著者

早川 由紀夫 小山 真人

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.43, no.5, pp.403-407, 1998-10-30 (Released:2017-03-20)

参考文献数

21

被引用文献数

9

著者

山科 健一郎

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.44, no.2, pp.71-82, 1999

参考文献数

79

被引用文献数

1

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Associated with the 1914 great eruption at Sakurajima volcano, southwestern Japan, the maximum height of volcanic cloud is discussed based on collected documents, sketches and photographs in those days. A series of photographs up to around 10 : 40 on January 12 (in Japanese Standard Time) represents that the volcanic cloud height attained to 7,000 to 8,000 m above sea level. After then, it proved that several documents reported the height to be 9,500-15,000 m, or even more than 18,000 m a.s.l, although it is difficult to obtain reliable evidences. Considering these reports and other observations from a distance, the height of 15,000 m is tentatively proposed here as a possible maximum value. According to an empirical relation, an eruption rate of small pyroclastic materials is suggested as, roughly speaking, 5,000 tons per second or 20 millions of tons per hour, if the volcanic cloud was 15,000 m in height.

著者

下司 信夫 小林 哲夫

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.51, no.1, pp.1-20, 2006-02-28

被引用文献数

2

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Volcanic history of Kuchinoerabujima Volcano in the last 30,000 years is reconstructed based on tephra stratigraphy. Kuchinoerabujima is a volcanic island which is a cluster of at least nine volcanic edifices; Gokyo, Jyogahana, Ban-yagamine, Takadomori, Noike, Kashimine, Hachikubo, Furutake and Shintake. Eruptions within the last 30,000 years occurred from Noike, Hachikubo, Furutake and Shintake volcanoes. Two major pumice and scoria eruptions occurred between 15 and 11 ka after an inactive period since ca. 30ka. NoikeYumugi tephra (15-14ka, DRE>0.06km^3), erupted from the summit of Noike Volcano, consists of Yumugi pumice fall deposit and Nemachi pyroclastic flow deposit. Furutake-Megasaki tephra (12-11 ka, DRE ca. 0.8km^3) erupted from Furutake Volcano and consists of Furutake agglutinate, Furutake scoria flow deposit and Megasaki scoria fall deposits. Volcanic edifice of Older Furutake was built during the 12-11 ka eruption. Eruption style changed around 10ka, after the collapse of Older Furutake Volcano. Activities of Yougner Furutake and Shintake Volcanoes are characterized with effusion of lava flow and no major pumice eruption is recognized. Lithic tephra erupted from Younger Furutake and Shitake Volcanoes within the last 10,000 indicates repetitive Vulcanian-type and phreatomagmatic eruptions. All historical eruptions since 1841 occurred at and around Shintake crater and were Vulcanian-type explosions with emission of magmatic materials and phreatic explosions.

著者

宮地 直道 富樫 茂子 千葉 達朗

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.49, no.5, pp.237-248, 2004

参考文献数

34

被引用文献数

4

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A large-scale collapse occurred at the eastern slope of Fuji volcano about 2900 years ago, based on calibrated ¹⁴C age of a wood sample collected in the resulting debris avalanche deposit. The collapsed slide deposit, called "Gotemba debris avalanche deposit" (Goda), is distributed on the eastern foot of the volcano covering an area of more than 53 km² The source amphitheater is not preserved because it became covered by younger tephra erupted from the summit crater. This avalanche deposit is overlain by the "Gotemba, mudflow deposits" (Gomf) emplaced repeatedly after the avalanche. Some now units of the Goda and Gomf entered pre-existing rivers and were finally emplaced as fluvial deposits. The Goda is composed of debris-avalanche blocks, showing jigsaw cracks, along with smaller blocks ranging from several tens of centimeters up to l m in diameter. The debris-avalanche matrix is a mixture of smaller nieces of blocks and ash-sized materials due to mainly shearing and fragmentation of large blocks. Igneous rocks include fresh and altered gray basaltic lava, weathered tephra including red scoria and white clay. Petrographical and geochemical data indicate that most blocks were derived from the Older Fuji volcano. The volumes of the Goda and Gomf are about l.05km^3 and 0.71km^3 respectively, based on presently available geological and borehole data. Since the blocks of Goda are composed mostly of the products of the Older Fuji volcano and the older stage lavas of Younger Fuji volcano do not extend to the eastern foot of Fuji volcano, a bulge of Older Fuji volcano must have existed in the eastern flank of Fuji volcano preventing the older stage lavas to now to the east. This bulge collapsed in the form of three blocks from the foot of the mountain. The abundance of hydrothermally altered deposits in the Goda and the absence of fresh volcanic products within the Goda suggest its origin as a rupture inside the altered deposits possibly triggered by a large earthquake or phreatic eruption.

