We have studied four lava dome eruptions which occurred in 45–10 ka in Haruna volcano. Enclave parts (SiO₂ 50.9–55.1 wt%) and host parts (SiO₂ 59.5–64.5 wt%) in lava samples are all products of magma mixing. Characteristics of felsic endmember magmas are the same among four eruptions, while those of mafic endmember magmas vary slightly in terms of bulk composition. The felsic magma had SiO₂ ≥ 63 wt% and a temperature of 760°C–860°C, and contained ≥60 vol% of orthopyroxene, amphibole, plagioclase, quartz, and Fe-Ti oxides. The mafic magma had SiO₂ 48–51 wt% and contained 0–10 vol% of olivine. The enclave magmas resulted from higher contribution of mafic magma and thus had higher temperature than the host magmas, which led to formation of enclave upon their interaction. Similarities of endmember magmas between the four eruptions and the Futatsudake-Ikaho eruption (late 6th–beginning of 7th century) suggest structure of magma plumbing system and eruption triggering process have been basically unchanged in past 45,000 years. The felsic magmas were commonly mush-like and had high viscosity. Therefore, generation of low-viscosity magma through magma mixing, and vent-opening by the low-viscosity magma are mandatory for eruption to initiate. Unlike the Futatsudake-Ikaho eruption, the older four eruptions did not proceed to eruptive phase where felsic magma erupts without mixing and explosively. The absence of quartz only in felsic magma of Futatsudake-Ikaho eruption is consistent with its less-evolved bulk composition and slightly higher temperature than those of older four eruptions.

1. [1] N. Geshi and K. Takeuchi, “Geology of the Haruna San district,” Quadrangle Series, 1:50,000, Geological Survey of Japan, AIST, 2012 (in Japanese).
2. [2] O. Oshima, “Geology, petrology, and mineralogy of Haruna volcano,” Ph.D thesis, The University of Tokyo, p. 280, 1983.
3. [3] O. Oshima, “Haruna volcano,” Editorial Committee of Kanto, Part 3 of Regional Geology of Japan (Eds.), “Regional Geology of Japan, Part 3 Kanto Region,” pp. 222-224, Kyoritsu Shuppan, 1986 (in Japanese).
4. [4] N. Geshi and M. Oishi, “The ¹⁴C ages of the late Pleistocene – Holocene volcanic products erupted from the Haruna volcano,” Bull. Geol. Surv. Japan, Vol.62, pp. 177-184, doi: 10.9795/bullgsj.62.177, 2011 (in Japanese).
5. [5] M. Takahashi, Y. Watanabe, S. Seki, T. Kanamaru, and H. Takemoto, “Whole-rock chemistry for eruptive products of Haruna volcano, central Japan: Summary of 235 Analytical data,” Proc. of the Inst. of Natural Sciences, Nihon Univ., Vol.51, pp. 179-219, 2016 (in Japanese).
6. [6] Y. Suzuki and S. Nakada, “Remobilization of highly crystalline felsic magma by injection of mafic magma: Constraints from the middle 6th century eruption at Haruna volcano, Honshu, Japan,” J. Pet., Vol.48, No.8, pp. 1543-1567, doi: 10.1093/petrology/egm029, 2007.
7. [7] Y. Suzuki, M. Nagai, F. Maeno, A.Yasuda, N. Hokanishi, T. Shimano, M. Ichihara, T. Kaneko, and S. Nakada, “Precursory activity and evolution of the 2011 eruption of Shinmoe-dake in Kirishima volcano-insights from ash samples,” Earth, Planets and Space, Vol.65, No.6, pp. 591-607, doi: 10.5047/eps.2013.02.004, 2013.
8. [8] A. Tomiya, I. Miyagi, H. Hoshizumi, T. Yamamoto, Y. Kawanabe, and H. Satoh, “Essential material of the March 31, 2000 eruption of Usu volcano: Implication for the mechanism of the phreatomagmatic eruption,” Bull. Geol. Surv. Japan, Vol.52, Issues 4-5, pp. 215-229, doi: 10.9795/bullgsj.52.215, 2001 (in Japanese).
9. [9] T. Soda, “Two 6th century eruptions of Haruna volcano, central Japan,” The Quaternary Research (Daiyonki-Kenkyu), Vol.27, No.4, pp. 297-312, doi: 10.4116/jaqua.27.297, 1989 (in Japanese).
10. [10] T. Yamamoto, “Quantitative re-description of tephra units since 0.3 Ma in the Tochigi-Ibaraki region, NE Japan,” Bull. Geol. Surv. Japan, Vol.64, Nos.9-10, pp. 251-304, doi: 10.9795/bullgsj.64.251, 2013 (in Japanese).
11. [11] N. Hokanishi, A. Yasuda, and S. Nakada, “Major and Trace element analysis of silicate rocks using fused glass beads with an X-ray fluorescence spectrometer,” Bull. Earthq. Res. Inst., Univ. Tokyo, Vol.90, pp. 1-14, doi: 10.15083/0000032410, 2016 (in Japanese with English abstract).
12. [12] A. Peccerillo and S. R. Taylor, “Geochemistry of eocene calc-alkaline volcanic rocks from the Kastamouu area, Northern Turkey,” Contrib. Mineral. Petrol., Vol.58, pp. 63-81, doi: 10.1007/BF00384745, 1976.
13. [13] M. J. Rutherford and P. M. Hill, “Magma ascent rates from amphibole breakdown: An experimental study applied to the 1980–1986 Mount St. Helens eruptions,” J. Geophys. Res., Vol.98, Issue B11, pp. 19667-19685, doi: 10.1029/93JB01613, 1993.
14. [14] B. E. Leake, A. R. Woolley, C. E. S. Arps, W. D. Birch, M. C. Gilbert, J. D. Grice, F. C. Hawthorne, A. Kato, H. J. Kisch, V. G. Krivovichev, K. Linthout, J. Laird, J. Mandarino, W. V. Maresch, E. H. Nickel, N. M. S. Rock, J. C. Schumaker, D. C. Smith, N. C. N. Stephenson, L. Ungaretti, E. J. W. Whittaker, and G. Youzhi, “Nomenclature of amphiboles: Report of the subcommittee on amphiboles of the International Mineralogical Association, Commission on New Minerals and Mineral Names,” Can. Mineral., Vol.35, Issue 1, pp. 219-246, 1997.
15. [15] K. Putirka, “Amphibole thermometers and barometers for igneous systems and some implications for eruption mechanisms of felsic magmas at arc volcanoes,” Am. Mineral., Vol.101, No.4, pp. 841-858, doi: 10.2138/am-2016-5506, 2016.
16. [16] K. Hattori and H. Sato, “Magma evolution recorded in plagioclase zoning in 1991 Pinatubo eruption products,” Am. Mineral., Vol.81, Nos.7-8, pp. 982-994, doi: 10.2138/am-1996-7-820, 1996.
17. [17] M. J. Rutherford and J. D. Devine, “Preeruption pressure–temperature conditions and volatiles in the 1991 dacite magma of Mount Pinatubo,” C. G. Newhall and R. S. Punongbayan (Eds.), “Fire and Mud. Eruptions and Lahars of Mount Pinatubo, Philippines,” pp. 751-766, University of Washington Press, 1996.