Options
Alfano, F.
Loading...
Preferred name
Alfano, F.
2 results
Now showing 1 - 2 of 2
- PublicationRestrictedConduit dynamics of highly explosive basaltic eruptions: The 1085 CE Sunset Crater sub-Plinian events(2019)
; ; ; ; ; ; ; ;; ; ; ; ;Basaltic volcanoes produce a range of eruptive styles, from Strombolian to low-intensity fire fountaining to, much more rarely, highly explosive Plinian eruptions. Although the hazards posed by highly explosive eruptions are considerable, controlling mechanisms remain unclear, and thus improving our understanding of such mechanisms is an important research objective. To elucidate these mechanisms, we investigate the magma ascent dynamics of basaltic systems using a 1D numerical conduit model. We find that variations in magmatic pressure at depth play a key role in controlling modelled eruption characteristics. Our most significant result is that a decrease in pressure at depth, consistent with the emptying of a magma chamber, results in enhanced volatile exsolution and in deepening fragmentation depth. The corresponding decrease in conduit pressure ultimately produces a collapse of the conduit walls. This type of collapse may be a key mechanism responsible for the cessation of individual explosive eruptions, a notion previously explored for silicic eruptions, but never before for basaltic systems. Using previously published field and sample analysis to constrain model parameters, we simulate scenarios consistent with sub-Plinian eruptions, similar to those at Sunset Crater volcano in ~1085 CE in terms of mass eruption rates and duration. By combining these analyses with a chamber-emptying model, we constrain the size of the magma chamber at Sunset Crater to be on the order of tens of km3. During the 1085 CE Sunset Crater eruption, there were three main sub-Plinian events that erupted between 0.12 and 0.33 km3 of tephra (non-DRE), indicating that ~1% of the total chamber volume was erupted during each sub-Plinian pulse.260 4 - PublicationRestrictedTephra sedimentation during the 2010 Eyjafjallajökull eruption (Iceland) from deposit, radar, and satellite observations(2011)
; ; ; ; ; ; ; ; ;Bonadonna, C.; Section of Earth and Environmental Sciences, University of Geneva, Geneva, Switzerland ;Genco, R.; Dipartimento di Scienze della Terra, Università di Firenze, Firenze, Italy ;Gouhier, M.; Laboratoire Magmas et Volcans, Université Blaise Pascal, Clermont-Ferrand, France ;Pistolesi, M.; Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy ;Cioni, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Alfano, F.; Section of Earth and Environmental Sciences, University of Geneva, Geneva, Switzerland ;Hoskuldsson, A.; Institute of Earth Sciences, University of Iceland, Reykjavik, Iceland ;Ripepe, M.; Dipartimento di Scienze della Terra, Università di Firenze, Firenze, Italy; ; ; ; ; ; ; The April–May 2010 eruption of the Eyjafjallajökull volcano (Iceland) was characterized by a nearly continuous injection of tephra into the atmosphere that affected various economic sectors in Iceland and caused a global interruption of air traffic. Eruptive activity during 4–8 May 2010 was characterized based on short-duration physical parameters in order to capture transient eruptive behavior of a long-lasting eruption (i.e., total grain-size distribution, erupted mass, and mass eruption rate averaged over 30 min activity). The resulting 30 min total grain-size distribution based on both ground and Meteosat Second Generation-Spinning Enhanced Visible and Infrared Imager (MSG-SEVIRI) satellite measurements is characterized by Mdphi of about 2 and a fine-ash content of about 30 wt %. The accumulation rate varied by 2 orders of magnitude with an exponential decay away from the vent, whereas Mdphi shows a linear increase until about 18 km from the vent, reaching a plateau of about 4.5 between 20 and 56 km. The associated mass eruption rate is between 0.6 and 1.2 × 105 kg s−1. In situ sampling showed how fine ash mainly fell as aggregates of various typologies. About 5 to 9 wt % of the erupted mass remained in the cloud up to 1000 km from the vent, suggesting that nearly half of the ash >7 settled as aggregates within the first 60 km. Particle sphericity and shape factor varied between 0.4 and 1 with no clear correlation to the size and distance from vent. Our experiments also demonstrate how satellite retrievals and Doppler radar grain-size detection can provide a real-time description of the source term but for a limited particle-size range.172 26