A 2024 event on the Southeast Indian Ridge was captured in situ for the first time, showing 4.2 meters of valley-floor subsidence, more than 1 meter of horizontal extension and about 160 million cubic meters of lava erupted in 16 days.
Hydroacoustic, pressure and acoustic-ranging data indicate a sill-like magma reservoir deflated as dykes raced along the ridge axis, driving rapid faulting, seafloor collapse and lava outpouring that likely began within hours of the initial quake swarm.
Modeling suggests the event released roughly 39 years of plate divergence, with 2.1 to 4.0 meters of total extension split between dyke opening and normal-fault slip; about 76% of that fault slip was aseismic.
Seismicity then jumped to the adjacent Boomerang and Amsterdam transform faults, including a Mw 5.9 quake, indicating ridge-axis magma intrusion can trigger nearby transform activity.
The findings help explain why mid-ocean ridges show a long-noted earthquake deficit: much of their deformation may build quietly for decades, then release in short magmatic-tectonic bursts.