The August 1991 eruptions of Hudson volcano produced similar to 2.7 km(3) (dense rock equivalent, DRE) of basaltic to trachyandesitic pyroclastic deposits, making it one of the largest historical eruptions in South America. Phase 1 of the eruption (P1, April 8) involved both lava flows and a phreatomagmatic eruption from a fissure located in the NW corner of the caldera. The paroxysmal phase (P2) began several days later (April 12) with a Plinian-style eruption from a different vent 4 km to the south-southeast. Tephra from the 1991 eruption ranges in composition from basalt (phase 1) to trachyandesite (phase 2), with a distinct gap between the two erupted phases from 54-60 wt% SiO2. A trend of decreasing SiO2 is evident from the earliest part of the phase 2 eruption (unit A, 63-65 wt% SiO2) to the end (unit D, 60-63 wt% SiO2). Melt inclusion data and textures suggest that mixing occurred in magmas from both eruptive phases. The basaltic and trachyandesitic magmas can be genetically related through both magma mixing and fractional crystallization processes. A combination of observed phase assemblages, inferred water content, crystallinity, and geothermometry estimates suggest pre-eruptive storage of the phase 2 trachyandesite at pressures between similar to 50-100 megapascal (MPa) at 972 +/- 26A degrees C under water-saturated conditions (log fO(2) -10.33 (+/- 0.2)). It is proposed that rising P1 basaltic magma intersected the lower part of the P2 magma storage region between 2 and 3 km depth. Subsequent mixing between the two magmas preferentially hybridized the lower part of the chamber. Basaltic magma continued advancing towards the surface as a dyke to eventually be erupted in the northwestern part of the Hudson caldera. The presence of tachylite in the P1 products suggests that some of the magma was stalled close to the surface (< 0.5 km) prior to eruption. Seismicity related to magma movement and the P1 eruption, combined with chamber overpressure associated with basalt injection, may have created a pathway to the surface for the trachyandesite magma and subsequent P2 eruption at a different vent 4 km to the south-southeast.
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Univ Catania, Dipartimento Sci Biol Geol & Ambientali, Corso Italia 57, I-95129 Catania, ItalyUniv Catania, Dipartimento Sci Biol Geol & Ambientali, Corso Italia 57, I-95129 Catania, Italy
Zuccarello, Francesco
Schiavi, Federica
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Univ Clermont Auvergne, CNRS, IRD, OPGC,Lab Magmas & Volcans, Clermont Ferrand, FranceUniv Catania, Dipartimento Sci Biol Geol & Ambientali, Corso Italia 57, I-95129 Catania, Italy
Schiavi, Federica
Viccaro, Marco
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Univ Catania, Dipartimento Sci Biol Geol & Ambientali, Corso Italia 57, I-95129 Catania, Italy
Ist Nazl Geofis & Vulcanol, Sez Catania, Osservatorio Etneo, Catania, ItalyUniv Catania, Dipartimento Sci Biol Geol & Ambientali, Corso Italia 57, I-95129 Catania, Italy
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Cornell Univ, Dept Earth & Atmospher Sci, Ithaca, NY 14850 USACornell Univ, Dept Earth & Atmospher Sci, Ithaca, NY 14850 USA
DeVitre, Charlotte L.
Gazel, Esteban
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Cornell Univ, Dept Earth & Atmospher Sci, Ithaca, NY 14850 USACornell Univ, Dept Earth & Atmospher Sci, Ithaca, NY 14850 USA
Gazel, Esteban
Allison, Chelsea M.
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Cornell Univ, Dept Earth & Atmospher Sci, Ithaca, NY 14850 USACornell Univ, Dept Earth & Atmospher Sci, Ithaca, NY 14850 USA
Allison, Chelsea M.
Soto, Gerardo
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Univ Costa Rica, Escuela Ctr Amer Geol, San Jose 2060, Costa Rica
Univ Costa Rica, Red Sismol Nacl, San Jose 2060, Costa RicaCornell Univ, Dept Earth & Atmospher Sci, Ithaca, NY 14850 USA
Soto, Gerardo
Madrigal, Pilar
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Univ Costa Rica, Escuela Ctr Amer Geol, San Jose 2060, Costa Rica
Univ Costa Rica, Red Sismol Nacl, San Jose 2060, Costa RicaCornell Univ, Dept Earth & Atmospher Sci, Ithaca, NY 14850 USA
Madrigal, Pilar
Alvarado, Guillermo E.
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Univ Costa Rica, Escuela Ctr Amer Geol, San Jose 2060, Costa Rica
Univ Costa Rica, Red Sismol Nacl, San Jose 2060, Costa Rica
Comis Nacl Prevenc Riesgos & Atenc Emergencias, Unidad Invest & Anal Riesgo, San Jose, Costa RicaCornell Univ, Dept Earth & Atmospher Sci, Ithaca, NY 14850 USA
Alvarado, Guillermo E.
Lucke, Oscar H.
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Univ Costa Rica, Escuela Ctr Amer Geol, San Jose 2060, Costa Rica
Univ Costa Rica, Red Sismol Nacl, San Jose 2060, Costa RicaCornell Univ, Dept Earth & Atmospher Sci, Ithaca, NY 14850 USA