著者

井村 隆介

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.43, no.5, pp.373-383, 1998-10-30 (Released:2017-03-20)

参考文献数

27

被引用文献数

5

---

The eruptive sequence of the An-ei eruption of Sakurajima volcano (1779-1782) is revealed by historical records. From the evening of November 7, 1779 (the 29th day of the 9th month in the 8th year of An-ei), Kagoshima and its environs were shaken frequently. At 11 a.m. of the next day, the water in the wells in the island boiled up, spouting at several points and the color of sea became purple. On the noon of the same day, minor white plumes rose up from the Minamidake summit crater. At about 2 p.m., plinian eruption oecurred at the southern upper slope of Minamidake, and several tens of minutes later, at the northeastern flank of Kitadake. The height of eruption column reached about 12000 meters. It is estimated that a pyroclastic flow was generated at 5 p.m. The plinian eruption climaxed from the evening of November 8, to the morning of next day, and later was followed by emission of lava flows. The activity of the southern craters ceased within a few days, but lava emission from northeastern craters lasted for a long period. On November 11, the lava flow from northeastern craters entered into the sea. Since then, submarine explosions occurred repeatedly off the northeastern coast, and it continued to January 18, 1782. Nine small islands produced by this submarine volcanic activity during a year. Submarine explosions caused small tsunamis on August 6 and 15, September 9, October 3 1, November 9, 1780 and April 11, 1781.

著者

須藤 靖明 筒井 智樹 中坊 真 吉川 美由紀 吉川 慎 井上 寛之

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.51, no.5, pp.291-309, 2006-10-31

被引用文献数

5

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So far the ground deformation associated with a magma supply system of Aso Volcano had not been discussed because any clear signals in ground deformations and volcanic earthquake activity had been hardly observed near the Nakadake active crater during its activity enhancement cycles. In this article, however, the deflation source and magma supply system is investigated by the long-term geodetic surveys. The secular subsidence is observed in the Kusasenri area about 3km west of the Nakadake active crater from the 1951's levelling survey in compiled levelling surveys along the Bouchuu-line since 1937. While the ground deformation near the active crater has been obscure. The source of this deflation near the Kusasenri area is estimated on the basis of the spherical pressure source model through the non-linear least square method with using recent survey data which include the Bouchuu-line and an extended survey route. The deflation source is located beneath the Kusasenri area at about 5km depth. However, recent volume changes at the spherical deflation source are smaller than before 1959. The location of the deflation source coincides with the low P- and S-wave velocity body in the 3D seismic velocity structure. This fact supports a hypothesis that the low seismic wave velocity body represents a magma reservoir. Therefore this magma reservoir beneath the Kusasenri area must be connected to the Nakadake active crater. We inferred a rigid conduit in the magma supply system from the obscure ground deformation in the vicinity of the Nakadake crater.

著者

早川 由紀夫

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.40, no.3, pp.177-190, 1995

参考文献数

47

被引用文献数

24

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Loam is an international scientific term, however, it has been used in a peculiar way in Japan. Japanese loam is a massive, brown, weathered rock unit composed of silt, clay, sand and occasional lapilli. It extensively covers coastal terraces, river terraces, ignimbrite plateaus and other uplands around volcanoes. Loam is not a product of soil forming process operated beneath the earth surface against rock bodies ; but it is a sediment accumulated slowly on the earth surface. Small-magnitude volcanic eruptions play a very minor role for the sedimentation. An eolian reworking process of pre-existing fine-grained deposits by the wind plays a major role. This is proved by following facts : 1) loam has accumulated even during the time when no ash-fall was observed ; 2) a volcano infrequently erupts explosively and the intensity of ash fallout is far lower than the sedimentation rate of loam ; it is about 0.1 mm/year ; 3) loam is hardly thickening toward a volcano. Very small particles carried from continental China by the westerlies at a high altitude are contained in loam, however, in the area around volcanoes their contribution is little for the formation of loam compared with eolian dust carried from nearby bare grounds by local winds at a low altitude. Loam does not accumulate all the year round. Just before and during fresh verdure, occasional strong winds pick up fine particles into the air from a bare ground which is dried up by a high-angle sunlight and high-temperatures. Eventually fine particles will settle down in vegetation. The most favorable season for loam deposition is April to May, in which more than half of an annual amount is achieved. It is convenient and practical to define a single eruption by a tephra layer which is not interbedded with loam. The thickness of loam can be used for the quantitative measurement of geologic time intervals, in years to thousands years, on certain conditions. Lithology of Japanese loam and the mechanism of sedimentation are identical to those of loess in other areas, such as China, northern Europe, northern America and New Zealand. There is no reason to hesitate to designate Japanese loam loess.

