U.S. Department of the Interior / U.S. Geological Survey As the Nation's principal conservation JSG^ agency, the Department of the Interior S-§sa has responsibility for most of our nation- Glaciers: ~4j3] ally owned public lands and natural and s&y cultural resources. This includes foster- -^/ ing sound use of our land and water A Water Resource resources; protecting our fish, wildlife, and biological diversity; preserving the environmental and cultural values of our national parks and historical places; and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to ensure that their develop­ ment is in the best interests of all our people by encour­ aging stewardship and citizen participation in their care. The Department also has a major responsibility for American Indian reservation communities and for people who live in island territories under U.S. administration. What Is A Glacier? Glaciers: Any large mass of snow and ice on the land that persists for many years may be called A Water Resource a glacier. Glaciers are formed where, over a by Mark Meier and Austin Post number of years, more snow falls than melts. As this snow accumulates and becomes thicker, it is compressed and changed into dense, solid ice. Also, the mass of snow and ice tends to flow due to its own weight downhill if it is on a slope or out in all directions from the center if it is on a flat area. The ice in a glacier flows from the area of surplus snow accumulation to the area where yearly melting exceeds accumulation. Where the rate of iceflow balances the rate of icemelt or the rate of calving into the sea, the glacier ends. A strict definition of "glacier" is virtually impossible. Just as bodies of standing water range in size from huge lakes to small ponds, perennial ice masses range in size from the Antarctic ice sheet to tiny pockets of ice less than an acre in size. Few scientists would call Most Americans have never seen a glacier, these tiny ice patches "glaciers," yet they are and most would say that glaciers are rare fea­ hydrologically indistinguishable from glaciers in tures found only in inaccessible, isolated wilder­ all characteristic- but size and rate of flow. ness mountains. Are they really so rare? Or are Glaciers co,..j in many forms. Some are they really potentially important sources of water found in protected amphitheaters carved out of supply? Consider these facts: mountainsides by ice erosion (cirque glaciers) or on exposed slopes (slope glaciers). Others are About three-fourths of all the fresh water formed in the lee of ridges where snow is in the world equivalent to about 60 years of deposited by wind (drift glaciers). Large moun­ precipitation over the entire globe is stored as tain glaciers may flow down valleys (valley glaci­ glacial ice. ers). Relatively smooth land surfaces in high latitudes or on mountaintops may nourish radi­ In North America the volume of water ally flowing icedomes (icecaps). Extensive stored as snow and ice in glaciers is many times mountain glaciers (icefields) fill many adjoining greater than that stored in all the lakes, ponds, valleys, so that only the highest peaks and rivers, and reservoirs on the continent. ridges rise above the ice surface. Ice from glaci­ ers in the mountains may spread out at the foot In some States, such as Washington of a mountain range (piedmont glaciers). Vast and Alaska, glaciers exert an influential even a land areas covered by ice (ice sheets) occur in dominating effect on the supply of dry-season Greenland and Antarctica; these are similar in water and regulate naturally the streamflow to many respects to the ice sheets that covered balance the seasonal and year-to-year varia­ large parts of North America, Europe, and Asia tions in precipitation. during the ice ages. Where Do Glaciers Occur? California, Colorado, Idaho, and Nevada. Most In the conterminous (48) States, about of these are tiny cirque glaciers. The total sum­ mer streamflow derived from these glaciers in 1,650 glaciers cover a total area of about 587 an average year is equivalent to about 1.4 billion square kilometers (227 square miles) in parts of Washington, Wyoming, Montana, Oregon, cubic meters (360 million gallons or 1,107,000 Glacier Statistics by State Approximate Total Estimated July-August State number of glacier area streamflow from glaciers glaciers in km2 (mi2) in millions of m3 (gal.)* Alaska ** ? 