Minute-scale dynamics of recurrent dike intrusions in Iceland with fiber-optic geodesy.

Continuous geodetic measurements near volcanic systems can image magma transport dynamics, yet resolving dike intrusions with high spatiotemporal resolution remains challenging. We introduce fiber-optic geodesy, leveraging low-frequency distributed acoustic sensing (LFDAS) recordings along a telecommunication fiber-optic cable, to track dike intrusions near Grindavík, Iceland, on a minute timescale. LFDAS revealed distinct strain responses from nine intrusive events, six resulting in fissure eruptions. Geodetic inversion of LFDAS strain reveals detailed magmatic intrusions, with inferred dike volume rate peaking systematically 15 to 22 min before the onset of each eruption. Our results demonstrate DAS's potential for a dense strainmeter array, enabling high-resolution, nearly real-time imaging of subsurface quasistatic deformations. In active volcanic regions, LFDAS recordings can offer critical insights into magmatic evolution, eruption forecasting, and hazard assessment. Editor's summary: After 800 quiet years, curtains of lava are erupting through fissures on Iceland's Reykjanes Peninsula, cutting across towns and forcing evacuations. Tracking the flow of magma can help to forecast eruptions, but the best satellite methods resolve over hours to days. Using a distributed acoustic recording system attached to an existing telecommunication cable, Li et al. captured magma-migration ground movement on a minute-by-minute basis for nine recent eruptions. Their recordings showed peak magma flow 15 to 22 minutes before each eruption and were behind an early warning issued in the half hour ahead of the largest eruption. —Angela Hessler [ABSTRACT FROM AUTHOR]