Caldera-forming volcanism represents one of the most catastrophic geohazards on Earth. Driven by the rapid evacuation of large volumes of magma from the shallow crust, these eruptions form kilometer-scale collapse depressions and are capable of reshaping regional landscapes and altering planetary climate and ecology. Caldera-forming systems at the land–sea interface generate cascading hazards, including tsunamis, seafloor deformation, and atmospheric shockwaves, yet are poorly understood despite their significant socio-economic risks. The Hunga eruption in 2022 underscored this vulnerability, exposing a global lack of preparedness rooted in incomplete understanding of eruption mechanisms, precursory activity and cyclic behavior of marine caldera-forming eruptions. Marine eruptive records, together with greater knowledge of how external factors (e.g., tectonics, sea-level changes, flank collapses) may affect the eruption systematics, are crucial to quantify the hazards of those systems arising for society, economics, and environment.
Kikai Caldera, a large, mostly submarine complex located south of Kyushu, Japan, is an ideal natural laboratory to overcome these limitations. Its most recent caldera-forming event, the catastrophic Akahoya eruption at 7.3 ka, was the largest eruption of the Holocene and generated tsunamis and pyroclastic flows traveling over water for >80 km to reach mainland Japan, impacting early Japanese society and culture. Yet because of Kikai’s vast offshore extent, its eruptive history and caldera cycle dynamics, and their relationship to those of other large calderas of Kyushu, are poorly constrained. Obtaining the buried submarine sedimentary and volcanic record at Kikai to establish a robust eruption time series, including eruptive volumes, distribution patterns and geochemistry, and to determine past climate and biological responses, will elucidate the interplay between repeated large eruptions and the ecosystem, paleoclimate and oceanography.
Environmentally, drilling the Kikai caldera-forming eruptions provides a unique possibility to investigate if and how repeated large eruptions and hydrothermalism influence the ability of the ecosystem, and especially the deep biosphere to recover or even benefit from the volcanic eruptions. Similarly, the combined volcanic and sedimentary records offer insight into how paleoclimate and oceanography (e.g. the Kuroshio current) have been modulated or influenced by volcanism in the region.
Developing robust eruption cycle models and accurate assessments of past global atmospheric loading require quantitative and detailed knowledge of eruptive volumes and geochemistry from offshore volcanic deposits and older, buried volcanic sequences that can be recovered only through deep drilling. These considerations prompted us to submit an IODP3 pre-proposal (IODP 1122-Pre, ‘SHREK’, Submarine Hazards, Responses, and Eruption cycles from Kikai caldera).
The main aim of that workshop is to develop an IODP3 full drilling proposal for the R/V Chikyu by elaborating on the scientific hypotheses and questions based on the feedback from SEP on the pre-proposal, identify and modify drilling locations and scenarios, expanding the scientific team and incorporate new expertise, as well as to coordinate future site survey expeditions.
