著者

宮縁 育夫 飯塚 義之 遠入 楓大 大倉 敬宏

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.3, pp.157-169, 2021-09-30 (Released:2021-10-29)

参考文献数

19

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Prior to the onset of magmatic activity at the Nakadake first crater, Aso Volcano (SW Japan) from July 2019 to June 2020, multiple small eruptions occurred between April and May 2019. The May 3-5 eruption was one of the largest events during the pre-magmatic activity period. An ash-fall deposit from the early stage of that eruption (15 : 00-18 : 00 in JST on May 3) was distributed to the south of the source crater, whereas the ash erupted after 20 : 00 on May 3 was dispersed southwestwards. The May 3 15 : 00-18 : 00 ash was composed mainly of fine particles (<0.25 mm in diameter) and fell as accretionary lapilli (<0.8 mm). In contrast, ash after 20 : 00 on May 3 consisted mainly of 0.5 mm grains but lacked silt and clay content. Based on an isomass map, the total discharged mass of the May 3-5, 2019 eruption was about 700 tons. Although lithic (50 %) and altered glass (30-40 %) grains were dominant in both ash-fall deposits, they also included small amounts of black to pale-brown fresh glass shards (2-4 %) inferred to be juvenile material originating from newly ascending magma. After the May 3-5 event, small ash emissions occurred intermittently until July 2019. The proportions of fresh glass shards included in the May-July 2019 ash-fall deposits gradually increased; ash erupted in early July contained 7 % fresh glass grains. Small-scale magmatic activity began on July 26, 2019, and continued to mid-June 2020. The April to early July 2019 ash emissions at Nakadake first crater are inferred to be precursor phenomenon of the late July 2019 to mid-June 2020 magmatic eruptions. It is very important to clarify temporal variations in the mass and component characteristics of erupted materials for understanding the sequence of events and predicting future eruptive activity.

著者

宮縁 育夫 飯塚 義之 大倉 敬宏

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.4, pp.441-452, 2022-12-31 (Released:2023-01-30)

参考文献数

12

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After the July 2019-June 2020 small-scale magmatic activity, surface unrest of the Nakadake first crater, which is located at the center of Aso caldera, SW Japan, had been mostly calm for fourteen months, and a lake had reformed inside the crater by late-August 2021. An eruption producing ballistic clasts and a tephra fall deposit occurred within the first crater of Nakadake at 04:44 on October 14, 2021. A large number of ballistic clasts were distributed from the west-northwestern rim of the Nakadake first crater to the southern rim of the second crater, with ballistics also reaching at least 450 m south of the center of the first crater. The largest clast (70×32×31 cm) was ejected a distance of 300 m SW of the center of the first crater. Several impact craters, which were<1 m in diameter, were observed in the surface ash layer at the crater rim. The ballistic clasts were dominated by basaltic-andesite lithic fragments of lavas and pyroclastic rocks, and were not thought to derive from a newly ascending magma. The tephra fall deposit was distributed to the southeast, extending approximately 30 km from the source crater. At the crater rim, the fall deposits were composed mainly of sand-size particles with small amounts of lapilli (<17 %), and were aggregated at sizes of a few mm to 1 cm. The aggregated muddy ash (a few millimeters in diameter) adhered to plant leaves and the surface of man-made constructions in the southeastern part of Aso caldera (4-10 km), indicating that the rising plume contained large amounts of condensed water vapor. Based on the isomass map, the total discharged mass of the October 14, 2021 eruption was calculated at approximately 2500 tons. Gray to white lithic grains (40-50 %) were dominant in the tephra deposits (0.125-0.25 mm fraction), while black to brown glass shards (8-16 %) were also observed. Although a very small proportion of glass particles appeared to be fresh, most of glass shards showed varying degrees of alteration based on microscope observation and electron micro-probe analysis. These combined lines of evidence suggest that the October 14, 2021 eruption of the first crater at Nakadake was probably a purely phreatic eruption.

著者

飯塚 義之

出版者

金沢大学

雑誌

研究活動スタート支援

巻号頁・発行日

2017-08-25

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日本を含め多くの地域で、発掘収蔵品、特に岩石同定調査はほとんど行われておらず、正しい化学分析による、客観的な岩石の記載に不備があった。本研究では携帯型蛍光X線分析装置(pXRF)を用い石製遺物の化学的分析と岩石同定を行うことで、先史時代の石材の把握と地質考古学的検討を試みている。第1年度は研究対象地域を、日本でも縄文時代の大規模遺跡として広く認知されている富山市の同市北代遺跡(縄文時代中期)および小竹貝塚遺跡(縄文時代初期)に注目して、同地域から出土した石斧の石材分析に取り組んだ(2017年11月)。北陸地方はヒスイ文化の中心地でもある。一方、同じくヒスイの原産地でもあるミャンマー中部地域の先史時代(新石器~青銅器時代)の遺跡から発掘された石製遺物についても、現地でのpXRF分析を試みた(2018年1月)。更にタイ、チュンポーン(2018年3月)での現地から出土した石製遺物の分析を行った。これまで日本の縄文時代石製遺物については、多くが蛇紋岩あるいは緑色岩を用いて製作されていると認識されていたが、今回の分析によって、蛇紋岩製石斧はごく少数しかなく、ほとんどのものが角閃石岩、その中でも多くがネフライト(緑閃石岩)製であることがわかった。縄文前期から中期にかけてヒスイ製の装飾品は存在することあれ、量的にはネフライトが大多数であった。一方、ミャンマーでは、安山岩、蛇紋岩を用いた石斧も確認できたが、これまでに分析したなかで約15試料がネフライト製の腕輪が認められた。また今回はじめてヒスイ製の装飾品を1つ確認することができた。一方、タイ南部のチュンポーンでは、青銅器時代も重要拠点遺跡(Khao Sek)から、ネフライト製のリンリンオー耳飾りと双獣頭ペンダントを確認できた。これまでの東南アジアの調査でもっとも南西から出土したものとして報告準備中である。

著者

飯塚 義之

出版者

一般社団法人 日本鉱物科学会

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.91, no.3, pp.73-85, 1996 (Released:2006-12-13)

参考文献数

22

被引用文献数

2 1

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Komochi volcano (1,296 m), located at the southernmost part of NE Japan arc, is a Quaternary composite volcano with a diameter of approximately 6 km and a volume of approximately 10 km3. The basement is composed of the Kirigakubo Formation, a member of the Miocene rhyolitic tuff formation, and Iwamoto volcanoes, dacite lava domes (ca. 6 Ma). The rocks of the Komochi volcano consist of low-K andesites with small amounts of basaltic andesite and dacite. All rocks of the Komochi volcano belong to the hyperthenic rock series. The volcanic activity of the Komochi volcano can be divided into following three stages: Ayado stage (c.a. 1.6 Ma), Early Komochi (0.9 Ma-) and Late Komochi (0.6-0.2 Ma) volcano stages which is subdivided into the two kinds of activities: stratovolcano-forming and lava dome-forming. At any stage, a large number of andesitic dikes intruded, which comprise radial dike swarm in the circumference of the Daikokuiwa neck. The Komochi volcano has a life span of about 1.4 m.y. and calculated production rate of 0.14-0.25 km3/104 yr., which is very small compared to lager volcanoes around Komochi volcano, for example Myoko and Hakone volcanoes, and even smaller than similar volcanoes in the Shin-etsu Highland area.