Explosive volcanic eruptions-VIII. The role of magma recycling in controlling the behaviour of Hawaiian-style lava fountains

Abstract

S U M M A R YExplosive eruptions of mafic magmas produce lava fountains whose heights are a function o f the exsolved volatile content of the magma, its erupted mass flux, and the geometry of the vent (which may be an elongate fissure or a localized. near-circular conduit). The geometry of the initial vent (and the cruptive behaviour) can be distinctly modified by lava drainback and accumulating ejecta. Hot pyroclasts landing near the vent may coalesce to form rootless flows, some of which may drain back into the vent to be recycled into the eruption products. Rootless flows may be at least partially confined by preexisting topographic features, or by spatter or cinder ramparts being built up by the eruption itself, so that they accumulate into a lava pond over and around the vent. The erupting jet of magmatic gas and pyroclasts must force its way through such a pond and will entrain some of the pond lava as it does so. The energy expended in entraining and accelerating previously crupted materials will reduce the eruption velocity and the lava fountain height by an amount which can be calculated as a function of the eruption conditions and the lava pond depth (or lava drainback rate). The results of such calculations are presented, and are used to assess the influence of this process on attempts to infer magma volatile contents from field observations of lava fountain heights.

Paroxysmal Explosions, Lava Fountains and Ash Plumes at Etna Volcano: Eruptive Processes and Hazard Implications

“…They are generated when large volumes of volatiles rapidly exsolve from the magma during its ascent and decompression along the conduit (Wilson et al, 1995). The mixture of gas and pyroclasts emerges from the vent as a jet (Wilson et al, 1995), expanding vertically into an eruptive column, where three main regions can be identified. The lowest portion is the gas-thrust region, and comprises the lava fountains (Sparks et al, 1997;Bonaccorso and Calvari, 2017).…”

“…Interestingly enough, the wind speed has important effects not just on the fine-grained portion of the plume, but even on the bombs and ballistics, being able to transport large ejecta for several kilometers down wind, causing damage to cars, solar panels, and windows (Andronico et al, 2015). It is difficult to univocally forecast plume height because it is related to the conditions and properties of the erupting system, such as magma discharge rate (Carey and Sparks, 1986), exsolved volatiles from magma, magma/water interaction (Schmith et al, 2018), and vent geometry (either elongated fissure or near-circular conduit; Wilson and Head, 1981;Wilson et al, 1995). Given that discharge rate and ultimately erupted volume have been measured from the lava fountain height Carbone et al, 2015;Bonaccorso and Calvari, 2017), there must be a direct connection between lava fountain height and maximum plume elevation, although this last parameter is also affected by wind speed (e.g., Bonadonna et al, 2015).…”

The role of collapsing and cone rafting on eruption style changes and final cone morphology: Los Morados scoria cone, Mendoza, Argentina

“…50 -1000 m 3 /s) [1,22,23]. In contrast, Strombolian activity typically produces pyroclasts that are relatively coarse grained and vesicular, but finer grained than those produced by Hawaiian style eruptions, reflecting more effective magma fragmentation [6,24]. Strombolian style eruptions are associated with a significantly lower magma flux rate (i.e.…”

Neogene-Quaternary Volcanic forms in the Carpathian-Pannonian Region: a review

“…Brought to you by | MIT Libraries Authenticated Download Date | 5/9/18 10:40 PM cosity and the gas content of the magma [99,100] producing Hawaiian [101,102] and Strombolian-style eruptions [38,103]. In general, the Strombolian-style magma fragmentation occurs at shallow depth (upper part of the magma column), when the over-pressurized and segregated gas-bubbles break and burst out from the rising, mostly mafic, magmas [38,[103][104][105].…”