Dynamics of wind-affected volcanic plumes: The example of the 2011 Cordón Caulle eruption, Chile

The 2011 Cordón Caulle eruption represents an ideal case study for the characterization of long-lasting plumes that are strongly affected by wind. The climactic phase lasted for about 1 day and was classified as subplinian with plumes between ~9 and 12 km above the vent and mass flow rate (MFR) on the order of ~107 kg s-1. Eruption intensity fluctuated during the first 11 days with MFR values between 106 and 107 kg s-1. This activity was followed by several months of low-intensity plumes with MFR<106 kg s-1. Plume dynamics and rise were strongly affected by wind during the whole eruption with negligible upwind spreading and sedimentation. The plumes that developed on 4–6 and 20–22 June can be described as transitional, i.e., plumes showing transitional behavior between strong and weak dynamics, while the wind clearly dominated the rise height on all the other days resulting in the formation of weak plumes. Individual phases of the eruption range between Volcanic Explosivity Indices (VEIs) 3 and 4, while the cumulative deposit related to 4–7 June 2011 is associated with VEIs 4 and 5. Crosswind cloud and deposit dispersal of the first few days are best described by a linear combination of gravitational spreading and turbulent diffusion, with velocities between 1 and 10 ms-1. Downwind cloud velocity for the same days is best described by a linear combination of gravitational spreading and wind advection, with velocities between 17 and 45ms1. Results show how gravitational spreading can be significant even for subplinian and small-moderate eruptions strongly advected by wind and with low Richardson number and low MFR.