Record of tide gauges indicate that sea level generally is rising at an average rate of about 10 cm per century. The uplift in Fennoscandia and North America is investigated, and maps showing the rate of uplift are given. A discussion of the new material and historic evidence leave no doubt 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 meters in Fennoscandia and possibly more in North America, where the present rate of uplift has its maximum of about 2 meters per century in the region of Hudson Bay. 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.
Theoretical investigations on the plastic flow in the interior of the earth connected with the uplift are critically discussed and extended. The movements affect the whole interior of the earth below the regions of uplift; their amplitudes decrease slowly in the upper 1000 km. If one assumes a strong lithosphere with a thickness of about 70 km and below the asthenosphere with a viscosity of the order of 1022 poises, but little or no strength to prohibit plastic flow, there is no disagreement with observations related to isostasy or deep-focus earthquakes. Tectonic processes connected with isostatic anomalies larger than those in the regions of postglacial uplift must be connected with plastic flow at least down to the core. The importance of the effects of small forces acting during long periods is pointed out
- Received 12 November 1940.
- © 1941 Geological Society of America