Deep magma underpressure and connectivity drive large dike intrusions

Large dikes are the main mechanism of crustal extension in volcanic areas, but the processes in the underlying magma system that supply the required volumes remain unclear. We show that 1.4 cubic kilometers of magma propagated under the Ethiopian rift in December 2024 and continued for ~3 months. Geodesy and seismicity reveal that the dike was fed from a network of magma reservoirs between 6 to 12 kilometers in depth with pathways rapidly forming between them. We calculate pressure changes in the reservoirs and show that underpressure developed in the deeper portion, creating the conditions to drain large magma volumes. We find that tectonic stress and availability of magma alone are not enough to drive intrusion of massive dikes. These events will start only after magma connectivity and deep underpressure develop. Similar conditions may be important for the transfer of large magma volumes from the mantle and the formation of large igneous provinces.