Systematic retrieval of ejecta velocities and gas fluxes at Etna volcano using L-Band Doppler radar

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 $V_{{\max }}^p = {94}.{7}\pm {24} {\text{m/s}}$, a bulk lava jet velocity of ${V_{{{\text{PW - rad}}}}} = {37}.{6}\pm {1}.{9} {\text{m/s}}$, and an initial gas velocity at the source vent of $V_0^g = {118}.{4}\pm {36} {\text{m/s}}$. The time-averaged particle diameter is found to be about ${D_{{{\text{PW - rad}}}}} = {4}.{2}\pm {2}.{1} {\text{cm}}$. The volume and mass gas fluxes are estimated from time-averaged source gas velocities over the sequence duration at $Q_v^g = {3} - {11} \times {1}{0^{{3}}}{{\text{m}}^{{3}}}{\text{/s}}$ and $Q_m^g = 0.{5} - {2} \times {1}{0^{{3}}}{\text{kg/s}}$, respectively.