著者

及川 輝樹 原山 智 梅田 浩司

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.46, no.1, pp.21-25, 2001-02-27 (Released:2017-03-20)

参考文献数

23

被引用文献数

3

著者

西来 邦章 石毛 康介 島田 駿二郎 中川 光弘

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.62, no.2, pp.83-94, 2017-06-30 (Released:2017-07-25)

参考文献数

39

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Zircon fission-track (FT) and uranium-lead (U-Pb) dating were carried out to determine the ages of the Biei, Tokachi, and Sounkyo pyroclastic flow deposits in the Biei and Kamikawa areas of central Hokkaido, northern Japan. We collected pumiceous tuff samples of the Biei pyroclastic flow deposits from two sites in the middle and lower reaches of the Biei River, and Tokachi pyroclastic flow deposits from one site to the west of Tokachi caldera. A sample of welded tuff from the Sounkyo pyroclastic flow deposits was obtained from one site in the lower reaches of the Antaroma River. The FT ages of the Biei pyroclastic flow deposits are 0.81±0.08 Ma and 0.72±0.08 Ma, identical to each other within 1σ error. However, they differ from an age of 1.91±0.06 Ma reported previously from the upper reaches of the Biei River. Based on the present data and previous results on the ages and petrographical characteristics of the deposits, they can be divided at least two geological units with different eruption ages. A FT age of 0.058±0.018 Ma (1σ) was obtained from the Sounkyo pyroclastic flow deposits. On the basis of previous studies concerning the distribution and petrographical characteristics of the deposits, this age was obtained from Hb-type pyroclastic flow deposit among the Hb- and Py-type flows of the Sounkyo pyroclastic flow deposits. The Tokachi pyroclastic flow deposits yielded a U-Pb age of 1.24±0.02 Ma (2σ), which falls within the wide range of ages reported in previous studies. Because the Tokachi pyroclastic flow deposits have a wide distribution and a wide range of ages, they can be divided into several geological units with different eruption ages, as with the Biei pyroclastic flow deposits.

著者

上澤 真平

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.53, no.6, pp.171-191, 2008-12-29 (Released:2017-03-20)

参考文献数

48

被引用文献数

1

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On May 24th 1926, the eruption of Tokachidake volcano, in central Hokkaido, efficiently melted the snow pack on the hill slope, triggering the Taisho lahar which killed 144 people in the towns of Kamifurano and Biei. A geological survey and paleomagnetic and granumetric studies were conducted on the northwestern slope of Tokachidake volcano to reconstruct the sequence of the 1926 eruption and decipher the triggering mechanism for the Taisho lahar. The Taisho lahar deposits in the proximal area of the volcano are divided into five distinct units (unit L1, L2, and A through C, from oldest to youngest). Unit L1 is an older lahar deposit that underlies the 1926 deposits. The 1926 sequence consists of debris avalanche deposits (unit A and C), a laminated sandy debris flow deposit (unit B), and a lahar deposit including scoria clasts (unit L2). Each unit contains hydrothermally altered rocks and clay material with more than 5 wt.% fragments smaller than 2mm in diameter. The progressive thermal demagnetization experiments show that the natural remanent magnetization (NRM) of all samples in unit A, B and C have a stable single or multi-component magnetization. The emplacement temperatures are estimated to be normal temperatures to 620℃ for unit A, 300 to 450℃ for unit B, and normal temperature to 500℃ for unit C. On the basis of geological and paleomagnetic data and old documents, a sequence for the eruption and the mechanism of formation and emplacement of the Taisho lahar can be reconstructed. The first eruption at 12: 11 May 24th triggered a small lahar (unit L2). Collapse of central crater at 16:17 May 24th 1926 then resulted in a debris avalanche containing highly altered hydrothermal rocks with hot temperatures ranging from 300 to 620℃ (unit A). The debris avalanche flowed down the slope of the volcano, bulldozing and trapping snow. Immediately following the collapse, a hot (approximately 400℃) hydrothermal surge (unit B) melted snow and transformed into a lahar causing significant damage and deaths in the towns downstream. Just after the generation of the lahar, another collapse occurred at the crater causing another debris avalanche (unit C).

