New Insights Into the 2070calyrBP Pyroclastic Currents at El Misti Volcano (Peru) From Field Investigations, Satellite Imagery and Probabilistic Modeling
Résumé
Pyroclastic currents (PCs) are the most challenging volcanic hazards for disaster planners
in populated areas around volcanoes. “El Misti” volcano (5,825 m above sea level), located
only 17 km from the city center of Arequipa (>1.1 million inhabitants), South Peru, has
produced small-to-moderate volume (<1 km3) PCs with a frequency of 2,000–4,000 years
over the past 50 kyr. The most recent Plinian eruption dated at 2070 cal yr BP (VEI 4) has
been selected as one of the reference events for the hazard assessment and risk mitigation
plan of Arequipa. Associated pumice- and lithic-rich PC deposits were emplaced from at
least four phases of column-collapse into the radial valleys draining the volcano as far as
13 km toward the city. Field mapping and stratigraphic surveys conducted in seven valleys
affected by the 2070 cal yr BP PCs were combined with a new high-resolution (2m) digital
surface model of the volcano to better estimate the distribution of individual PC volumes.
Such data acquisition is particularly critical for two of these valleys (San Lázaro and
Huarangal-Mariano Melgar) for which the medial and distal reaches now cross the suburbs
of Arequipa. The total area covered by the PC deposits is estimated at 141 km2 for a total
bulk volume estimated at 406 ± 140 × 106m3. These volumes were used as input
parameters to better calibrate probabilistic numerical simulations of future similar PC
events using the two-layer VolcFlow model and assess the impacts of both the
concentrated and dilute portions of these currents in the San Lázaro and Huarangal
valleys. We discuss probability values of PC inundation obtained from these simulations
both in terms of their implications for the dynamics of such hazardous PCs at El Misti and
for their integration into its current multi-hazard assessment. Modeling results demonstrate
that the risk of overbank processes and spreading of unconfined PCs inside Arequipa
should be refined. This multi-disciplinary study aims to help the civil authorities’
understanding of the likely effects of PCs associated with a similar VEI 4 eruption of El
Misti on the urban area of Arequipa
Origine : Fichiers éditeurs autorisés sur une archive ouverte
Loading...