Comparison of esker morphology and sedimentology with former ice-surface topography, Burroughs Glacier, Alaska

Abstract

Topographic maps ofthe Burroughs Glacier ice surface and the surrounding land surface from 1948 to 1990 were used to generate subglacial hydraulic head maps and compare esker paths to hydraulic gradients. Hydraulic gradient at the glacier bed is controlled predominantly by ice-surface slope, but it is also influenced by the slope of the glacier bed. Eskers at Burroughs Glacier have been observed forming in subglacial and englacial tunnels. Most of the eskers formed in subglacial stream tunnels oriented parallel to the calculated hydraulic gradient. Where the former ice-surface slope and slope of the bed do not coincide, the relative influence of these factors on esker paths is analyzed. One esker is oriented parallel to the land-surface contours and perpendicular to hydraulic head contours, implying an esker path controlled by the ice-surface slope. In another area, a set of subglacially engorged eskers trends perpendicular to the land contours (directly down the slope of the former glacier bed) and parallels the calculated hydraulic head contours. These eskers formed beneath thin ice in tunnels that were air-filled much of the time, and thus the slope of the glacier bed controlled the esker paths. In a third area where the hydraulic gradient and glacier bed slope in the same direction, a subglacially engorged esker trends down the land slope and the calculated hydraulic gradient Most of the eskers at Burroughs Glacier are