Tracking magma with earthquakes.

According to classical thinking, magma—a mixture of molten rocks, crystals, and gas—rises vertically from a deep reservoir to feed eruptions at the center of a volcanic system. By contrast, magma may propagate horizontally over tens of kilometers beneath Earth's surface under the effect of extensional stress, which can cause hazardous eruptions away from a volcanic center (1–3). As magma moves, it can displace preexisting fractures in Earth's crust, called faults, or create new ones, resulting in seismic activity. Nonetheless, the magmatic origin of this induced seismicity is not always clearly identified. On page 806 of this issue, Lomax et al. (4) report that the early 2025 earthquakes near the Greek island of Santorini were caused by a vertical fault, which was filled with laterally propagating magma. Such observations will improve models of magma transport within Earth's crust and help in hazard assessment and forecasting eruptions. [ABSTRACT FROM AUTHOR]