Geoid anomalies and dynamic topography from convection in cylindrical geometry: applications to mantle plumes on Earth and Venus

Abstract

A variety of evidence suggests that at least some hotspots are formed by quasi‐cylindrical mantle plumes upwelling from deep in the mantle. We model such plumes in cylindrical, axisymmetric geometry with depth‐dependent, Newtonian viscosity. Cylindrical and sheet‐like, Cartesian upwellings have significantly different geoid and topography signatures. However, Rayleigh number‐Nusselt number systematics in the two geometries are quite similar. The geoid anomaly and topographic uplift over a plume are insensitive to the viscosity of the surface layer, provided that it is at least 1000 times the interior viscosity. Increasing the Rayleigh number or including a low‐viscosity asthenosphere decreases the geoid anomaly and the topographic uplift associated with an upwelling plume. Increasing the aspect ratio increases both the geoid anomaly and the topographic uplift of a plume. The Nusselt number is a weak function of the aspect ratio, with its maximum value occurring at an aspect ratio of slightly less than 1. Copyright © 1992, Wiley Blackwell. All rights reserved