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ABSTRACT:The terms used to define the clastic deposits related to volcanic activity have important implications for the society in volcanic regions. Taking into account the importance of using a common terminology when considering natural hazards in the Spanish-speaking world, this study presents a classification of volcaniclastic deposits. This classification attempts to integrate the terminology related to the formational and depositional processes (eruptive and non-eruptive) taking place at volcanoes with the resulting volcaniclastic deposits and their constituent components. The classification emphasizes on how both physical and temporal variations in volcanic activity are responsible for observed differences in the related deposits. The purpose of this classification is to be a reference for the Spanishspeaking scientific community in order to avoid the numerous inconsistencies derived from the existing translations from multiple authors. Additionally, we present a flow diagram in both Spanish and English to illustrate that this classification system can be used to define and classify consolidated/lithified, and unconsolidated deposits. The appropriate classification of volcaniclastic deposits and their constituents can ultimately improve the definition and communication of potential volcanic hazards.

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Unheralded "blue-sky" eruptions from dormant volcanoes cause serious fatalities, such as at Mt. Ontake (Japan) on 27 September 2014. Could these events result from magmatic gas being trapped within hydrothermal system aquifers by elemental sulfur (S e ) clogging pores, due to sharp increases in its viscosity when heated above 159 • C? This mechanism was thought to prime unheralded eruptions at Mt. Ruapehu in New Zealand. Impurities in sulfur (As, Te, Se) are known to modify S-viscosity and industry experiments showed that organic compounds, H 2 S, and halogens dramatically influence S e viscosity under typical hydrothermal heating/cooling rates and temperature thresholds. However, the effects of complex sulfur compositions are currently ignored at volcanoes, despite its near ubiquity in long-lived volcano-hydrothermal systems. Changes in S-viscosity, leading to system sealing and sudden failure, can potentially occur at other volcanoes worldwide, including calderas, not only during phreatic eruptions. Models of impure S behavior must be urgently formulated to detect pre-eruptive warning signs before the next "blue-sky" eruption.