Chemical Signals in Tree Rings from Northern Patagonia as Indicators of Calbuco Volcano Eruptions since the 16th Century

Lizette J Bertin,Duncan A Christie,Claudio Alvarez,Ariel A Muñoz,Paul R Sheppard,Antonio Lara

doi:10.3390/f12101305

Abstract

The Calbuco volcano ranks third in the specific risk classification of volcanoes in Chile and has a detailed eruption record since 1853. During 2015, Calbuco had a sub-Plinian eruption with negative impacts in Chile and Argentina, highlighting the need to determine the long-term history of its activity at a high-resolution time scale to obtain a better understanding of its eruptive frequency. We developed a continuous eruptive record of Calbuco for the 1514–2016 period by dendrochemical analysis of Fitzroya cupressoides tree rings at a biennium resolution using inductively coupled plasma–mass spectrometry. After comparing the chemical record of 20 elements contained in tree rings with historical eruptions, one group exhibited positive anomalies during (Pb/Sn) and immediately after (Mo/P/Zn/Cu) eruptions, with a Volcanic Explosivity Index (VEI) ≥ 3, and so were classified as chemical tracers of past eruptions (TPE). The tree-ring width chronology also exhibited significant decreases in tree growth associated with eruptions of VEI ≥ 3. According to these records, we identified 11 new eruptive events of Calbuco, extending its eruptive chronology back to the 16th century and determining a mean eruptive frequency of ~23 years. Our results show the potential to use dendrochemical analysis to infer past volcanic eruptions in Northern Patagonia. This information provides a long-term perspective for assessing eruptive history in Northern Patagonia, with implications for territorial planning.

Highlights

Along the vast Chilean portion of the Circum-Pacific ring of fire, nearly 90 volcanoes are active, resulting in a high exposure to volcanic hazards [1]
The co-eruptive tracers of past eruptions (TPE) (Pb and Sn) that showed an increase in concentration in the year of the eruption would enter the tree quickly directly as nanoparticles through the leaves after being affected by falling tephra, which is a faster entry mechanism than through the roots [24]
While the late response shown by the post-eruptive TPE may be due to the fact that the chemical elements would most probably enter the tree through the roots, either as direct input from the tephra deposited in the soil after the eruption (i.e., Zn, Cu, and P that may be available to plants [20,21]), or indirectly when the fall of tephra triggers a decrease in soil pH [25] that induces a change in the bioavailability of elements already contained in the soil, but which orests 2021, 12, x FOR PEER REVIEW

Summary

Introduction

Along the vast Chilean portion of the Circum-Pacific ring of fire, nearly 90 volcanoes are active, resulting in a high exposure to volcanic hazards [1]. To develop hazard maps and risk mitigation planning nationwide, accounts of regional eruption records must be obtained to accurately determine eruptive frequency and recurrence rates. 14 C dating has low temporal resolution, which limits precise estimates of eruptive frequency and recurrence rates. Volcanic eruptions can generate tree growth anomalies, resulting in the narrowing or even absence of annual rings [5,6,7,8] as a consequence of physical damage to the leaves and stems of trees [9] and/or low temperatures induced by emissions of aerosols [10].

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