Systematic retrieval of ejecta velocities and gas fluxes at Etna volcano using L-Band Doppler radar |
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| Authors: | Mathieu Gouhier Franck Donnadieu |
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| Institution: | 1.Clermont Université,Université Blaise Pascal, OPGC, Laboratoire Magmas et Volcans,Clermont-Ferrand,France;2.CNRS, UMR 6524, LMV,Clermont-Ferrand,France;3.IRD, R 163, LMV,Clermont-Ferrand,France |
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| Abstract: | Strombolian-type volcanic activity is characterized by a series of gas bubbles bursting at the top of a magma column and leading
to the ejection of lava clots and gas emission at the surface. The quantitative analysis of physical parameters (e.g., velocity,
size, and mass fluxes) controlling the emission dynamics of these volcanic products is very important for the understanding
of eruption source mechanisms but remains difficult to obtain in a systematic fashion. Ground-based Doppler radar is found
to be a very effective tool for measuring ejecta velocities at a high acquisition rate and close to the emission source. We
present here a series of measurements carried out at Mt. Etna’s Southeast crater, using an L-band volcanological Doppler radar,
during the 4 July 2001 Strombolian eruptions. Doppler radar data are supplemented by the analysis of video snapshots recorded
simultaneously. We provide here a set of physical parameters systematically retrieved from 247 Strombolian explosions spanning
15 min and occurring during the paroxysm of the eruption from 21:30 to 21:45 UT. The time-average values give a maximum particle
velocity of
Vmaxp = 94.7±24 \textm/s V_{{\max }}^p = {94}.{7}\pm {24} {\text{m/s}} , a bulk lava jet velocity of
V\textPW - rad = 37.6±1.9 \textm/s {V_{{{\text{PW - rad}}}}} = {37}.{6}\pm {1}.{9} {\text{m/s}} , and an initial gas velocity at the source vent of
V0g = 118.4±36 \textm/s V_0^g = {118}.{4}\pm {36} {\text{m/s}} . The time-averaged particle diameter is found to be about
D\textPW - rad = 4.2±2.1 \textcm {D_{{{\text{PW - rad}}}}} = {4}.{2}\pm {2}.{1} {\text{cm}} . The volume and mass gas fluxes are estimated from time-averaged source gas velocities over the sequence duration at
Qvg = 3 - 11 ×103\textm3\text/s Q_v^g = {3} - {11} \times {1}{0^{{3}}}{{\text{m}}^{{3}}}{\text{/s}} and
Qmg = 0.5 - 2 ×103\textkg/s Q_m^g = 0.{5} - {2} \times {1}{0^{{3}}}{\text{kg/s}} , respectively. |
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