Heat Transfer by Hydrothermal Systems in the East African Rifts

Abstract

Moderately intense volcanic and geothermal activity occurs along the two continental rifts in East Africa, each c. 2 000 km long. An inventory of known major geothermal and volcanic systems in the rifts is presented.
Volcanism and rifting started in the Eastern Rift (Eritrea/Djibouti to Northern Tanzania) at least 15 Mill. yr ago. Over 30 major hydrothermal systems occur along this branch (almost half have steaming ground) together with at least 10 volcanic-geothermal and 10 volcanic systems which have been active during the last 2 000 yr. The hydrothermal systems discharge heat at a rate of at least 4 000 MW. Volcanism and rifting began c. 10 Mill. yr ago in the Western Rift (Northern Uganda to Southern Malawi). However, there are only 3 major high temperature systems in this rift together with 4 active volcanic systems. A few concealed advective geothermal systems occur at the margin and probably at the bottom of deep rift lakes. The total anomalous heat discharged by the Western Rift is an order-of-magnitude less than that discharged by the Eastern Rift. There appears to be an overall inverse relation between the energy released by crustal earthquakes and that transferred by geothermal systems.