Abstract

Skelton Inlet, Antarctica, a deep-water arm of the Ross Sea, is about 60 km long and ranges in width from 16 km at the mouth where it meets the Ross Ice Shelf, to about 5 km near the junction with the grounded ice. The cover of floating ice increases in thickness from about 500 m at the Ross Ice Shelf to more than 1500 m at the head of the inlet. For the last 12 km near the head of the inlet, the bottom of the ice cover appears to be in contact with the bottom sediments, but available evidence indicates that it is floating. The maximum observed water depth, 1933 m below sea level, is well inside the inlet; this is nearly 500 m deeper than the water near the mouth. These abnormal depths are partly attributed to depression by the Antarctic ice sheet. The floor of the inlet, where sounded by seismic reflections, is quite rough, possibly owing to high moraines.

The decrease in ice thickness down the inlet results from the drop in horizontal pressure owing to the shear stresses on the side walls and the consequent creep of the floating ice. This decrease is inversely proportional to the width of the valley, with the ice thickness and volume of outflow having only secondary effects. An approximate formula for determining the change in ice thickness, Z, per unit length, x, is 11.17 dZ/dx = σxY/Y where σxY is the shear stress in bars on the side walls, probably in the range −0.5 to −1.5, and Y is the half-width of the inlet in km. Since the morphology of the sediments on the floor must, to a large extent, be determined by the configuration of the lower boundary of the ice, this provides a mechanism for the formation of fiords. A common characteristic of all fiords is the increased water depth inland, as compared with the thresholds near the mouths. Multiple basins such as the Skelton Inlet, could result from multiple glaciation under different boundary conditions.

The gravity survey shows large decreases in Bouguer anomalies, more than 1 mgal per km, extending from the Ross Ice Shelf to the Victoria Land Plateau by way of the Skelton Inlet, evidence of a considerable change in crustal thickness. Thus tectonics may have been a factor in the original formation of the valley.

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