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

Erta ʹAle 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 ʹAleʹs lava lakes have probably persisted for ≥ 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 ≈ 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 die 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 ʹAleʹs morphology which is characterised by very gentle (< 3 °) slopes and a summit caldera.