Hydrothermal system of the Papandayan Volcano from temperature, self-potential (SP) and geochemical measurements

International audiencePapandayan volcano in West Java, Indonesia, is characterized by intense hydrothermal activities manifested by numerous fumaroles at three craters or kawah, i.e. Mas, Manuk and Baru. The latter was created after November 2002 phreatic eruption. Since 2011, numerous volcano-tectonic B events are encountered and the volcano was set on alert status on several occasions. The purpose of the present study is to delineate the structure of the summital hydrothermal system from Self-Potential (SP), soil temperature and gas concentrations in the soil (CO2, SO2 and H2S) data. This combination of geophysical and geochemical methods allows identification of the weak permeable zones serving as preferential pathways for hydrothermal circulation and potential candidates to future landslides or flank collapses. This study is an on-going collaborative research project and we plan to conduct electrical resistivity tomography (ERT) and also Induced-Polarization (IP) surveys. Additional data would allow the 3D imaging of the studied area. The IP parameters will be used to characterise and to quantify the degree of alteration of the volcanic rocks as has been shown very recently in the laboratory studies. There are also rocks and soil samples that will undergo laboratory analyses at ISTerre for IP and complex resistivity parameters at the sample scale that will help to interpret the survey results

First study of the heat and gas budget for Sirung volcano, Indonesia

International audienceWith at least four eruptions over the last 20 years, Sirung is currently one of the more active volcanoes in Indonesia. However, due to its remoteness, very little is known about the volcano and its hyperacid crater lake. We report here on the first measurements of gas and heat emissions from the volcano. Notable is the substantial heat loss from the crater lake surface, amounting to 220 MW. In addition, 17 Gg of SO2, representing 0.8% of Indonesian volcanic SO2 contribution into the atmosphere, 11 Gg of H2S, 17 Gg of CO2, and 550 Gg of H2O are discharged into the atmosphere from the volcano annually. The volatiles degassed from Sirung magmas are subjected to hydrothermal fluid-rock interactions and sulfide depositions, initiated by the disproportionation of SO2. These processes lead to distinct gas compositions and changing lake water chemistry (in the sub-craters and the main crater lake). However, the occurrence of SO2-rich fluids and strong gas flux appear to highlight a rapid fluid transfer to surface, avoiding re-equilibration with lower temperature rocks/fluids in the conduits

Bromo activity over the last decade: consistent passive degassing and source magma evolution

International audienceBromo is among the very active volcanoes in Indonesia and is known for its recurrent and long-lasting eruptive manifestations. Past volcanic gas studies have revealed Bromo as one of the principal sources of volcanic degassing in Indonesia. This high degassing from Bromo volcano is further characterized in this work, based on more than 10 years of intermittent ground-based gas measurements, combined with daily SO2 mass, captured by the OMI sensor. Over the past decade, Bromo has released 0.7 Tg of SO2 into the atmosphere, representing 3% of the volcanic degassing budget of Indonesia and 0.3% of the global volcanic SO2 emission budget outside eruptive periods. Results also reveal that 18.8 Tg of H2O, 2.0 Tg of CO2, 0.1 Tg of H2S, and 0.005 Tg of H2 were released from the Bromo volcano in one decade. About 81% of these gases are released passively between eruptive events. The chemistry of the eruptive products, sampled between 2001 and 2019, indicate that Bromo volcanic activity is sustained by a basaltic-andesite to basalt trachy-andesite magma source with a transition from medium-K to high-K composition. Such an evolution associated to a C-rich gas likely resulted from a low partial melting and sediment contribution to the genesis of the source magma. New magma injections into the reservoir and fractional crystallization have further amplified the changes of magma composition. Finally, we speculate that the shallow reservoir replenishment, in response to the continuous strong degassing is the driving mechanism behind the Bromo frequent eruptive events