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Journal of Volcanology and Geothermal Research

Journal of Volcanology and Geothermal Research

Archives Papers: 1,048
Elsevier
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Structure of the acid hydrothermal system of Papandayan volcano, Indonesia, investigated by geophysical methods
S. Byrdina; H. Grandis; P. Sumintadireja; C. Caudron; D.K. Syahbana; E. Naffrechoux; H. Gunawan; G. Suantika; J. Vandemeulebrouck;
Abstracts:Papandayan (2665 m asl) is an Indonesian stratovolcano located at 50 km from Bandung in west Java and characterized by an intense hydrothermal activity. An advanced alteration takes place where acid fluids interact with rocks, weakening the edifice, so that even minor explosive eruptions threaten the stability of its flanks. The purpose of the current study is to delineate the geometry of the acid hydrothermal plume using Electrical Resistivity Tomography (ERT). We used self-potential, pH measurements in water (in situ) and of soil samples, SO2 and CO2 soil concentration mappings to better understand the resistivity structure. Measurements have been performed inside the 1772 crater with a maximal depth of investigation of about 250 m for electrical resistivity tomography.
Application and reliability of calcic amphibole thermobarometry as inferred from calc-alkaline products of active geothermal areas in the Andes
Andrea Gorini; Filippo Ridolfi; Filippo Piscaglia; Marco Taussi; Alberto Renzulli;
Abstracts:Igneous thermobarometry may contribute to locate the upper-crust heat source/s representing one of the main factors required to establish the potential of high enthalpy geothermal areas through models of the heat flux. To test this possibility, we applied amphibole thermobarometry to some of the youngest lavas and pyroclastics (andesite to rhyolite) of Apacheta and La Torta (Chile) and Chachimbiro (Ecuador) areas representing medium to high enthalpy geothermal systems located in two different crustal contexts along the Andean active continental margins of South America. We used the robust application of Ridolfi and Renzulli (2012) allowing to estimate the intrinsic physico-chemical parameters with reasonably low uncertainties (T ± 24 °C, P ± 12%, fO2 ± 0.4 log units) and the composition of the melt in equilibrium with Mg-rich calcic amphibole in a wide range of conditions, up to 1130 °C and 2.2 GPa. In addition, analyses of the intra-crystalline compositional and textural variations allowed us to propose a method to distinguish between chemically homogeneous and heterogeneous amphiboles, avoiding some incorrect applications of the Ridolfi and Renzulli (2012)'s equations and thus unreliable results.
Magmatic sulfide immiscibility at an active magmatic-hydrothermal system: The case of La Fossa (Vulcano, Italy)
P. Fulignati; A. Gioncada; S. Costa; D. Di Genova; F. Di Traglia; M. Pistolesi;
Abstracts:Magmatic sulfide minerals preserved in fresh volcanic rocks can be used to trace sulfur and chalcophile element evolution in magmatic systems and to constrain the potential magmatic contribution to ore-forming fluids. In this work, we present a petrographic and microanalytical study of magmatic sulfides in the products of La Fossa (Vulcano, southern Italy), an active arc-related volcano currently with a shallow acidic hydrothermal system, and discuss the results with petrological data obtained from melt inclusions. While the sulfur-rich basalts feeding the plumbing system were oxidized and sulfide-undersaturated, as common in arc-basalts, a major event of sulfide melt separation from the silicate melt occurred at the trachytic stage, in the shallow reservoir (minimum depth based on H2O content of melt inclusions is 1200–2200 m), promoted by the lowering of fO2. Sulfide immiscibility was unrelated to magnetite fractionation and was encountered after a notable sulfur loss at the transition from mafic to intermediate magma composition. The late sulfide saturation implies that the silicate melt became enriched in Cu with differentiation. This is indicated by the relatively high Cu concentration in the analyzed sulfide blebs, comparable to the composition of sulfides found in other active arc volcanoes as well as in magmatic systems associated with porphyry copper mineralization. The newly reported occurrence of sulfide immiscibility in the La Fossa shallow reservoir has implications for the evolution of sulfur in the plumbing system and for the contribution of magmatic sulfur and metals to surface fumaroles, as well as to the deep hydrothermal fluids during non-eruptive periods. The results indicate that La Fossa volcano is a possible active analogue of mineralizing magmatic-hydrothermal systems.
