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| Titel |
Similarities in basalt and rhyolite lava flow emplacement processes |
| VerfasserIn |
Nathan Magnall, Mike James, Hugh Tuffen, Charlotte Vye-Brown |
| 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 |
250129128
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| Publikation (Nr.) |
 EGU/EGU2016-9199.pdf |
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| Zusammenfassung |
| Here we use field observations of rhyolite and basalt lava flows to show similarities in flow
processes that span compositionally diverse lava flows. The eruption, and subsequent
emplacement, of rhyolite lava flows is currently poorly understood due to the infrequency
with which rhyolite eruptions occur. In contrast, the emplacement of basaltic lava flows are
much better understood due to very frequent eruptions at locations such as Mt Etna and
Hawaii.
The 2011-2012 eruption of Cordón Caulle in Chile enabled the first scientific
observations of the emplacement of an extensive rhyolite lava flow. The 30 to 100 m thick
flow infilled a topographic depression with a negligible slope angle (0 - 7˚ ). The flow split
into two main channels; the southern flow advanced 4 km while the northern flow advanced 3
km before stalling. Once the flow stalled the channels inflated and secondary flows or
breakouts formed from the flow front and margins. This cooling rather than volume-limited
flow behaviour is common in basaltic lava flows but had never been observed in rhyolite lava
flows.
We draw on fieldwork conducted at Cordón Caulle and at Mt Etna to compare the
emplacement of rhyolite and basaltic flows. The fieldwork identified emplacement features
that are present in both lavas, such as inflation, breakouts from the flow font and
margins, and squeeze-ups on the flow surfaces. In the case of Cordón Caulle, upon
extrusion of a breakout it inflates due to a combination of continued lava supply
and vesicle growth. This growth leads to fracturing and breakup of the breakout
surface, and in some cases a large central fracture tens of metres deep forms. In
contrast, breakouts from basaltic lava flows have a greater range of morphologies
depending on the properties of the material in the flows core. In the case of Mt Etna,
a range of breakout morphologies are observed including: toothpaste breakouts,
flows topped with bladed lava as well as breakouts of pahoehoe or a’a lava. This
range in breakout morphologies is in stark contrast to breakouts observed at Cordón
Caulle.
We also compare the cooled crusts that form on the surface of the flows; in basalts this is
of order tens of centimetres thick, in rhyolite flows the crust is of order several metres thick
(based on field observations and theoretical values). This surface crust may control the
flow advance in the latter phases of the flow evolution, causing stalling of the flow
front and subsequent breakout formation. The similarities in flow features between
compositional end members hints at a more universal model for lava flow emplacement. |
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