74,700 (28,842) 187,000 (49,405,400) Washington 950 420 (162) 1,070 (282,694) California 290 50 (19) 80 (21,136) Wyoming 100 50 (19) 100 (26,420) Montana 200 42 (16) 80 (21,136) Oregon 60 22 (8) 50 (13,210) Colorado 25 1.5 (0.6) 2 (528.4) Idaho 20 1.5 (0.6) 3 (792.6) Nevada 5 0.3 (0.1) 0.5 (132.1) Utah 1 0.1 (0.04) 0.1 (26.4) * One million cubic meters is 264 million gallons, and would cover 811,000 acres to a depth of 1 foot, or would fill 24,000 standard railway tank cars (making a train about 240 miles long). ** See chart pages6and7 for breakdown of Alaska.! glaciers. Yentna Glacier, Alaska, is a fine example of a large valley glacier having many tributaries. The even, undistorted medial moraines mark the juncture of ice streams from adjacent tributaries. In the Location of glaciers in the Western United States. background is Mount Foraker (5,300 m or 17,400 ft.). 4 acre-feet) of water for the 2 months. Washing­ About 3 percent of Alaska (about 74,700 ton State alone has about 950 glaciers covering square kilometers or 28,800 square miles) is 420 square kilometers (160 square miles) yield­ covered by glaciers, which are mostly in moun­ ing a summer streamflow of about 1.1 billion tains not far from major population centers. Most cubic meters (280 million gallons or 870,000 of the major rivers originate at these glaciers. acre-feet) of water. The peculiar characteristics of glacial runoff peak flows in midsummer, distinct day-to-night differences in runoff, large silt content of stream water, and occasional outburst floods have a pronounced effect on the economy and pattern of life in Alaska. Data on the number, location, and area of glaciers in the United States are approximate; many glaciers occur in relatively inaccessible and poorly mapped areas. Inventories of glacial ice have been made in the North Cascade Range of Washington (1971) and the Sierra Nevada of California (1975). All ice masses that are at least 0.1 square kilometer (about 0.04 square mile) in area were counted. The larger number of glaciers in the latest inventory reflects the counting of smaller ice masses not counted in previous inventories, rather than an increase in ice-covered areas. Location of glaciers in Alaska. Alaskan Glaciers Approximate Area in km2 (mi2) NORTH Brooks Range 723 (279) WEST Seward Peninsula 3? (1.2)7 Kilbuk-Wood River Mtns. 230? (89)? SOUTHWEST Aleutian Islands 960 (371) Alaska Peninsula 1,250 (483) INTERIOR Alaska Range 13,900 (5,367) Talkeetna Mtns. 800 (309) Wrangell Mtns. 8,300 (3,205) SOUTH-CENTRAL Kenai Mtns. 4,600 (1,776) Chugach Mtns. 21,600 (8,340) SOUTHEAST St. Elias Mtns. 11,800 (4,556) Coast Mtns. 10,500 (4,055) APPROXIMATE TOTAL 74,700 (28,842) Changes in Glacial Streamflow Runoff, South The importance of glaciers as a source of Cascade Glacier water for use by people stems partly from the fact that the water is stored in winter when the need for irrigation and domestic water is least and becomes available during the heat of mid­ summer when the need for it is greatest. This unusual pattern can be seen by comparing streamflows in two watersheds in the North Cascade Range. Day Creek, draining rugged terrain with no perennial snow or ice, has a sea­ sonal distribution of streamflow that closely fol­ lows the seasonal precipitation pattern. The South Fork of the Cascade River, however, draining a high mountain basin about half cov­ ered with perennial snow and ice, has a stream- flow pattern in which the peak is in midsummer Jan. Feb. Mar. April May June July Aug. Sept. Oct. Nov. Dec. when very little precipitation occurs. Runoff and precipitation for two small drainage basins in the Glacier-fed streamflow not only varies with North Cascade Range, Washington. The basin of Day Creek is in the foothills and contains no perennial snow or the season but also changes markedly during a ice. Note that runoff from Day Creek follows precipitation single summer day. Usually the flow reaches a closely except from January to March, when a small amount peak in the late afternoon or early evening and a of the precipitation is stored as snow, and from April to June, when this water is released to the stream. On the other low in the early morning. Icemelt is usually hand, the seasonal runoff from South Cascade Glacier, as greatest at midday; the delay in the runoff peak measured near the glacier in the South Fork of the Cascade is due to the storage and movement of water in River, shows a pattern completely different from that of pre­ cipitation. Runoff is highest in July and August, which are the glacier. also the 2 months of least precipitation, and runoff declines almost to zero during the winter months of high precipitation. Blue Glacier, Olympic Mountains, I Washington, shows crevasses near the ' margin. The Natural Regulation of more runoff.