Abstract
A main challenge in open conduit volcanoes is to detect and interpret the ultra-small strain (<10–6) associated with minor but critical eruptions such as the lava fountains. Two years after the flank eruption of December 2018, Etna generated a violent and spectacular eruptive sequence of lava fountains. There were 23 episodes from December 13, 2020 to March 31, 2021, 17 of which in the brief period 16 February to 31 March with an intensified occurrence rate. The high-precision borehole dilatometer network recorded significant strain changes in the forerunning phase of December 2020 accompanying the final magma migration at the shallower levels, and also during the single lava fountains and during the entire sequence. The source modeling provided further information on the shallow plumbing system. Moreover, the strain signals also gave useful information both on the explosive efficiency of the lava fountains sequence and the estimate of erupted volume. The high precision borehole dilatometers confirm to be strategic and very useful tool, also to detect and interpret ultra-small strain changes associated with explosive eruptions, such as lava fountains, in open conduit volcanoes.
Highlights
The magma uprising processes leading to volcanic eruptions produce ground deformation and strain changes
We show that the strain data constrained the shallow intrusion occurring during the seismic swarm on 19 December and how this represents a crucial turning point preceding the eruptive activity
The strain changes recorded during the single lava fountains and during the discharge phase in FebruaryMarch infer a vertically elongated source with its centroid positioned near 0.5–1 km b.s.l. confirming the position previously obtained for the lava fountains of 2011–2013 by Bonaccorso et al (2013)
Summary
The magma uprising processes leading to volcanic eruptions produce ground deformation and strain changes. Highly sensitive instruments, such as deep borehole dilatometers, are usually able to detect small strain changes up to a precision of 10–10 providing useful information during this eruptive activity (Currenti and Bonaccorso, 2019). The first one (Figure 2A), clearly observable at DRUV and DEGI, occurred in concomitance with a seismic swarm at a shallow depth a few kilometers below the summit crater area This episode was followed by two lava fountains 2 days later (Figure 2A). The second one, only detected at DRUV (Figure 1), preceded by about 15 h a second seismic swarm that instead occurred more distant from the crater area in the lower western flank at a depth of 9–14 km b.s.l. The decompression phase was characterized by a middle-term decompression and short-term step-like variations at the time of each lava fountain event. The recorded and expected values at each station are reported in Supplementary Table S2
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
