Japan Geoscience Union Meeting 2014

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Oral

Symbol S (Solid Earth Sciences) » S-VC Volcanology

[S-VC54_1AM2] Volcanic and igneous activities, and these long-term forecasting

Thu. May 1, 2014 11:00 AM - 12:30 PM 411 (4F)

Convener:*Teruki Oikawa(Institute of Geology and Geoinformation, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Daisuke MIURA(Geosphere Sciences, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry), Takeshi Hasegawa(Department of Earth Sciences, College of Science, Ibaraki University), Nobuo Geshi(Geological Survey of Japan, The National Institute of Advanced Industrial Science and Technology), Yoshihiro Ishizuka(Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Chair:Daisuke Miki(Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University), Fukashi Maeno(Earthquake Research Institute, University of Tokyo)

11:00 AM - 11:15 AM

[SVC54-06] The change time from magmatic to phreatomagmatic eruption, in the Hachodaira caldera eruption at Miyakejima Volcano

*Teruki OIKAWA1, Nobuo GESHI1 (1.GSJ, AIST)

Keywords:volcano, caldera, Miyakejima, eruption, Miscanthus

The Miyakejima volcano formed the caldera in 2000. This volcano erupted Hachodaira Scoria and Hachodaira Ash at ca.3ka of Hachodaira caldera collapse. Many plant fossils (Miscanthus sp.) are recognized in Hachodaira Scoria and Ash. Based on plant fossils in these tephras occurrence, deposition late of soil in the Miyakejima volcano, and form of the boundary of Hachodaira Scoria and Ash, The change time from magmatic eruption (Hachodaira Scoria eruption) to phreatomagmatic eruption (Hachodaira Ash) is under 1 year, probably it is several days or less. Thus, there was no time gap almost between magma eruption and phreatomagmatic eruption. This eruption style change can be explained such as 2000 eruption (Geshi and Oikawa,2008:JVGR) as follows. The altitude of the summit part approached the sea level by caldera collapse; as a result, phreatomagmatic eruption occurred.