POSTGLACIAL UPLIFT AND THE MOBILITY OF THE EARTH'S INTERIOR

Abstract

BGUTENBERG of the Pasadena Seismological Observatory, California, has recently completed a study of the above problem (“Changes in Sea Level, Postglacial Uplift, and Mobility of the Earth's Interior”, by Beno Gutenberg, Bull. Geol. Soc. Amer., 52, 721–72; May 1, 1941). The author has examined carefully the records of tide gauges throughout the world, and finds that these indicate that sea–level generally is rising at an average rate of about 10 cm. a century. In particular, maps have been constructed to show the rate of uplift in Fennoscandia and North America. A discussion of the new material and historic evidence appears to indicate that the uplift is a consequence of isostatic readjustment of the equilibrium disturbed by the postglacial melting of the ice. The remaining uplift is about 200 m. in Fennoscandia and possibly more in North America, where the present rate of uplift has its maximum of about 2 m. per century in the region of Hudson Bay. Simultaneously with the glaciation in Fennoscandia, the British Isles were covered by ice with a centre in the Hebrides where the postglacial uplift exceeded 30 m., decreasing towards Scotland; the zero isobase for the recent millennia intersects northern Ireland and northern England. There is some indication that the zero isobase at present lies south and west of Great Britain. Originally, the time needed to reduce the defect in mass to one half under the regions of uplift was less than 10,000 years, but it has been increasing with time and now exceeds 20,000 years.