The composition and fluxes of volcanic gases released by persistent open-vent degassing at Bromo Volcano, east Java (Indonesia), were characterised in September 2014 from both in-situ Multi-GAS analysis and remote spectroscopic (dual UV camera) measurements of volcanic plume emissions. Our results demonstrate that Bromo volcanic gas is water-rich (H 2 O/SO 2 ratios of 56-160) and has CO 2 /SO 2 (4.1 ± 0.7) and CO 2 /S tot (3.2 ± 0.7) ratios within the compositional range of other high-temperature magma-derived gases in Indonesia. H 2 /H 2 O and H 2 S/SO 2 ratios constrain a magmatic gas source with minimal temperature of~700°C and oxygen fugacity of 10 , which is ten times higher than reported from few previous studies. Our results indicate that Bromo ranks amongst the strongest sources of quiescent volcanic SO 2 emission measured to date in Indonesia, being comparable to Merapi volcano in central Java. By combining our results for the gas composition with the SO 2 plume flux, we assess for the first time the fluxes of H 2 O (4725 ± 2292 t d ) and H 2 (1.1 ± 0.8) from Bromo. Our study thus contributes a new piece of information to the still limited data base for volcanic gas emissions in Indonesia, and confirms that much remain to be done to fully assess the contribution of this very active arc region to global volcanic gas fluxes.

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Abstract. Indonesia hosts 79 active volcanoes, representing 14% of all active volcanoes worldwide. However, little is known about their passive degassing into the atmosphere due to isolation and access difficulties. Existing SO2 emission budgets for the Indonesian archipelago are based on extrapolations and inferences as there is a considerable lack of field assessments of degassing. Here, we present the first SO2 flux measurements using DOAS for Papandayan and Bromo, two of the most active volcanoes in Indonesia. Results indicate mean SO2 emission rates of 1.4 t d−1 from the fumarolic activity of Papandayan and more than 22–32 t d−1 of SO2 released by Bromo during a declining eruptive phase.

Abstract. Bromo is an active type-A volcano located inside Tengger caldera in Eastshow that the deformation of Bromo volcano is typically in order of a few cm, with the inflation and deflation processes before and after the eruption. Estimated location of the pressure source is found to be beneath the active crater with depth of about 1 km below the caldera floor.

Abstract. We analyze 25 episodes of volcanic tremor recorded from 22 November until 31 December 2009 at Mt Semeru volcano in order to investigate their spectral and dynamical properties. The overtone frequencies for most of the tremor events indicate a pattern of period-doubling, which is one possible route that can lead a system to chaotic behavior. Exponential divergence of the phase space orbits is a strong indicator of chaos and was quantified by estimating the maximal Lyapunov exponent (MLE) for all tremor events. MLEs were found to vary linearly with the number of frequency overtones present in the tremor signals. This implies that the tremor source at Semeru fluctuates between a quasi-periodic state with few overtone frequencies (2-3) and small MLEs (~0.013), and a chaotic one with more overtones (up to 8) and larger MLEs (up to 0.039). These results agree well with the tremor generation model suggested previously by Julian (1994), which describes wall oscillations of a crack excited by unsteady fluid flow. In this model, as fluid pressure increases, a period-doubling cascade leads to numerous new frequencies and a chaotic tremor signal. The temporal variation of MLEs exhibited significant fluctuations from 23 until 31 December when the eruptive activity shifted from explosive to effusive. Such a situation may reflect variable fluid pressure conditions inside the conduit, where at first magma is accumulated and subsequently is erupted, releasing the buildup of pressure. Our results give further evidence for the role of nonlinear deterministic processes in generating volcanic tremor and call for similar investigations to be conducted in other volcanoes.