Publication Date:
2021-06-16
Description:
Over the last twenty yearsMount Etna has produced more than one hundred explosive events ranging fromlight
ash emissions to violent sub-plinian eruptions. Significant hazards arise from tephra plumes which directly
threaten air traffic, and generate fallout affecting surrounding towns and infrastructures. We describe the first
radar system, named VOLDORAD 2B, fully integrated into a volcano instrumental network dedicated to the continuous
near-source monitoring of tephra emissions from Etna's summit craters. This 23.5 cmwavelength pulsed
Doppler radar is operated in collaboration between the Observatoire de Physique du Globe de Clermont-Ferrand
(OPGC) and the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo (INGV-OE) since 2009. Probed
volumes inside the fixed, northward-pointing conical beam total about 1.5 km in length, covering the summit
craters which produced all recent tephra plumes. The backscattered power, related to the amount of particles
crossing the beam, and particle along-beamvelocities are recorded every 0.23 s, providing a proxy for the tephra
mass eruption rate. Radar raw data are transmitted in real-time to the volcano monitoring center of INGV-OE in
Catania and are used to automatically release alerts at onset and end of eruptive events. Processed radar parameters
are also made available fromthe VOLDORAD database online (http://voldorad.opgc.fr/). In addition to eruptive
crater discrimination by range gating, relative variations of eruption intensity can be tracked, including
through overcast weather when other optical or infrared methods may fail to provide information. Short-lived
dense ash emissions can be detected as illustrated for weak ash plumes from the Bocca Nuova and New South
East craters in 2010. The comparison with thermal images suggests that the front mushroom of individual ash
plumes holds the largest particles (coarse ash and small lapilli) and concentrations at least within the first hundred
meters. For these short-lived ash plumes, the highest particle mass flux seems to occur typically within the
first 10 s.Wealso analyze data fromthe first lava fountain generating an ash and lapilli plumeon 12 January 2011
that initiated a series of 25 paroxysmal episodes of the New South East Crater until April 2012. We illustrate the
pulsating behavior of the lava fountain and showthat vertical velocities reached 250ms−1 (with brief peaks exceeding
300ms−1), leading to mean and maximumtephra fluxes (DRE) of 185 and 318m3 s−1 (with peaks exceeding
380 m3 s−1) respectively, and a total volume of pyroclasts emitted during the lava fountain phase of
1.3 × 106m3. Finally, we discuss capacities and limits of the instrument, alongwith future work aimed at providing
source term inputs to tephra dispersal models in order to improve hazard assessment and risk mitigation at
Etna.
Description:
Published
Description:
26-39
Description:
5V. Sorveglianza vulcanica ed emergenze
Description:
JCR Journal
Description:
restricted
Keywords:
Doppler radar
;
04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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