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The caldera-forming Samalas eruption of the Samalas–Rinjani volcanic complex on Lombok, Indonesia, in 1257 CE ranks as one of the most explosive and sulphur-rich eruptions of the past thousand years. Along with other significant events (e.g. Tambora 1815, El Chichón 1982), Samalas 1257 forms a class of powerful eruptions of magmas of intermediate alkaline composition, which remain relatively understudied. This study aims to better understand the pre-eruptive magma reservoir conditions and volatile storage capacities of intermediate alkaline systems, using the 1257 Samalas eruption as a case study. Systematic partial-equilibrium experiments were run to constrain potential magma reservoir conditions (25–200 MPa and 850–1000°C) by examining changes in the chemistry and textures of experimental glass and mineral products. Natural trachydacite pumice from the 1257 Samalas eruption was used as the experimental charge for a series of water-saturated experiments run in cold-seal pressure vessels, buffered at an oxygen fugacity ƒO2 of NNO/NNO + 1 log units. Assessing the match between natural and experimental glass compositions and mineral phases and textures reveals that pre-eruptive magma reservoir conditions were between 875°C and 930°C and ca. 100–150 MPa (4.5 ± 1km depth). Breakdown of experimental amphibole at pressures below 75 MPa, and plagioclase instability at 950°C/100 MPa, provide the strongest constraints on phase stabilities that are consistent with the magma storage region. In the observed temperature and pressure range, the natural compositions of plagioclase, amphibole and orthopyroxene are replicated in experimentally precipitated rims. Clinopyroxene and high anorthite plagioclase (An>64) in the natural mineral assemblage could not be replicated in the experiments, implying that these compositions most likely did not grow in the shallow pre-eruptive reservoir of Mt Samalas. The pre-eruptive storage depths of trachydacite magma are significantly shallower than the postulated magma storage at the currently active basaltic-andesite magmatic system at Rinjani, and thus monitoring magma storage depth may be a useful indicator of changing magma composition in the future. Our findings show that highly explosive VEI 7 eruptions of intermediate alkaline magma can be fed from a relatively limited range of storage pressures (100–150 MPa), suggesting accumulation of magma in one place, rather than the rapid extraction of magma from a vertically extensive, transcrustal magma system.

Explosive volcanism is one of the deadliest volcanic hazards. The characteristics of the magma chamber that cause explosive eruptions need to be studied more deeply. Raung Volcano in East Java is an example of volcano that has a history of explosive eruptions that marked by a 2 km wide caldera. Petrographic analysis was carried out on selected 4 basaltic lava samples to determine the composition and proportion of minerals. Then, an analysis of the viscosity of the magma was carried out in relative terms using the shape and size configuration of the crystals. The comparison between the percentage of crystals and the relative viscosity value shows a positive correlation which indicates that there is an effect of the number of crystals on the viscosity of the magma. The increase in the viscosity of magma that occurred in the pre-caldera lava eruption of Raung Volcano indicates an intensive crystallization. This is supported by petrographic data which shows a porphyritic texture with a phenocryst of more than 40%. Plagioclase crystals become quite dominant crystals (> 30%). Based on this, it can be interpreted that the crystallization process occurred intensively in the shallow magma pocket of Raung Volcano.

We use satellite imagery to investigate the shoreline changes associated with volcanic activity in 2018&ndash, 2019 at Anak Krakatau, Indonesia, spanning a major lateral collapse and period of regrowth through explosive activity. The shoreline changes have been analyzed and validated through the adaptation of an existing methodology based on Sentinel-2 multispectral imagery and developed on Google Earth Engine. This work tests the results of this method in a highly dynamic volcanic environment and validates them with manually digitized shorelines. The analysis shows that the size of the Anak Krakatau Island increased from 2.84 km2 to 3.19 km2 during 15 May 2018&ndash, 1 November 2019 despite the loss of area in the 22 December 2018 lateral collapse. The lateral collapse reduced the island area to ~1.5 km2 but this was followed by a rapid increase in area in the first two months of 2019, reaching up to 3.27 km2. This was followed by a period of little change as volcanic activity declined and then by a net decrease from May 2019 to 1 November 2019 that resulted from erosion on the SW side of the island. This history of post-collapse eruptive regrowth and coastal erosion derived from the shoreline changes illuminates the potential for satellite-based automated shoreline mapping to provide databases for monitoring remote island volcanoes.

