The global variation of terrestrial heat flow

Abstract

Over 900 measurements of surface heat flow have been analyzed in order to obtain the continent-ocean averages and a contour representation. An orthogonal function representation of 757 values yields a global mean of 63.9±3.4 erg cm−2 sec−1 (1.53 μ cal cm−2 sec−1). The average over continents is 68.9 erg cm−2 sec−1 (1.65 μcal cal−2 sec−1) and the oceanic aver-age is 62.0 erg cm−2 sec−1 (1.48 μcal cm−2 sec−1). The difference between the continents and oceans is not significant at the 95 per cent confidence level. The contour representation of the heat flows shows certain similarities to the geoid. The correlation is in the sense that where gravity is high the heat flow is low, and vice versa. This correlation is consistent with that expected from convection motions in the upper mantle. An order of magnitude calculation shows that for convection extending over a depth of 1000 km a vertical velocity of 15 cm year−1 is required to explain the associated mass and heat-flow anomalies.