Anatomy of a volcanic eruption undersea: Submarine flows from the Hunga Tonga–Hunga Ha‘apai eruption decimated seafloor cables

n December 2021, an undersea volcano in the southern Pacific Ocean, the Hunga Tonga–Hunga Ha‘apai (hereafter called the Hunga volcano) began erupting. In January 2022 the eruption reached a powerful climax, triggering atmospheric waves that traveled around the globe and a tsunami that swept across the Pacific Ocean. An estimated 75% of Earth's volcanoes are underwater, and 20% of all fatalities caused by volcanic eruptions since 1600 CE have been associated with underwater volcanism. Yet, explosive underwater eruptions are poorly understood. On page 1085 of this issue, Clare et al. report that volcanic debris from the Hunga eruption traveled under the sea at an unprecedented distance and at record-breaking speed—more than 100 km, at velocities reaching 122 km/hour — and destroyed a vast network of seafloor telecommunication cables. Given that 95% of global communications are carried by seafloor cables, the findings highlight system vulnerabilities to underwater volcanism.