Pyroclastic density currents associated with the 2008-2009 eruption of Chaitén Volcano (Chile): Forest disturbances, deposits, and dynamics

Explosive activity at Chaitén Volcano in May 2008 and subsequent dome collapses over the following nine months triggered multiple, small-volume pyroclastic density currents (PDCs). The explosive activity triggered PDCs to the north and northeast, which felled modest patches of forest as far as 2 km...

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Autores principales:	Major,Jon J, Pierson,Thomas C, Hoblitt,Richard P, Moreno,Hugo
Lenguaje:	English
Publicado:	Servicio Nacional de Geología y Minería (SERNAGEOMIN) 2013
Materias:	Chaitén Volcano Pyroclastic density current Directed explosions Dome collapse Block-and-ash flow Dynamic pressure Flow velocity Temperature
Acceso en línea:	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062013000200009
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spelling	oai:scielo:S0718-710620130002000092013-07-31Pyroclastic density currents associated with the 2008-2009 eruption of Chaitén Volcano (Chile): Forest disturbances, deposits, and dynamicsMajor,Jon JPierson,Thomas CHoblitt,Richard PMoreno,Hugo Chaitén Volcano Pyroclastic density current Directed explosions Dome collapse Block-and-ash flow Dynamic pressure Flow velocity Temperature Explosive activity at Chaitén Volcano in May 2008 and subsequent dome collapses over the following nine months triggered multiple, small-volume pyroclastic density currents (PDCs). The explosive activity triggered PDCs to the north and northeast, which felled modest patches of forest as far as 2 km from the caldera rim. Felled trees pointing in the down-current direction dominate the disturbance zones. The PDC on the north flank of Chaitén left a decimeters-thick, bipartite deposit having a basal layer of poorly sorted, fines-depleted pumice-and-lithic coarse ash and lapilli, which transitions abruptly to fines-enriched pumice-and-lithic coarse ash. The deposit contains fragments of mostly uncharred organics near its base; vegetation protruding above the deposit is uncharred. The nature of the forest disturbance and deposit characteristics suggest the PDC was dilute, of relatively low temperature (<200°C), and to first approximation had a dynamic pressure of about 2-4 kPa and velocity of about 30-40 ms-1. It was formed by directionally focused explosions through the volcano's prehistoric, intracaldera lava dome. Dilute, low-temperature PDCs that exited the caldera over a low point on the east-southeast caldera rim deposited meters-thick fill of stratified beds of pumice-and-lithic coarse ash and lapilli. They did not fell large trees more than a few hundreds of meters from the caldera rim and were thus less energetic than those on the north and northeast flanks. They likely formed by partial collapses of the margins of vertical eruption columns. In the Chaitén River valley south of the volcano, several-meter-thick deposits of two block-and-ash-flow (BAF) PDCs are preserved. Both have a coarse ash matrix that supports blocks and lapilli predominantly of lithic rhyolite dome rock, minor obsidian, and local bedrock. One deposit was emplaced by a BAF that traveled an undetermined distance downvalley between June and November 2008, apparently triggered by partial collapse of a newly effused lava dome that started growing on 12 May. A second, and larger, BAF related to another collapse of the new lava dome on 19 February 2009 traveled to within 3 km of the village of Chaitén, 10 km downstream of the volcano. It deposited as much as 8-10 m of diamict having sedimentary characteristics very similar to the previous BAF deposit. Charred trees locally encased within the BAF deposits suggest that the flows were of moderate temperature, perhaps as much as 300°C. Erosion of the BAF deposits filling the Chaitén River channel has delivered substantial sediment loads downstream, contributing to channel instability and challenged river management.info:eu-repo/semantics/openAccessServicio Nacional de Geología y Minería (SERNAGEOMIN)Andean geology v.40 n.2 20132013-05-01text/htmlhttp://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062013000200009en10.5027/andgeoV40n2-a09
institution	Scielo Chile
collection	Scielo Chile
language	English
topic	Chaitén Volcano Pyroclastic density current Directed explosions Dome collapse Block-and-ash flow Dynamic pressure Flow velocity Temperature
spellingShingle	Chaitén Volcano Pyroclastic density current Directed explosions Dome collapse Block-and-ash flow Dynamic pressure Flow velocity Temperature Major,Jon J Pierson,Thomas C Hoblitt,Richard P Moreno,Hugo Pyroclastic density currents associated with the 2008-2009 eruption of Chaitén Volcano (Chile): Forest disturbances, deposits, and dynamics
