著者

中村 有吾 松本 亜希子 中川 光弘

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.114, no.4, pp.549-560, 2005-12-25 (Released:2009-11-12)

参考文献数

18

被引用文献数

8 6

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The AD1663 ejecta of Usu volcano, western Hokkaido, northern Japan, have a thickness of approximately 200, cm and are divisible into 7 units on the eastern foot of Usu volcano. The basal deposit, Unit-A, is composed of fine-grained, poorly sorted pumice and ash with well-developed stratification. It contains base surge beds near the sources, and is interpreted as phreatomagmatic in origin. Unit-B is typical in many respects of the product of plinian activity. It is characterized by coarse grain size and wide dispersal, combined with low lithic contents and poor development of internal stratification. This fallout deposit (Usu-b tephra) can be seen in the eastern regions of Usu volcano, and has a thickness of about 4 cm at 200 km from the vent. Unit-C, Unit-E, Unit-F, and Unit-G have characteristics that are satisfactorily interpreted as a consequence of phreatomagmatic activity : fine grain size near source, poor sorting, well-developed stratification and base surge bedforms. Unit-D is typical of phreatic deposits, being composed largely of non-juvenile lithic fragments.According to historical records, the eruption was preceeded by earthquake swarms for 3 days from August 13, 1663. The first eruption (Unit-A) occurred on August 16, followed by an eruption associated with a large amount of pumice and ash (Unit-B) on August 17. The explosive eruptions lasted approximately 20 days.The petrographic properties of the plinian product differ considerably from those of the phreatomagmatic products. The pumice clasts of Unit-B contain abundant glass and little phenocryst (plagioclase, orthopyroxene, and hornblende). The glass has a relatively high refractive index (n = 1.490-1.492) and a low SiO2 content. Orthopyroxene in Unit-B has a relatively high refractive index (γ = 1.735-1.740) and low Mg#. The phreatomagmatic products are rich in massive glass. This glass has a relatively low refractive index (n = 1.475-1.490) and a high SiO2 content, with values differing among horizons. The compositional diversity of the 1663 products indicates the existence of some magma. Presumably, their mixing triggered the 1663 eruption of Usu volcano.

著者

増渕 佳子 石崎 泰男 白井 智仁 松本 亜希子 宮坂 瑞穂 中川 光弘

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.122, no.10, pp.533-550, 2016-10-15 (Released:2017-01-20)

参考文献数

29

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沼沢火山の先カルデラ期とカルデラ形成期の噴出物の岩石記載,斑晶鉱物組成,全岩主・微量成分組成および同位体組成から,沼沢火山では,噴火期ごとに流紋岩~デイサイト質マグマで満たされた珪長質マグマ溜りが再生されたことが明らかとなった.マグマ蓄積率を求めると,カルデラ形成噴火では他の噴火期に比べ2~40倍の早さでマグマが蓄積されたと考えられる.また,4.3万年前の惣山噴火以降,珪長質マグマとともに安山岩質マグマが噴出している.先カルデラ期で噴出した安山岩質マグマは,噴火の主体となった珪長質マグマと同じ同位体組成をもち,起源物質は同じであると考えられる.一方で,カルデラ形成噴火で噴出した3種類のマグマは異なる同位体組成をもつことから,地下の多様な場でマグマが発生し,それが地殻中の浅所マグマ溜りに集積したことが示唆され,このことが大規模なカルデラ形成噴火を発生させた原因の一つになった可能性が高い.

著者

松本 亜希子 中川 光弘 井口 正人

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.61, no.3, pp.545-558, 2016-09-30 (Released:2016-11-08)

参考文献数

38

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On the 24th July, 2012, a large scale explosion occurred at Minamidake Summit crater of Sakurajima volcano, for the first time in last 1.5 years. This eruption is characterized by a clear, large preceding inflation ca.22 hours before the eruption. The juvenile glass particles in the volcanic ash of this eruption have less amount of microlite than those of Showa crater. The crystal size of microlite is also smaller. In contrast, their microlite number densities (MND) of plagioclase and pyroxenes are similar to those of Showa crater. According to the results of the decompression experiments by previous studies, the variations of crystallinity of microlite with the constant MND can be explained by the difference in the length of the duration for decompression, and/or the duration until the quench after the decompression. Considering these results, the juveniles of the summit eruption are derived from the eruption induced by relatively rapid decompression with rapid quench, and the juveniles from Showa crater are the products of the eruptions accompanied with the relatively slower decompression and/or the longer annealing after decompression. Therefore, it is interpreted that the 24th July, 2012 eruption was caused by rapid magma ascent with much shorter stagnation in the conduit. In contrast, the eruptions at Showa crater might have been induced by slower magma ascent and/or longer stagnation at a shallower depth of the conduit. This interpretation agrees with the data of geophysical observations. On matrix glass chemistry, juveniles of this summit eruption show the distinct trend from those of Showa crater. This feature can be produced by the difference in mode of microlite, which are crystallized during magma ascent. Accordingly, it is possible to evaluate the difference in magma ascent process, using the matrix glass chemistry.

