Geological Survey Professional Paper 715—A Combined Ice and Water Balances of Gulkana and Wolverine Glaciers, Alaska, and South Cascade Glacier, Washington, 1965 and 1966 Hydrologic Years

GULKANA GLACIER

Gulkana Glacier is a branched valley glacier in interior Alaska on the south-facing flank of the eastern Alaska Range. These mountains are generally high, having individual peaks up to 3,000 m in altitude, and are very rugged. Bedrock is a complex of Precambrian metamorphic rocks, Mesozoic intrusive and volcanic rocks, and sedimentary rocks ranging from Paleozoic to Quaternary in age. Some of the larger glaciers of the area, such as the Gakona, Canwell, and Black Rapids, are subject to periodic surging; there is some evidence that the Gulkana Glacier may have surged 20 or more years ago. Gulkana Glacier is easily accessible from the Richardson Highway near Isabel Pass (pl. 2A, map).

Ice and snow in four adjacent cirques form the accumulation area of Gulkana Glacier. These cirque glaciers converge in a simple south-flowing tongue that forms the ablation area, 4 km in length; the terminus, which is lightly covered by debris, has an altitude of approximately 1,160 m (pl. 2A, photo). The ELA is about 1,800 m. Gulkana Glacier drainage basin (31.6 km²) contains Gulkana Glacier (21.8 km²), several smaller glaciers and perennial snowfields (2.6 km²), and a fairly large area of ice-cored moraine (1.5 km²). In this report, the snow and ice balances of all active glaciers and perennial snowfields (69 percent of the basin area) are reported together. Ablation from the ice-cored moraine is reported in the basin totals only. Drainage from the glacier flows over an outwash plain and in the past has flowed into Summit Lake, 11.5 km south of the glacier; in recent years the stream has been directed westward to the Delta River (pl. 2A, map).

Gulkana Glacier has the highest latitude of the four discussed here (63°15' N.). Although it is within the Pacific Mountain System, the Chugach Mountains and the Copper River Lowland lie between the glacier and the Pacific Ocean. The local climate verges on the continental, as is indicated by the following low values, measured in recent years: A1, 6 mm/m; winter balance, 1.0 m; and annual exchange, 2.2 m. In mean altitude, accumulation, ablation, and recent activity, Gulkana Glacier is considered to be fairly representative of the glaciers in this region.

This glacier has been studied by University of Alaska research groups frequently since International Geophysical Year investigations were initiated in 1957. The recent history of Gulkana Glacier shows advances in 1580, 1650, 1830, and 1875. The maximum advance, in 1830, extended more than 2.5 km beyond the present terminus position. Since 1875 this glacier has been steadily retreating (Reger, 1968). Measurements of snow and ice balances in Gulkana Glacier basin were begun in 1966 as part of the United States contribution to IHD studies of combined balance on selected glaciers.

WOLVERINE GLACIER

Wolverine Glacier is a valley glacier in the Kenai Mountains, Kenai Peninsula, in south-central Alaska. The glacier is 12 km southwest of Kings Bay, a fiord extending inland from the Gulf of Alaska (pl. 2B, map). Although the Kenai Mountains are fairly low, extensive icefields (fig. 2) and many hundreds of small glaciers are present. The large ice masses result from extremely heavy snowfall; their mean ELA averages about 1,000 m—the lowest in western North America. The bedrock is primarily eugeosynclinal deposits of slate, graywacke, and pillow basalts intruded by granodiorite. Access to Wolverine Glacier is usually by skiplane landing on the glacier or by floatplane landing on Paradise Lakes 3 km to the southwest.

The accumulation area of Wolverine Glacier is in a gently sloping basin 4 km wide; from this basin the ice descends by a steep icefall to a valley tongue 5 km long and tapers from a width of 1.5 km to a sharp-pointed terminus at an altitude of 370 m (pl. 2B, photo). The glacier is almost free of debris, is moderately crevassed, and is the most active glacier of those described in this report. Wolverine Glacier drainage basin (24.9 km²) includes Wolverine Glacier and several perennial snow fields (18.0 km²), two small areas of ice-cored moraine (0.13 km²), and numerous small lakes in an unglacierized tributary basin. The glacier and perennial snowfields constitute 72 percent of the basin area. The stream issuing from the glacier flows down a narrow gorge to Nellie Juan River, which empties into Kings Bay. The glacier was approximately 1 km longer 50-100 years ago.

Wolverine Glacier lies in the precipitation shadow of the Sargent Icefield. Even so, it has a very maritime climate characterized by fairly high precipitation totals. The winter balance, 2.5 m, and annual exchange, 5.5 m, are high; the ELA, 1,200 m, is low; and the A1, 9 mm/m, is moderate. Wolverine Glacier is considered to be fairly representative of the small glaciers of the Kenai Mountains and the coastal side of the Chugach and St. Elias Mountains.