著者

上野 寛 森 博一 碓井 勇二 宮村 淳一 吉川 一光 浜田 信生

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.47, no.5, pp.689-694, 2002-11-29 (Released:2017-03-20)

参考文献数

14

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We studied high-frequency earthquake swarm associated with the eruption of the Usu volcano in 2000 using the data observed by a national seismic network in southern Hokkaido. To get a precise hypocenter location, we applied the double-difference method and station correction to hypocenter determination. Systematic shift of epicenters possibly caused by heterogeneous velocity structure of the upper crust is needed to be consistent with the initial motions of the seismograms at the nearest station. Concentration of hypocenters under the northern flank of the volcano in the initial stage suggests that the magma started its activity at about 5 km in depth at the region. Concentric expansion of swarm area occurred before the eruption and formed doughnut pattern of which center is located near the summit of the volcano. Doughnut pattern may represent relaxation of stress under the volcano which is caused by magma movement and pore pressure change under the volcano.

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

被引用文献数

6

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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

上木 賢太 寺田 暁彦

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.57, no.4, pp.235-251, 2012-12-28 (Released:2017-03-20)

参考文献数

32

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

被引用文献数

4

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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 6,000m^3 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 (20×5m^2) 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 S0_2(<30ppm) and H_2S(<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

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.38, no.6, pp.223-226, 1993-12-20 (Released:2017-03-20)

参考文献数

7

被引用文献数

1

著者

宮縁 育夫

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.62, no.1, pp.1-12, 2017-03-31 (Released:2017-03-28)

参考文献数

27

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Janoo Volcano (550-750 m in basal diameter;150 m in height) is located in the northwestern part of the post-caldera central cones of Aso Volcano, central Kyushu, southwestern Japan. The volcano had been thought to be a cinder cone composed entirely of scoria-fall deposit and older than 7.3 ka. Fieldwork in and around the volcano has re-examined the detailed tephra stratigraphy and eruption age of Janoo Volcano. A black humic paleosol divides an upper pumice-fall deposit from a lower scoria-fall deposit. The upper pumice-fall deposit shows only two pure pumice bed sections with pumice clasts scattered in a brown massive ash elsewhere in the deposit. The deposit is composed mainly of light gray well-vesiculated dacitic (SiO2=65.4-67.7 wt.%) pumiceous clasts containing biotite phenocrysts, and abundant banded pumices, suggesting a mixture of silicic and mafic magmas. Based on the phenocryst assemblage and age, the pumice-fall deposit is correlated to the Aso central cone pumice 1 (ACP1;4.1 ka), which is the only pumice-fall deposit erupted from Aso Volcano during Holocene time. The lower scoria-fall deposit is more than 30 m thick and constitutes most of the Janoo cinder cone. It includes brownish black to brown well-vesiculated basaltic andesite (SiO2=54.7-55.5 wt.%) scoriaceous clasts and cauliflower bombs with radially arranged cooling joints. The Akamizu lava (SiO2=57-59 wt.%) distributed west of the Janoo cinder cone, whose source was previously unknown, is attributed to Janoo Volcano based on the lava’s petrographic characteristics. A 14C age of 3830±30 years BP, which corresponds to 4.2-4.1 ka, was obtained from the humic paleosol interbedded between the ACP1 and Janoo scoria. The stratigraphy and characteristics of the tephra deposits suggest the following eruption sequence. The initial eruption at Janoo Volcano occurred at 4.9-4.3 ka and was strombolian in style forming the Janoo cinder cone. After lying in repose for a few hundred years, Janoo Volcano erupted again, and produced the ACP1 tephra containing abundant banded pumices and Akamizu lava at 4.1 ka. The southern half of the Janoo cinder cone was destroyed probably by the effusion of Akamizu lava. Volcanic activity forming Kishimadake, Ojodake, Komezuka and Kamikomezuka volcanoes in the northwestern part of post-caldera central cones at 4-3.3 ka was derived from basaltic to basaltic andesite magmas, whereas the eruption products of Janoo Volcano have a wide range in chemistry from basaltic andesite to dacite. Activity of Janoo Volcano is characterized by the presence of a dormant period (a few hundred years), allowing a paleosol to develop on the scoria-fall deposit, before ejection of both mafic and silicic magmas in the late eruption.

