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Combined
ice and water balances of Gulkana and Wolverine Glaciers, Alaska, and South
Cascade Glacier, Washington, 1965 and 1966 hydrologic years
By Meier, M.F., Tangborn, W.V., Mayo, L.R., and Post, Austin
U.S. Geological Survey Professional Paper 715-A, 23 p.
ABSTRACT
Glaciers occur in northwestern North America between lat 37°
and 69° N. in two major mountain systems. The Pacific Mountain
System, near the west coast, receives large amounts of precipitation, has very mild temperatures, and contains perhaps 90 percent
of the glacier ice. The Rocky Mountain or Eastern System, on the
other hand, receives nearly an order of magnitude less precipitation, has temperatures that range from subpolar to subtropic, and
contains glaciers that are much smaller in both size and total area.
As a contribution to the International Hydrological Decade program on combined balances at selected glaciers, the U.S. Geological
Survey is conducting studies of ice and water balance on four glaciers in the Pacific Mountain System: Wolverine and Gulkana
Glaciers in Alaska, South Cascade Glacier in Washington, and
Maclure Glacier in California. Similar data are being collected by
other organizations at five glaciers in western Canada, including
two in the Rocky Mountain System, and at one glacier in the
Rocky Mountain System in northern Alaska.
Gulkana, Wolverine, South Cascade, and Maclure Glaciers have
dissimilar mass balances, and each is fairly representative of the
glaciers for its particular region. Gulkana Glacier (lat 63°15' N.,
Alaska Range, Alaska) normally has an equilibrium line at an altitude of 1,800 m (meters), an activity index of about 6 mm/m
(millimeters per meter), a winter balance of about 1.0 m, and an
annual exchange of about 2.2 m. (Balance values are given in terms of
water-equivalent measure; the winter balance of 1 m, for example, indicates a volume of ice equal in mass to a volume of water
1 m in depth covering the area of the glacier.) The normal approximate parameters for the other glaciers studied are as follows:
Wolverine Glacier (lat 60°24/ N., Kenai Mountains, Alaska)
equilibrium-line altitude 1,200 m, activity index 9 mm/m, winter
balance 2.5 m, and annual exchange 5.5 m; South Cascade Glacier
(lat 48°22' N., North Cascades, Wash.)-equilibrium-line altitude
1,900 m, activity index 17 mm/m, winter balance 3.1 m, and
annual exchange 6.6 m; and Maclure Glacier (lat 37°45' N., Sierra
Nevada, Calif.)-equilibrium-line altitude 3,600 m, activity index
23 mm/m, winter balance 2.3 m, and annual exchange 4.6 m.
Mass balances of these four glaciers and their drainage basins
are measured annually by standard glaciological techniques. In
addition, the hydrologic balance is calculated using streamflow and
precipitation measurements. Combining these independent measurements results in fairly well defined values of water and ice
balance for the glaciers and drainage basins. A revision of the
standard International Hydrological Decade mass-balance system
permits combination of annual and stratigraphic terms.
The annual balance of South Cascade Glacier at the end of the
1965 hydrologic year was slightly positive (+0.07 m averaged over
the glacier), but continued ablation and deficient accumulation in
October 1965 resulted in slightly negative net balances for both the
glacier and the drainage basin. Factors tending to produce this
near-zero balance were the above-average late-winter balance
(3.48 m) and the numerous summer snowfalls. Ice ablation averaged about 39 mm of water per day during the main melt season.
Runoff during the summer ablation season was lower than the
1958-64 average.
The South Cascade Glacier annual balance in 1966 (-0.94 m) was
considerably more negative mainly owing to the deficient winter snowpack (the late-winter balance was only 2.52 m) and the
warm dry summer. Ice ablation averaged about 44 mm of water
per day during the melt season. The loss in storage of this
and other glaciers in the North Cascades increased the runoff of
many valley streams by approximately 50 percent during August
and September.
The 1966 Gulkana Glacier annual balance was slightly positive
(+0.06 m); on the basis of past observations and the rapid terminus retreat of this glacier, this value is considered unusual.
Accumulation (late-winter balance) was probably near the average
of recent years. The ablation season was quite short, ending over
most of the glacier on August 15; this factor alone probably
accounts for the slightly positive balance. Ice ablation averaged
approximately 26 mm of water per day during the melt season.
Runoff from this glacier was not measured in 1966 but is estimated
on the basis of ice-balance and precipitation data to be about 2 m,
which is 5-10 times the amount measured in nearby lower altitude
basins.
In the Kenai Mountains of Alaska, the 1966 Wolverine Glacier
annual balance was negative (- 0.26 m); the winter balance
(1.83 m) was based on precipitation records at nearby Seward and
was probably deficient. Ice ablation was heavy during the summer
(about 50 mm of water per day average).
Collection of data on ice and water balance for Maclure Glacier
began in late 1966 and will be given in subsequent reports.
Contents
Abstract
Introduction
Regional physical and climatic setting
Geology
Climate
Ice balance and altitude
Glaciers of the Pacific Mountain System
Glaciers of the Rocky Mountain or Eastern System
Glaciers of the Interior System
Descriptions of individual glaciers
Gulkana Glacier
Wolverine Glacier
South Cascade Glacier
Maclure Glacier
Measurements
Ice-balance terms
Evaluation of errors
1965 hydrologic year
South Cascade Glacier
1966 hydrologic year
South Cascade Glacier
Gulkana Glacier
Wolverine Glacier
References
Meier, M.F., Tangborn, W.V., Mayo, L.R., and Post, Austin, 1971, Combined
ice and water balances of Gulkana and Wolverine Glaciers, Alaska, and South
Cascade Glacier, Washington, 1965 and 1966 hydrologic years: U.S. Geological
Survey Professional Paper 715-A, 23 p. 6 pl.
[Full report body, Acrobat PDF (12
MB)] [6 Plates, Acrobat PDF (76
MB)]
Report from USGS
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Maintainer: Rod March
Last update:
Tuesday, June 05, 2007 04:14 PM
URL: http://ak.water.usgs.gov/glaciology/reports/1971_pp715A/index.htm
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