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All Journal Indonesian Journal of Geography Journal of Geoscience, Engineering, Environment, and Technology Journal of Applied Geology
Indranova Suhendro
Department of Environmental Geography, Faculty of Geography, Universitas Gadjah Mada
Civil Engineering, Building, Construction & Architecture Earth & Planetary Sciences Energy Engineering Environmental Science Physics

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Rock characteristics of post-caldera volcanoes in Dieng volcanic complex (DVC), Central Java, Indonesia Indranova Suhendro; Muhammad Nadafa Isnain; Rizky Wahyudi
Journal of Geoscience, Engineering, Environment, and Technology Vol. 7 No. 4 (2022): JGEET Vol 07 No 04 : December (2022)
Publisher : UIR PRESS

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.25299/jgeet.2022.7.4.10015

Abstract

The Dieng volcanic complex (DVC) has one of the densest post-caldera volcanisms activity presents in Indonesia, yet its population density is considerably high. Therefore, it is important to identify the rock characteristics produced by the DVC post-caldera volcanoes to understand the risks and future hazards (i.e., eruption style). Based on lithology, we have classified DVC post-caldera volcanoes as (1) pyroclastic domain (PD; including Pagerkandang, Merdada, and Pangonan), and (2) lava domain (LD; including Prambanan, Kendil, Pakuwaja, Sikunir, Sikarim, and Seroja). PD is characterized by the domination of pyroclastic materials (mostly ash and lapilli) with oxidized scoria and volcanic lithics (fresh and/or altered) as the main components. The oxidized scoria clasts are moderately vesicular (27–41 % vesicularity; ) and phenocryst poor (<5 % phenocryst crystallinity, ), with plagioclase, pyroxene, and oxides as the main phenocryst phases. The LD is composed predominantly of lava. The observed lavas are typically dense (mostly <1 % , phenocryst rich (21–47 % ), and include plagioclase, pyroxene, biotite, amphibole, and oxides as the main phenocryst phases. Such differences in mineralogy and textures (i.e., vesicularity and crystallinity) suggest that PD and LD were likely sourced from different magmatic sources with different eruption styles (explosive and effusive styles, respectively). We have suggested that civilization settlements near PD are facing major threats from explosive magmatic, phreatomagmatic, and phreatic eruptions that could produce significant fallouts, ballistic materials, and highly destructive pyroclastic density currents. LDs pose a threat in the form of effusive magmatic eruptions such as lava flows and/or domes.
Cooling history (from magma ascent to lava extrusion) of the Watuadeg pillow lava, Berbah, Yogyakarta, Indonesia Indranova Suhendro; Agung Harijoko; Nugroho Imam Setiawan; Haryo Edi Wibowo
Journal of Applied Geology Vol 8, No 1 (2023)
Publisher : Geological Engineering Department Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.22146/jag.73942

Abstract

The Watuadeg pillow lava (WPL) is known as one of the most famous pillow lava outcrops in Yogyakarta, Indonesia, and its origin has been attributed to rapid-cooling process of subaqueous lava extrusion. However, there is no quantitative evidence that implies such hypotheses. Therefore, this study aims to reduce such a gap by revealing the cooling times (t) of WPL on the basis of a quantitative approach. In particular, we measured the size distribution (CSD) and number density (MND) of plagioclase microlites from the core, medial, and marginal (rim) domains of WPL. We found that the CSD slope significantly increases towards marginal zones, namely 30.4ᵒ for the core, 53.4ᵒ for the medial, and 228.1ᵒ for the rim. Because CSD slope is inversely proportional to cooling time ( ), by assuming a typical plagioclase microlite growth rate (G) of 1×107 mm/s, it is therefore inferred that the rim experienced the fastest cooling time (±12.1 hours), followed by the medial and core ((±52.0 and 91.4 hours, respectively). The fact that MNDs value increases toward the marginal zones also does not deny this idea (0.3×1016 m-3 for the core, 1.4×1016 m-3 for the medial, and 2.4×1016 m-3 for the rim), as higher MND with the domination of acicular-spherulitic habit represents a higher degree of undercooling. Because microlite is syn-eruptive product, our estimation represents the cooling time of magma since it migrated from the reservoir to the surface.
Typology of Indonesian Stratovolcanoes: Insights from Geomorphological and Geological aspects Indranova Suhendro; Eko Haryono
Indonesian Journal of Geography Vol 55, No 2 (2023): Indonesian Journal of Geography
Publisher : Faculty of Geography, Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.22146/ijg.74692

Abstract

This study aims to provide the first general typology of Indonesian stratovolcano (number of analyses=154), including various types of rock compositions and diverse volcanic hazards. Several parameters were evaluated, including average radius (r), average slope (S), surface roughness (RMS), rock compositions, mineralogy, and deposit characteristics. Four types were identified as follows: (1) small-least dissected cones, (2) broad-dissected cones, (3) extremely broad-dissected cones with caldera, and (4) residual-highly dissected cones. Type I is typically small (r=2.1 km), steep (S=19.8ᵒ), rough (RMS=88.8), less evolved (predominantly basic to intermediate), having abundant mafic (olivine, clinopyroxene) and minor hydrous (amphibole, biotite) minerals, with rare pumice and lava domes (mostly scoria and lava flows). Type II has moderate values of r, s, and RMS (8.8 km, 15.2ᵒ, and 47.7, respectively) with predominantly intermediate rocks, minor olivine with abundant hydrous minerals, and abundant pumice and lava domes. Type III is typically large (r=18.1 km), gentle (S=9.2ᵒ), smooth (RMS=40.1), producing abundant felsic rocks and felsic minerals (quartz and sanidine), and characterized by the occurrence of thick ignimbrite deposits. Type IV has relatively similar size to type II (r=8.2 km), but the slope is gentler with coarser surface textures (S=10.7ᵒ and RMS=56.8), includes more portion of ultrabasic rocks and mafic minerals, and has no feature of lava domes with common exposure of intrusions (e.g., dyke). We suggest that the evolution from type I to type III corresponds to maturation stage, whereas the formation of type IV represents erosional stage.
Co-Authors Agung Harijoko Eko Haryono Haryo Edi Wibowo Muhammad Nadafa Isnain Nugroho Imam Setiawan Rizky Wahyudi