The 2017 Eruption of Erta 'Ale Volcano, Ethiopia: Insights Into the Shallow Axial Plumbing System of an Incipient Mid-Ocean Ridge

Abstract

The final stage of continental breakup is often accompanied by abundant magmatism. Erta 'Ale volcano lies on the Nubia-Arabia extensional boundary in Afar, Ethiopia, an incipient mid-ocean ridge. A fissure on the south flank of Erta 'Ale began erupting on 21 January 2017 and has remained active until at least July 2019. We use Sentinel-1 synthetic aperture radar acquisitions to create a time series of ground displacement measurements at Erta 'Ale from October 2014 to June 2019, covering the eruption and its buildup. In the preeruption period, we observe gradual extension centered on the lava lake, consistent with the opening of an axis-aligned dike. Using synthetic aperture radar intensity shadows, we show that the long-lived Erta 'Ale lava lake was stable in this period, indicative of a steady pressure state in the shallow plumbing system. During the initial eruption, we observe surface displacements consistent with a shallow dike intrusion below the eruption site and conduit contraction below the lava lake. The pressure change associated with the cointrusive drop in the lava lake level is sufficient to reproduce the deformation pattern suggesting that the lava lake is well connected to the shallow plumbing system. Subsidence and contraction during the long-lived eruption indicates the presence of an off-rift vertically extensive source. We suggest that this may represent a system of stacked sources throughout the upper crust, with melt being more distributed. We also propose that high magma flux on the slow-spreading Erta 'Ale segment may be facilitating the presence of shallow axial magma bodies.