Combining Visible- and Infrared-Wavelength Observations With Numerical Modeling to Describe Vulcanian Eruption Plumes at Sabancaya, Peru

Abstract

Sabancaya volcano (Peru), is a stratovolcano in the Central Volcanic Zone of the Andes. Since November 2016, it has been in constant activity, marked by daily multiple Vulcanian explosions. In this contribution, we first characterize the plumes generated by the explosions using visible- and infrared-wavelength imagery, describing plume morphologies and quantifying rise rates. Through an analysis of plume morphology and rise rates, we find that plumes fall on a continuum between two end-member classifications. Class A plumes are characterized by an amorphous head containing multiple vortices which may combine to form a vortex ring. These plumes have higher initial velocities (generally $\gtrsim 10$ m $s^{-1}$ and up to 40 m $s^{-1}$) which monotonically decrease as the plume rises. Conversely, class B plumes have narrow, cylindrical morphologies and lack large vortical structures in the head. They have smaller initial velocities ($\lesssim 12$ m $s^{-1}$) and, after an initial rise, undergo stagnation followed by a short acceleration in rise velocity, before slowing down again. Secondly, we use a numerical model to invert our observations for eruptive source conditions, including the initial temperature, gas mass fraction and bulk density, as well as the air entrainment coefficient. From our numerical inversions, we find that these plumes have entrainment coefficients between 0.03 and 0.11. This work provides insight into the dynamics of transient plumes and highlights the need for better models to describe their dynamics.