The extraordinary of geodiversity together with the ecological resources and profound cultural heritages provide a valuable basic of geotourism and geopark development. The purpose of this paper is to show the possibilities of geological interpretation, geotourism, and cultural heritages in the area of Gorontalo province that would become valuable basic to promote geopark. The collected data was carried out by field observation and literature review. The results of this study indicate that the Gorontalo has the potential of geopark and would serve as tourist destination in Sulawesi by applying the concept of Geotourism which accentuate natural side, by optimizing the management of destination attractions, facilities and services, and accessibilities.

Argoland is a piece of Gondwana that collided to the southeastern margin of Sundaland during Late Cretaceous to Early Tertiary. Recently, the existence and continuation of the missing Argoland beneath southern Java have become a hot topic related to geological exploration. The involvement of crustal assimilation of Argoland plays an important role in magma genesis. It controls eruption style, magma composition and also mineral deposit type. Although some studies have indicated the presence of micro continent beneath the southern part of West and East Java, they still could not explain its existence precisely and there are some difficulties to connect one to another. Petrological and geochemical studies of twenty active volcanoes from west to east were combined with tomographic study result to elucidate the problem and give better understanding of crust architecture and interior in Java. Our study shows that some of these magmas derived from Active Continental Margin represent those produced by partial melting of mantle wedge induced by natural fluid in subduction system due to interaction of continental and oceanic crusts. In agreement with geochemical data, high velocity zone from tomographic data are clearly shown in the southern part of Late Cretaceous to Early Tertiary Melange. If that is so, the extension of Argoland in East Java seems to continue to the Central and West Java. A new map of Argoland distribution, crust architecture and interior of Java is proposed.

Shoreline changes occur due to abrasion and accretion processes that are triggered due to intensive human activities in coastal areas. The shoreline in the Kendal region is dynamic, and shows mixed results from tidal and dominated by riverine activity. The Shoreline changes have different impacts, all of which may not be visible. Coastal dynamics in the Kendal region cause spatial-temporal shoreline changes. To observe these we need a long and continuous set of data. The purpose of this study is to determine changes in the shoreline in parts of the Kendal coastal district and to calculate the value of the changes. The data used were derived from TM data 1990, to OLI data 2017. To derive the shoreline from the satellite data, a band ratio of Red band to IR band was employed. The shorelines were digitized and saved along with the appropriate MM/DD/YYYY added to the attribute table. The Digital Shoreline Analysis System (DSAS) was used to compute rate-of-change statistics. The Digital Shoreline Analysis System (DSAS) is an extension of ArcGIS, developed by USGS. Using the extension, transects were laid every 100 m. Then, using NET SHORELINE MOVEMENT (NSM), LINEAR REGRESSION RATE (LRR) and END POINT RATE (EPR), the changes every 100 meters were analyzed and stored in a table. Subsequently, using the table, erosion, and accretion, were analyzed, and understood. The farthest accretion process was 1763.29 m and 792.14 m for the abrasion processes.

We report the atmospheric Hg contamination in an artisanal and small-scale gold mining (ASGM) area in North Gorontalo, Indonesia. It is well known that atmospheric Hg contaminates the air, water, soil, and living organisms, including trees. In this study, we calculated total weight of heavy metals, especially Hg, and quantitatively measure the concentrations of heavy metals, especially Hg, in tree bark from an ASGM area. Tree bark can be used for the environmental assessment of atmospheric contamination because it attaches and absorbs heavy metals. Atmospheric Hg and other heavy metals, including Fe and Mn, and As were detected on the tree bark samples. The total weight of Hg, As, Fe, and Mn in the tree bark samples ranged from undetectable (ND) to 9.77, ND to 81.3, 124–4028, 37.0–1376 µg dry weight (DW), respectively per weight of sample. Based on quantitatively analysis micro-PIXE, the highest concentrations of all these metals were detected in the outer part of the bark. We conclude that tree bark can adsorb atmospheric contamination, which is then absorbed into the inner tissues.

