Modeling Tephra Fall and Sediment-Water Flows to Assess Their Impacts on a Vulnerable Building Stock in the City of Arequipa, Peru

Abstract

Arequipa, Peru’s second economic center hosting c. 1,110,000 inhabitants, is the largest South American city exposed to a large variety of natural hazards. At least 200,000 live in areas likely to be affected by hazards from El Misti volcano, located 17 km to the NE. A multidisciplinary project aims to address the impacts of tephra fall and frequent mass flows on the vulnerable building stock and roofs along two ravines that cross the city, enabling decision-makers to undertake retrofitting projects and improve urban risk planning. Two recent eruptions, that is, the 1440–1470 CE Vulcanian event and c. 2070 years BP Plinian eruption, were chosen as references for probable scenarios of potential tephra fall impacts from El Misti on the building roofs. Tephra fall impacts on the city depend on the eruptive style, column height, and patterns of wind directions and velocities over south Peru and roof mechanical resistance. Estimates of potential damage levels and cost range values rely on nine structural types and four classes of vulnerable roofs. Simulation runs of hyperconcentrated flows (HCF) and debris flows (DF), using three depth-averaged flow models (Titan2F, VolcFlow, and Flo-2D) along two drainage basins on the SW flank of El Misti and across Arequipa, examined three scenarios from a database of 39 recent events and other historical lahars. Simulation results showcase the extent toward the city, inundation depths ≤4.6 m, flow velocities ≤9 m/s, and dynamic pressure up to 100 kPa from three different magnitude HCFs and DFs. In both ravines, overbank flows occurred in key urban areas due to channel sinuosity and constrictions near bridges. Potential impacts on habitat stem from ranges of flow dynamic pressure and measurements of construction material. We estimated the monetary loss of buildings according to hyperconcentrated flows and debris flows scenarios to contribute to retrofitting procedure, implementation of defense work, and relocation policy.

Lahar events in the last 2,000 years from Vesuvius eruptions. Part 1: Distribution and impact on densely-inhabited territory estimated from field data analysis

“…In terms of local impact in the Pollena case study (the largest one), while most of the calculated points (44) fall in the range of lahar velocity of 2-4 m/s and dynamic pressure of 4-8 kPa, a few peak values of velocity of 13-15 m/s and dynamic pressure of 90-115 kPa are also calculated, which are directly related to meter-sized clasts entrained into the lahars on the steep slopes, then deposited downstream of alluvial fans. Such values of the velocity and dynamic pressure are well comparable with those calculated for lahars that occurred recently at Ruapehu in 2007 (Lube et al, 2012) and Merapi in 2011 (Jenkins et al, 2015), and in historical times at El Misti (Thouret et al, 2022). In particular, the estimated velocities and pressure agree with those of Lube et al (2012) and Jenkins et al (2015).…”

“…where a > 0 depends on clast properties, and its square has dimension of pressure. On the other hand, it is not straightforward to constrain local flow velocities with unique values of flow densities, mostly because small variations of velocity correspond to large variations of density, and this is particularly valid for volcaniclastic mass flows (Carling, 2013;Jenkins et al, 2015;Roche, 2015;Martí et al, 2019;Guzman et al, 2020;Thouret et al, 2022). At some locations in the study area, we found lahar deposits against meter-scale manufacturing obstacles (Di Vito et al, 2009).…”

Attempt to Model Lava Flow Faster Than Real Time: An Example of La Palma Using VolcFlow

“…), and it is able to calculate the advection of additional variables (density and temperature) in modified versions. From its beginning to the present, Vol-cFlow has been successfully used for simulating debris avalanches [80,[122][123][124][125], pyroclastic flows [81,126], tsunamis [127], and lava flows [33,52,128]. Additionally, it has provided very accurate and fast results in benchmark tests [21,67,68], and it is very well documented that it is very well balanced in terms of complexity and usability.…”

Riesgo y vulnerabilidad frente a peligros hidrogeológicos de movimientos en masa en La Quebrada del Diablo, Tacna, Perú

“…Debido a la ocupación antrópica, no había un cauce definido, lo que afectó las asociaciones de vivienda El Mirador, La Florida y San Pedro, así como al mercado principal y la terminal terrestre de Tacna, que se encuentran en la zona baja (Instituto Geológico Minero y Metalúrgico [INGEMET], 2020). Según afirma Thouret et al (2022), el evento repentino se produjo debido al entorno árido o semiárido, donde la lluvia se acumuló en un corto lapso y el suelo tenía poca capacidad para absorberla, lo que resultó en un rápido escurrimiento en las pendientes pronunciadas poco después de que comenzó la lluvia.…”