Abstract The Aso-4 explosive eruption on Kyushu, Japan, 89,500 years ago was one of the biggest eruptions in the last one hundred millennia, with a magnitude of approximately M8. Modern society requires the likelihood of natural events with potentially disastrous consequences to be evaluated, even if probabilities of occurrence are diminishingly small. For some situations, it is not satisfactory to assert an event scenario probability is “negligible” or can be “ignored”. Judicial hearings or litigation may require risk levels to be quantified, in which case, statements of scientific confidence could be decisive. Internationally, e.g., for nuclear site safety evaluations, event likelihoods on order of 10 –7 /year are often considered for quantitative assessment. At such hazard levels, this might include evaluating the proposition that a particular volcano can deliver a future super-eruption, a supposition that could be attached to Aso volcano. But, simplistically taking the average recurrence interval between past caldera-forming eruptions at a given volcano is an unreliable guide to the likelihood of a future repeat: each past event represented a unique set of tectonic and magmatic conditions within a continually evolving volcanic system. Such processes are not temporally stationary nor statistically uniform. To evaluate the probability of a new M8 event at Aso, within the next 100 years, we performed a comprehensive stochastic probability uncertainty analysis using a model implemented with advanced computational Bayes Net (BN) software. Our eruption process model is informed by multiple strands of evidence from volcanology, petrology, geochemistry and geophysics, together with estimates of epistemic (knowledge) uncertainty, adduced from reviews of published data, modelling and from expert judgement elicitation. Several lines of evidence characterise the likely structure, magmatic composition and eruptive state of the present-day Aso volcano, which has had numerous smaller eruptions since Aso-4. To calculate the probability of another M8 eruption of Aso, we implemented probabilistic ‘Importance Sampling’ in our model. With this approach, we find the chance of an Aso-4 scale eruption (characterised by mean volume 500 km 3 DRE and approximate 90% credible interval [210 ‥ 1200] km 3 DRE) is less than 1–in–1 billion in the next 100 years (i.e., &lt; 10 –9 probability). Based on current volcanological understanding and evidence, we believe this probability estimate is robust to within an order of magnitude. 

Aso volcano, Japan: assessing the 100-year probability of a new caldera-forming eruption based on expert judgements with Bayes Net and Importance Sampling uncertainty analysis


 The southern part of the Kuril Island Arc is one of the world’s most active modern volcanic zones, with widespread felsic caldera volcanism, but it has been less well studied compared with other arcs. The Mendeleev caldera-forming eruption (40 ka) on Kunashir Island, southern Kurils, is one of the most explosive Pleistocene eruptions to have occurred in this region. This study aimed to establish the origin and storage conditions of magma preceding the Pleistocene caldera eruption of Mendeleev volcano. Mineralogical and melt inclusion analyses reveal that the primary melts had felsic compositions and that the early stage of magmatic evolution involved amphibole breakdown into a two-pyroxene, plagioclase, and Fe–Ti oxide assemblage under pressure–temperature conditions of 107–314 MPa and 807–932 °C. The caldera-forming products are represented by dacitic pumice composed of plagioclase + augite + hypersthene+ quartz + Fe–Ti oxides and melt with uniform low-K rhyolite composition. Pre-eruptive magma was stored in a reservoir at 77–195 MPa (3.0–7.6 km depth) and 830–890 °C under H2O-saturated conditions. The mechanism of magmatic evolution implies the following two-step scenario: (1) generation of magma by the partial melting of an amphibole-bearing substrate accompanied by the formation of early Mg-rich clino- and orthopyroxene, plagioclase, Fe–Ti oxides, and peritectic rhyolitic melt; and (2) crystallization of late plagioclase and quartz directly from these partial melts. Local or regional extension during the Pleistocene, accompanied by increasing heat flow in the supra-subduction mantle, generated an active mafic intrusion into the upper crust. This process was accompanied by abundant subaerial eruptions of basaltic volcanoes and could have caused intense heating and partial melting of upper-crustal rocks. Our results indicate that the partial melting of amphibole-bearing substrates in island arcs may serve as a universal mechanism for the generation of silicic magmas during powerful caldera eruptions in young island arcs.

Partial melting under shallow-crustal conditions: a study of the Pleistocene caldera eruption of Mendeleev volcano, southern Kuril Island Arc

Additional file 8. Densities of H2O and CO2 gases at temperatures of 870, 928, 944, and 1030 °C calculated by the Modified Redlich–Kwong equation of state (Holloway 1981). 

Additional file 8 of Magma ascent and degassing processes of the 2011 and 2017–18 eruptions of Shinmoedake in Kirishima volcano group, Japan, based on petrological characteristics and volatile content of magmas

Additional file 7. Magma temperature and oxygen fugacity estimated from Fe–Ti oxide thermometry applied to coexisting Fe–Ti oxide pairs in the 1716-17, 2011 and 2018 products. 

Additional file 7 of Magma ascent and degassing processes of the 2011 and 2017–18 eruptions of Shinmoedake in Kirishima volcano group, Japan, based on petrological characteristics and volatile content of magmas

Abstract This short report introduces one of the ways to quickly and accurately aim melt inclusions in phenocryst using NanoSIMS. 

Gamma mark: An ingenuity to ease the aiming of melt inclusions in phenocrysts with NanoSIMS


 This paper presents the chemical composition (including H2O and CO2) of matrix glass, melt inclusions in phenocrysts, and their host minerals in eruptive products from Aso caldera. We found a group of melt inclusions with clearly lower potassium (0.6–2 wt.% K2O at 50–70 wt.% SiO2) than previously reported high-K2O whole-rock compositions (3–5 wt.% K2O at 55–70 wt.% SiO2). While most of the high-K2O intermediate to felsic melt inclusions are vapor undersaturated and show the features of H2O, CO2, and K2O accumulation, the low-K2O basaltic melt already has higher H2O and CO2. We reconcile this discrepancy with a model in which (1) the volatile-rich basalt magmas degas near the surface, (2) migrate back to depths of ≥12 km in the crust, and (3) crystallize feldspar and quartz to produce high-K2O felsic melt, (4) magma mixing among the undegassed, degassed, and evolved magmas. By crystallization, about five times as much low-K2O basaltic magma is required to produce high-K2O felsic magma. The quantity of felsic magma ejected from 270 ka (Aso-1) to 90 ka (Aso-4) requires a basalt magma supply rate of 18-31 km3/ka. This magma supply rate is comparable to or less than the present-day production rate of degassed magma (73 km3/ka) at an active center of Aso, Nakadake. These findings suggest volcanic gas flux monitoring has the potential to be a ‘basalt usage meter’ during the dormant period of caldera volcanoes.

Importance of long-term shallow degassing of basaltic magma on the genesis of massive felsic magma reservoirs: A case study of Aso caldera, Kyushu, Japan

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Importance of long-term shallow degassing of basaltic magma on the genesis of massive felsic magma reservoirs: A case study of Aso caldera, Kyushu, Japan