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

Friday, 19 December 2014: 2:10 PM
Costanza Bonadonna1, Marco Pistolesi2, Raffaello Cioni3, Wim Degruyter4, Manuela Elissondo5 and Valerie Baumann5, (1)University of Geneva, Section of Earth and Environmental Sciences, Geneva, Switzerland, (2)University of Pisa, Pisa, Italy, (3)Università degli Studi di Cagliari, Firenze, Italy, (4)Georgia Institute of Technology, Atlanta, GA, United States, (5)SEGEMAR, Buenos Aires, Argentina
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 4th-5th 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 4th-7th, 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.