description	Explosive activity at Chaitén Volcano in May 2008 and subsequent dome collapses over the following nine months triggered multiple, small-volume pyroclastic density currents (PDCs). The explosive activity triggered PDCs to the north and northeast, which felled modest patches of forest as far as 2 km from the caldera rim. Felled trees pointing in the down-current direction dominate the disturbance zones. The PDC on the north flank of Chaitén left a decimeters-thick, bipartite deposit having a basal layer of poorly sorted, fines-depleted pumice-and-lithic coarse ash and lapilli, which transitions abruptly to fines-enriched pumice-and-lithic coarse ash. The deposit contains fragments of mostly uncharred organics near its base; vegetation protruding above the deposit is uncharred. The nature of the forest disturbance and deposit characteristics suggest the PDC was dilute, of relatively low temperature (<200°C), and to first approximation had a dynamic pressure of about 2-4 kPa and velocity of about 30-40 ms-1. It was formed by directionally focused explosions through the volcano's prehistoric, intracaldera lava dome. Dilute, low-temperature PDCs that exited the caldera over a low point on the east-southeast caldera rim deposited meters-thick fill of stratified beds of pumice-and-lithic coarse ash and lapilli. They did not fell large trees more than a few hundreds of meters from the caldera rim and were thus less energetic than those on the north and northeast flanks. They likely formed by partial collapses of the margins of vertical eruption columns. In the Chaitén River valley south of the volcano, several-meter-thick deposits of two block-and-ash-flow (BAF) PDCs are preserved. Both have a coarse ash matrix that supports blocks and lapilli predominantly of lithic rhyolite dome rock, minor obsidian, and local bedrock. One deposit was emplaced by a BAF that traveled an undetermined distance downvalley between June and November 2008, apparently triggered by partial collapse of a newly effused lava dome that started growing on 12 May. A second, and larger, BAF related to another collapse of the new lava dome on 19 February 2009 traveled to within 3 km of the village of Chaitén, 10 km downstream of the volcano. It deposited as much as 8-10 m of diamict having sedimentary characteristics very similar to the previous BAF deposit. Charred trees locally encased within the BAF deposits suggest that the flows were of moderate temperature, perhaps as much as 300°C. Erosion of the BAF deposits filling the Chaitén River channel has delivered substantial sediment loads downstream, contributing to channel instability and challenged river management.
author	Major,Jon J Pierson,Thomas C Hoblitt,Richard P Moreno,Hugo
author_facet	Major,Jon J Pierson,Thomas C Hoblitt,Richard P Moreno,Hugo
author_sort	Major,Jon J
title	Pyroclastic density currents associated with the 2008-2009 eruption of Chaitén Volcano (Chile): Forest disturbances, deposits, and dynamics
title_short	Pyroclastic density currents associated with the 2008-2009 eruption of Chaitén Volcano (Chile): Forest disturbances, deposits, and dynamics
title_full	Pyroclastic density currents associated with the 2008-2009 eruption of Chaitén Volcano (Chile): Forest disturbances, deposits, and dynamics
title_fullStr	Pyroclastic density currents associated with the 2008-2009 eruption of Chaitén Volcano (Chile): Forest disturbances, deposits, and dynamics
title_full_unstemmed	Pyroclastic density currents associated with the 2008-2009 eruption of Chaitén Volcano (Chile): Forest disturbances, deposits, and dynamics
title_sort	pyroclastic density currents associated with the 2008-2009 eruption of chaitén volcano (chile): forest disturbances, deposits, and dynamics
publisher	Servicio Nacional de Geología y Minería (SERNAGEOMIN)
publishDate	2013
url	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062013000200009
work_keys_str_mv	AT majorjonj pyroclasticdensitycurrentsassociatedwiththe20082009eruptionofchaitenvolcanochileforestdisturbancesdepositsanddynamics AT piersonthomasc pyroclasticdensitycurrentsassociatedwiththe20082009eruptionofchaitenvolcanochileforestdisturbancesdepositsanddynamics AT hoblittrichardp pyroclasticdensitycurrentsassociatedwiththe20082009eruptionofchaitenvolcanochileforestdisturbancesdepositsanddynamics AT morenohugo pyroclasticdensitycurrentsassociatedwiththe20082009eruptionofchaitenvolcanochileforestdisturbancesdepositsanddynamics
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Pyroclastic density currents associated with the 2008-2009 eruption of Chaitén Volcano (Chile): Forest disturbances, deposits, and dynamics

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