Mechanisms and implications of the 2011 eruption of Nabro volcano, Eritrea

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The eruption of Nabro in Eritrea is of great scientific interest and has had substantial impacts even in the remote part of Afar in which it is located. It is sited in the extensional zone of Afar, but just south of the Mesozoic crustal block of the Danakil Alps. It is a predominantly trachytic edifice, with an 8-km-diameter caldera and associated ignimbrites. This is the first eruption of Nabro on record, highlighting the potential of caldera systems to erupt without warning. It is also the first seismicity of note recorded in this particular part of the rift. Comparatively little is known about magma differentiation, storage and transport mechanisms and eruptive processes in such tectonic settings. The urgency reflects the hope of reaching the site before cessation of lava and gas emissions, while seismicity rates remain high, and to sample undisturbed tephra and lavas. We are the only international group to be invited to visit and study the eruption site. The field data will complement satellite observations of deformation and gas emission. The eruption resulted in seven fatalities and has displaced 5000 people, requiring an ongoing humanitarian response. Aviation was disrupted by ash clouds, adding considerably to work of the Toulouse Volcanic Ash Advisory Centre, which was also tracking the Puyehue plume above southern Africa. Based on satellite observations, the eruption began shortly before 20:42 UTC on 12 June following intense seismicity. The eruption was detected via infrasound records in Djibouti, and already (emissions continue at the time of writing) ranks among the largest sources of SO2 to the atmosphere since the 1991 Pinatubo eruption (~2 Tg of SO2 released according to retrievals of Ozone Monitoring Instrument data). The main aims of the project are to arrive at a detailed synthesis of the nature and causes of the eruption, to evaluate the events in the context of understanding restless calderas worldwide, and to compare and contrast activity of Nabro with the fissural basaltic systems that have been the focus of research by the NERC Afar Consortium (http://www.see.leeds.ac.uk/afar/).