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Fig. 3 | Earth, Planets and Space

Fig. 3

From: Chronology of the 2015 eruption of Hakone volcano, Japan: geological background, mechanism of volcanic unrest and disaster mitigation measures during the crisis

Fig. 3

Heat flux of Owakudani area (1983–2015). a Total, steam well and natural heat flux. b Relationship between steam well and natural heat fluxes. Note that the heat flux of the steam well has decreased in these three decades almost constantly. On the other hand, natural heat flux has increased. Since only 35% of heat flux reduction in steam wells contributes to the increase in natural heat flux at the ground surface as inferred from the regression line in (b), total heat flux is known to decrease with steam well reduction. Observations from 2013 to 2015, which seem to depart significantly from the regression line, infer an altered hydrothermal system (see text). Natural heat flux by fumaroles is calculated based on the distribution of underground temperature at 50 cm deep and its relationship with observed heat flux (Sugiyama et al. 1985); 7.4 W/m2 (> 30 °C), 13.4 W/m2 (> 50 °C), 21.5 W/m2 (> 70 °C), 29.0 W/m2 (> 85 °C) and 837 W/m2 (> 90 °C). The latest distribution of underground temperature appears in Fig. 15

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