著者

黒墨 秀行 土井 宣夫

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.48, no.3, pp.259-274, 2003-07-10

被引用文献数

5

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The Nigorikawa Caldera in southwest Hokkaido, Japan, is 3 km in diameter at the outer rim. Drilling data from 42 geothermal wells of up to -3,000 masl (m above sea level) has been used to study the internal structure of the caldera. Interpretation of the data shows an angular funnel shape, with a wide upper region (3×2.5 km) tapering to a narrower lower region (0.7×0.5 km). The shear zone is the same shape as the caldera, that is, rectangular with a NE-SW elongation. The caldera is infilled with vent-fill material, lake and alluvial deposits, landslide deposits, and post-caldera intrusions. The vent-fill material is a gray, non-welded lapilli tuff and tuff breccia, which homogeneously includes accidental lithics and shattered fragments, which were sheared during pyroclastic eruption, as well as accretionary lapilli occurring up to -824 masl. The vent-fill is intercalated with many lithic bands or lithic dominant zones that dip toward the caldera center. No large fault displacement can be recognized around the caldera wall. The Nigorikawa Caldera was formed ca 12,000 years ago by violent pyroclastic flow eruption, fall-back, and the following subsidence by compaction with degassing.

著者

前田 美紀 宮地 直道

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.57, no.1, pp.19-35, 2012-03-30 (Released:2017-03-20)

参考文献数

42

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Formation mechanism of basaltic pyroclastic flows has not been sufficiently clarified yet because basaltic pyroclastic flows do not occur as frequently as felsic ones. We studied the Osawa pyroclastic flow 3 deposit (OsPfl-3), which took place on the western flank of the Fuji volcano between 2.9 and 3.0 ka. OsPfl-3 has two flow units and one cooling unit, which have a combined volume of 6.2 × 106m3. The flow overlies another unit composed of two scoria fallout deposits (YokSfa-2a and 2b) which sandwich a pyroclastic flow deposit (OtPfl). OsPfl-3 mainly consists of welded blocks and dense blocks with composition and petrographical characteristics of basaltic andesite. Some of the dense blocks have cracks on their surfaces and look like “cauliflower-shaped bomb”. They have a flat surface on one side with concentration of vesicles near the surface. The matrix of OsPfl-3 has dense fragments that are thought to have originated from dense lava blocks and poorly vesiculated scoria. The emplacement temperature of the blocks is estimated to be higher than 580℃ from thermoremanent magnetization measurements. These observations indicate that the blocks in the OsPfl-3 originated from welded pyroclasts, lava flow or lava lake at the summit crater. The sequence of the eruptions that formed OsPfl-3 and underlying deposits are summarized as follows: Stage 1: Deposition of fallout tephras (YokSfa-2a and 2b) and an intercalated pyroclastic flow (OtPfl) which are composed of fairly vesiculated scoria; Stage 2: Formation of lava flow or lava lake at the summit crater, and deposition of pyroclastics on the lava; Stage 3: Occurrence of the pyroclastic flow (OsPfl-3) caused by collapse of lava and pyroclastics. OsPfl-3 is prominently distributed on the western flank. This observation implies that the westward flow from the source lava that filled the summit crater could cross the lower part of the crater rim.

