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| Titel |
Timescales of bubble coalescence, outgassing, and foam collapse in decompressed rhyolitic melts |
| VerfasserIn |
Caroline Martel, Giada Iacono-Marziano |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250126403
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| Publikation (Nr.) |
 EGU/EGU2016-6117.pdf |
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| Zusammenfassung |
| The timescale of degassing and outgassing in hydrous rhyolitic melts is investigated in a wide
range of conditions by means of decompression experiments. The evolution of
vesicularity, bubble diameter, and number density is characterized as a function of time
either of decompression or spent at final pressure, in order to determine the effect
of final pressure, temperature, syn- versus post-decompression degassing, melt
composition, and microlites, on the timescale of bubble growth, coalescence, and
outgassing.
The result suggest that different bubble evolution and degassing-outgassing timescale
corresponding to explosive and effusive eruption regimes can be cast in bulk viscosity (melt +
bubbles; nbulk) versus decompression time (rather than path) space. The nbulk–time
relationships defines three domains of (i) bubble nucleation and growth, restricted to short
durations and high nbulk (< ∼0.03 h for nbulk ∼105−6Pa.s), (ii) equilibrium degassing
with coalescence increasing from negligible (permeability > 10−13 m2) to extensive
(permeability ∼10−11−12 m2), and (iii) outgassing, restricted to long durations and low
nbulk(> ∼10 h for nbulk < 106 Pa.s; permeability >10−10 m2) that eventually leads to
foam collapse.
These findings are applied to the case studies of Mt Pelée and Mt Pinatubo to infer the
transition from pumice to dense pyroclasts in volcanic eruptions and the possibility of
evolving from an explosive Plinian eruption to an effusive dome-growth event by giving the
vesicular magma enough time to outgas and collapse (i.e. hundreds to tens of hours for
nbulk ∼105 to 104 Pa.s, respectively). We also show the drastic effect of microlites on
re-arranging preexistent bubbles and potentially triggering a late nucleation event. |
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