448 research outputs found
Using high-resolution Pb isotopes to unravel the petrogenesis of Sakurajima Volcano, Japan
No full textSakurajima volcano on the rim of Aira caldera erupts daily, threatening the major nearby population centre of Kagoshima. Before 1955, eruptions have typically consisted of intermittent plinian and effusive activity, but since 1955 frequent vulcanian explosions have occurred, indicating a change in pre-eruptive processes. High resolution Pb isotopes are used here to constrain the components, including crustal assimilants, and petrogenetic processes contributing to the composition of both pre and post 1955 magmas. Sakurajima eruptive products have more radiogenic Pb (206Pb/204Pb = 18.40-18.42) than nearby Sumiyoshiike basalts (206Pb/204Pb = 18.24); a proxy for the primitive magma feeding the Sakurajima-Aira system. Sakurajima samples lie along a mixing line between these basalts and locally exposed crustal compositions. Their Pb isotopes are consistent with addition of ~5 % average crustal melt to the primitive basaltic magma. The narrow range of Pb isotope ratios, despite variable SiO2 contents (56.6 – 72.3 wt %), suggests that the final erupted magmas are derived from fractional crystallization of a mafic precursory magma displaying relatively consistent levels of crustal contamination. Andesites erupted between 4-3.7 ka and the 1995 eruption are contaminated to a greater extent, indicating that magmas with distinct compositions can feed phases of activity or individual eruptions. Post 1955 andesitic pyroclastics have lower SiO2 and higher MgO than older lavas, yet equivalent Pb isotope ratios. The more mafic composition of post 1955 eruptive products can be attributed to increased throughput ofmafic magma to the system
Micro droplets generated on a rising bubble through an oppositely charged oil/water interface
No full textThe mass transfer between immiscible two-liquid phases can be greatly enhanced by bubbling gas through a reactor. Numerous micro water droplets breaking out from a ruptured water film around a rising bubble through the oil (upper phase)/water (lower phase) interface were demonstrated in the preceding paper (Uemura T., Ueda Y. and Iguchi M., Europhys. Lett., 92(2010)34004). In this letter, we attempt to oppositely charge the oil and water layers, taking into account the findings of the preliminary study (Uemura T., Ueda Y. and Iguchi M., J. Visualization, 13(2010)85). As a result, this study successfully produces more and finer water droplets than the preceding experiments
Self-potential measurements in Satsuma-Iwojima
No full text薩摩硫黄島で自然電位観測を行った結果, 硫黄岳では, 山麓から順に, 地形効果と考えられる低電位, 高電位勾配, 正異常の領域が見られ, 山頂火口付近をピークとする250mV程度のルート(√)字型の自然電位分布を示すことが明らかになった。山麓で見られた低電位は, 天水及び熱水の下降流に起因し, 高電位勾配は, 地質構造に深く関わっていると推測される。一方, 鬼界カルデラの境界付近では, 透水性の高い構造に起因すると考えられる負の異常が見られた。Shin'you MORI, Wataru KANDA and Masato IGUCHISatsuma-Iwojima is located in the northwestern margin of the Kikai Caldera that erupted about 6300years before.Iwodake (rhyolitic lava dome) located at the eastern part of the island has continued its fumarolicactivity for hundreds years.Self-potential (S.P.) observation was aimed to reveal the hydrothermal systembeneath Satsuma-Iwojima volcano. A positive S.P. anomaly around the summit crater and a negative one at thefoot of Iwodake were observed. They can be interpreted as electrokinetic potentials assoceated with theascending and descending flows of the hydrothennal fluid, respectively. A large potential gradient observedaround 300m a.s.l. was suggested to be caused by the difference in geological structure. Compared with othervolcanoes, it is characteristic that magnitude of the positive anomaly is relatively smallHigh temperature vapor, which cannot carry the positive charge, and upward fluid flow beneath the active vent may contribute thispositive anomaly.薩摩硫黄島で自然電位観測を行った結果,硫黄岳では,山麓から順に,地形効果と考えられる低電位,高電位勾配,正異常の領域が見られ,山頂火口付近をピークとする250mV程度のルート(√)字型の自然電位分布を示すことが明らかになった。山麓で見られた低電位は,天水及び熱水の下降流に起因し,高電位勾配は,地質構造に深く関わっていると推測される。一方,鬼界カルデラの境界付近では,透水性の高い構造に起因すると考えられる負の異常が見られた。