Geophysical Investigations conducted by the U. S. Geological Survey on Fletcher's Ice Island (T-3) during the International Geophysical Year and associated Images | ARC Archives Catalog
Fletcher's Ice Island Publication (PDF Document, 18.12 MB)
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Prepared for Air Force Cambridge Research Laboratories Office of Aerospace Research United States Air Force, Bedford, Massachusetts
Abstract: During 1958 and 1959, the United States Geological Survey conducted geophysical investigations on Fletcher's Ice Island (T-3) while it was drifting southwestward along the Arctic coast of Canada. Seismic reflection rveys were used to determine water depths, which ranged from 200 to 2500 meters. For the most part, it appeared the path of the island was along the outer edge of the continental shelf and along the steep slope outside the shelf.
Variations in gravity field were observed and tied to base stations at Thule, Greenland, and Barrow, Alaska, where absolute values of the gravity field are known. Values for the Bouguer gravity anomaly range from -11 milligals to +185 milligals, with values being predominantly positive. Positive values of Bouguer gravity anomaly indicate the Arctic Ocean is a normal ocean basin, with a shallow crustal layer covering the mantle. Free-air anomaly values are small and positive, indicating that this part of the Arctic Ocean basin is near isostatic equilibrium, with the water forming a normal part of the oceanic crustal section.
Attempts at measuring ocean-bottom resistivity were generally unsuccessful, with the depth of water being too great to penetrate with the equipment which was used. The thickness of the island was found to vary between 140 and 160 feet, using electromagnetic coupling measurements. Magnetic.vector measurements were made using a flux-gate magnetometer part of the time and a magnetic microbalance variagraph part of the time. Forty-three hand samples were collected from mounds of rock and dirt on Fletcher's Ice Island. None were sedimentary in origin. Most were gneisses, schists, metaquartzites and breccias. A few samples were slightly altered diabase.