The U.S. Geological Survey studies initiated in 1966 are the first scientific investigations made on this glacier. Reconnaissance measurements of snow and ice balances in Wolverine Glacier basin were begun in 1966 as part of the United States contribution to the IHD.

SOUTH CASCADE GLACIER

South Cascade Glacier is a valley glacier on the western slope of the main divide of the North Cascades in north-central Washington State (pl. 2C, map). These rugged mountains, consisting of a complex of high ragged ridges and deep narrow valleys, were heavily glaciated in Pleistocene time, and the peaks and valleys are strikingly sculptured by ice erosion. More than 700 glaciers, ranging in size from ice patches 0.1 km² in area to glaciers covering up to 7 km², are on the high peaks and ridges in the west and central part of the mountains (Post and others, 1971) where winter precipitation is very heavy (up to 4,500 m annually). East of the Cascade divide precipitation is much less; the glaciers are small and are restricted to the highest peaks. Bedrock in the vicinity of South Cascade Glacier includes banded inigmatite, quartz diorite, biotite schist, and metaquartz diorite.

South Cascade Glacier is in the heart of the North Cascades in the Glacier Peak Wilderness Area. Access to the glacier is generally by foot over rugged brushy terrain through the canyon of the South Fork Cascade River. A special agreement between the Geological Survey and the U.S. Forest Service permits limited access by helicopters and aircraft for scientific purposes.

Glaciers in the North Cascades are so varied in size and configuration that no single glacier can be considered typical. South Cascade Glacier is larger, has a lower gradient, and lies at a lower altitude than most other glaciers in the region. Perhaps its most distinctive characteristic is a low accumulation basin which actually lies below the altitude of trees on some adjoining slopes. The basin occupies a small north-facing valley, and the glacier now terminates at the edge of a small deep lake. The lake drains to the South Fork Cascade River, a tributary of the Skagit River which discharges into Puget Sound 100 km to the west. The area covered by the trunk or main glacier and by snow or ice in the drainage basin that remains permanently connected to the main glacier is 2.9 km². The South Cascade Glacier drainage basin (6.1 km²) is approximately 54 percent glacierized; the main glacier accounts for 47 percent and the disconnected patches of snow and ice 7 percent of the total drainage area. The A1 of South Cascade Glacier, 17 mm/m, is relatively high; ELA, 1,900 m, is moderately low; the winter balance, 3.1 m, is high; and the annual exchange, 6.6 m, is also high.

In recent times South Cascade Glacier shows evidence of advances in 2700-2900 B.C., the 16th century, and the middle and late 19th century (Meier, 1964). The maximum advance, when the terminus was 1.4 km beyond its present position, occurred about 1600. Since 1928, when the glacier filled the basin of the present lake (pl. 2C, photos), the glacier has thinned and retreated almost continuously. Between 1928 and 1944, the annual balance was estimated to have averaged approximately -1.7 m; between 1945 and 1965, it averaged approximately -0.6 m (Tangborn, 1968). The dynamic response characteristics of South Cascade Glacier have been analyzed by Nye (1963, 1965). Detailed glaciological studies have been conducted on this glacier by the Geological Survey since the International Geophysical Year (Meier and Tangborn, 1965).

MACLURE GLACIER

Maclure Glacier is one of several small cirque glaciers near the crest of the Sierra Nevada in Yosemite National Park, Calif. The High Sierras embraces an area approximately 600 km long north to south and 130 km m width. Unlike the North Cascades and other mountains farther north, the Sierra Nevada chiefly consists of a high, rolling, moderately dissected upland. Here massive granitic rocks have been unroofed by erosion. Much of the area displays spectacular effects of Pleistocene glaciation—Yosemite Valley is one of the world's finest examples of glacial erosion. The present glaciers are tiny vestiges of ice confined to protected nooks in the highest parts of the range. Maclure Glacier occupies a high shallow cirque on the north side of Mount Maclure and is the easternmost of the Lyell Glaciers (pl. 2D). Access is by foot from Tuolumne Meadows or by helicopter.

Maclure Glacier is 0.5 km long and covers an area of 0.2 km². Below the clean ice of the glacier, a thick moraine, probably ice cored, presumably represents the Neoglacial extent of this glacier. The local climate shows maritime characteristics (Maclure Glacier's A1 is 23 mm/m, its winter balance is 2.3 m, and its annual exchange is 4.6 m) in spite of a very high ELA of 3,600 m. Runoff from the 0.97-km² drainage basin containing Maclure Glacier flows into Tuolumne River, which flows west into the San Joaquin Valley of California.

It is interesting to note that the first quantitative glacier studies on the continent were evidently conducted on this glacier in 1872 by the famous naturalist John Muir. Among his studies were observations of glacier movement, which amounted to about 2 cm per day near the center of the glacier. Since then the glacier has been observed by many visitors in Yosemite National Park, and its growth and decline have been measured by the U.S. National Park Service at frequent intervals. Studies of ice and water balances were initiated by the Geological Survey in the summer of 1966 as part of the United States contribution to the IHD. These data will be presented in subsequent reports.