Eruption type probability and eruption source parameters at Cotopaxi and Guagua Pichincha volcanoes (Ecuador) with uncertainty quantification

Abstract

Future occurrence of explosive eruptive activity at Cotopaxi and Guagua Pichincha volcanoes, Ecuador, is assessed probabilistically, utilizing expert elicitation. Eight eruption types were considered for each volcano.Type event probabilities were evaluated for the next eruption at each volcano and for at least one of each type within the next 100 years. For each type, we elicited relevant eruption source parameters (duration, average plume height and total tephra mass). We investigated the robustness of these elicited evaluations by deriving probability uncertainties using three expert scoring methods. For Cotopaxi, we considered both rhyolitic and andesitic magmas. Elicitation findings indicate that the most probable next eruption type is an andesitic hydrovolcanic/ash-emission (~26-44% median probability), which has also the highest median probability of recurring over the next 100 years. However, for the next eruption at Cotopaxi, the average joint probabilities for sub-Plinian or Plinian type eruption is of order 30-40% -a significant chance of a violent explosive event. It is inferred that any Cotopaxi rhyolitic eruption could involve a longer duration and greater erupted mass than an andesitic event, likely producing a prolonged emergency. For Guagua Pichincha, future eruption types are expected to be andesitic/dacitic, and a vulcanian event is judged most probable for the next eruption (median probability ~40-55%); this type is expected to be most frequent over the next 100 years, too. However, there is a substantial probability (possibly >40% in average) that the next eruption could be sub-Plinian or Plinian, with all that implies for hazard levels.

Tephra Fallout Probabilistic Hazard Maps for Cotopaxi and Guagua Pichincha Volcanoes (Ecuador) With Uncertainty Quantification

“…The comparison to previous estimates based on temporal models of the eruptive record is thoroughly discussed in Tadini et al. (2021). A major advance was related to having obtained a probability distribution of eruption occurrence over an uncertainty range, thus enabling a doubly stochastic approach (Bevilacqua et al., 2016, 2018, 2020; Marzocchi et al., 2008, 2010; Neri et al., 2008; Tadini, Bisson, et al., 2017).…”

“…The three main ESPs (eruption duration, total mass of tephra fallout deposit, and average plume height) have been sampled directly from the distributions provided by Tadini et al. (2021) and reported in Figure 3.…”

“…The uncertainty distributions of these probabilities have been estimated in Tadini et al. (2021) and are reported in Figure 2a for Cotopaxi and Figure 2b for Guagua Pichincha, for both the next eruption and the next 100 years cases. While the former is used in our merging procedure, the second is considered when analyzing the maps related to single eruption types in terms of a comprehensive hazard assessment of the next 100 years, and it is not used in this section.…”

“…To provide a quantification of the uncertainty in future eruption occurrences at both Cotopaxi and Guagua Pichincha volcanoes, Tadini et al. (2021) performed an expert elicitation session aimed at quantifying such values, which we will use in the merging of maps/curves (see Section 3.3.3). In general, during an elicitation session (Aspinall, 2006; Aspinall et al., 2019; Bevilacqua et al., 2015; Neri et al., 2008; Tadini, Bevilacqua, et al., 2017) selected experts are asked to provide their judgments (in the form of three percentiles, normally the 5th, 50th, and 95th) on two different questionnaires.…”

“…Such distributions were defined by the expert elicitation session thoroughly described in Tadini et al. (2021) and summarized in Section 3.2.1. We report these uncertainty distributions in Figure 3 and the mean values of such distributions in Table 2, while the three elicited percentiles (5th, 50th, and 95th) are reported in Tables S1 and S2 in Supporting Information S1.…”