Characterization of the ashes from the 2014-2015 Turrialba Volcano eruptions by means of Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy

Abstract

El volcán Turrialba es un estratovolcán localizado aproximadamente 35 km al noroeste de San José, la ciudad capital de Costa Rica. Desde el 29 de octubre de 2014, hasta al menos el fin del año 2015, el volcán mostró una serie de erupciones que representan su actividad más significativa desde la década de los 1860s. Estas erupciones dispersaron un volumen significativo de cenizas, las cuales alcanzaron las áreas más pobladas del país. En este artículo, se analizan las características de las partículas de ceniza con el fin de establecer el tipo de erupciones que ocurrieron en 2014 y 2015, así como monitorear la evolución de los procesos eruptivos. El análisis se llevó a cabo mediante las técnicas de microscopía y estereoscopía óptica, así como técnicas novedosas de microscopía electrónica de barrido (MEB), que involucran la adquisición de imágenes y el análisis de composición elemental por medio de espectroscopía de rayos-x por energía dispersiva (EDX). Los resultados muestran la evolución de las erupciones del volcán Turrialba desde eventos freáticos en 2014, con cenizas compuestas en su totalidad por partículas no-juveniles, hacia eventos freato-magmáticos, comenzando en marzo de 2015 con la presencia de una fracción apreciable de componentes juveniles en la ceniza.

Are the ashes from the latest eruptions (2010–2016) at Turrialba volcano (Costa Rica) related to phreatic or phreatomagmatic events?

“…Similarly, Lücke and Calderón (2016) reported analyses from recent Turrialba ash surfaces with high silica and low alkali content, which probably do not reflect true magmatic compositions. Rather, our analyses provide strong geochemical evidence indicating juvenile magma interaction with hydrothermal fluids, supporting a phreatomagmatic eruption mechanisms.…”

“…Such material could be due to the reworking or erosion of tephra from the walls of the conduit and active crater, as has been observed in other ashes and similar cases (Mastin, 1991;Suzuki et al, 2013;and references cited therein). Lücke and Calderón (2016) use scanning electron microscopy (SEM) and energy disperse X-ray spectroscopy for analyzing the ash from 2014 to 2015 under the fraction 2.7 phi fraction (fine ash), and they concluded that the 2014 eruption was phreatic because they concluded that the ashes were composed entirely of non-juvenile fragments, and only the 2015 eruption was phreatomagmatic. Alvarado et al (2016) conclude that the 2014 eruption was instead phreatomagmatic based on the presence of hydratation cracks, and describe in Spanish the current eruption in detail, the tephra deposits, including granulometric and Xray diffraction analyses, petrography and mineralogy, and applied the sequential fragmentation/transport theory.…”

“…At Turrialba volcano, the vent opening phases and the successive cleaning phases were previously interpreted as phreatic eruptions (Reagan et al, 2011;Soto and Mora, 2013;Duarte, 2014;González et al, 2015;Lücke and Calderón, 2016; among internal reports of the local volcanological observatories). Thus, it was not clear whether the volcanic activity from 2010 to 2016 was purely phreatic and therefore not related to the intrusion of new magma (e.g., Martini et al, 2010), or related to the intrusion of a small volume of magma disrupting the pre-existing hydrothermal system (e.g., Campion et al, 2012).…”

Volcano hazard and surveillance in Costa Rica

“…The monitoring network of RSN (UCR and ICE) is detailed in Table 1. RSN contains a laboratory of geochemistry and a laboratory of petrology for aqueous and rock samples, that together with other laboratories at University of Costa Rica, makes RSN able to carry out specific research [Lücke and Calderón 2016]. Gravity measurement campaigns are conducted by RSN for specific research at volcanoes [Argüello et al 2019].…”

Geomorphological Insights on Human-Volcano Interactions and Use of Volcanic Materials in Pre-Hispanic Cultures of Costa Rica through the Holocene

“…Turrialba started with phreatic activity in 2010, and since 2015, juvenile magma has been involved in the eruptions (Lücke and Calderón, 2016). Meanwhile, the volcanic activity at Poás started in April 2017 with a phreatomagmatic eruption, which led to the closure of the national park (one of the most visited national parks in Central America) and impacting the daily lives of people near the volcano (Ruiz and Suárez, 2017).…”