3:30 PM - 3:45 PM
[SVC25-06] Continuous ash investigation trials for understanding eruption sequence in southern Kyushu, Japan
★Invited Papers
Keywords:color spectroscopy, volcanic eruption, volcanic ash, monitoring
We have been carried out continuous monitoring of eruptive materials at some volcanoes in southern Kyushu, Japan. Here we discuss the strategy for investigation of such materials from sampling method through preparation and petrological investigation to analyses with other observation data using statistical methods based on trials at Sakurajima, Suwanosejima, and Shinmoedake volcanoes during activity in 2000-10's. At Sakurajima, probabley one of the best monitored volcanoes in the world, we deployed automatic ash sampling machine, SATSUMA, and monitored color quantitatively by spectroscopic colorimeter of daily samples for more than ten years. The color values of ash samples are not straight forward to interpret because ash samples consist of wide range in componentry and grain size distribution. However, the color values of bulk samles are likely to reflect fine fraction for most of the time range of observation whereas the effect of coarsening is parallelled by color value change whem increase of activation occurs. Sieved samples show different tendency in color among different classes of size although it takes much more time to prepare sieved samples. For continuous monitoring the bulk colorimetry can provide information about eruption styles broadly, and PCA analysis shows that the standard deviation, or variation of color values, are the first principle component rather than the color value itself. Such results are consistent with the observation that colors of ash samples are broadly similar for long time but the componentry of coarse fraction changes with activity. In addition, the time series analysis with geophysical data, such as ground deformatio, show some lag time for best correlation before eruption occurs, and such lag time is stable ca. 3-4 months during stable vulcanian phase whereas it decreases from more than 6 months toward 0 month at the initiation of activation.
At Suwanosejima volcano, also one of the most active volcanoes continuously in the world, showed changes in glass composition as well as the componentry of ash particles. Such change is also observed in the deposit before or in the beginning phase of VEI 4 sub-plinian eruption in 1813. This implies that activation of eruption are triggered by some injection events of fresh instantaneous mafic magma which confirms the importance of continuous monitoring of ash samples for these types of eruptions or volcanoes.
At Shinmoe-dake volcano, we experienced some major to minor events in recent dacade. Especially in the 2018 eruption, we sampled ash samples continuously during the waxing phase toward lava effusion of 10^6-7 m3 when componentry of ash samples changed widely. We introduced color microspectroscopy for ash samples and carried out quantitative classification of ash partilces which anyone can dereive similar results for the same samples by using regression of visible spectra forms.
At Suwanosejima volcano, also one of the most active volcanoes continuously in the world, showed changes in glass composition as well as the componentry of ash particles. Such change is also observed in the deposit before or in the beginning phase of VEI 4 sub-plinian eruption in 1813. This implies that activation of eruption are triggered by some injection events of fresh instantaneous mafic magma which confirms the importance of continuous monitoring of ash samples for these types of eruptions or volcanoes.
At Shinmoe-dake volcano, we experienced some major to minor events in recent dacade. Especially in the 2018 eruption, we sampled ash samples continuously during the waxing phase toward lava effusion of 10^6-7 m3 when componentry of ash samples changed widely. We introduced color microspectroscopy for ash samples and carried out quantitative classification of ash partilces which anyone can dereive similar results for the same samples by using regression of visible spectra forms.