5:15 PM - 6:30 PM
[SVC29-P05] Volcanic ash from the June 17, 1962 eruption of Yakedake volcano, and its water-soluble components
Keywords:Yakedake volcano, the June 17, 1962 eruption, phreatic eruption, volcanic ash, water-soluble components
Mt. Yakedake is one of the active volcanoes, and several phreatic eruptions have been recorded. The most recent eruptions occurred in 1962-1963. The ash fall from the June 17 eruption, the first eruption in the series of 1962-63 eruptions, was distributed mainly on the eastern flank of this volcano [1]. The volcanic ash from this eruption has already been analyzed by Ossaka and Ozawa, and it is considered that the 1962 eruption was not caused by ascending magma but by an explosion in a mud reservoir because volcanic ash does not contain essential materials but contains montmorillonite [2]. On the other hand, for example, microscopic images of the ash particles and analytical results of water-soluble components of the ash have not been available as far as we know. In this presentation, we present the results of microscopic observation and analysis of water-soluble components of the volcanic ash from the June 17, 1962 eruption.
The ash sample we analyzed in this study was collected from the roof of a house on the morning after the eruption on June 17, 1962, which was collected before being exposed to rainfall or contaminated by soil materials. Water-soluble Cl and SO4 were analyzed by ion-chromatography after the ultrasonic extraction into pure water. The ash after extraction was rinsed and dried for microscopic observation.
Under microscopic observation, most of the ash before ultrasonic extraction was less than 500μm in size, covered with fine particles, and gray in color. On the other hand, the washed volcanic ash is dominated by particles smaller than 100-200 μm. Most of these particles are transparent to white, accompanied by altered rock and crystal fragments that appear to be pyrite. No particle that was clearly derived from fresh magma was found. On the other hand, as a result of the analysis of water-soluble components, 1,250 mg of Cl and 10,800 mg of SO4 were detected per 1 kg of ash sample. These amounts of water-soluble components are clearly higher than those of volcanic ashes discharged from typical magmatic eruptions (e.g., the 1707 Hoei eruption of Mt. Fuji and the 2017 eruption of Nishinoshima) and are consistent with the characteristics of volcanic ashes discharged from phreatic eruptions (e.g., the 1982-83 eruption of Kusatsu-Shirane volcano and the 2015 eruption of Hakone volcano). These results suggest that the June 17, 1962 eruption was not caused by fresh magma ascending but by a phreatic explosion in the hydrothermal alteration zone, and this suggestion is consistent with previous studies. In this presentation, we also show another analytical result, such as powder XRD analysis, and the geochemical characteristics of this ash will be discussed.
[1] Murai I. (1962) Bull. Earthq. Res. Inst., 40, 805-814. [2] Ossaka J. and Ozawa T. (1966) Bull. Volcanol. Soc. Japan, 11, 17-29.
The ash sample we analyzed in this study was collected from the roof of a house on the morning after the eruption on June 17, 1962, which was collected before being exposed to rainfall or contaminated by soil materials. Water-soluble Cl and SO4 were analyzed by ion-chromatography after the ultrasonic extraction into pure water. The ash after extraction was rinsed and dried for microscopic observation.
Under microscopic observation, most of the ash before ultrasonic extraction was less than 500μm in size, covered with fine particles, and gray in color. On the other hand, the washed volcanic ash is dominated by particles smaller than 100-200 μm. Most of these particles are transparent to white, accompanied by altered rock and crystal fragments that appear to be pyrite. No particle that was clearly derived from fresh magma was found. On the other hand, as a result of the analysis of water-soluble components, 1,250 mg of Cl and 10,800 mg of SO4 were detected per 1 kg of ash sample. These amounts of water-soluble components are clearly higher than those of volcanic ashes discharged from typical magmatic eruptions (e.g., the 1707 Hoei eruption of Mt. Fuji and the 2017 eruption of Nishinoshima) and are consistent with the characteristics of volcanic ashes discharged from phreatic eruptions (e.g., the 1982-83 eruption of Kusatsu-Shirane volcano and the 2015 eruption of Hakone volcano). These results suggest that the June 17, 1962 eruption was not caused by fresh magma ascending but by a phreatic explosion in the hydrothermal alteration zone, and this suggestion is consistent with previous studies. In this presentation, we also show another analytical result, such as powder XRD analysis, and the geochemical characteristics of this ash will be discussed.
[1] Murai I. (1962) Bull. Earthq. Res. Inst., 40, 805-814. [2] Ossaka J. and Ozawa T. (1966) Bull. Volcanol. Soc. Japan, 11, 17-29.