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Understanding magmatic plumbing within the Earth's crust is important for understanding volcanic systems and improving eruption forecasting. We discuss magma plumbing under Baroarbunga volcano, Iceland, over a 4year period encompassing the largest Icelandic eruption in 230years. Microseismicity extends through the usually ductile region of the Earth's crust, from 7 to 22km depth in a subvertical column. Moment tensor solutions for an example earthquake exhibits opening tensile crack behavior. This is consistent with the deep (>7km) seismicity being caused by the movement of melt in the normally aseismic crust. The seismically inferred melt path from the mantle source is offset laterally from the center of the Baroarbunga caldera by similar to 12km, rather than lying directly beneath it. It is likely that an aseismic melt feed also exists directly beneath the caldera and is aseismic due to elevated temperatures and pervasive partial melt under the caldera.

Plain Language Summary Understanding where molten rock travels within the Earth's crust is important for understanding how volcanoes are fed, useful for improving eruption forecasting. We discuss the location of molten rock pathways under Bardarbunga volcano, Iceland, before, during and after the largest Icelandic eruption in 230 years. Earthquakes (triggered by molten rock moving through the Earth's crust) are found at 7-22 km depth in a sub-vertical column. These earthquakes are located at depths in the crust where earthquakes would not normally occur. The observed path of molten rock is not under the center of the main volcano caldera, but rather similar to 12 km to the south-east. It is likely that a route for molten rock up through the crust also exists directly beneath the volcano, but we do not observe this, likely due to the Earth's crust being too hot here.