Tracking dynamics of magma migration in open-conduit systems

Abstract

Open-conduit volcanic systems are typically characterized by unsealed volcanic conduits feeding permanent or quasi-permanent volcanic activity. This persistent activity limits our ability to read changes in the monitored parameters, making the assessment of possible eruptive crises more difficult. We show how an integrated approach to monitoring can solve this problem, opening a new way to data interpretation. The increasing rate of explosive transients, tremor amplitude, thermal emissions of ejected tephra, and rise of the very-long- period (VLP) seismic source towards the surface are interpreted as indicating an upward migration of the magma column in response to an increased magma input rate. During the 2014 flank eruption of Stromboli, this magma input pre- ceded the effusive eruption by several months. When the new lateral effusive vent opened on the Sciara del Fuoco slope, the effusion was accompanied by a large ground deflation, a deepening of the VLP seismic source, and the cessation of summit explosive activity. Such observations suggest the drainage of a superficial magma reservoir confined between the crater terrace and the effusive vent. We show how this model successfully reproduces the measured rate of effusion, the observed rate of ground deflation, and the deepening of the VLP seismic source. This study also demonstrates the ability of the geophysical network to detect superficial magma recharge within an open-conduit system and to track magma drainage during the effusive crisis, with a great impact on hazard assessment

Exploring the explosive‐effusive transition using permanent ultraviolet cameras

“…All recent effusive eruptions on Stromboli (2003, 2007, and 2014) are accompanied by gravitational failure of the upper volcano's flank, causing drainage of magma in upper feeding conduits [ Ripepe et al ., ]. Such flank failure events come after periods (months) of unusually strong strombolian activity at the summit craters [ Ripepe et al ., , ; Calvari et al ., ; Barberi et al ., ; Valade et al ., ]. UV cameras are, at least in principle, particularly suitable for identifying such preeffusion escalating strombolian activity because, in contrast to UV scanning techniques that target the “bulk” distal plume [ Galle et al ., ], they contribute near‐vent gas observations discriminating between passive (quiescent) and active (explosive) SO 2 degassing modes [ Tamburello et al ., ].…”

“…Our novel permanent UV camera at ROC (Figure ) offers a proximal view on the crater terrace (Figure ) and is thus ideal for charactering active versus passive degassing modes at Stromboli. Although possibly underestimating (by a factor up to 50%) the real total volcanic SO 2 fluxes, with a fraction of emissions from the SW + Central craters potentially escaping detection, the permanent UV camera system makes a unique observational spot on the northeastern segment of the crater terrace, which has been the theater of all recent Stromboli's effusive unrests [ Ripepe et al ., , ; Calvari et al ., ; Valade et al ., ].…”

“…As in previous eruptions, onset of the effusive event was preceded by ~2 months of escalating explosive activity at the summit craters [ Valade et al ., ]. This was followed by gravitational failure of the upper northeastern portion of the crater terrace, with the opening of a lateral effusive vent along the Sciara del Fuoco on 7 August 2014, at 05:00 GMT [ Valade et al ., ]. Effusive rates were very high (>20 m 3 /s) in the first 2 days, resulting in the emission of ∼1.6 × 10 6 m 3 of lava, due to rapid drainage of the upper conduit system [ Ripepe et al ., ].…”

“…The eruption exhibited a number of similarities as with recent effusive crises in 1985 [ De Fino et al ., ], 2002–2003 [ Calvari et al ., ] and 2007 [ Barberi et al ., ]. As in previous eruptions, onset of the effusive event was preceded by ~2 months of escalating explosive activity at the summit craters [ Valade et al ., ]. This was followed by gravitational failure of the upper northeastern portion of the crater terrace, with the opening of a lateral effusive vent along the Sciara del Fuoco on 7 August 2014, at 05:00 GMT [ Valade et al ., ].…”

“…This increased magma transport in the shallow feeding conduit(s) initially causes intensification of strombolian activity and finally leads to fracture opening within the gravitationally unstable Sciara del Fuoco scar and onset of lava effusion. The precursory acceleration of strombolian activity is typically detected by large variations in geophysical parameters [ Ripepe et al ., , ; Valade et al ., ] but is more difficult to identify in the gas flux record.…”