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.
Highlights
The determination of Eruptive Source Parameters (ESPs) is crucial to understand, assess, and forecast the hazards associated with volcanic eruptions (e.g., Costa et al, 2006; Scollo et al, 2008; Folch, 2012; Bonadonna et al, 2015; Beckett et al, 2020; Aubry et al, 2021)
In terms of characterization of small, poorly exposed tephra-fallout deposits we have shown how: 1) all empirical integrations used and the inversion of ground accumulation data with TEPHRA2 provide similar estimates of TEMDEP (1.4 ± 0.0 × 108 kg vs 1.8 ± 0.1 × 108), which could be due to the limited size of the tephra-fallout deposit; 2) plume height of small paroxysms that are not associated with large clasts can be derived from tephrafallout deposits based on inversion of ground accumulation data as well as on the variation of MdΦ values with distance from vent; 3) poorly-exposed tephra-fallout deposits associated with large sampling gaps related to critical sedimentation regimes should be carefully treated for the determination of Whole Deposit GrainSize Distribution (WDGSD)
We show that synthetic data, validated by both the comparison with observed data from other Etna paroxysms and simulations with TEPHRA2, can be used to reconstruct WDGSD that would otherwise result in a bimodal distribution
Summary
The determination of Eruptive Source Parameters (ESPs) (e.g., the vent location, Total Erupted Mass - TEM, Mass Eruption Rate - MER, Plume Height - Ht, Total Grain-Size Distribution - TGSD) is crucial to understand, assess, and forecast the hazards associated with volcanic eruptions (e.g., Costa et al, 2006; Scollo et al, 2008; Folch, 2012; Bonadonna et al, 2015; Beckett et al, 2020; Aubry et al, 2021). The radius of umbrella clouds can represent a key ESP of large eruptions (Constantinescu et al, 2021). ESPs are derived based on the application of dedicated models either to deposit data or to real-time geophysical observations. The exposure of tephra deposits and/or the availability of accurate geophysical data are of crucial.
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