Shallow magma pre-charge during repeated Plinian eruptions at Sakurajima volcano

Naoki Araya,Tomoki Sato,Atsushi Yasuda,Nobuo Geshi,Masato Iguchi,Michihiko Nakamura,Satoshi Okumura,Daisuke Miki

doi:10.1038/s41598-019-38494-x

Abstract

Vigorous explosive eruptions that produce continuous high eruption plumes (Plinian eruptions) are generally assumed to tap a magma reservoir. The 1914 Plinian eruption at the Sakurajima volcano located on the Aira caldera rim is one such case, where the main magma reservoir was assumed to be located approximately 10 km beneath the caldera. However, we report that estimated magma storage depths immediately prior to the eruption were much shallower (0.9–3.2 km) on the basis of pressure at which volatiles within the phenocryst melt inclusions and plagioclase rims were finally equilibrated. The same is observed for two historic Plinian eruptions in 1471 and 1779. This depth is even shallower than the shallowest magma reservoir estimated from the pressure source for geodetic deformation during recent Vulcanian explosions (4 km beneath the crater). We propose that the magmas were fed from a thick conduit pre-charged from deeper reservoirs. The ground subsidence observed after 1914 within the Aira caldera may have been caused by conduit recharge following the eruption. Voluminous conduit recharge could be key to forecasting the next possible large eruption at the Sakurajima volcano.

Highlights

Forecasting the initiation of future eruptions is a challenging but rewarding task in volcanology
The inclusion-hosting phenocrysts, both plagioclase and pyroxene, have a wide compositional range (Supplementary Fig. S1) as they were mostly derived from the endmember magmas of mixing, some were formed after mixing
The analytical accuracy of the FTIR analysis is shown in c. (e) Magma storage depths estimated from the final equilibrated pressure of H2O contents in melt inclusions calculated with the H2O solubility model[32]

Summary

Introduction

Forecasting the initiation of future eruptions is a challenging but rewarding task in volcanology. An imminent concern for this volcano is if, when, and how the eruption of similar magnitude will occur because the surface level within the Aira caldera, which subsided during the 1914–1915 eruption, has almost returned to its original pre-eruption level[7,8], suggesting that the main magma reservoir has been almost fully recharged. We calculated H2O contents in matrix melts in equilibrium with plagioclase phenocryst rims based on plagioclase-hygrometers to further constrain pre-eruptive volatile contents. From these data, we demonstrate that the erupted magmas were pre-charged in the shallow conduit immediately prior to the eruptions. The petrochemical details of the endmember magmas are described in Supplementary Information

Methods

Results

Conclusion