History of large magnitude explosive volcanism in the Japan region: implications for tectonics and long term hazards

Ocean drilling occurs all around the world, and allows scientists to examine sediments that were on the ocean floor many millions of years ago. Cores (effectively of a drain pipe full of sediment) are drilled throughout research expeditions, extending several kilometres down into the sediments and rocks on the ocean floor. These cores often contain volcanic ash layers, which provide a major resource to reconstruct the history of large volcanic eruptions. In the Kyushu region of Japan, comparison of volcanic records on land with tectonic plate reconstructions (Mahony et al., 2011) shows that major changes in the style of volcanic activity occurred at a similar time to changes in the direction and rate of tectonic plate motion.
International Ocean Discovery Program (IODP) Expedition 350 provides an outstanding opportunity to test hypotheses for these marked changes, to advance understanding of the causative tectonic and volcanic processes, assess factors that preserve marine ash layers, and to integrate these studies to elucidate the relationship between tectonics and large magnitude explosive eruptions.

The aims of this study are to answer the following questions:
- Can rates of explosive volcanism be related to plate tectonic behaviour?
- What causes these relationships?
- What is the significance of a record of large magnitude volcanic eruptions in terms of the underlying magmatic activity?

To answer these questions, a series of volcanic ash layers drilled during IODP Expedition 350 will have samples taken and analysed. First, the source eruption, volcano or region the ash originated from will be identified by looking at the chemistry of the volcanic ash. Next the size of volcanic particles in each ash layer will be studied, to establish is there is a correlation between the grain sizes, the thickness of the ash layer, the distance from the source volcano, and the magnitude of the eruption which produced the ash layer. Analysis of the uncertainty related to variations in ash layer thickness will also be investigated. Finally all of this information will be integrated to test the study aims.

One ultimate goal of the research is to provide estimates of the return periods of large magnitude explosive eruptions and their attendant uncertainties. Studies such as these are important for the siting of sensitive facilities vulnerable to extreme volcanic events (e.g. nuclear power stations).

References:
Mahony, S.H., Wallace, L.M., Miyoshi, M, Villamor, P, Sparks, R.S.J. & Hasenaka, T. 2011. Volcano-tectonic interactions during rapid plate-boundary evolution in the Kyushu region, SW Japan. Geol. Soc. Am. Bull, 123, 2201-2223.

There are multiple beneficiaries of this research, including academics, industry, government, policy makers, and schools.
An immediate benefit will be to the UK and international scientific community, as generation of data from this project will be a valuable resource which will be made available 18 months after Expedition 350, and can be used in other studies. Insights gained from analysis of the data of volcanic-tectonic-igneous interactions and the magnitude-frequency relationship of volcanism in Japan has the potential to be used by several beneficiaries, for example industry (e.g. nuclear), government and policy makers and the insurance sector. All of these end-users have an interest in extreme events and volcanic eruption recurrence rates. Japan are one of the many countries looking for a suitable site to build a geological repository for high level nuclear waste and there is currently great concern about the potential impact of future extreme natural events, including volcanic eruptions, with respect to their civil nuclear power programme. These concerns relate to the Tohoku earthquake and tsunami and the devastating effects on the Fukushima nuclear power station. The results of this project can contribute directly to evidence-based policy-making and will influence nuclear waste repository siting policy at a national level. The scientific outcomes of this study will aid the assessment of potential sites to host a geological repository may influence other governments assessments of their own nuclear waste repository siting programs in relation to volcanic hazards.
The insurance sector is another potential beneficiary. Bristol has a complementary project with Munich Re on assessing volcanic risk in Japan, in particular to Tokyo. Again recurrence rates of extreme volcanic events is of particular significance. The wider public will benefit, as greater understanding of large scale geological processes will input into policy to improve public safety. It is hoped that many school groups will benefit from ship-to shore interaction during Expedition 350, where they can be introduced to the issues that this project hopes to clarify, and enjoy learning about the methods we will use. Increased public engagement will hopefully help explain the larger problems faced in current science, and inspire younger generations to further their studies in physical sciences.