Multi-level magma plumbing at Agung and Batur volcanoes increases risk of hazardous eruptions

Harri Geiger; Valentin R Troll; Ester M Jolis; Frances M Deegan; Chris Harris; David R Hilton; Carmela Freda

doi:10.1038/s41598-018-28125-2

Multi-level magma plumbing at Agung and Batur volcanoes increases risk of hazardous eruptions

Sci Rep. 2018 Jul 12;8(1):10547. doi: 10.1038/s41598-018-28125-2.

Authors

Harri Geiger¹, Valentin R Troll^{2

3

4}, Ester M Jolis^{1

5}, Frances M Deegan^{1

6}, Chris Harris⁷, David R Hilton⁸, Carmela Freda⁶

Affiliations

¹ Section for Mineralogy, Petrology and Tectonics, Department of Earth Sciences, Uppsala University, Uppsala, Sweden.
² Section for Mineralogy, Petrology and Tectonics, Department of Earth Sciences, Uppsala University, Uppsala, Sweden. valentin.troll@geo.uu.se.
³ Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy. valentin.troll@geo.uu.se.
⁴ Faculty of Geological Engineering, Universitas Padjajaran (UNPAD), Bandung, Indonesia. valentin.troll@geo.uu.se.
⁵ Geomar Helmholtz Centre for Ocean Research, Kiel, Germany.
⁶ Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy.
⁷ Department of Geological Sciences, University of Cape Town, Cape Town, South Africa.
⁸ Geosciences Research Division, Scripps Institution of Oceanography, La Jolla, USA.

Abstract

The island of Bali in Indonesia is home to two active stratovolcanoes, Agung and Batur, but relatively little is known of their underlying magma plumbing systems. Here we define magma storage depths and isotopic evolution of the 1963 and 1974 eruptions using mineral-melt equilibrium thermobarometry and oxygen and helium isotopes in mineral separates. Olivine crystallised from a primitive magma and has average δ¹⁸O values of 4.8‰. Clinopyroxene records magma storage at the crust-mantle boundary, and displays mantle-like isotope values for Helium (8.62 R_A) and δ¹⁸O (5.0-5.8‰). Plagioclase reveals crystallisation in upper crustal storage reservoirs and shows δ¹⁸O values of 5.5-6.4‰. Our new thermobarometry and isotope data thus corroborate earlier seismic and InSAR studies that inferred upper crustal magma storage in the region. This type of multi-level plumbing architecture could drive replenishing magma to rapid volatile saturation, thus increasing the likelihood of explosive eruptions and the consequent hazard potential for the population of Bali.