Seismic Evidence of Shallow Permafrost Beneath Islands in the Beaufort Sea, Alaska

Abstract

Shallow ice-bonded permafrost has been shown by seismic refraction methods to exist beneath several islands in the Beaufort Sea. The marked contrast of seismic velocities in bonded materials (>2500 m/sec) and unbonded materials (<2100 m/sec) was used to determine the location of permafrost. In many cases these data were confirmed by shallow probing and drill holes. Several general conclusions are made about the distribution of shallow bonded permafrost beneath islands in the Beaufort Sea. Shallow permafrost occurs under areas where remnants of tundra still exist. These conditions exist on the larger islands that have not been eroded away by the ocean. Islands which have been eroded by the ocean, leaving only accumulation of sand and gravel, are generally moving westward and landward and for the most part are not underlain by shallow permafrost. However, the oldest and most persistent parts of these islands are in some cases underlain by shallow permafrost. This is believed to be a consequence of repeated freezings and thawings causing a reduction of salt brine in the sediments and allowing the materials to freeze.