Scaling Heights for Volcanic Plumes Rising Under Wind Stress: Inter-comparison Using Analogue Laboratory Experiments and Observations.
Abstract:The maximum height of volcanic plumes rising into Earth’s atmosphere is governed mostly by the atmospheric stratification, the rate of turbulent entrainment of atmospheric air into the plume, the buoyancy flux at the vent and wind. Turbulent entrainment is commonly assumed to increase proportionally with the average plume rise velocity and the wind stress. There exist multiple scalings linking eruption source conditions to plume height. However, most scalings are empirical and/or incompletely verified with: i) analogue experiments that do not capture the full range of dynamical conditions under which explosive eruption occur; ii) direct observations of a restricted number of eruptions; or iii) numerical models with parameterized turbulent entrainment physics.
In this study, we produce a self-consistent intercomparison of scalings commonly used in the literature. We use extensive analogue laboratory experiments on buoyant jets rising into a uniform wind field and a set of observations from 27 explosive eruptions (Mastin, 2014) to test each scaling.
We show that predictions for the heights of natural eruptions under various though average wind stress conditions are unsurprisingly similar. On the other hand, existing scalings for plume height vary widely in their predictions for the heights of analog plumes spanning a broader though realist range of wind forcing. Using new analytical scaling that best predict the heights of analog plumes, we improve calibration of turbulent entrainment rates, in turn.