Catching a submarine volcano in the act

Eighty-five percent of Earth’s volcanism occurs under water in the deep ocean. Out of sight and largely out of reach, the volcanoes are hard to study, and researchers have mostly relied on land-based analogues as a guide for how they work. But thanks to recent advances in sea floor monitoring, researchers can now probe underwater volcanism directly, continuously, and in unprecedented detail. So when Axial seamount—a volcano sitting on a mid-ocean ridge 300 miles off the coast of Oregon—erupted last year, a collaboration of 16 researchers from 6 universities and institutes was ready for it, instruments in place. Their measurements made before, during, and after the event reveal a gradual rise of the floor in the run-up to the eruption, a swarm of thousands of earthquakes just preceding it, and a sudden drop of the sea floor as lava began spewing from the volcano’s summit and flanks. The researchers used a robotic submersible to map the volcano’s topography before the eruption, hydrostatic-pressure gauges to monitor the sea floor’s ongoing deformation, and hydrophones to record the sounds of rock cracking and magma moving. A second bathymetry survey after the eruption revealed details of the lava flow. The image shows Axial seamount, with its caldera bordered in red at the highest elevation. (W. W. Chadwick Jr et al., Nat. Geosci. 5, 474, 2012; R. P. Dziak et al., Nat. Geosci. 5, 478, 2012; D. Caress et al., Nat. Geosci. 5, 483, 2012.)–R. Mark Wilson