著者

町田 洋 新井 房夫 百瀬 貢

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.30, no.2, pp.49-70, 1985-07-01

被引用文献数

41

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The Aso-4 pyroclastic flow is one of the largest of late Pleistocene age in Japan covering extensive areas of Kyushu around the Aso caldera and western part of Honshu. We have recently discovered a distal ash which has very similar petrographic and chemical properties to the flow deposits at several localities of Japan, and is assumed to be an airfall part of the Aso-4 unit. The ash, named the Aso-4 ash, is a crystal-vitric fine-grained ash, consisting of rhyodacitic bubble-walled glass shards, and brown hornblende and orthopyroxene (bronzite) as mafic phenocrysts. Its identification is carried out by combined parameters ; refractive index of glass ranges 1.506-1.511, low refractive index of orthopyroxene (γ=1.699-1.701) and relatively high index of hornblende (n_2=1.687-1.688). In addition glass in the ash is characteristically rich in potassium. These properties are similar to those of the Aso-4 pyroclastic flows. It is suggested that the ash is a coignimbrite airfall deposit of fine-grained materials from the upper part of an eruption column formed at the same time as the Aso-4 flow. The ash mantles extensive areas from Kyushu to Hokkaido and is also recognized and identified in several piston cores from the Sea of Japan and the northwest Pacific Ocean. The fallout area of this ash is now known to attain approximately 4×10^6 km^2. It is striking that in the eastern part of Hokkaido, ca. 1700 km distant from the source, the ash with the thickness of 15 cm is well preserved immediately below the Kutcharo pyroclasitc flow deposits II/III. The bulk volume of this ash is estimated to be more than 400 km^3, possibly larger than that of the flow deposits. The stratigraphic position of this ash in standard sequence of South Kanto shows that it occurs after the Obaradai interstade (ca. 80 ka) and before the Misaki interstade (ca. 60 ka). Thus the Aso-4 ash provides a very important datum plane in late Pleistocene sequence in and around Japan.

著者

小林 淳 萬年 一剛 奥野 充 中村 俊夫 袴田 和夫

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.51, no.4, pp.245-256, 2006

参考文献数

45

被引用文献数

1 4

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We discovered a set of phreatic explosion deposits, herein referred to as the Owakidani tephra group, on the northern slope of Mt. Kamiyama and in the Owakidani fumarolic area of the Hakone Volcano. The tephra group is the product of the volcanic activities since the latest magmatic eruption of Hakone Volcano at around 2.9ka. It comprises five units named Hk-Ow1 to Hk-Ow5 in the ascending order. Both Hk-Ow1 and Hk-Ow2 comprise tephra fall deposits and secondary debris flow deposits. In addition to these deposits, Hk-Ow2 is also associated with surge deposits. Hk-Ow3, Hk-Ow4 and Hk-Ow5 consist of tephra fall deposits. The ash of these tephra fall deposits and the matrix of the secondary debris flows are principally composed of clay, altered lithics and secondary minerals supposed to be of fumarolic area origin. It is possible that Hk-Ow1 and Hk-Ow2 erupted from a fissure on the northeastern ridge of Mt. Kamiyama, while Hk-Ow3, Hk-Ow4 and Hk-Ow5 erupted at Owakidani. No juvenile material was found within the deposits of these eruptions except for Hk-Ow2, while the surge deposit of Hk-Ow2 contained trace amounts of volcanic glass fragment. Although it is considered that the principal nature of the eruptions of the Owakidani tephra group is phreatic, the deformation of the edifice around the source area implies the possibility of magma intrusion to shallow levels. Based on the calendar ages of the Owakidani tephra group and the stratigraphic position of the Kozushima-Tenjosan tephra, we estimated that Hk-Ow3, Hk-Ow4 and Hk-Ow5 erupted in relatively short intervals between the latter half of the 12th and 13th centuries. On the other hand, Hk-Ow1 and Hk-Ow2 erupted at around 3 kyr BP and 2kyr BP, respectively. The eruption ages of the Owakidani tephra group generally correspond to the seismic events that occurred in the Kozu-Matsuda Faults and the Tanna-Hirayama tectonic line. It is suggested that the activity of the Hakone Volcano may be closely related to the tectonic events in this region.

