Islands of Grounded Ice

Abstract

In August 1972, the U.S. Coast Guard icebreaker Burton Island confirmed the existence of a large ice formation located at about 160 km northwest of Point Barrow, which had first been observed by 1971 satellite imagery of the U.S. National Ocean and Atmospheric Administration (NOAA-1). Visual observations made from a distance indicated that the relief of the ice formation, which appeared to rise as much as nine meters above the sea, was highly irregular. Although it was at first described as a large hummock field of pressured sea ice, news quickly spread that it was a large piece of tabular shelf ice, i.e., an "ice island." ... With the launching into orbit of the Earth Resources Technology Satellite (ERTS-1) in July 1972, there became available for the first time multi-spectral imagery of sufficiently high resolution to allow detailed sea ice studies to be performed. Through the sequential imagery provided by the satellite during its passage over the High Arctic, measurements could be made of the deformation and drift of the ice pack and a continuous observation kept on the formation and break up of fast ice along the Alaska coast. The discovery of the "ice island," together with the availability of satellite imagery, thus provided a unique opportunity to locate and monitor the movement of a specific ice feature for an extended period of time. ... This report serve the demonstrate the usefulness of ERTS-1 imagery for the location of islands of grounded ice, and for observing the growth and decay of these features with time. Through the imagery there has also been revealed a possible error on bathymetric charts for the location of two shoals in the southern Chukchi Sea. ...