Detailed observations of an underwater volcano reveal a gradual rise of the sea bed in the run-up to eruption, accompanied by a swarm of earthquakes just before the eruption, and followed by a rapid drop of the sea bed at the time of the eruption. This finding is reported in three complementary studies published online this week in Nature Geoscience. Submarine volcanism - the vast majority of volcanism on Earth - has had little scientific attention, making the new observations of Axial Seamount volcano in the Pacific Ocean particularly valuable.

William Chadwick Jr, Robert Dziak, David Caress and colleagues surveyed Axial Seamount before and after an eruption in April 2011. They used a robotic submersible to analyse the seafloor topography, pressure sensors to measure inflation and deflation of the sea bed, and hydrophones to record waterborne signals of small earthquakes caused by magma moving in the Earth’s crust. They record gradual inflation of the sea bed in the years leading up to the eruption, as the magma reservoir beneath the volcano gradually filled. Thereafter, the sea bed deflated as the magma intruded into the oceanic crust and erupted as lava flows on the sea floor. In the two hours before the eruption, a swarm of intense earthquakes occurred.

In an accompanying News and Views article, Neil Mitchell writes that the studies "highlight the pulsed nature and rapid growth and collapse of submarine volcanoes during eruptions."