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Syn-eruptive conduit processes during basaltic-andesite to dacite Plinian eruption of Raung volcano, East Java, Indonesia: insight from the textural studies of pumice and scoria

Mradipta Lintang Alifcanta Moktikanana1 , Tsukasa Ohba1, Takashi Hoshide1, Indranova Suhendro2

  • Affiliations: 1Department of Earth Resource Sciences, Graduate School of International Resource Sciences, Akita University, Japan; 2Department of Environmental Geography, Faculty of Geography, Gadjah Mada University

  • Presentation type: Talk

  • Presentation time: Monday 14:15 - 14:30, Room S150

  • Programme No: 3.6.1

  • Theme 3 > Session 6

Abstract

The behavior of volcanic eruption is controlled by pre-eruptive processes in magma chamber and syn-eruptive processes during magma ascent in the conduit. Different magma composition controls the physico-chemical magma properties, leading to distinct eruptive behavior. Raung volcano in Indonesia has an interesting history, where basaltic-andesite to dacite magma caused the VEI 4-5 Plinian eruption of pumice fall (Rjp1; 0.7--1.3 km3) and scoria fall (Rjp2; 0.3 km3 and Rjp3; 0.1--0.2 km3) between 1200 and 1600 CE. Our study aims to investigate the distinct eruptive processes responsible for triggering explosive eruptions in contrasting magma composition within a single volcano. We conducted petrography, whole rock geochemistry, mineral chemistry, and thermobarometry to assess the pre-eruptive processes. Additionally, textural analysis of vesicle and crystal in pumice and scoria was performed to investigate the syn-eruptive processes. Vesicles and crystals were quantified to determine vesicle size distribution (VSD), pheno-vesicle and matrix-vesicle number density (PVND & MVND), and microlite number density (MND). Our results show that both dacite and andesite eruptions were initiated by high PVND, indicating magma chamber overpressure before the eruption. Pumice fall eruption in dacitic magma resulted from the ideal condition of explosive eruption, caused by pressure accumulation of trapped gas in viscous magma. Conversely, positive correlation of MVND and MND in scoria suggests that explosive eruption in basaltic-andesite to andesite magma is related to increased magma viscosity due to microlite crystallization. These findings confirm that explosive eruptions with distinct mechanisms can be caused by variable magma composition within a single volcanic center.