Tephra characterization and multi-disciplinary determination of Eruptive Source Parameters of a weak paroxysm at Mount Etna (Italy)

Abstract

The determination of Eruptive Source Parameters (ESPs) is a major challenge especially for weak volcanic explosions associated with poorly exposed tephra-fallout deposits. In such a case, the combination of deposit analyses and remote sensing observations can provide fundamental insights. We use the 29 August 2011 weak paroxysm at Mount Etna (Italy) as a case study to discuss some of the challenges associated with multi-disciplinary determination of ESPs of poorly exposed tephra-fallout deposits. First, we have determined the erupted mass from a combination of field and synthetic data to fill a significant gap in data sampling; synthetic data have been derived based on extrapolation of field observations and validated based on comparisons with other tephra deposits at Etna and TEPHRA2 modelling. Second, we have combined the estimates of erupted mass and grain-size distribution as derived both from deposit observations and satellite retrievals. Analytical modelling was applied to characterize the size fractions most likely represented in satellite retrievals and tephra deposits, respectively. In addition, the Rosin-Rammler distribution fitting is shown to inform on missing parts of the grain-size distributions and reproduce a tail of very fine ash (1–20 μm) whose mass proportion is close to the satellite estimates (1.3–1.6% versus 1.9%, respectively). Finally, it was found that this very-fine-ash fraction increases as a function of satellite-derived Mass Eruption Rate for a set of eruptions for which independent estimates are available. This critical combination of field observations, analytical modelling and satellite retrievals demonstrates the potential and importance of multidisciplinary strategies for the derivation of ESPs even for small-size explosive events and poorly exposed deposits such as that of the 29 August 2011 paroxysm of Mt. Etna.