Abstract
We present a synthesis of diverse observations of the first recorded eruption of Nabro volcano, Eritrea, which began on 12 June 2011. While no monitoring of the volcano was in effect at the time, it has been possible to reconstruct the nature and evolution of the eruption through analysis of regional seismological and infrasound data and satellite remote sensing data, supplemented by petrological analysis of erupted products and brief field surveys. The event is notable for the comparative rarity of recorded historical eruptions in the region and of caldera systems in general, for the prodigious quantity of SO2 emitted into the atmosphere and the significant human impacts that ensued notwithstanding the low population density of the Afar region. It is also relevant in understanding the broader magmatic and tectonic significance of the volcanic massif of which Nabro forms a part and which strikes obliquely to the principal rifting directions in the Red Sea and northern Afar. The whole-rock compositions of the erupted lavas and tephra range from trachybasaltic to trachybasaltic andesite, and crystal-hosted melt inclusions contain up to 3,000 ppm of sulphur by weight. The eruption was preceded by significant seismicity, detected by regional networks of sensors and accompanied by sustained tremor. Substantial infrasound was recorded at distances of hundreds to thousands of kilometres from the vent, beginning at the onset of the eruption and continuing for weeks. Analysis of ground deformation suggests the eruption was fed by a shallow, NW–SE-trending dike, which is consistent with field and satellite observations of vent distributions. Despite lack of prior planning and preparedness for volcanic events in the country, rapid coordination of the emergency response mitigated the human costs of the eruption.
Highlights
On 12 June 2011, Nabro volcano was the site of an eruption that had significant societal and environmental consequences
In addition to those described below, we have incorporated datasets obtained from operational Ozone Monitoring Instrument (OMI) SO2 retrievals (Yang et al 2007; Sealing 2013) and a Comprehensive Nuclear Test-Ban Treaty Organisation (CTBTO) infrasound station (IS32) in Nairobi, 1,708 km from Nabro (Fee et al 2013)
The 2011 Nabro eruption offers a valuable opportunity to develop our understanding of unrest and eruptive activity of caldera systems, the local interactions between tectonics and volcanism and between neighbouring volcanoes and the origins and significance of the off-axis volcanic ranges in the wider Afar region
Summary
On 12 June 2011, Nabro volcano was the site of an eruption that had significant societal and environmental consequences. Ash clouds and tephra fall associated with the 1861 eruption disrupted navigation in the Red Sea. Nabro volcano, some 25 km southwest from Dubbi, is part of a much larger massif referred to as the Bidu Volcanic Complex (Wiart and Oppenheimer 2005; Fig. 1), which is comprised of two calderas (Nabro and, just across the international border in Ethiopia, Mallahle). Felt earthquakes on the volcano, occurring over several hours before the eruption, did prompt a rapid evacuation of settlements, notably those within Nabro’s caldera. About 12,000 people were displaced and cared for in temporary camps in the region (Solomon 2012)
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