Some Characteristics of Grounded Floebergs near Prudhoe Bay, Alaska

Abstract

During the winter of 1974-75, a large number of floebergs (fragments of multi-year pressure ridges) were found incorporated in the fast ice northwest of Prudhoe Bay, Alaska. Many of them had been driven up onto the sea floor and become stranded, as was indicated by their high free-board. ... In order to gather information on the shape and structure of floebergs, and their effect upon the sea bed during groundings, studies were undertaken in April 1975 in the area located approximately 35 km northwest of Prudhoe Bay (70 35 N, 148 50 W). These studies included the determination of the surface relief of two floebergs (henceforward designated A and B) by means of standard surveying techniques; snow thickness measurements; the profiling of the floeberg keels by a sonar technique developed by Kovacs, and an examination of the internal structures of the floebergs, including voids and impurities, as observed in fracture faces on their sails and the portions of their keels uplifted upon grounding. The fast ice surface in the immediate area of the floebergs was highly irregular, due largely to the incorporation of ice fragments into the ice sheet. The surface was covered with a layer of snow that varied in thickness from 10 to 40 cm, depending on the relief of ice.