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Huequi, a little-known volcano in the southern part of the Andean southern volcanic zone (SSVZ), shows a regionally unusual eruption style, mineralogy and geochemistry. The volcano comprises multiple highly-eroded lava domes. Past eruptions were accompanied by relatively minor explosive activity, most recently from 1890-1920. The rocks erupted by Huequi range from basaltic andesite to dacite, and are highly distinctive when compared to other volcanoes of the SSVZ, being K-poor and Al-rich, and containing euhedral hornblende phenocrysts. Overall compositions suggest a notably water-rich magma source, evolving through high levels of fractionation and subsequent degassing to produce highly porphyritic dome-forming andesites. The ultimate causes of water-rich magmas at this point in the arc remain unclear.El volcán Huequi es poco conocido, que se ubica en la provincia sur de la zona Volcánica Sur de los Andes (ZVSS). Sus tipos de erupción y características mineralógicas y geoquímicas son poco comunes a nivel regional. El volcán presenta múltiples domos poco erosionados. Las erupciones estuvieron acompañadas por una actividad explosiva secundaria, siendo las más recientes las ocurridas entre los años 1890 y 1920. Los magmas del Huequi son de composición andesítico-basáltica a dacítica. Si se las compara con rocas eruptadas por otros centros volcánicos de la ZVSS de los Andes, las del Huequi se caracterizan por ser pobres en K, ricas en Al y por presentar fenocristales euhedrales de anfíbola. Las composiciones totales sugieren una fuente magmática rica en H2O, que se desarrolla a través de niveles de cristalización fraccionada y desgasificación subsecuente, que producen domos volcánicos andesíticos altamente porfíricos. Sin embargo, la causa última que genera magmas ricos en H2O, en esta parte de los Andes, sigue aún sin explicación.

Volcanic islands form the highest topographic structures on Earth and are the sites of some of the planet's largest landslides. These landslides can rapidly mobilize hundreds of cubic kilometers of rock and sediment, and potentially generate destructive tsunamis on ocean-basin scales. The main unknown for tsunami hazard assessment is the way in which these landslides are emplaced. Understanding of landslide dynamics relies on interpretation of deposits from past events: it is necessary to understand where material within the deposit originated and the temporal sequence of the deposit's formation. The degree of fragmentation in a volcanic landslide is controlled by its relative proportions of dense lavas and weak pyroclastic rocks; fragmentation is generally reduced during subaqueous relative to subaerial transport. In the submarine environment, the seafloor-sediment substrate commonly fails during emplacement of a volcanic landslide. However, in many cases, this sediment failure remains almost in situ as a deformed package rather than disaggregating to form a debris flow. Because seafloor sediment makes up a large proportion of many landslide deposits around volcanic islands, the magnitude of the primary volcanic failure cannot be readily assessed without a clear understanding of deposit constituents. Both the dimensions of the volcanic failure and the way in which it fails are of key importance for tsunami generation. Turbidite deposits suggest that some volcanic landslides occur in multiple retrogressive stages. This significantly reduces potential tsunami magnitude relative to models that assume emplacement of the landslide in a single stage.

The 2008 eruption of Chaitén Volcano was widely cited as the first activity at the volcano for over 9000 years. However, we have identified evidence from proximal pyroclastic deposits for three additional explosive eruptions of Chaitén within the past 5000 years. Chaitén has therefore produced at least five explosive eruptions in the Holocene, making it among the most active volcanoes, in terms of explosive output, in the southern part of the Andean Southern Volcanic Zone. All of the five identified Holocene explosive eruptions produced homogeneous high-silica rhyolite, with near identical compositions. Based on our pyroclastic sequence, we suggest that the largest-volume Holocene eruption of Chaitén occurred at ~4.95 ka, and we correlate this with the Mic2 deposit, which was previously thought to originate from the nearby Michinmahuida Volcano.