WEATHER DURING THE 1967 HYDROLOGIC YEAR
The weather along the west coast of North America during the 1966-67 accumulation season (October 1966 through May 1967) was notable for two reasons. First, persisting low pressure troughs from lat 30° to 50° N. in the east Pacific during November, December, January, and April caused an increased westerly flow of moist Pacific air and produced extremely high precipitation in California and above normal precipitation in Washington and other Western States. North of this intense cyclonic activity a blocking ridge of high pressure extended from the mid-Pacific often into the Aleutians. This high pressure system replaced the usual low pressure storm track in this region. The resulting flow created unusually dry conditions in coastal Alaska from November through May.
During the summer ablation season, conditions were nearly reversed. A strong ridge of high pressure developed over the Rockies in July, causing subnormal precipitation and high temperatures along the Western Coastal States. Conversely, an Arctic low persisted throughout most of the summer, directing cold air flow and a southwesterly current of warm moist Pacific air from a low pressure cell in the Bering Sea produced extremely heavy precipitation in central and southern Alaska (U.S. Department of Commerce, 1967).
The problem of making accurate measurements on glaciers to balance properly the solid and liquid input and output to the hydrologic system is well known (Schytt, 1970; Stenborg, 1970; Björnsson, 1971; Tangborn and others, 1975). Accurate surface measurements of precipitation and ablation are difficult to obtain over large, rugged areas of glacier-clad mountains. Measurements of outflow (runoff) are usually considered more accurate but important hydrologic information is masked by the space and time integration of streamflow. The glacier interior and bottom are poorly known regions in which measurements are difficult. The water flow and storage in a glacier is complicated by the fact that ice and snow permeability is strongly affected by the presence and passage of water; thus one cannot apply the simple laws of flow and storage in porous media. The result is that glaciologic and hydrologic events in a glacier basin are usually non-synchronous and attempts to relate them directly, without a complete understanding of the glacier's internal drainage system, lead to serious errors. Relating ice and water balances over a year avoids some but not all of the errors.
In this report, the results of the ice and water balance measurements made on four glaciers are presented but no attempt is made to interpret the water transmission and storage in the glaciers. Discrepancies between the glaciologic and hydrologic measurements which occur could be due either to errors in the data or to the delay of stored water. In general, these measurements are not accurate enough to detect, with any certitude, subtle changes in liquid storage within the glaciers as was done on South Cascade Glacier in 1970 (Tangborn and others, 1975).
The glaciologic measurements to obtain ice and snow balance values follow the combined annual and stratigraphic system defined earlier (Mayo and others, 1972). All reported balances, precipitation, and runoff are water equivalent values. It is important to remember that mass changes as observed on a glacier's surface are not necessarily immediately reflected in stream discharge from the glacier and drainage basin. The result is a complex and highly variable relationship between ablation, glacier storage, and runoff.
Last Updated: 28-Mar-2006