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.38, no.6, pp.223-226, 1993-12-20

被引用文献数

4 9

著者

津金 達郎 牧野 州明 三宅 康幸 高橋 康

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.49-61, 2006-02-28

被引用文献数

4

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The September 2004 eruptions of Asama volcano, central Japan, ejected essential materials such as pumice with bread crust on September 1st and scoria on September 23rd. The textural and chemical analyses on the materials reveal the crystallization processes in a deep magma chamber and a shallow vent. Two distinct stages of crystallization can be recognized in size distributions and morphology of plagioclase phenocryst and microlite both in the pumice and scoria. First stage (range I ): In a deep magma chamber, pyroxene phenocryst began to crystallize out at 1150℃, and then pyroxene and plagioclase continued to nucleate and grow slowly. Second stage (range II) is divided into two sub-stages for pyroxene or three (range IIa-c) for plagioclase. II a: Magma left the chamber and rose slowly through the vent with ever increasing nucleation rate. II b-c: In a shallow vent beneath the crater, numerous plagioclase microlites like swallow-tailed shape precipitated rapidly under a high undercooling condition induced by decompression. Plagioclase microlite in the pumice and scoria developed a characteristic population density like a bell with a peak at the grain size of 0.003mm, which is interpreted to reflect a decrease in nucleation rate of plagioclase, in response to crystallization and establishment of equilibrium during the time duration when the magma stayed in the vent. Magmatic temperatures estimated from plagioclase-glass equilibrium decreased to 850℃ before the September 1st eruption. The similarity in crystal size distribution of the pumice and scoria implies that they had a common ascent history, although groundmass in the scoria has lower crystallinity than that in the pumice, suggesting that the magma of the Sept. 23rd eruption stood lower in the magma column than the Sept. 1st magma.

著者

山岡 耕春

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.39, no.4, pp.141-153, 1994-09-20

被引用文献数

2 3

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Relations between activity of volcanic earthquakes in Izu-Oshima volcano and stress and/or strain state around it are investigated. In this paper three kinds of relations are examined during and after the 1986 eruption of Izu-Oshima volcano : (1) How did big earthquakes affect on the volcanic activity of Izu-Oshima? (2) How did the pressure decrease of magma reservoir induce earthquakes around it. (3) How did the dike intrusion induce big earthquakes. The results are as follows : (1) Nine earthquakes of M>5.0 occurred from 1987 through 1990 within the epicentral distance of 100 km from Izu-Oshima volcano. They gave influences on the activity of volcanic earthquakes and/or volcanic tremor when they exerted normal strain of over 10^<-8> on the vertical plane trending N30W. (2) Swarm-like seismic activity in north and western part of Izu-Oshima volcano during the summit eruption is interpreted as an induced swarm due to pressure decrease of magma reservoir. The earthquake swarms occurred both sides of the magma reservoir whose location is estimated from the data of crustal movement. The location of two-lobed earthquake swarm is well explained by a simple model ; infinite two-dimensional elastic medium under differential stress with a circular hole. (3) Large earthquakes accompanied the dike intrusion of 1986 eruption of Izu-Oshima. Two biggest earthquakes occurred at both ends of the dike. A M 5.1 event occurred at the northwestern end and M 6.0 occurred at the southeastern end. Both events may played a role to stop the further propagation of dike intrusion.

著者

小野 晃司 渡辺 一徳 星住 英夫

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.212-213, 1995-07-31

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.211-212, 1995-07-31

著者

横山 泉

出版者

The Volcanological Society of Japan

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.58, no.1, pp.77-90, 2013-03-29 (Released:2017-03-20)

参考文献数

34

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桜島火山は歴史時代において,数度にわたり大噴火が起こり,溶岩流出と地盤の変動が記録されている.それらの中で,1914年噴火は当時の水準で種々の定量的観測がなされている.ここでは特にこの噴火によって生じた沈降の回復を詳論した.水準測量の結果は1916年の発表以来,しばしば議論されているが,姶良カルデラ周辺の沈降の中心は,海域のためもあり,その位置の決定には任意性がある.今回,噴火直後の三角測量の結果をも参考にして,従来より広範囲の沈降について,その中心の位置を桜島の北岸辺に決めた.そして,1914年噴火に伴った大規模の沈降の回復をB.M.2474を例にとり解析した.その際,活動的なこの地域で変動の基準を決めることは極めて難しい.本来は歪みなしの状態(No-strain level)を基準とすべきであるが,ここでは全く便宜上,1914年噴火に先立つ1892年(水準測量の開始)を基準(Reference level)にした.従来,観測を重ねることにより,漸近的に,歪みなしの状態を決められるであろう.結論として,その永年変化は地盤の粘弾性的回復と桜島直下の圧力源の増強との2要素で説明される.1914年噴火直後から粘弾性的回復が進行した(遅延時間は約16.6年).平行して,次第に圧力源へマグマが蓄積するに従って,約20年を経て,その効果が沈降回復へ寄与している.2000年現在は,沈降歪みは既に1892年の基準まで回復して,それにマグマ圧の効果が蓄積している状態である.この議論に付随して,姶良カルデラ地域の地殻上部の粘性を求めた.このような火山地域における粘弾性的地殻変動の他の例として,1983年三宅火山噴火後の沈降を論じ,上記と同じ桁の粘性値を得た.

