Predicted timing of the disintegration of the lower reach of Columbia Glacier, Alaska

Abstract

Grounded, iceberg-calving glaciers terminating in shallow water advance or retreat slowly; those terminating in deep (>80 m) water retreat rapidly (>.5 km/y, table 1). Columbia Glacier is retreating off a terminal-moraine shoal so that the water depth at its terminus is deepening with time. This report predicts that the rate of retreat of Columbia Glacier will accelerate during the next two or three years, and that the annual discharge of icebergs will increase to a peak of about 8-11 km 3 /y (6-8 times the 1978 value) in the period 1982 to 1985 (figure 8). This prediction has an uncertainty of timing of at least one year. The maximum rate of calving is expected to be in late summer. It is expected that the glacier will have retreated about 8 km by 1986, and that retreat will continue for several decades. This prediction could be refined markedly by comparing the predictions with new monitoring activities on the glacier.

Iceberg calving and the glacioclimatic record

“…Echelmeyer and Harrison (1989;) measured velocity variation of as much as 35% with the tide, whereas velocities at grounded calving fronts only vary by about 10% with tide (Walters and Dunlap, 1987;Krimmel and Vaughn, 1987;Walters, 1989). Grounded calving events are statistically uncorrelated with the state of the tide (Meier et al, 1980;Brown et al, 1982). Cyclic level changes of lakes are seasonal rather than diurnal, but spring lake rises can lead to substantial calving events (Holdsworth, 1973;Theakstone, 1989).…”

“…ii Subglacial runoff During observation periods of less than a year, there is a strong, apparently causal relationship between calving and subglacial water discharge: calving speed increases follow increased activity of the basal hydrological system (Theakstone and Knudsen, 1986;Meier et al, 1980). Additions to the subglacial meltwater system can lead to increased basal sliding on scales of hours to months (Meier and Post, 1987;Meier, 1989).…”

“…Some quantification of this relationship has been provided by Post (1975;1980a;1980b;1980c;1980d;, and by Meier et al (1980) from studies of 52 calving tidewater glaciers in Alaska. They proposed a calving relation, refined by Brown et al (1982;, as follows:…”

Topography and former Scottish tidewater glaciers

“…A grounded tidewater glacier can only advance into deep water on a protective moraine shoal which must be maintained at its terminus by sediment supply and submarine slumping (Mayo 1988). In Alaska, it is uncommon for glaciers to advance rapidly into water more than 80m deep (Meier et al 1980 Ballantyne (1989), Bennett (1991), Boulton et al (1981), Gray (1975), Gray andBrooks (1972), McCann (1966), Peacock (1971), Peacock et al(1989), Sutherland (1981), Thorp (1984Thorp ( , 1986Thorp ( , 1991 deep water. Retreat may continue to the head of the fjord where the water depth decreases, leaving the glacier with a highly positive mass balance.…”

A preliminary forecast of the advance of Hubbard Glacier and its influence on Russell Fiord, Alaska

“…At Columbia Glacier, late-summer/autumn retreat of the terminus is caused by an increase in the calving speed that is associated with seasonally increased runoff from melt and rain; the late-winter/spring advance is a response to seasonally increased ice speed and decreased runoff (Sikonia and Post, 1980). The seasonal advances and retreats of Columbia Glacier's terminus continue to occur, even as drastic retreat is ongoing (Krimmel, 1987).…”