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| Titel |
Stability of volcanic conduits: insights from magma ascent modelling and possible consequences on eruptive dynamics |
| VerfasserIn |
Alvaro Aravena, Mattia de' Michieli Vitturi, Raffaello Cioni, Augusto Neri |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250137761
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| Publikation (Nr.) |
 EGU/EGU2017-576.pdf |
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| Zusammenfassung |
| Geological evidences of changes in volcanic conduit geometry (i.e. erosive processes) are
common in the volcanic record, as revealed by the occurrence of lithic fragments in most
pyroclastic deposits. However, the controlling factors of conduit enlargement mechanisms are
still partially unclear, as well as the influence of conduit geometry in the eruptive dynamics.
Despite physical models have been systematically used for studying volcanic conduits, their
mechanical stability has been poorly addressed.
In order to study the mechanical stability of volcanic conduits during explosive eruptions,
we present a 1D steady-state model which considers the main processes experimented by
ascending magmas, such as crystallization, drag forces, fragmentation, outgassing and
degassing; and the application of the Mogi-Coulomb collapse criterion, using a set of
constitutive equations for studying typical cases of rhyolitic and trachytic explosive
volcanism.
From our results emerge that conduit stability is mainly controlled by magma rheology
and conduit dimensions. Indeed, in order to be stable, feeding conduits of rhyolitic eruptions
need larger radii respect to their trachytic counterparts, which is manifested in the higher
eruption rates usually observed in rhyolitic explosive eruptions, as confirmed by a small
compilation of global data. Additionally, for both magma compositions, we estimated a
minimum magma flux for developing stable conduits (∼3⋅106 kg/s for trachytic magmas and
∼8⋅107 kg/s for rhyolitic magmas), which is consistent with the unsteady character
commonly observed in low-mass flux events (e.g. sub-Plinian eruptions), which would be
produced by episodic collapse events of the volcanic conduit, opposite to the mainly
stationary high-mass flux events (e.g. Plinian eruptions), characterized by stable
conduits.
For a given magma composition, a minimum radius for reaching stable conditions can be
computed, as a function of inlet overpressure and water content. Under the assumption that
magma chamber conditions during a typical volcanic eruption follow a depressurizing trend,
a continuous conduit widening process is expected. This process could explain the pervasive
and continuous presence of lithic fragments in most pyroclastic deposits, even with stationary
properties and conditions of the magma source (e.g. water content, temperature,
composition). |
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