Shin'you MORI, Wataru KANDA and Masato IGUCHISatsuma-Iwojima is located in the northwestern margin of the Kikai Caldera that erupted about 6300years before.Iwodake (rhyolitic lava dome) located at the eastern part of the island has continued its fumarolicactivity for hundreds years.Self-potential (S.P.) observation was aimed to reveal the hydrothermal systembeneath Satsuma-Iwojima volcano. A positive S.P. anomaly around the summit crater and a negative one at thefoot of Iwodake were observed. They can be interpreted as electrokinetic potentials assoceated with theascending and descending flows of the hydrothennal fluid, respectively. A large potential gradient observedaround 300m a.s.l. was suggested to be caused by the difference in geological structure. Compared with othervolcanoes, it is characteristic that magnitude of the positive anomaly is relatively smallHigh temperature vapor,which cannot carry the positive charge, and upward fluid flow beneath the active vent may contribute thispositive anomaly
<Disaster Reports>An Examination on the Announcement of Special Warnings Due to the Sakurajima Explosion
No full textAfter the vulcanian eruption on July 24, 2022 at Sakurajima volcano, a special warning (Level 5) was issued with an alert zone of 3 km from the Minamidake summit crater, and residents were evacuated from the southern villages of Sakurajima. Problems of issuing information, warning, and evacuation orders regarding this eruption are summarized. The flight distance of volcanic bombs estimated by JMA remains questionable. It is essential to have an accurate state of volcanic activity. It took 45 minutes from the onset of the eruption to issue the special warning, and 90 minutes to issue an evacuation order. It takes too much time to respond to the eruption. Rapid evacuation decision-making is necessary. The volcanic alert level is an index that indicates the extent of the area requiring alert. Level 5 means that the warning is required even in residential areas, but the keyword “Level 5” alone no longer indicates the extent of the alert zone. It is necessary to issue warning that pushes the range of the alert zone to the forefront
Oregon Health Authority interim long-term care facility (LTCF) COVID-19 vaccination report
No full textLisa Iguchi, MPH, Mike Hicks, Rachel Currans-Henry.Title from PDF cover (viewed on June 18, 2021)."OHA 3768 (6/15/21)"--Back cover.This archived document is maintained by the State Library of Oregon as part of the Oregon Documents Depository Program. It is for informational purposes and may not be suitable for legal purposes.Includes bibliographical references.Mode of access: Internet from the Oregon Government Publications Collection.Text in English
ON THE RELATION BETWEEN "HIGH-FREQUENCY ACOUSTIC WAVES" IN THE GROUNDWATER AND VOLCANIC ACTIVITY OF SAKURAJIMA VOLCANO
No full textA borehole with the depth of 405m was drilled in the lava dome, which is 2.8km northwestof the active crater of Minami-dake, Sakurajima Volcano. A hydrophone was installed inthe groundwater at the bottom of the borehole to observe acoustic waves associated with thevolcanic activity.The acoustic waves observed by the hydrophone are classified into two types by thewaveforms. One is a low-frequency acoustic wave of which dominant frequency is 8.8Hz.The acoustic waves of this type are inferred to be caused by seismic waves. The other isa high-frequency acoustic wave (HAW) of which dominant frequencies are both 25Hz and8.8Hz. No significant seismic events are observed at the time of the occurrence of HAW.Examining the relationship among the numbers of occurrence of HAW, seismic activityand the concentration of hydrogen gas monitored in Mochiki borehole-C which is 4.0kmsouthwest of the active crater, the following results were obtained.1) The increases in numbers of occurrence of HAW are observed after the significantincreases in the concentration of hydrogen gas.2) The increases in numbers of occurrence of HAW are observed at the almost same timewhen A-type earthquakes occurred beneath the active crater.3) The change of numbers of the occurrence of the HAW is similar to that of B-typeearthquakes. The increases in numbers of HAW are observed before B-type earthquakeswarms and eruptions occur.A borehole with the depth of 405m was drilled in the lava dome, which is 2.8km northwestof the active crater of Minami-dake, Sakurajima