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Aggregation-dominated ash settling from the Eyjafjallajökull volcanic cloud illuminated by field and laboratory high-speed imaging
Author(s)
Language
English
Obiettivo Specifico
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
/39 (2011)
Publisher
Geologica Society of America
Pages (printed)
891–894
Issued date
September 2011
Keywords
Abstract
The recent Eyjafjallajökull (Iceland) eruption strikingly under-lined the vulnerability of a globalized society to the atmospheric
dispersal of volcanic clouds from even moderate-size eruptions. Ash
aggregation controls volcanic clouds dispersal by prematurely remov-ing fi ne particles from the cloud and depositing them more proxi-mally. Physical parameters of ash aggregates have been modeled and
derived from ash fallout deposits of past eruptions, yet aggregate
sedimentation has eluded direct measurement, limiting our ability to
predict the dispersal of volcanic clouds. Here we use fi eld-based, high-speed video analysis together with laboratory experiments to provide
the fi rst in situ investigation and parameterization of the physical fea-tures and settling dynamics of ash aggregates from a volcanic cloud.
In May 2010, high-speed video footage was obtained of both ash par-ticles and aggregates settling from the Eyjafjallajökull volcano erup-tion cloud at a distance of 7 km from the vent; fallout samples were
collected simultaneously. Experimental laboratory determinations of
the density, morphology, and settling velocity of individual ash par-ticles enable their distinction from aggregates. The combination of
fi eld and experimental analyses allows a full characterization of the
size, settling velocity, drag coeffi cient, and density distributions of ash
aggregates as well as the size distribution of their component par-ticles. We conclude that ash aggregation resulted in a tenfold increase
in mass sedimentation rate from the cloud, aggravating the ash haz-ard locally and modifying cloud dispersal regionally. This study pro-vides a valuable tool for monitoring explosive eruptions, capable of
providing robust input parameters for models of cloud dispersal and
consequent hazard forecast
dispersal of volcanic clouds from even moderate-size eruptions. Ash
aggregation controls volcanic clouds dispersal by prematurely remov-ing fi ne particles from the cloud and depositing them more proxi-mally. Physical parameters of ash aggregates have been modeled and
derived from ash fallout deposits of past eruptions, yet aggregate
sedimentation has eluded direct measurement, limiting our ability to
predict the dispersal of volcanic clouds. Here we use fi eld-based, high-speed video analysis together with laboratory experiments to provide
the fi rst in situ investigation and parameterization of the physical fea-tures and settling dynamics of ash aggregates from a volcanic cloud.
In May 2010, high-speed video footage was obtained of both ash par-ticles and aggregates settling from the Eyjafjallajökull volcano erup-tion cloud at a distance of 7 km from the vent; fallout samples were
collected simultaneously. Experimental laboratory determinations of
the density, morphology, and settling velocity of individual ash par-ticles enable their distinction from aggregates. The combination of
fi eld and experimental analyses allows a full characterization of the
size, settling velocity, drag coeffi cient, and density distributions of ash
aggregates as well as the size distribution of their component par-ticles. We conclude that ash aggregation resulted in a tenfold increase
in mass sedimentation rate from the cloud, aggravating the ash haz-ard locally and modifying cloud dispersal regionally. This study pro-vides a valuable tool for monitoring explosive eruptions, capable of
providing robust input parameters for models of cloud dispersal and
consequent hazard forecast
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