著者

岡田 肇 横山 勝三

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.27, no.1, pp.67-69, 1982-04-30

著者

三宅 康幸 小坂 丈予

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.43, no.3, pp.113-121, 1998-06-10 (Released:2017-03-20)

参考文献数

14

被引用文献数

2

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A steam explosion occurred at about 14:30 JST, February 11th, 1995, in the hot-spring area near Yakedake volcano, central Japan. More than six workers were near the site of the explosion for the road construction, and four of them were buried by the ejected material and killed. A small initial explosion began at the bottom of a 4m deep moat dug by a backhoe and it was followed by the maximum explosion, which ejected about 6,000m3 of blocks (maximum length is more than 2m) and mud, with steam and volcanic gas. The ejecta contain gravels of welded tuff, granite and mesozoic sedimentary rocks, which are the components of a pyroclastic dike of Pliocene age, and pumiceous lapilli tuff derived from the terrace sediments covering the pyroclastic dike. The explosion caused a landslide from the western cliff and the vent was buried by the slid debris, most of which was blown away by the second explosion. All of these processes took place within a few minutes. A small depression (20×5m2) on the west of the mound of the ejecta may represent part of the vent; its depth is estimated to be about 60m or more. Gaseous S02(<30ppm) and H2S(<90ppm) were detected at the explosion site for three days after the explosion. The chemical composition of gas collected from the holes drilled after the explosion were nearly same as the gas from the summit crater of the Yakedake volcano. Because a wall-like Low-Q zone is suggested by seismologists beneath Yakedake volcano and the explosion site, it is most probable that there existed a magma beneath the explosion site and that the heat for the explosion was supplied by the magma and gas exsolved from the magma.

著者

萬年 一剛

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.66, no.2, pp.101-117, 2021-06-30 (Released:2021-07-27)

参考文献数

62

---

Tephra simulation codes were originally developed to estimate tephra fall hazards; however, existence of several unknown parameters inhibits accurate calculation without elaborate parameter tunings. One of the most sensitive unknown parameters is source magnitude distribution (SMD), which describes amount of particle release as a function of distance from the vent along the plume axis. SMD can be obtained using inversion technique from real eruption products. Inversion techniques are also required to obtain other parameters; plume height of the eruption and the wind system at the time of the eruption are the most important ones among them. Although plume height and wind system can be observable for the recent eruptions, they could have some uncertainties and require further refinements. Additionally, they are totally unknown for unobserved ancient eruptions; however, they are essential parameters to describe eruptions. There are two types of relationship between amounts of tephra deposition and eruptive parameters; linear and non-linear. Inversions for linear and non-linear parameters need different approaches and they are briefly reviewed here. Since SMD (linear) and other parameters (non-linear) are often needed to be obtained at a time, combined inversion approach, which is a hybrid of linear and non-linear inversions, was proposed and discussed in this review. The results of inversion can be evaluated using satellite data and other plume models including 3D simulations, and help to understand structure of eruption plumes. Since accurate inversions highly rely on granulometric data of the surface deposit, further developments of techniques to obtain granulometric data with lesser time and effort are also required. The SMDs obtained by recent studies show logarithmic decay and a classic theory of particle segregation from turbulent plume can be applicable; however, more case studies are needed, especially to evaluate effect of particle aggregation and in-situ observation of falling particle is critically important.

著者

金子 克哉 伊藤 公一 安部 祐一

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.55, no.2, pp.109-118, 2010-04-30

参考文献数

10

---

Monitoring of volcanic phenomena close to active volcanic vents and inside active craters is needed to predict change of volcanic activities and to understand dynamics of volcanic eruptions. In order to carry out safe volcanic monitoring, we have developed a prototype of a mobile sensor for volcanic observation "HOMURA" which is a new robotic system that has been designed to observe volcanic phenomena inside active volcanic craters. HOMURA is a small unmanned ground vehicle (approx. 780×560×300mm in dimension and 10kg in weight) with six wheels driven by electric motors and it is operated by wireless remote control at a distance of more than 1km. Data measured by some sensors in HOMURA are sent to the base station in real time. Materials of the vehicle body and wheels are aluminum with 2mm thick and plywood with 9mm thick, respectively. HOMURA can climb up and down a rough surface with slope angle of 30 degree. In addition, HOMURA does not readily become undrivable even in overturning during climbing because it has a unique body shape with a horizontal symmetry plane. HOMURA can be made and transported to mission fields at small costs. These allow us to make a new vehicle even if HOMURA should be lost by accident during missions and promptly to explore a sudden volcanic event by HOMURA. In test campaigns at Aso volcano and Izu-Oshima volcano, we confirmed that HOMURA has planned abilities on moving on rough surfaces and wireless communication.

