extremely turbid water. The turbidity is assumed to be introduced into the basal hydraulic system by initiation of the fast motion of a mini-surge at a time and location on the upper glacier known from other measurements. The mean water velocity in the hydraulic system over the intervening distance is thereby determined (0.3 ms −1 ). The mean water velocity, together with the water discharge (≈16 m 3 s −1 at the terminus), places constraints on the distribution of water velocity u and total cross-sectional area A T of the flow paths along the glacier base. This leads to the conclusion that within the zone of mini-surge occurrence in its unperturbed state: u is about 0.1 ms −1 or possibly less; A T is about 10 2 m 2 or possibly more, and it must be divided into a very large number of small passageways, be blocked by constrictions, or both. The total water cross-section corresponds to a layer 0.1–0.2 m thick when spread uniformly over the glacier width. The water velocity is close to or less than the propagation velocity of the mini-surges. Between the zone affected by mini-surges and the stream, a dynamically less active lower section of the glacier is probably underlain by a small number of conduits, in which the water velocity may be very high (≥ 2 m s −1 ). Water discharge following the mini-surges puts an upper limit on water-storage changes associated with the anomalous ice motion.