Volcano. A hydrophone was installed inthe groundwater at the bottom of the borehole to observe acoustic waves associated with thevolcanic activity.The acoustic waves observed by the hydrophone are classified into two types by thewaveforms. One is a low-frequency acoustic wave of which dominant frequency is 8.8Hz.The acoustic waves of this type are inferred to be caused by seismic waves. The other isa high-frequency acoustic wave (HAW) of which dominant frequencies are both 25Hz and8.8Hz. No significant seismic events are observed at the time of the occurrence of HAW.Examining the relationship among the numbers of occurrence of HAW, seismic activityand the concentration of hydrogen gas monitored in Mochiki borehole-C which is 4.0kmsouthwest of the active crater, the following results were obtained.1) The increases in numbers of occurrence of HAW are observed after the significantincreases in the concentration of hydrogen gas.2) The increases in numbers of occurrence of HAW are observed at the almost same timewhen A-type earthquakes occurred beneath the active crater.3) The change of numbers of the occurrence of the HAW is similar to that of B-typeearthquakes. The increases in numbers of HAW are observed before B-type earthquakeswarms and eruptions occur
DISTRIBUTION OF THE INITIAL MOTIONS OF VOLCANIC MICROEARTHQUAKES (B-TYPE)AT SAKURAJIMA VOLCANO
No full textVolcanic microearthquakes called "B-type" are closely related with explosive activity.Previous researchers devided B-type earthquakes into subclasses by the predominant frequen-cy. However, hypocenters and focal mechanism of the individual subclasses in B-typeearthquakes have not been determined because of the unclear onsets.In order to detect the initial motions clearly, seismometers were installed in the boreholesaround the active crater of Sakurajima Volcano. In this paper, B-type earthquakes whosedominant frequecies are 1-3 Hz and 5-8 Hz, are named as BL-type and BH-type earthquakes, respectively. The hypocenters and distribution of the initial motions of BL-type and BH-type earthquakes were examined. The results were summarised as follows.(1) Focal depths of BL-type earthquakes were determined at the depth of less than 2 kmbelow the sea level. BH-type earthquakes had deeper hypocenters than BL-type. Themaximum depth of BH-type was 2.5 km.(2) Most of BL-type earthquakes which occurred isolatedly and BH-type earthquakeshad all compressional arrivals. BL-type earthquakes which occurred in swarms had allcompressional or all dilatational arrivals, with the ratio of 61% to 35%. The initial motionsof the remaiders were mixed with compressions and dilatations. The distributions of initialmotions did not show that focal mechanisms of BL-type and BH-type earthquakes werequadrant types.Volcanic microearthquakes called "B-type" are closely related with explosive activity.Previous researchers devided B-type earthquakes into subclasses by the predominant frequen-cy. However, hypocenters and focal mechanism of the individual subclasses in B-typeearthquakes have not been determined because of the unclear onsets.In order to detect the initial motions clearly, seismometers were installed in the boreholesaround the active crater of Sakurajima Volcano. In this paper, B-type earthquakes whosedominant frequecies are 1-3 Hz and 5-8 Hz, are named as BL-type and BH-type earthquakes,respectively. The hypocenters and distribution of the initial motions of BL-type and BH-type earthquakes were examined. The results were summarised as follows.(1) Focal depths of BL-type earthquakes were determined at the depth of less than 2 kmbelow the sea level. BH-type earthquakes had deeper hypocenters than BL-type. Themaximum depth of BH-type was 2.5 km.(2) Most of BL-type earthquakes which occurred isolatedly and BH-type earthquakeshad all compressional arrivals. BL-type earthquakes which occurred in swarms had allcompressional or all dilatational arrivals, with the ratio of 61% to 35%. The initial motionsof the remaiders were mixed with compressions and dilatations. The distributions of initialmotions did not show that focal mechanisms of BL-type and BH-type earthquakes werequadrant types
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