著者

長谷川 健 菊池 文太 柴田 翔平 井村 匠 伴 雅雄 常松 佳恵 山本 裕二 大場 司 鈴木 和馬 戸丸 淳晴 楠 稚枝 岡田 誠

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.68, no.3, pp.189-196, 2023-09-30 (Released:2023-11-02)

参考文献数

22

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Volcanic bomb is one of the most common eruption products around their source craters. Although paleomagnetic studies on volcanic bombs have a potential to provide high-resolution chronology of volcanic activity, particularly when compared with the known geomagnetic secular variation records, there are only a few such studies. In this contribution, we made an attempt to determine paleomagnetic directions from large (>1 m in diameter) volcanic bombs around “Tsubakuroswa craters”, located in Azuma volcano, for evaluating the potential use of volcanic bombs for paleomagnetic dating. Six oriented mini-cores were drilled from the central part of each large volcanic bomb, five in total, located on a gentle slope a few hundred meters south from the craters. All of the mini-cores were subjected to thermal demagnetization analysis, giving a well-determined characteristic remanent magnetization (ChRM) direction for each bomb as follows: site mean declination (Dm) of 350.6‒358.0º and inclination (Im) of 48.9‒50.8º with a 95 percent confidence limit (α95) smaller than 2.4º. The ChRM directions were consistent among the bombs, supporting the availability of volcanic bombs for further paleomagnetic dating research. Referring the geomagnetic secular variation record in this area, an all-site mean ChRM direction from the five bombs (Dec=355.5º, Inc=50.1º, α95=1.9º) most likely accounts for the derivation of the volcanic bombs by the Meiji Era (1893 CE) eruption. Historic pictures and descriptions are consistent with and support this interpretation. Previous reports suggested that the Meiji Era eruption did not eject magmatic materials and that the last magmatic eruption of this volcano was probably in 1331 CE. However, our results suggest that magmatic eruptions might have occurred here only ca. 130 years ago and may be largely affecting the current activity of this crater area. Our study suggests that volcanic bombs are potentially useful materials for paleomagnetic studies such as dating and establishing geomagnetic secular variation records.

著者

宮縁 育夫 増田 直朗 渡辺 一徳

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.49, no.5, pp.267-282, 2004

参考文献数

31

被引用文献数

7

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The western part of post-caldera central cones of Aso Volcano, southwestern Japan, is characterized by wide chemical variation of lava flows (SiO₂=49-73 wt.%) and complicated topography. Geologic history of the area was reconstructed by stratigraphic relationships between lava flows and airfall tephra layers. Stratigraphy and chronology of lavas and tephra distributed on the western slope of the central cones are as follows: Ayugaerinotaki lava, Matsuhata pumice (MhP), Tochinoki lava (73±10 ka; K-Ar age), Aso central cone pumice 4 (ACP4), Tateno lava. Aso central cone pumice 3 (ACP3), Takanoobane lava (51±5ka), Eboshidake lava, Karisako lava, Akase lava (30 cal ka ; calibrated ¹⁴C age), Sawatsuno lava (27±6ka), Kusasenrigahama pumice (Kpfa; 31 cal ka), Otogase lava and Aso central cone pumice 1 (ACPI ; 4 cal ka), in ascending order. Between about 70,000 to 50,000 years ago Tochinoki lava, Tateno lava and Takanoobane lava accompanied precursor pumice-fall deposits. A catastrophic eruption occurred in and around the Kusasenrigahama crater at 31 cal ka. The eruption was initiated by the dacite Sawatsuno lava now and produced the largest plinian numice-fall deposit (Kpfa; 1.2 km³ in DRE volume). In the western part of post-caldera central cones of Aso Volcano, total discharge volumes of felsic and mafic magmas from about 70,000 to 30,000 years ago were estimated to be about 2.4 km³ and 0.47km³ respectively.

