The Izu-Oshima volcano is one of the most active volcanoes in Japan, and has generated relatively large-scale eruptions every 30—40 years for the past years. As more than 30 years have passed since the last eruptions in —87, volcanic activity is expected to resume in the near future. The whole-rock compositions are significantly scattered in the Harker variation diagrams, suggesting that the compositional diversity was established by at least two independent magmatic processes. The application of principal component analysis on the whole-rock major element data suggests that one magmatic process was crystal fractionation of crystal-poor magmas, and the other process was either plagioclase accumulation or mixing of plagioclase-rich magmas. Based on this observation, and combined with the petrological analysis and previous geophysical studies, we propose that aphyric magmas, stored in an 8—10 km-deep magma chamber, progressively differentiated over time from the 7th to 20th century. Furthermore, the compositional variations in basalts resulted from the mixing of the differentiating aphyric magmas with variable proportions of porphyritic magmas derived from a 13—18 km-deep magma chamber. Because recent eruptions have been triggered by the ascent of porphyritic magma from the 13—18 km-deep magma chamber, and its injection into the 8—10 km-deep magma chamber, it is important to monitor the deeper magma chamber to predict future volcanic activity.
Volcanic crystals as time capsules of eruption history
Deep anal eruptions - watch and download video
Supported by flash tests, and by cross-checking with a content analysis of information given within the newspaper, we find that the front page is an effective gauge for the hazard frame which, for the case examined here, involved six volcanic hazards pit-crater collapse, lava flows, gas, air fall, ocean entry lava flow and bench collapse , as well as the issue of evacuation. We found that crater collapse and lava flow hazards were framed using their natural colors and clear imagery of the phenomenon, tied to context-setting explanations within the newspaper. However, for lava flows in particular there was an element of spectacle and promotion of sightseeing, with photographs always featuring sightseers invariably taking photographs. After the end of the eruption reporting became almost entirely focused on tourists and sightseeing. Gas and ash fall hazard were framed using images and words of the victims, so that it became worrying and frightening, and associated with panic.