著者

宮城 磯治 前嶋 美紀

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.57, no.1, pp.45-50, 2012-03-30 (Released:2017-03-20)

参考文献数

13

---

For better estimation of the temperature of red-hot volcanic ejecta from their images taken by online digital cameras at night, we studied the applicability of a new pyrometer to the images. Our pyrometer applies the theory of black-body radiation to the color of red-hot object. We examined the color of red-hot volcanic ejecta, a heated basaltic rock with known temperature, and infra-red LEDs. Because of the sensitivity to infra-red ray, a digital camera Nikon D40 can visualize hot basalt specimen at temperatures much lower (ca. 370℃) than the naked eyes (500~550℃). As a side-effect of this capability, color data of the hot basalt discord from the isothermal color lines calculated from the black-body radiation and the CIE colorimetric system. Night photographs taken by the online digital camera aimed at the explosive ash eruptions of Asama volcano (2 a.m. 2 Sep., 2009) indicated that the color of red-hot volcanic ejecta was disturbed by the influence of infra-red ray in the same manner as observed on the heated basalt specimen in the laboratory. As a result, the temperature of the volcanic ejecta would be much lower than their appearance in digital images (e.g., 1000℃) but higher than the detection limit (370℃). Comparison of the color of red-hot volcanic ejecta and isothermal color lines revealed that some of the volcanic ejecta fell along the 600℃ isotherm line of the black-body radiation, which suggests that volcanic cloud reduces the influence of infra-red ray. The estimated temperature (600℃) is consistent with those deduced from petrological observation and thermodynamic computation (600〜700℃). We conclude that color analysis of the images of red-hot ejecta taken by online digital cameras are useful in temperature evaluation when images suffer less influence of infra-red ray.

著者

星住 英夫 宮縁 育夫 宮城 磯治 下司 信夫 宝田 晋治

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.1, pp.91-112, 2022-03-31 (Released:2022-04-26)

参考文献数

71

---

Aso volcano produced four huge ignimbrite-forming eruptions named Aso-1, 2, 3 and 4 in ascending order, among which Aso-4 is considered the largest eruption in Japan in the last 1 million years. This paper describes the tephra sequence between the Aso-4 and Aso-3 eruptions (Aso-4/3 tephra group). The reconstruction of the eruptive history for Aso-4/3 tephra group presented here provides a valuable contribution to the understanding of caldera volcanism by outlining the preparatory processes of a catastrophic ignimbrite eruption. The eruption sequence of the Aso-4/3 tephra group, which is composed of at least 37 units of pumice-fall, scoria-fall, and ash-fall deposits, is divided into five stages. Stage 1 is characterized by the eruption of mafic scoria (VEI 3-4) during 133-114.1 ka, after the eruption of Aso-3. Stage 2 is characterized by the frequent eruptions of mafic scoria and ash (VEI 3-4) during 114.1-108.4 ka. The magma composition became more felsic during explosive eruptions (VEI 3-4) from 108.4-104.7 ka (Stage 3). During the most active stage from 104.7-97.7 ka (Stage 4), voluminous felsic pumice-falls erupted (VEI 4-5). The ABCD tephra (97.7 ka) is the largest plinian pumice-fall deposit of Aso volcano. Stage 5 (97.7-88 ka) is a relatively dormant period, during which only a biotite dacite pumice-fall was deposited (VEI 4). The low number of eruptions during stage 5 suggests that the magma supply rate decreased during the 10 thousand years that preceded the Aso-4 ignimbrite eruption. The estimated total tephra volume for the Aso-4/3 tephra group is 23 km3, which corresponds to 10 km3 in dense rock equivalent (DRE). The estimated the long-range tephra discharge rate (0.23 km3 DRE/ky) is similar to that in the post-caldera stage of Aso-4 (0.2 km3 DRE/ky).

著者

鹿野 和彦 大口 健志 林 信太郎 矢内 桂三 石塚 治 宮城 磯治 石山 大三

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.126, no.5, pp.233-249, 2020-05-15 (Released:2020-09-17)

参考文献数

38

被引用文献数

2

---

田沢湖カルデラから2-1.8Maのある時期に噴出した火砕流密度流起源のテフラを記載した.下部は多面体~平板型ガラス片と岩片に富むテフラで,マグマ水蒸気爆発に伴ってカルデラ崩壊が始まったことを示唆する.上部は淘汰不良無層理の気泡型ガラス片に富むテフラで,岩屑なだれ堆積物と共存しており,カルデラ形成噴火最盛期に放出されたことを示唆する.これらは長期的にわたって侵食され田沢湖近傍でさえほとんど残っていない.カルデラ形成後の1.8-1.6Maには2つの溶岩ドームがカルデラ床に,2つの溶岩流が外輪山に噴出している.また,カルデラ形成前にはカルデラ南縁で少量の安山岩が噴出している.