著者

東宮 昭彦

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.61, no.2, pp.281-294, 2016-06-30 (Released:2016-09-12)

参考文献数

105

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Recent developments in the understanding of magma chambers (reservoirs), pre-eruptive magma processes, and the conditions that lead to volcanic eruptions are reviewed mainly from a petrological point of view. A “magma reservoir” consists of inner “magma chamber (s)” filled with eruptible magma containing less than ca. 50% crystal, and outer “mush” region with more than ca. 50% crystal. Most of magma reservoirs are in a state of mush, so that “rejuvenation” or “remobilization” is necessary before eruption. Magma can erupt if its viscosity is less than ca. 106 Pa s. More viscous magma can erupt only after a precursory eruption of less viscous magma, such as a hybrid magma between the viscous magma and a less viscous mafic magma. In this context, pre-eruptive magma viscosity, i.e. magma viscosity at the magma reservoir, is an important measure to evaluate magma eruptibility. Dating for whole mineral or even its local point (e.g., zircon age) and diffusion analysis for various types of minerals (e.g., magnetite, olivine, pyroxene, and plagioclase) have revealed timescales of pre-eruptive magma processes. Eruption triggers, such as injection of high-temperature magma, are inferred to occur days to months before the eruption in many cases. Magma residence times, during which the magmas are in eruptible conditions, are years to decades for typical magma systems, but may reach hundreds of thousand years for large caldera systems.

著者

小林 武彦

出版者

特定非営利活動法人日本火山学会

雑誌

火山. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.26, no.2, 1981-07-01

著者

高橋 正樹

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.40, no.1, pp.33-42, 1995

参考文献数

22

被引用文献数

6 7

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There is no positive correlation between the long-term eruption rate of large-scale felsic volcanism and its discharge volume of a single eruptive episode. This means that the storage of voluminous felsic magma at high-level in the crust is caused not by high magma production rate but by continuous accumulation of magma during a long repose time, if the long-term eruption rate reflects the averaged magma production rate. If the cruslal defomation is weak, the magma chamber could be stable in the crust; it is favorable for efficient accumulation of voluminous magma. In fact, the large-volume felsic volcanism occurs exclusively in the region of low crustal strain rate. The low crustal strain rate is considered to be essential for the formation of large-scale felsic volcanism. The large-volume felsic volcanic activity is present in the compressional tectonic stress field as well as in the extensional one; the difference in arrangement of principal stress axes is not related to the occurrence of voluminous felsic volcanism.

著者

杉森 玲子 前野 深

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.68, no.2, pp.59-73, 2023-06-30 (Released:2023-07-27)

参考文献数

41

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Historical materials have revealed that the Hokkaido-Komagatake Volcano erupted in 1640. In this study, we reviewed in detail the historical materials from a period closer to the eruption, which had yet to be investigated. We then evaluated the reliability of the historical materials and tried to interpret their descriptions from a volcanological point of view. As a result, we found descriptions that support the previous understanding of the number of deaths, tsunamis, and volcanic edifice collapses, or provide more detailed information. In contrast, we also found descriptions of the duration of the 1640 eruption, which lasted about one day and night, of the fallout tephra containing charred wood chips suggesting the occurrence of high-temperature phenomena and subsequent buoyant plumes, and of the volcanic activity that continued for a long time after the eruption. Examination of these historical materials revealed a picture of the eruption that could not be understood from the historical materials used in the past. This study demonstrates that investigating the characteristics of historical materials and the reliability of their descriptions and comparing the information obtained from them with volcanological knowledge can be useful in clarifying the phenomena and processes of past volcanic eruptions.

著者

新村 太郎 三好 雅也 角野 浩史 上田 恭裕 森 康 長谷中 利昭 荒川 洋二 長尾 敬介

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.67, no.2, pp.135-147, 2022-06-30 (Released:2022-07-28)

参考文献数

36

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To clarify the age of the volcanic activity of Nekodake volcano, the authors conducted K-Ar dating on ten samples of volcanic materials, using the sensitivity method. Four samples yielded ages approximately 50 to 82 ka. These newly obtained K-Ar age data indicate that Nekodake volcano was active during the post-caldera stage of Aso volcano. Based on the obtained ages, petrological characteristics, and lithofacies, the volcanism of Nekodake can be summarized as follows. 1) Effusive eruption of basaltic andesite magma produced thick lava flows at about 82 ka, and also formed agglutinates over a wide area at about 66 ka. The main volcanic body was formed by these eruptions. 2) Andesitic magma intruded the central part of the volcano at about 64 ka (late stage or just after the formation of the main part) forming dykes in an ENE-SSW direction. 3) Basaltic andesite magma intruded the central part of the volcano at about 50 ka and formed dykes in a NW-SE direction.