Isomass and Probability Maps of Ash Fallout Due to Vulcanian Eruptions at Tungurahua Volcano (Ecuador) Deduced from Historical Forecasting

Abstract

Since April of 2015, the ash dispersion and ash fallout due to Vulcanian eruptions at Tungurahua, one of the most active volcanoes in Ecuador, have been forecasted daily. For this purpose, our forecasting system uses the meteorological Weather Research and Forecasting (WRF) and the FALL3D models. Previously, and based on field data, laboratory, and numerical studies, corresponding eruption source parameters (ESP) have been defined. We analyzed the historically forecasted results of the ash fallout quantities over four years (April 2015 to March 2019), in order to obtain the average isomass and probability maps for three-month periods: February–March–April (FMA), May–June–July (MJJ), August–September–October (ASO), and November–December–January (NDJ). Our results indicate similar ash fallout shapes during MJJ and ASO, with a clear and defined tendency toward the west of the volcano; this tendency is less defined during NDJ and FMA. The proximal region west of the volcano (about 100 km to the west) has the highest probability (>70%) of being affected by ash fallout. The distant region to the west (more than 100 km west) presented low to medium probabilities (10%–70%) of ash fallout. The cities of Guaranda (W, 60% to 90%), Riobamba (SW, 70%), and Ambato (NW, 50% to 60%) have the highest probabilities of being affected by ash fallout. Among the large Ecuadorian cities, Guayaquil (SW, 10% to 30%) has low probability, and Quito (N, ≤5%) and Cuenca (SSE, <5%) have very low probabilities of being affected by ash fallout. High ash clouds can move in different directions, compared to wind transport near the surface. Therefore, it is possible to detect ash clouds by remote sensing which, in Ecuador, is limited to the layers over the meteorological clouds, which move in a different direction than low wind; the latter produces ash fallout over regions in different directions compared to the detected ash clouds. In addition to the isomass/probability maps and detected ash clouds, forecasting is permanently required in Ecuador.

Probabilistic hazard assessment for pyroclastic density currents at Tungurahua volcano, Ecuador

“…In total, over 25,000 people live in zones that could be affected by lahars, PDCs and other volcanic products of Tungurahua volcano (Hall et al 1999;Samaniego et al 2008). However, in spite of: (1) the numerous contributions on Tungurahua activity that have been recently published (Anderson et al 2018;Battaglia et al 2019;Bernard et al 2014;Douillet et al 2013;Eychenne et al 2012;Fee et al 2010;Gaunt et al 2020;Hall et al 2013;Kelfoun et al 2009;Mothes et al 2015;Palacios et al 2023;Parra et al 2020;Samaniego et al 2011); (2) the continuous effort of the Instituto Geofísico of the Escuela Politécnica Nacional (IG-EPN) in monitoring and understanding the internal dynamics of this volcano; and (3) major improvements in computational capacity, numerical models and uncertainty quantification (Aravena et al 2020;de' Michieli Vitturi et al 2019;Esposti Ongaro et al 2016;Flynn and Ramsey, 2020;Kelfoun, 2017;Kelfoun et al 2009;Neri et al 2015a;Sobradelo & Martí, 2010;Tadini et al 2020;de' Michieli Vitturi et al 2023), the Tungurahua volcano hazard map has not been updated since 2008 (Samaniego et al 2008). In this work, we present a probabilistic, scenario-based hazard assessment for PDCs produced during explosive eruptions at Tungurahua volcano.…”

Reducing uncertainty in building vulnerability and impact assessment for tephra hazards

“…Such maps have been used to forecast exposure to and impacts from tephra fall hazards in several previous studies (e.g. Biass et al, 2017;Parra et al, 2020;Reyes-Hardy et al, 2021). However, because probabilistic isomass maps aggregate a large number of simulations and treat them on a cell-by-cell basis, they do not represent the hazard associated with individual tephra dispersals possible in a future eruption.…”