著者

松本 亜希子 中川 光弘 小林 卓也 石塚 吉浩

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.4, pp.255-279, 2021-12-31 (Released:2022-02-22)

参考文献数

37

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The Tokachidake volcano group, central Hokkaido, is one of the most active volcanoes in Japan; three magmatic eruptions occurred from the crater area on the northwestern flank of Tokachidake in the 20th century. The Sandan-yama, Kamihorokamettokuyama, and Sampōzan edifices are on the southern flank of the volcano, and the first two bound the west-facing Nukkakushi crater. Although fumarolic activity and hydrothermal alteration are ongoing at Nukkakushi crater, its eruptive history remains unknown. Therefore, we performed a geological investigation of the Nukkakushi crater area. Based on topographical features, we inferred the following eruptive history. Sampōzan and Kamihorokamettokuyama formed during ca. 70-60 ka, after which the northern flank of Sampōzan collapsed and a new edifice (Nukkakushi volcano) was built within the collapse scarp. Finally, the collapse of the western flank of Nukkakushi formed Nukkakushi crater—perhaps during the Holocene, according to previous work. We identified eight Holocene eruptive products generated from the Nukkakushi crater area, the most recent of which was generated from a crater on the western flank of Sandan-yama sometime since the early 18th century. We also recognized three debris avalanche/landslide deposits that were generated within the last 750 years. Comparing the eruptive products of the northwestern crater area of Tokachidake with those of the Nukkakushi crater area revealed that magmatic eruptions from the two craters alternated until 1.8 ka. Their distinct magmatic compositions suggest the simultaneous existence of two isolated magma systems beneath Tokachidake and Nukkakushi, at least until that time. Since 1.8 ka, magmatic eruptions at the northwestern crater area of Tokachidake and phreatic eruptions at the Nukkakushi crater area have occurred in parallel. Moreover, around Nukkakushi crater, small-scale collapses/landslides have occurred. Previous studies recognized hydrothermal changes at Nukkakushi crater area, originating from the northwestern crater area of Tokachidake around the last two magmatic eruptions; it is therefore presumed that the Nukkakushi crater area was hydrothermally altered, even during periods of little eruptive activity. Such continuous and pervasive hydrothermal alteration explains the frequent collapses of edifices. The parallel yet contrasting eruptive activities in these adjacent areas are important for forecasting future eruptive activities and mitigating volcanic hazards.

著者

松本 亜希子 宮坂 瑞穂 中川 光弘

出版者

北海道大学大学院理学研究院

雑誌

北海道大学地球物理学研究報告 (ISSN:04393503)

巻号頁・発行日

no.78, pp.1-9, 2015-03

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We examined the analysis method of the compositions of volcanic glass using WDS-EPMA, focusing on Na migration caused by electron-beam bombardment. As a result of the comparison among the beam current in 10 μm square area, it is concluded that Na migration occurs in any cases at 15 kV. During the first 30 seconds, Na decay is not observed, and therefore, the detection of Na must be finished within the first 30 seconds. Considering the variations of other elements, the 15 kV accelerating voltage and 7 nA beam current with raster scanning of 10 μm square area is the best condition for the determination of volcanic glass compositions. This can prevent "grow-in" of Si and Al, as well as can make smaller the deviations of the minor elements. Using this condition, we can discuss the variations of volcanic glass compositions (except for Na) without any corrections.

著者

水谷 令子 久保 さつき 松本 亜希子 成田 美代

出版者

一般社団法人日本調理科学会

雑誌

日本調理科学会誌 (ISSN:13411535)

巻号頁・発行日

vol.31, no.3, pp.192-197, 1998-08-20

参考文献数

11

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元来すしは魚や肉の貯蔵法の一つで, 魚と飯から作られ, 現在のすしとは違って酢を使用しないで発酵させる。あゆずしは, 三重県では, 宮川(伊勢市)と北山川(紀和町)の流域に伝承されている。あゆずしを調製するのは冬季で, 塩漬けしたアユと冷ました飯を合わせて, 木の桶にきつく詰め, 重石をして30〜40日間熟成させる。通常は正月のご馳走として, 家庭内で消費され, 市販されてはいない。1996年11月下旬に伊勢市大倉町で本漬けされたあゆずしについて, 水分, pH, 塩分, カルシウム量および各種有機酸の量を調べた。結果は次のようである。1) すしあゆ(あゆずしの魚部分)のpHは, 38日間熟成した場合は5.10, 65日では4.10で, 魚と飯のpH差はほとんどなかった。2) 塩漬けしたあゆの食塩濃度(23.2%)は, 5回水洗いすると8.7%まで下がり, これを飯と共に熟成させている間に2.1%まで下がった。3) 塩付けあゆの骨のカルシウム量は55.5mg/g, 38日間熟成したものは25.0mg/g, 65日では16.8mg/gであった。頭部のカルシウム量は65日間熟成すると著しく減少した。4) すしあゆ中の有機酸量は乳酸, 酢酸, コハク酸の順に多かった。これらの酸は, いずれも熟成中に徐々に増加した。すしあゆの乳酸量は65日間の熟成で約26倍に増加した。有機酸量は魚の方が飯より多かった。5) すし桶の上層部に漬けてあったすしは, 桶の中央部に漬けたものより熟成が速かった。また一旦逆押ししたすしを保存すると, その間に熟成は進行し, 食味に変化が生じた。

著者

松本 亜希子 大平 充宣 石原 昭彦

出版者

日本体力医学会

雑誌

体力科學 (ISSN:0039906X)

巻号頁・発行日

vol.55, no.6, 2006-12-01