Video-based measurements of the entrainment, speed and mass flux in a wind-blown eruption column at Eyjafjallajökull volcano, Iceland

Abstract

On May 4 2010 a wind-blown ash plume issued from Eyjafjallajökull volcano in Iceland. Analysis of a 17-minute long video recording of the eruption suggests that within $2-2.5$ km of the vent, the flow was moving with the wind and rising under buoyancy, following a trajectory directly analogous with laboratory experiments of turbulent buoyant plumes in a cross-flow. The visible radius of the time-averaged ash cloud grew with height $z$ at a rate $r=0.48 z$, corresponding to an entrainment coefficient of $0.4$, again consistent with laboratory experiments. By analysing the frames in the video and comparing the shape of the plume to that predicted by the model, we estimate that during the 17 minutes recorded, the eruption rate gradually decreased by about 43$\%$ from an initial eruption rate of $1.11\times 10^4$ kg/s to $0.63\times 10^4$ kg/s. The analysis reported herein opens the way to assess eruption rates and eruption column processes from video recordings during explosive volcanic eruptions