Dynamics of Wind-Affected Volcanic Plumes: The Example of the 2011 Cordon Caulle Eruption, Chile

Abstract:

The 2011 Cordon 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 one day and was classified as subplinian to small-moderate with plumes between 9-12 km above the vent and Mass Flow Rate (MFR) on the order of 10⁷ kg/s. The first 10 days of the eruption had MFR values >10⁶ kg/s and were followed by several months of low-intensity plumes. Plume dynamics and rise were strongly affected by wind during the whole eruption, with negligible up-wind spreading. Pyroclastic Density Currents (PDCs) due to column collapse were mostly observed on June 4^th-5^th when wind velocity was lowest and MFR highest, suggesting that PDC generation can be reduced by wind advection. Individual phases of the eruption range between VEI 3-4, while the cumulative deposit associated with June 4^th-7^th, 2011, is associated with a VEI 5 and a minimum magnitude of 4.8. Crosswind cloud spreading and deposit dispersal of the first few days could be best described by a linear combination of gravitational spreading and turbulent diffusion, with velocities between 1-10 m/s and diffusion coefficients that are consistent with measured values for atmospheric diffusivity. Downwind cloud spreading could be best described by a linear combination of gravitational intrusion and wind advection, with velocities between 17-45 m/s. Our results show how gravitational spreading can be significant even for small-moderate eruptions strongly advected by wind and with relatively low Richardson number and low MFR.