Continental rifting is initiated by a dynamic interplay between tectonic stretching and mantle upwelling. Decompression melting assists continental breakup through lithospheric weakening and enforces upflow of melt to the Earth's surface. However, the details about melt transport through the brittle crust and storage under narrow rift‐aligned magmatic segments remain largely unclear. Here we present a crustal‐scale electrical conductivity model for a magmatic segment in the Ethiopian Rift, derived from 3‐D phase tensor inversion of magnetotelluric data. Our subsurface model shows that melt migrates along preexisting weak structures and is stored in different concentrations on two major interconnected levels, facilitating the formation of a convective hydrothermal system. The obtained model of a transcrustal magmatic system offers new insights into rifting mechanisms, evolution of magma ascent, and prospective geothermal reservoirs.

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Caldera systems are often restless and experience pulses of uplift and subsidence, with a weak, but significant link to eruption. Characterizing the spatial and temporal patterns of deformation episodes provides insight into the processes responsible for unrest and the architecture of magmatic and hydrothermal systems. Here we combine interferometric synthetic aperture radar images with data from Global Positioning System and a network of seismometers at a continental rift caldera Corbetti, Ethiopia. We document inflation that started mid‐2009 and is ongoing as of 2017, with associated seismicity. We investigate the temporal evolution of the deformation source using a Hastings‐Metropolis algorithm to estimate posterior probability density functions for source model parameters and use the Akaike information criterion to inform model selection. Testing rectangular dislocation and point sources, we find a point source at a depth of 6.6 km (95% confidence: 6.3 − 6.8 km) provides the statistically justified fit. The location of this source is coincident with a conductive anomaly derived from magnetotelluric measurements. We use a joint inversion of two geodetic data sets to produce a time series, which shows a volume input of 1.0 × 107 m3/year. This is the first observation of a prolonged period of magma reservoir growth in the Main Ethiopian Rift and has implications for hazard assessment and monitoring. Corbetti is < 20 km from two major population centers and has estimated return periods of ∼500 and ∼900 years for lava flows and Plinian eruptions, respectively. Our results highlight the need for long‐term geodetic monitoring and the application of statistically robust methods to characterize deformation sources.

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Two different models of the Icelandic crust and upper mantle have recently competed.The thin-crust model involves a crust ~10-15 km thick beneath the axial rift zones, thickening to ~25 km beneath older Tertiary areas. At the base of the crust is a thin layer containing 5-10% partial melt at temperatures around 1100 °C and with high electrical conductivity. Below the crust is an anomalous ultramafic mantle or an intermediate layer of mantle and crustal material containing 1-5% melt. According to the thick-crust model, the crust is ~20-30 km thick close to the coast and thickens toward the center of the island to as much as 40 km. A large amount of magnetotelluric data were reevaluated and a map constructed, which shows that the conducting layer is continuous beneath whole of Iceland except along the south coast. Joint interpretation of electrical, seismic, and temperature data provides many more constraints and more reliable results than does the use of one method only. There is a good correlation between the depth to the highly conductive layer, temperature gradient, and maximal focal depths. The uppermost 10-15 km of the crust are mainly formed by dike intrusions, lava eruptions, and continuous subsidence and mixing of magma in the rift zones. The lower crust is created by upflow of magma in layer 4, intrusions and underplating causing thickening of the crust with age. The thin-crust model explains the major features of crustal and mantle structure better than does the thick-crust model.