Implications of longeval lava lakes for geomorphological and plutonic processes at Erta 'Ale volcano, Afar

Erta 'Ale volcano, sited within the Afar Triangle of Ethiopia, is one of the least visited of perennially active, subaerial volcanoes. Satellite images recorded over the past thirty years illustrate the sustained activity of the volcano and complement the few brief periods of field observation. We consider that Erta 'Ale's lava lakes have probably persisted for greater than or equal to 90 years, placing them among the longest-lived yet recorded. Despite sustained surface heat fluxes of 100-400 MW, the net surface growth rate integrated over the interval 1968-1995 was only approximate to 10 kg s(-1). We speculate that this minimal lava discharge cannot be used to infer a low magma supply rate to the volcano, since heat losses from the lava lakes inhibit eruption by increasing magma density. This implies growth of the underlying crust by formation of dikes and sills containing cumulates, accommodated, and possibly promoted, by regional extension and intrusion loading. Open vent degassing and rift kinematics are clearly reflected in Erta 'Ale's morphology which is characterised by very gentle( <3 degrees) slopes and a summit caldera. (C) 1998 Elsevier Science B.V.