Abstract
The morning of November 23, 2013, a lava fountain formed from the New South-East Crater (NSEC) of Mt. Etna (Italy), one of the most active volcanoes in Europe. The explosive activity was observed from two ground-based radars, the X-band polarimetric scanning and the L-band Doppler fixed-pointing, as well as from a thermal-infrared camera. Taking advantage of the capability of the microwave radars to probe the volcanic plume and extending the volcanic ash radar retrieval (VARR) methodology, we estimate the mass eruption rate (MER) using three main techniques, namely surface-flux approach (SFA), mass continuity-based approach (MCA), and top-plume approach (TPA), as well as provide a quantitative evaluation of their uncertainty. Estimated exit velocities are between 160 and 230 m/s in the paroxysmal phase. The intercomparison between the SFA, MCA, and TPA methods, in terms of retrieved MER, shows a fairly good consistency with values up to $2.4\times 10^{6}$ kg/s. The estimated total erupted mass (TEM) is $3.8\times 10^{9}$ , $3.9\times 10^{9}$ , and $4.7\times 10^{9}$ kg for SFA with L-band, X-band, and thermal-infrared camera, respectively. Estimated TEM is between $1.7\times 10^{9}$ kg and $4.3\times 10^{9}$ for TPA methods and $3.9\times 10^{9}$ kg for the MCA technique. The SFA, MCA, and TPA results for TEM are in fairly good agreement with independent evaluations derived from ground collection of tephra deposit and estimated to be between $1.3\,\,\pm \,\,1.1\times 10^{9}$ and $5.7\times 10^{9}$ kg. This article shows that complementary strategies of ground-based remote sensing systems can provide an accurate real-time monitoring of a volcanic explosive activity.
Highlights
The characterization of the source parameters of explosive eruptions is of significant interest due to the environmental, climatic, and socioeconomic impact of tephra dispersal and sedimentation which might cause hardship and damages in areas surrounding volcanoes, including threat to aviation [9]
Three different approaches have been presented and compared to determine mass eruption rate from microwave radars at L band (23.5 cm wavelength) and X band (3.1 cm wavelength), namely the surface-flux approach (SFA), the mass-continuity approach (MCA) and the top-plume approach (TPA). These approaches exploit the radar Doppler or polarimetric capabilities as well as fixed-pointing or scanning mode and both radar data have been processed by means of the model-based volcanic ash radar retrieval (VARR) methodology
We have discussed the overall formulation and some assumptions behind both Surface-Flux Approach (SFA) and Top-Plume Approach (TPA) methods, showing how these uncertainties can reflect into the estimate of the total erupted mass as well as time-average discharge rates
Summary
The characterization of the source parameters of explosive eruptions is of significant interest due to the environmental, climatic, and socioeconomic impact of tephra dispersal and sedimentation which might cause hardship and damages in areas surrounding volcanoes, including threat to aviation [9]. On 23 November 2013 an intense explosive eruption formed from the NSEC and lasted for about an hour This eruption has been widely analyzed in previous works, focusing on the eruptive processes and tephra volumes [3], integration of observational data [10], tephra fallout characterization [1], plume dynamics [36] and total grain-size distribution retrieval [38]. In this respect, few instrument-based estimates are available for the time series of the mass eruption rate, that is the amount of material erupted per unit time, a key parameter for evaluating hazard assessment and for ash plume dispersion model initialization [45], [4], [33], [34]
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