Giant rhyolite lava dome formation after 7.3 ka supereruption at Kikai caldera, SW Japan

Yoshiyuki Tatsumi,Kazuki Hayashi,Reina Nakaoka,Haruhisa Morozumi,Keiko Suzuki-Kamata,Hikaru Iwamaru,Hiroshi Ichihara,Nobukazu Seama,Tatsuro Chiba,Koji Kiyosugi,Kazuo Nakahigashi,Satoshi Shimizu,Hiroko Sugioka,Mamoru Sano,Tetsuo Matsuno,Yojiro Yamamoto,Hideaki Takizawa

doi:10.1038/s41598-018-21066-w

Abstract

Kikai submarine caldera to the south of the Kyushu Island, SW Japan, collapsed at 7.3 ka during the latest supereruption (>500 km3 of magma) in the Japanese Archipelago. Multi functional research surveys of the T/S Fukae Maru in this caldera, including multi-beam echosounder mapping, remotely operated vehicle observation, multi-channel seismic reflection survey, and rock sampling by dredging and diving, provided lines of evidence for creation of a giant rhyolite lava dome (~32 km3) after the caldera collapse. This dome is still active as water column anomalies accompanied by bubbling from its surface are observed. Chemical characteristics of dome-forming rhyolites akin to those of presently active small volcanic cones are different from those of supereruption. The voluminous post-caldera activity is thus not caused simply by squeezing the remnant of syn-caldera magma but may tap a magma system that has evolved both chemically and physically since the 7.3-ka supereruption.

Highlights

Kikai submarine caldera to the south of the Kyushu Island, SW Japan, collapsed at 7.3 ka during the latest supereruption (>500 km[3] of magma) in the Japanese Archipelago
This structure, the outer and inner calderas having 24 × 19 and 17 × 15 km is confirmed and shown in Fig. 2 based on the location of the topographic depression and normally faulted displacement of subsurface layers documented by the present bathymetry together with the multi-channel seismic (MCS) survey results (Fig. 3)
Timing of the outer caldera formation is unknown at the present stage, there is no evidence suggesting that the outer caldera collapsed by older supereruptions

Summary

Introduction

Kikai submarine caldera to the south of the Kyushu Island, SW Japan, collapsed at 7.3 ka during the latest supereruption (>500 km[3] of magma) in the Japanese Archipelago. Multi functional research surveys of the T/S Fukae Maru in this caldera, including multi-beam echosounder mapping, remotely operated vehicle observation, multi-channel seismic reflection survey, and rock sampling by dredging and diving, provided lines of evidence for creation of a giant rhyolite lava dome (~32 km3) after the caldera collapse. Seven volcanoes prone to supereruptions are built in regions of low crustal strain rate, leading to the speculation that the viscous silicic melts that cause such eruptions can be readily segregated from the partially molten lower crust and form a large magma reservoir in such a tectonic regime[10] Many of these Japanese supereruptions are followed by formation of rather small post-caldera stratovolcanoes, cones and/or lava domes. Take-shima and Satsuma Iwo-jima, represent subaerial parts of the northern rim of this submarine caldera (Fig. 1)

Methods

Results

Conclusion