New Insights Into the 2070calyrBP Pyroclastic Currents at El Misti Volcano (Peru) From Field Investigations, Satellite Imagery and Probabilistic Modeling

Abstract

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 km 3) 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 (2 m) 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 km 2 for a total bulk volume estimated at 406 ± 140 × 10 6 m 3. 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 multidisciplinary 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.

Synthetic benchmarking of concentrated pyroclastic current models

“…and Kelfoun (2017), and confirmed/validated for CPCs inKelfoun et al (2009), Gertisser (2012), Gueugneau et al (2017) using an alternate version including pore pressure, and more recently inKelfoun et al (2017),Gueugneau et al (2019Gueugneau et al ( , 2020 andCharbonnier et al (2020) using the two-layer version of the code(Kelfoun 2017).TITAN2D(Patra et al 2005) was developed initially to model geophysical mass flows. It has been extensively used in volcanology to simulate CPCs.…”

Uncertainty Quantification of Eruption Source Parameters Estimated From Tephra Fall Deposits

“…We attribute this variability to the roughness of topography (i.e., deep and steep valleys separated by relatively flatter interfluves) combined with postdepositional processes (e.g., Buckland et al., 2020; Engwell et al., 2013; Green et al., 2016). While the tephra deposit was buried and compacted by thick pyroclastic flow deposits in the valleys (Charbonnier et al., 2020; Thouret et al., 2001), the exposed material on the interfluves was subjected to intense erosion (Cobeñas et al., 2012). Owing to the climatic conditions, deposits in the distal facies (>26 km from the vent) are poorly preserved and a vast area of the medial facies has been covered by the city of Arequipa.…”

“…The 2070 BP eruption of El Misti (Peru) was a Plinian (VEI 4) event that produced extensive pumice fall and flow deposits (Supplementary Note 1 in Supporting Information S1; Charbonnier et al, 2020;Cobeñas et al, 2012Cobeñas et al, , 2014Harpel et al, 2011;Thouret et al, 2001). We sample the lower-most lapilli-rich tephra fall unit from this complex eruption and measure its deposit thickness at 30 localities (Supplementary Note 1; Figure S1 in Supporting Information S1).…”

Probabilistic multi – hazard assessment at an active but under-monitored volcano: Ceboruco, Mexico

“…The ability to combine multiple sources of information, as well as the possibility of exploring various combinations of eruptive scenarios leads to a better estimate of the uncertainty associated with different hazard maps. Probabilistic hazard maps are usually conducted for a single volcanic phenomenon by using different numerical simulation tools (Charbonnier et al 2020;Gallant et al 2018). PyBetVH can merge the outputs of different simulation tools with geological data and assess the uncertainty range associated with the average prior probability presented in each map.…”