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dc.contributor.author
Cas, Raymond A. F.
dc.contributor.author
Wrigth, Heather M. N.
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Folkes, Chris B.
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Lesti, Chiara
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Porreca, Massimiliano
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Giordano, Guido
dc.contributor.author
Viramonte, Jose German
dc.date.available
2017-03-30T20:05:13Z
dc.date.issued
2011-12
dc.identifier.citation
Cas, Raymond A. F.; Wrigth, Heather M. N.; Folkes, Chris B.; Lesti, Chiara; Porreca, Massimiliano; et al.; The flow dynamics of an extremely large volume pyroclastic flow, the 2.08-Ma Cerro Galán Ignimbrite, NW Argentina, and comparison with other flow types; Springer Verlag Berlín; Bulletin Of Volcanology; 73; 10; 12-2011; 1583-1609
dc.identifier.issn
0258-8900
dc.identifier.uri
http://hdl.handle.net/11336/14555
dc.description.abstract
The 2.08-Ma Cerro Galán Ignimbrite (CGI) represents a >630-km3 dense rock equivalent (VEI 8) eruption from the long-lived Cerro Galán magma system (∼6 Ma). It is a crystal-rich (35–60%), pumice (<10% generally) and lithic-poor (<5% generally) rhyodacitic ignimbrite, lacking a preceding plinian fallout deposit. The CGI is preserved up to 80 km from the structural margins of the caldera, but almost certainly was deposited up to 100 km from the caldera in some places. Only one emplacement unit is preserved in proximal to medial settings and in most distal settings, suggesting constant flow conditions, but where the pyroclastic flow moved into a palaeotopography of substantial valleys and ridges, it interacted with valley walls, resulting in flow instabilities that generated multiple depositional units, often separated by pyroclastic surge deposits. The CGI preserves a widespread sub-horizontal fabric, defined by aligned elongate pumice and lithic clasts, and minerals (e.g. biotite). A sub-horizontal anisotropy of magnetic susceptibility fabric is defined by minute magnetic minerals in all localities where it has been analysed. The CGI is poor in both vent-derived (‘accessory’) lithics and locally derived lithics from the ground surface (‘accidental’) lithics. Locally derived lithics are small (<20 cm) and were not transported far from source points. All data suggest that the pyroclastic flow system producing the CGI was characterised throughout by high sedimentation rates, resulting from high particle concentration and suppressed turbulence at the depositional boundary layer, despite being a low aspect ratio ignimbrite. Based on these features, we question whether high velocity and momentum are necessary to account for extensive flow mobility. It is proposed that the CGI was deposited by a pyroclastic flow system that developed a substantial, high particle concentration granular under-flow, which flowed with suppressed turbulence. High particle concentration and fine-ash content hindered gas loss and maintained flow mobility. In order to explain the contemporaneous maintenance of high particle concentration, high sedimentation rate at the depositional boundary layer and a high level of mobility, it is also proposed that the flow(s) was continuously supplied at a high mass feeding rate. It is also proposed that internal gas pressure within the flow, directed downwards onto the substrate over which the flow was passing, reduced the friction between the flow and the substrate and also enhanced its mobility. The pervasive sub-horizontal fabric of aligned pumice, lithic and even biotite crystals indicates a consistent horizontal shear force existed during transport and deposition in the basal granular flow, consistent with the existence of a laminar, shearing, granular flow regime during the final stages of transport and deposition.
dc.format
application/pdf
dc.language.iso
eng
dc.publisher
Springer Verlag Berlín
dc.rights
info:eu-repo/semantics/openAccess
dc.rights.uri
https://creativecommons.org/licenses/by-nc-sa/2.5/ar/
dc.subject
Cerro Galán Caldera/ Ignimbrite
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Vei 8 Magnitude Eruption
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Crystal Rich Ignimbrite
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Laminar Like
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Vulcanología
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Ciencias de la Tierra y relacionadas con el Medio Ambiente
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CIENCIAS NATURALES Y EXACTAS
dc.title
The flow dynamics of an extremely large volume pyroclastic flow, the 2.08-Ma Cerro Galán Ignimbrite, NW Argentina, and comparison with other flow types
dc.type
info:eu-repo/semantics/article
dc.type
info:ar-repo/semantics/artículo
dc.type
info:eu-repo/semantics/publishedVersion
dc.date.updated
2017-03-29T14:45:28Z
dc.identifier.eissn
1432-0819
dc.journal.volume
73
dc.journal.number
10
dc.journal.pagination
1583-1609
dc.journal.pais
Alemania
dc.journal.ciudad
Berlin
dc.description.fil
Fil: Cas, Raymond A. F.. Monash University; Australia
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Fil: Wrigth, Heather M. N.. Monash University; Australia
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Fil: Folkes, Chris B.. Monash University; Australia
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Fil: Lesti, Chiara. Università di Roma Tre; Italia
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Fil: Porreca, Massimiliano. Università di Roma Tre; Italia
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Fil: Giordano, Guido. Università di Roma Tre; Italia
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Fil: Viramonte, Jose German. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Instituto Geonorte; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta. Instituto de Investigaciones en Energía no Convencional; Argentina
dc.journal.title
Bulletin Of Volcanology
dc.relation.alternativeid
info:eu-repo/semantics/altIdentifier/doi/http://dx.doi.org/10.1007/s00445-011-0564-y
dc.relation.alternativeid
info:eu-repo/semantics/altIdentifier/url/https://link.springer.com/article/10.1007%2Fs00445-011-0564-y
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