Exploring the explosive‐effusive transition using permanent ultraviolet cameras

Abstract

Understanding the mechanisms that cause effusive eruptions is the key to mitigating their associated hazard. Here we combine results from permanent ultraviolet (UV) cameras, and from other geophysical observations (seismic very long period, thermal, and infrasonic activity), to characterize volcanic SO2 flux regime in the period prior, during, and after Stromboli's August–November 2014 effusive eruption. We show that, in the 2 months prior to effusion onset, the SO2 flux levels are 2 times average level. We explain this anomalously high SO2 regime as primarily determined by venting of rapidly rising, pressurized SO2‐rich gas pockets produced by strombolian explosions being more frequent and intense than usual. We develop a procedure to track (and count), in the UV camera record, the SO2 flux pulses produced by individual explosions and puffing activity (active degassing). We find that these SO2 pulses are far more numerous (67 ± 47 events per hour) before the effusion onset than during normal activity (20 ± 15 events per hour). This observation, combined with geophysical evidence, demonstrates an elevated gas bubble supply to the shallow conduits, causing elevated explosive and puffing activity. This increase (≥0.1 m3 s−1) in magma transport rate in the north‐east feeding conduits finally triggers effusion onset. Active degassing remains elevated also during the effusive phase, supporting the persistence of explosive and puffing activity during the effusive eruption, deep in the volcanic conduit. Our results demonstrate that permanent UV cameras can valuably contribute to monitoring at high‐sampling frequency gas dynamics and fluxes, thus opening the way to direct comparison with more established geophysical observations.

The 2014 Effusive Eruption at Stromboli: New Insights from In Situ and Remote-Sensing Measurements

“…The SO 2 flux in the persistent Stromboli plume has been measured for two months before the onset of the eruption, detecting a strong increase above normal activity in the SO 2 pulses (puffing and explosions) before the effusion onset. This is consistent with the increase in gas bubble supply and magma transport rate feeding the uppermost storage system at Stromboli [47]. Ground displacement is consistent with the presence of a very shallow reservoir below the crater terrace [2].…”

Changes in SO2 Flux Regime at Mt. Etna Captured by Automatically Processed Ultraviolet Camera Data

“…In such cases, background sky detection within images might not be optimal and may then result in a main underestimation of the real SO2 column densities, as shown by the position of outliers ( Figure 6). Overall, this comparison validated the use of the automatic SO2 flux determination procedure, which paves the way to its full exploitation in real-time volcano monitoring, as already started on the Stromboli volcano (Italy) [32]. Figure 6.…”

“…We then calculated velocity (mean, maximum, and associated standard deviation) and absorbance distribution along an ideal profile positioned in the middle of the sub-area, derived from averaging a series of parallel profiles within the area of analysis. From this, the SO 2 density flux (in kgm −1 s −1 ) was calculated by multiplying column densities associated with each pixel of the profile with the corresponding normal velocity component of motion ( Figure 5, see also Reference [32]). Velocity profiles ( Figure 5) were obtained by averaging the calculated two-dimensional velocity fields, and filtering out velocity points with low coherence.…”

“…The first examples of fully automated, permanent UV camera systems [14,28,31,32] are particularly promising, since they are opening the way to routinely monitoring volcanic SO 2 flux at a high rate continuously (daily hours only). For example, Reference [32] has demonstrated the ability of UV cameras to capture a precursory phase of heightened SO 2 flux in the weeks prior to the 2014 effusive eruption at the Stromboli volcano (Italy).…”

Ultraviolet camera measurements of passive and explosive sulphur dioxide emissions at Yasur volcano, Vanuatu

“…Our approach is similar to the automated method of Delle Donne et al, (2017), which involved finding local peaks in timeseries data. For an example period ( Figure 7) we highlight the moving minimum, which is set to a window size of 20 s, which is generally the characteristic timeframe of large peaks and troughs associated with strombolian explosions (Delle Donne et al, 2017;.…”