The April 2015 Calbuco eruption pyroclastic density currents: deposition, impacts on woody vegetation, and cooling on the northern flank of the cone

Abstract

The 22-23 April 2015 eruption of the Calbuco volcano (Southern Andes, Chile) led to extensive pyroclastic density currents (PDCs) interactions with vegetation. We seek to describe the PDCs which affected both Tepu and Frío rivers, northern Calbuco, from their timing and deposition to cooling and erosion, as well as their impacts on forests. Our investigation is based on field stratigraphy, forest disturbance assessment, and geothermometry from degassing pipes and charcoal. These PDCs reached at least ~540-603 °C, as estimated from fumaroles, and consisted of both concentrated and dilute PDCs during the first pulse (22 April) at Tepu and mainly during the second pulse (23 April) at Frío. Effects of PDCs on forest vegetation recorded in Tepu consisted of heating, abrasion, burial, and impact force. On the valley floor, trees were buried with up to 4 m of deposits from the concentrated PDCs, and all trees in this deposition zone died with no subsequent sprouting. Conversely, in the margins of the valley, defoliated fallen trees and standing shrubs indicate scorching due to the passage of dilute PDCs, and some of them were later sprouting. Estimated impact forces required to produce toppling range from 1.5 to 3.7 kPa, and PDC velocities reached up to 36 m s-1. Charring of the buried wood involved an emplacement temperature of 400-550 °C within PDC deposits. The rapid watershed formation may have facilitated infiltration, decreasing the temperature in the basal part within the deposits at the Tepu river. Runoff during the subsequent months triggered lahars and caused the rivers to incise the deposits and transport sediment downstream. This set of observations provides valuable insights into how the interaction between volcanic phenomena and margine forest on the valley floors informs eruptive processes, dynamics, and impacts. Our study is also relevant to interpret the thermal history and potential hazards of PDCs.

Living in-between: Implications of local risk perceptions for the management of future eruptions at the Calbuco and Osorno volcanoes (Ensenada, Chile)

“…The accumulation of ash is also mentioned as a difficulty, as it caused infrastructure problems, impacted on soils, and reduced the availability of vegetation. The latter is consistent with recent research on ecological impacts and disturbances in native forests near the Calbuco volcano (e.g., Bertin et al, 2021;Romero et al, 2023).…”

“…1) are lava flows, debris flows (e.g., lahars), and tephra fall (Moreno, 1999a). Recorded volcanic activity is most certainly identified from 1575 onwards, with confirmed eruptions in 1790, 1834, 1835and 1837(Petit-Breuilh, 1999, implying an average eruption frequency of ~60 years for VEI≥4 and ~20 years for smaller-scale eruptions (Romero et al, 2023). The 1835 eruption is considered the most significant of Osorno in historical times in terms of intensity, impact, and erupted volume.…”

The Andean Southern Volcanic Zone: a review on the legacy of the latest volcanic eruptions

“…At Calbuco, PDCs occurred during the two eruptive pulses, reaching ~540-603 °C and velocities up to 36 m/s, which caused extensive damage to trees (Fig. 5C; Romero et al, 2023). Mixed avalanches formed by the interaction between PDCs, spatter agglutinates and ice were observed and described in the recent Llaima and Villarrica (Bertin et al, 2015b;Vera and Palma, 2017 2 ;Breard et al, 2020).…”

Geological heritage sites assessment in the northern flank of the Calbuco volcano (Southern Andes, Chile)

“…The eruption had three explosive pulses, two of them sub-Plinian with eruptive columns up to 23 km high with a noticeable dispersion towards the northeast (Bertin et al, 2015;Castruccio et al, 2016;Romero et al, 2021). During this eruption, PDCs, tephra fallout, and lahars were generated, all of which damaged public and private infrastructure (Mella et al, 2015;Castruccio et al, 2016;Romero et al, 2023). The distribution of these products was constrained within the volcanic hazard areas identified by Moreno (1999) (Romero et al, 2016).…”

“…8A). Laharic deposits up the Blanco River are of volcanological and geomorphological interest, and can be used to explain depositional and erosive processes in active fluvial systems influenced by volcanic processes as well as their interaction with the forest (Romero et al, 2023) (Fig. 8B).…”