Holocene record of large explosive eruptions from Chaitén and Michinmahuida Volcanoes, Chile

Abstract

ABSTRACT. Tephra fall deposits and one large ignimbrite close to Chaitén and Michinmahuida Volcanoes were analyzed for chemistry and radiocarbon dated to correlate the eruptive units and establish the timing of eruptions. These data suggest that both volcanoes were the source of large (VEI ≥5) and small to moderate (VEI <5) explosive eruptions throughout the Holocene. Four deposits are associated with volcanic activity from Chaitén Volcano, with two from Plinian eruptions at 9.9-9.5 and 5.3-4.9 (cal) ka BP that also generated pyroclastic density currents. The last event recognized from Chaitén (prior 2008) occurred a few hundred years ago, producing deposits that are similar to those of the 2008 eruption. All products from Chaitén are high-silica rhyolites; whole-rock compositions are indistinguishable but glass compositions are subtly different for some of the units. Seven deposits are related to eruptions of Michinmahuida Volcano, including a Plinian fall deposit at 7.6-7.3 ka BP and a large ignimbrite deposit at 10.5-10.2 ka BP. The chemical compositions of these products range from andesite to dacite. The last substantial explosive eruption event from Michinmahuida Volcano appears to have been a 0.5-0.3 ka BP sub-Plinian eruption, although younger scoria fall deposits likely derived from local pyroclastic cones are also found. Both volcanoes pose a wide variety of potential hazards to the region ranging from those derived from ignimbrite-forming eruptions to pyroclastic-cone formation. Valleys adjacent to the volcanoes were the areas most heavily affected by volcanic activity, because they were inundated by pyroclastic density currents and lahars. However, even regions located tens of kilometers east and north of the volcanoes experienced accumulations of tephra, which could harm both agriculture and infrastructure if similar events occurred today. RESUMEN. Registro de erupciones explosivas holocenas de los volcanes Chaitén y Michinmahuida, Chile. En las cercanías de los volcanes Chaitén y Michinmahuida se han estudiado un conjunto de depósitos piroclásticos de caída y un depósito ignimbrítico. Estos se han caracterizado mediante análisis químico (de roca total y microsonda en vidrio volcánico) y datados por medio de isótopos de radiocarbono. De esta forma, se ha establecido una nueva cronología eruptiva para estos centros. Los datos obtenidos sugieren que ambos volcanes presentan conspicua actividad explosiva durante el Holoceno de variada magnitud. En particular, se han identificado depósitos de al menos cuatro erupciones asociadas al volcán Chaitén, incluyendo dos Plinianos ocurridas entre 9.9-9.5 y 5.3-4.9 ka antes del presente, que generaron, además, corrientes piroclásticas en los valles adyacentes. El evento más reciente identificado para este volcán, corresponde a una erupción de similar magnitud a la del 2008 y habría ocurrido unos tres siglos antes del presente. Para este volcán, todos sus productos piroclásticos corresponden a riolitas, cuyas composiciones de roca total resultan prácticamente indi...

Conduit Dynamics in Transitional Rhyolitic Activity Recorded by Tuffisite Vein Textures from the 2008–2009 Chaitén Eruption

“…Bubble number density (BND) is a sensitive decompression rate meter in magmas, although heterogeneous nucleation can influence BND-decompression rate relationships (e.g., (Amigo et al, 2013;Pallister et al, 2013; 75.3 ± 0.3 wt. % SiO 2 ).…”

Stratigraphy, age and correlation of Lepué Tephra: a widespread c. 11 000 cal a BP marker horizon sourced from the Chaitén Sector of southern Chile

“…C). This same PDC deposit and surface was recognized by Amigo et al () and named Amarillo Ignimbrite. Two radiocarbon samples acquired from within and just above the Amarillo Ignimbrite were dated at 9260 ± 50 and 9510 ± 50 14 C a BP, respectively, and are broadly in accord with an age of 9785 ± 30 14 C a BP (LLNL‐122960) from our sample retrieved from Pumalín‐1.…”

An example of enhanced tephra deposition driven by topographically induced atmospheric turbulence

“…The eruption deposited an elongate lobe of tephra to the north of Chaitén (Naranjo and Stern 2004;Watt et al 2011; comprising ∼3.5 km 3 ), with additional deposition to the east from poorly mapped explosive phases (Amigo et al 2013;Fontijn et al 2014). Overall, the exposure of the deposit is relatively sparse, but it has been identified in several road cuttings 15-30 km north of Chaitén and in the Hualaihue region, 90-160 km north of Chaitén ).…”

“…2015; such a wind direction marked the initial stage of the Hudson 1991 eruption (Naranjo 1991)). The northward transport of the plume is likely to have meant that deposition was not complicated by additional phases of the Cha1 eruption (as suggested by the simple deposit characteristics), which followed prevailing wind directions towards the east (Amigo et al 2013).…”

“…The Cha1 tephra deposit volume of 5.5 km 3 (Amigo et al 2013) was derived from multiple isopachs modified from Watt et al (2011; two of which are shown in Fig. 1).…”