Stability assessment of the Crater Lake/Te Wai-ā-moe overflow channel at Mt. Ruapehu (New Zealand), and implications for volcanic lake break-out triggers
Lauren N. Schaefer; Ben M. Kennedy; Marlène C. Villeneuve; Stefan C.W. Cook; Arthur D. Jolly; Harry J.R. Keys; Graham S. Leonard;
Abstracts:The presence of lakes on active volcanoes gives rise to several unique volcano-hydrologic hazards, including those directly related to volcanic activity (e.g. phreatic explosions) and non-volcanic phenomena (e.g. lake outbursts). Mt. Ruapehu volcano hosts the 107 m3 Crater Lake/Te Wai-ā-moe in the active summit crater, making it prone to lahars due to the abundance of water stored at high elevation. Apart from eruptive periods when water is commonly ejected from the lake, large lahar events can occur when portions of the crater rim fail during quiescent periods, leading to partial lake drainage; the latter occurred recently in 1953 and 2007. Here, we investigate the potential of future lahars due to rim failure at the current overflow channel considering several triggering scenarios during non-eruptive periods. The geomechanical properties of a matrix-dominated breccia unit composing part of the overflow channel were analyzed using physical and mechanical laboratory methods. These properties, combined with previous geomechanical studies of lava units in the overflow channel, were used in finite element and limit equilibrium method-based groundwater and stability models. Groundwater models indicate that a low-permeability barrier inside the crater rim is preventing water from seeping through the unconsolidated and potentially permeable breccia unit of the overflow channel. The removal of this barrier, or weathering of a resistive lava cap, could cause water to seep through the overflow channel, elevating the potential of collapse. Slope stability models indicate that under certain conditions, the overflow channel is below a conservative threshold of stability and can be destabilized with continued mechanical or chemical weathering that reduces strength properties. This is also true during high magnitude tectonic or volcanic earthquakes, where large ground accelerations could result in several centimeters of displacement at the overflow channel, corresponding to high hazard categories of stability. In the worst-case scenario modeled here, full collapse of the overflow channel could result in the release of c. 2.4 million m3 of lake water. This could drive a lahar substantially larger than well-documented historic events, including the more common lahars produced during eruptions. The identification of key factors affecting stability can be used to inform future monitoring and the risk of these high impact events.
Forensic assessment of the 1999 Mount Cameroon eruption, West-Central Africa
Mabel N. Wantim; Costanza Bonadonna; Chris E. Gregg; Scira Menoni; Corine Frischknecht; Matthieu Kervyn; Samuel N. Ayonghe;
Abstracts:The 28 March to 22 April 1999 eruption of Mount Cameroon volcano in southwest Cameroon occurred from multiple vents along fissures at two sites. Vents opened first at the upper site 1 (2650 m) and were more explosive than vents at the lower site 2 (1500 m), which were more effusive. Earthquakes, lava flows, tephra fall, ballistics and gas emissions affected the volcano's west and south flanks, including forests, plantations, stock animals, water supplies, coastal communities and their people. Through an analysis of existing published data and new interview data, we provide an overview of the environmental, social and economic consequences of these hazards on infrastructure, human health, and socio-economic and agricultural activities of the four coastal communities most affected by the eruption: Batoke, Bakingili, Debundscha and Idenau. The collected data provide a more detailed description of the short- and long-term direct and indirect effects of the eruption and response than has been provided to date. Sedimentation of tephra and ballistics from site 1 produced both short-term and long-lasting impacts on people, through the contamination of plants and water supplies, which induced impacts on human health and commercial activities. A ~9.2 km long lava flow erupted from site 2 received significant short-term attention as it severed the only arterial coastal highway, forced the evacuation of some 600 residents of Bakingili, and interrupted commerce between communities. The agricultural sector also suffered due to burning of crops and soils. The only obvious significant benefit of the eruption appears to be that the long lava flow has become a tourist attraction, responsible for bringing in money for food, drink and lodging. However, the long-term cascading effects caused by the hazards have proven to be more severe than the immediate direct and indirect effects during the eruption.
Very rapid cooling of the energetic pyroclastic density currents associated with the 5 November 2010 Merapi eruption (Indonesia)
M. Trolese; G. Giordano; J.-C. Komorowski; S.F. Jenkins; P.J. Baxter; N. Cholik; P. Raditya; S. Corrado;
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