A pulse of mid-Pleistocene rift volcanism in Ethiopia at the dawn of modern humans.

William Hutchison,Jon D Blundy,Andrew T Calvert,Juliet Biggs,David M Pyle,Benjamin E Cohen,Raffaella Fusillo,Gezahegn Yirgu,Dan N Barfod,Richard A Brooker,Tamsin A Mather

doi:10.1038/ncomms13192

Abstract

The Ethiopian Rift Valley hosts the longest record of human co-existence with volcanoes on Earth, however, current understanding of the magnitude and timing of large explosive eruptions in this region is poor. Detailed records of volcanism are essential for interpreting the palaeoenvironments occupied by our hominin ancestors; and also for evaluating the volcanic hazards posed to the 10 million people currently living within this active rift zone. Here we use new geochronological evidence to suggest that a 200 km-long segment of rift experienced a major pulse of explosive volcanic activity between 320 and 170 ka. During this period, at least four distinct volcanic centres underwent large-volume (>10 km3) caldera-forming eruptions, and eruptive fluxes were elevated five times above the average eruption rate for the past 700 ka. We propose that such pulses of episodic silicic volcanism would have drastically remodelled landscapes and ecosystems occupied by early hominin populations.

Highlights

The Ethiopian Rift Valley hosts the longest record of human co-existence with volcanoes on Earth, current understanding of the magnitude and timing of large explosive eruptions in this region is poor
The Middle Pleistocene (781–126 ka) of Ethiopia spans a key juncture in hominin evolution, represented by the arrival of anatomically modern humans in the region at around 200 ka
While attempts to understand the links between past environmental change and human evolution have stimulated considerable research into African palaeoclimate[10], comparatively little attention has been paid to the role of explosive volcanism in influencing rift habitability[11]

Summary

Introduction

The Ethiopian Rift Valley hosts the longest record of human co-existence with volcanoes on Earth, current understanding of the magnitude and timing of large explosive eruptions in this region is poor. We use new geochronological evidence to suggest that a 200 km-long segment of rift experienced a major pulse of explosive volcanic activity between 320 and 170 ka During this period, at least four distinct volcanic centres underwent large-volume (410 km3) caldera-forming eruptions, and eruptive fluxes were elevated five times above the average eruption rate for the past 700 ka. Almost 40 years ago Mohr et al.[5] speculated that a paroxysm of crustal extension and silicic volcanism (that is, a flare-up) took place in the MER during the Middle Pleistocene (between 300 and 200 ka) This hypothesis has important implications for the evolution of environments and habitats across and along the MER6, and for past, present and future volcanic hazards in the region. The fundamental—and unanswered—questions are whether explosive volcanic activity in the MER has been steady or pulsed through the Quaternary; and whether eruptions, and the environmental disruption that followed, were of sufficient size to have caused significant dislocations in hominin populations and reduced their mobility along rift migration corridors

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