LAUSR

On the 7 August 2019, a 195 km2 raft of andesitic pumice was produced at 200 m below sea level at an unnamed submarine volcano in the Tonga Islands (Southwest Pacific Ocean). Drifting chiefly westward, the raft reached the Fiji Islands on the 19 September. Yachts that crossed the raft as early as 2 days post‐eruption provided an outstanding data set of raft characteristics and pristine samples. Further, exceptional tracking of raft dispersal by satellite images allows us to contrast virtual particle tracking methods with ocean model currents to explore the relative influence of surface currents, wind, and wave action on pumice flotsam dispersal over up to 2 years. Attenuation of ocean waves by large and compact pumice rafts appears to reduce the effect of Stokes drift. The coupling of real‐time satellite observations with oceanographic Lagrangian simulations allows near‐real time forecasting for global maritime hazard mitigation.