The industrial mining sector is one of the main contributors to environmental damage and toxic metal pollution, although some contamination originates from natural geological sources. Due to their position at the top of the food chain, cattle tend to bioaccumulate mercury (Hg) in their bodies. We used analyses of cattle hair samples to investigate Hg contamination in cattle farmed within and outside of an artisanal and small-scale gold-mining area in Bombana, Southeast Sulawesi, Indonesia. We also examined the factors that might have influenced the toxicity, such as the environmental conditions, sex, and age of the cattle. A total of 63 hair samples were analyzed by particle-induced X-ray emission spectrometry. The mean Hg concentration was significantly higher in hair from cattle farmed within the artisanal and small-scale gold mining area (11.44 μg/g hair) than in those farmed outside the area (2.89 μg/g hair, p < 0.05). A possible cause of this is contamination by mercury persistent in terrestrial food chain. The results indicates that the level of toxic metals such as Hg need to be controlled in food sources to protect human health, especially in Bombana, Indonesia.

甲理工博第436号

Sakurajima in Japan is one of the world’s most active volcanoes. This paper presents the results of a petrological study of the Showa Crater volcanic ash samples ejected from January 2011 to November 2012 from Sakurajima. The aim of this paper is to reconstruct the evolution in time of the conduit magma system, based on the compositions and physical properties of the studied volcanic ash. We analyzed the composition of interstitial glass and microcrystal of Black Volcanic Rock (BVR) and Black Vesicular Volcanic Rock (BVVR) in order to estimate the magma ascent rate. The results show that SiO2 content of interstitial glass and crystallinity of the BVR is generally higher than for BVVR. The different types of juvenile material likely resulted from cooling-induced crystallization and decompression-induced crystallization in the conduit. The conditions of magma transit within the conduit from 2011 to 2012 differ: in 2011, the decompression rate and magma ascent rate of BVR were higher than for BVVR, but, in 2012, the decompression rate and magma ascent rate between BVR and BVVR were similar. As such, monitoring the petrological features of dated eruptive materials could provide useful information for evaluating ongoing eruptive activity.

The objective of this study was to recognise the hydrodynamic pattern of sea surface current to find the potential of coastal circulation cells in Kendal coastal area. The initial identification of coastal circulation cells in this study used the modification of the band ratio method. Further identification related to the availability of coastal circulation cells utilise the results of aerial photography as a process of detailed validation and has never been done before. The results showed that there was a similar potential of coastal circulation cells in different seasons. In detail, the coastal circulation cells obtained the suspension of sediment, with also the potential of nutrient and alga, namely Rhodophyta Sp. Considered by the colour shown in the photograph of UAV.

Many petrological studies of volcanic rocks have attempted to better predict future volcanic activity. In this study, we examined volcanic ash samples from Showa Crater in Sakurajima, Japan, which were erupted from January to October 2013. This study was used two types of juvenile material; black vesicular volcanic rock (BVVR) and black non-vesicular volcanic rock (BNVVR) to determine the variable of magmatic processes in the magma conduit during the 2013 eruption. We divided the duration into three periods such as January to April, April to July, and July to October based on the variable tendency of SiO2 contents and volume abundance of the interstitial glasses in BVVR and BNVVR. The estimated melt compositions demonstrate that the variability of SiO2 contents and volume abundance of microcrystal in the groundmass (BVVR and BNVVR) over time were caused by micro-crystallization processes. The estimated of water contents and vesicle volume shows the influence of degassing process in the rock forming. Also, the correlation of petrological features with the number of eruptions and eruptive volumes, exhibit the variable of magma supply into conduit in each period. Consequently, careful monitoring of the petrological features of erupted materials may provide useful constraints on future eruptive activity and thereby assist in the mitigation of volcanic hazards.