著者

長谷川 健 松本 恵子 橋本 武志 畑 真紀 岩橋 くるみ 無盡 真弓 村松 弾 大橋 正俊 三反畑 修 嶋野 岳人 田中 良 安田 裕紀

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.105-113, 2023-06-30 (Released:2023-07-27)

参考文献数

10

著者

岡田 里奈 近藤 美左紀 梅田 浩司 古澤 明 天野 格

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.91-98, 2023-06-30 (Released:2023-07-27)

参考文献数

25

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The Zenikame-Menagawa tephra (Z-M) has been reported from distal terrestrial settings in the southern Hokkaido, with those erupted from Zenikame volcano, and provides an important stratigraphic marker for paleoenvironmental reconstructions of marine isotope stage 3 (MIS 3). We use both major element (EPMA) and trace element (LA-ICP-MS) analyses on proximal and distal Z-M shards to make the correlations to explosive eruptive events. Proximal stratigraphic succession is divided into deposits of two main eruptive phases with pyroclastic fall (Z-Mpfa) followed by pyroclastic flow (Z-Mpfl). The Z-Mpfl and Z-Mpfl deposits are geochemically distinct and thus their origins can be different. Considering geochemical characteristics of glass shards, the distal Z-M in the Tokachi district, located about 200 km west of the source volcano, can be identified as ash fall deposits associated with the Z-Mpfl eruption.

著者

田城 陽菜 八木原 寛

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.75-82, 2023-06-30 (Released:2023-07-27)

参考文献数

14

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We investigated temporal changes in the peak frequency of harmonic tremors accompanied by eruptions at the Showa crater of the Sakurajima volcano from January 1 to September 30, 2015. The peak frequency characteristics of harmonic tremors at the summit crater of Minamidake from 1982 to 2002 were also compared. We calculated the running spectrum of the harmonic tremors of eruptions at the Showa crater and detected their peak frequency based on the findings of Maryanto et al. (2008) by modifying the parameters. Based on the value of peak frequency and associated temporal changes, we classified harmonic tremors at the Showa crater into the following three types: nearly constant (NC), positive gliding (PG), negative gliding (NG), and others. A sharp transition, with abrupt peak frequency of the harmonic tremor changes over a brief period, was also observed at the Showa crater. Assuming that the fundamental frequency corresponds to changes in the length of the gas pocket, the length of the gas pocket was estimated to change from 110 m to 220 m at the Showa crater. Compared with the features of peak frequencies of harmonic tremors at the summit crater of Minamidake (Maryanto et al., 2008), those at the Showa crater present three differences: 1) Compared with HTB of the summit crater of Minamidake (Maryanto et al., 2008), Depending on the event, NC values had different frequency bands at the Showa crater. HTBs occur several hours after swarms of B-type earthquakes and their peak frequencies remained within a certain range (Maryanto et al., 2008). 2) The increase in f0 of PG at the Showa crater was smaller than that of HTE at the summit crater of Minamidake. HTEs occur several minutes after an eruption, as well as accompanying remarkably strong eruptions and their peak frequencies showed a gradual increase (Maryanto et al., 2008). 3) NG and sharp transitions were only recognized in harmonic tremors during volcanic activity at the Showa crater.