Impact of wind on the dynamics of explosive volcanic plumes inferred from analog experiments

Friday, 19 December 2014: 2:40 PM
Guillaume Carazzo1, Frederic Girault2, Thomas Jacques Aubry3, Helene Bouquerel1 and Edouard C Kaminski1, (1)Institut de Physique du Globe de Paris, Paris, France, (2)Ecole Normale Superieure, Paris, France, (3)University of British Columbia, Earth, Ocean and Atmospheric Sciences, Vancouver, BC, Canada
Volcanic plumes produced by explosive eruptions commonly interact with atmospheric wind causing plume bending and a reduction of its maximum height. Strength of the wind field and intensity of the eruption control the behavior of the column in the atmosphere, which may form either a strong plume that is little affected by the presence of wind or a weak plume that is bent-over in the wind field. To better understand the transition between weak and strong plumes, we present a series of new laboratory reproducing a buoyant jet rising in a stratified environment with a uniform cross-flow. The experiments consist in injecting downward fresh water in a tank containing an aqueous NaCl solution with linear density stratification. The jet source is towed at a constant speed through the stationary fluid in order to produce a cross-flow. We show that depending on the environmental and source conditions, the buoyant jet may form either a strong, distorted, or weak plume. The transition from one dynamical regime to another is governed by the strength of the horizontal wind velocity compared to the vertical buoyant rise of the plume. A review of field data on historical eruptions confirms that the experimentally-determined transition curves capture the behavior of volcanic columns. We quantify the impact of wind on the maximum height reached by the column, and we propose a universal scaling relationship to link the mass discharge rate feeding an eruption to its observed maximum height in the presence of wind.