Magma Reservoir Beneath Azumayama Volcano, NE Japan as Inferred from Three-dimensional Electrical Resistivity Image by Magnetotellurics

An electrical resistivity image beneath Azumayama Volcano, NE Japan is modeled using magnetotellurics to probe the magma/hydrothermal fluid distribution. The 3-D inversion modeling images the conductive magma reservoir beneath Oana crater at depths of 3–15 km. The resolution scale for the conductor is 5 km by checkerboard resolution tests and the 67 % and 90 % confidential intervals of resistivity are 0.2–5 Ωm and 0.02–70 Ωm, respectively, for the region of less than 3 Ωm resistivity. The shallower part of the conductor is not explained by a water-saturated (5.5 wt %) dacitic melt, and the more probable interpretation is that it consists of a water-saturated, dacitic melt-silicic rock-hydrothermal fluid complex. The deeper part of the conductor is interpreted as a water-saturated (8 wt %) andesitic melt-mafic rock complex. The Mogi inflation source determined from GNSS and tilt data is located near the top boundary of the conductor at a depth of 2.7–3.7 km, which suggests that the ascent of hydrothermal fluids exsolved from the dacitic melt is interrupted by the impermeable wall and conduit. Assuming two phases of hydrothermal fluid and silicic rock, the resistivity at the inflation source, regarded as the upper bound resistivity of the conductor, is realized by the hydrothermal fluid fraction below the percolation threshold porosity in an effusive eruption. This indicates that the percolation threshold porosity in an effusive eruption characterizes the impermeable wall and conduit associated with the Mogi inflation source.

The b-value of the Kelud Volcano in the Last Three Decades

Kelud volcano is located in the Kediri sub-district, East Java Province, Indonesia. This volcano is still active, with total population, in the radius of 10 km, is around 10 thousand people. Kelud volcano is a popular tourist destination. On the weekend, total visitor can reach 5,000 people per-day. These people are at high risk when the Kelud volcano erupts. The last eruption of the Kelud volcano occurred in 2014 and was explosive eruption. Previously, there was an effusive eruption in 2007. These two types of eruption have its own geo hazard risk. Thus, predict the eruption type could help hazard mitigation. In this study, two data sets of earthquakes, 1990-2007 and 2008-2020, were analysed to determine the b-value and its relationship to the eruption type of the Kelud volcano. The calculation of the b-value uses the Gutenberg-Richter relationship. Calculation of the b-value in 2007, when there was an effusive eruption, showed a value of 2.27, while in 2014 (when there was an explosive eruption) was 1.85. After 2009, the curve of the b-value against time shows decrease. As a long term precursor of the Kelud activity, this b-value curve should be analysed continuously, besides volcano tectonic seismicity monitoring.

Activation of the Sarychev Peak volcano in 2020–2021 (Matua Isl., the Central Kuril Islands)

This publication, based on remote sensing data, examines the features of the effusive eruption of the Sarychev Peak volcano (Matua Isl., the Central Kuril Islands), which took place from December 2020 till February 2021. On the basis of the analysis of the Sentinel satellite data, it was established that starting from December 2020, the crater of the Sarychev Peak volcano began to fill with lava. As of January 18, 2021, it was completely filled, then lava outpouring through a fissure in the north-northwest part began. A lava flow (length 2 km, width 80–90 m) descended along the bottom of the valley, which cuts the northwestern slope of the volcanic cone. The outpouring of lava was completed by February 7, 2021. The effusive eruption of the Sarychev Peak volcano in 2020–2021 is atypical for the modern stage of eruptive history, characterized mainly by explosive and explosive-effusive type of eruptions.

The age of the Tseax volcanic eruption, British Columbia, Canada

A recent volcanic eruption occurred at Tseax volcano that formed a series of tephra cones in northwestern British Columbia, Canada. The explosive to effusive eruption also formed a 32 km long sequence of Fe-rich Mg-poor basanite–trachybasalt lavas covering ∼40 km2. Oral histories of the Nisg_a’a Nation report that the eruption may have caused as many as 2000 fatalities. The actual eruption date and question of whether there was one or multiple eruptive episodes in the 14th and 18th centuries are, as of yet, unresolved. New radiocarbon dating of wood charcoal from immediately beneath vent-proximal tephra deposits and complementary age information suggest an eruption in 1675–1778 CE (95.4% probability) was responsible for the formation of the tephra cone. New paleomagnetic and geochemical data from the tephra cone and lava flows suggest there is, in fact, no statistically significant difference in time between the explosive and effusive deposits and that they formed during a single eruptive episode.

MEDIA SOSIAL DAN LITERASI KEBENCANAAN DI BALI

After a large, deadly explosive and effusive eruption during 1963-64, Indonesia's Mount Agung on Bali remained quiet until a new eruption began in November 2017 until 2019. Alert Level III (of four levels) remained in effect throughout the period with a 4 km exclusion radius around the volcano. Massive hysteria occurred when alert level reach the highest level (level IV). The situation get worsed when misinformation has been spreading in social media about Mt. Agung. This research discussing how literate was the Balinese in consuming disaster information. The research was in 2018 used positivisim paradigm. Data collected by using questionnaire with 410 sample from all the regency in Bali Province. Main theory was dependence theory. The result are (1) social media became the most sourceful media to gain disaster information, (2) but the Balinese people didn’t verify the information they gained (3) 30 percent respondent shared the information without verification. It showed Balinese’s literacy in gaining disaster information need to be improve and have a high dependence in using social media.