lava dome

Petrology of the Misen and Sankoho lava dome and their associated Pyroclastic flow deposits

Haruna Nishita

  1. Introduction

There are 111 active volcanoes in Japan and these volcanoes have a large impact on our society. A recent example of a volcanic disaster in Japan was the eruption of Mount Ontake on September the 27 September 2014. Mount Ontake erupted suddenly and caused more than 60 fatalities including missing persons (Kaneko et al., 2016). The eruption of Mt. Unzen between 1991-1995 is another example. This dome forming eruptive episode produced numerous pyroclastic density currents (PDC) which descended down the eastern slopes of the volcano. On June the 3 in 1993 a PDC traveled 3.6 km down the eastern flank of Unzen volcano and killed 43 people including volcanologists Harry Glicken and Maurice and Katia Krafft (Yamamoto et al., 1993).

A better understanding of the magmatic processes which leads to unrest and eruption will help to mitigate volcano-related disasters. Analysis of magma composition and mineral chemistry can help to understand the magma plumbing system of arc volcanoes. This will improve our ability to better interpret volcanic unrest of future upcoming eruptions.

 

  1. Daisen Volcano

Daisen volcano (Fig. 1) is a large Quaternary volcano with several amalgamated eruptive centers which are: Hiruzen, Karasugasen, Misen. It is located in the San-in district, SW Japan. The eruptive history of Daisen volcano began during the middle Pleistocene and continued until circa 17,000 years ago (Tsukui, 1984; Yamamoto, 2017).

Daisen volcano is divided into an Older Group and a Younger Group (Tsukui, 1984). The activity of the Older Group lasted from 1.0 to 0.4 Ma and produced several thick lava flows in conjunction with deposition of the voluminous Mizoguchi tuff breccia. The Older Group is covered by the Younger Group, which is subdivided into an Upper Tephra Group and a Lower Tephra Group. The Younger Group consists of large number of pyroclastic fall and flow deposits. During the two most recent eruptive episodes Sankoho and Misen lava dome formed. Both eruptive centers were the source of numerous block and ash flows which covered the eastern and northern flanks of the mountain.

Fig.1 Daisen Volcano
Fig.1 Daisen Volcano

 

  1. Aims
  • To reveal the stratigraphy of the Masumizuhara and Amidagawa pyroclastic flow deposits which are classified as part of the younger group of Mt. Daisen.
  • To characterize the magmatic system of Mt. Daisen during its youngest eruptive cycle.

 

  1. Methods
  • Fieldwork including mapping and the documentation of geological outcrops to understand and interpret past effusive and explosive activity and volcanic history of the uppermost part of the Younger tephra group at Daisen volcano
  • Tephra stratigraphy / sedimentary logging, description and dating of tephra sequences
  • Petrographic studies of different types of volcanic products using the optical microscope
  • Geochemical analytic of whole rock major and trace element composition
  • Analytic of mineral and glass chemistry using EPMA
  • Thermodynamic modelling of phase equilibria to determine intensive parameters of the magmatic systems during the most recent eruptions of Daisen volcano

 

  1. References

Kaneko, T., Maeno, F., and Nakada, S. (2016). 2014 Mount Ontake eruption: characteristics of the phreatic eruption as inferred from aerial observations. Earth Planets and Space 68, 72.

Tsukui, M. (1984). Geology of Daisen Volcano. The Journal of the Geological Society of Japan 90, 643–658.

Yamamoto, T. (2017). Quantitative eruption history of Pleistocene Daisen Volcano, SW Japan. Bulletin of the geological survey of Japan 68, 1–16.

Yamamoto, T., Takarada, S., and Suto, S. (1993). Pyroclastic flows from the 1991 eruption of Unzen volcano, Japan. Bull Volcanol 55, 166–175.