著者

長谷川 健 中川 光弘 宮城 磯治

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.123, no.5, pp.269-281, 2017-05-15 (Released:2017-07-25)

参考文献数

24

被引用文献数

4

---

北海道東部の活火山であるアトサヌプリ火山について,最近の爆発的噴火履歴,特に水蒸気噴火の発生履歴の再検討を行った.火口近傍の露頭および2本のボーリングコアを調査し,これまで未記載であった水蒸気噴火堆積物を新たに5層発見した.その結果,従来2回とされていた最新期の水蒸気噴火が,少なくとも最近2,700年間に7回を数えることができる.特に1,500~1,000年前の間は平均で100年に1回の噴火を繰り返す頻発期であり,最新の噴火は300~400年前であることも分かった.

著者

宝田 晋治 宮城 磯治 東宮 昭彦

出版者

特定非営利活動法人 日本火山学会

雑誌

日本火山学会講演予稿集 2018 (ISSN:24335320)

巻号頁・発行日

pp.116, 2018 (Released:2019-03-06)

被引用文献数

1

著者

宮城 磯治 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.47, no.6, pp.757-761, 2003-01-08 (Released:2017-03-20)

参考文献数

16

被引用文献数

3

---

We developed a new thermometer that uses color of volcanic ashes. A series of heating experiments for basaltic ashes under the atmospheric condition provided a quantitative relationship among color, heating temperature, and heating duration. The higher the heating temperature, the more the redness in color of heated ash. We applied the relationship to estimate heated temperature of the ash that was underlying below or contact with a cauliflower-shaped volcanic bomb ejected from the Miyakejima volcano on 18 August, 2000. The estimated temperature was about 390℃ for the ash underlying 1 cm below the volcanic bomb, and 550℃ for the ash in contact with the bomb. Numerical heat transfer calculations for the volcanic bomb on the ash layer suggested that temperature of its center at the time of landing is about 1,000℃. This is the first concrete evidence that the bomb was essential material and that the 18 August eruption was phreatomagmatic.

著者

宮城 磯治 圦本 尚義

出版者

The Volcanological Society of Japan

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.40, no.5, pp.349-355, 1995-10-31 (Released:2017-03-20)

参考文献数

32

被引用文献数

4

---

日本を含む島弧の火山では,しばしば爆発的な噴火が見られる.マグマ中の揮発性成分(主に水)の飽和・発泡・膨張にともなうマグマの急激な放出が,それらの要因である.火山噴火の理解の為には,マグマ含水量,マグマヘの水の溶解度,そして噴火時の脱水過程を理解する必要がある.しかし,噴出時の脱水のため,噴出前の含水量を火山岩から読みとることはきわめて困難である.これまでのところ,斑晶中のガラス包有物の含水量を分析することが,マグマ含水量を見積もるための最も有効な手段であると考えられる.ただし,斑晶中のガラス包有物の大きさは通常直径100μm以下であるため,微小領域の正確な含水量測定法が必要である.そこで本研究では,二次イオン質量分析計を用いた含水量分析の手法を開発した.これまでの研究により,ガラスの組成が異なると水素の二次イオン生成率も変化することが知られており,この手法の問題点であった.しかし本研究では,ガラスのシリカ濃度を用いてその生成率が補正できることを示し,この問題点を克服した.これにより玄武岩質〜流紋岩質ガラスの微小部分(半径約5μm)の含水量を正確(約±0.5wt.%)に分析する手法が確立された.この手法の応用として姶良カルデラの約2万2千年前の噴出物から取り出した斑晶メルト包有物の分析を行ったところ,5~7wt.%の含水量が示された.これはAramaki(1971)の水熱合成実験により得られている水分圧と水の溶解度から推定される含水量と良く一致する.

著者

宇都 浩三 風早 康平 斎藤 元治 伊藤 順一 高田 亮 川辺 禎久 星住 英夫 山元 孝広 宮城 磯治 東宮 昭彦 佐藤 久夫 濱崎 聡志 篠原 宏志

出版者

学術雑誌目次速報データベース由来

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.110, no.2, pp.257-270, 2001

被引用文献数

7 13

---

To understand the eruptive mechanism of the 2000 Miyakejima volcanic activity, we conducted intensive geological, petrographic, and mineralogical studies on the pyroclastics of the August 18 eruption. Volcanic ashes, which were rich in accretionary lapilli, covered most of the islands. Cauliflower-shaped bombs and lapilli were ejected along with accidental lava blocks. Black-colored angular scoriaceous particles with abundant vesicles 10 -100 μm in diameter are found among ashes, comprising about 40 wt. % of total constituents. These bombs, lapilli, and black ashes have identical bulk chemical compositions and constituent mineral compositions, suggesting a common origin. Existence of oxidized ashes and accretionary lapilli attached to a large flattened bomb and chemicallyreacted anhydrite particles trapped in the voids of bombs suggest that bombs were still hot and ductile when they were emplaced on the ground. We, therefore, conclude that the August 18 eruption was a phreatomagmatic eruption and cauliflower-shaped bombs and black ashes were essential magmatic materials. Significant SO<SUB>2</SUB> emissions from the volcano after August 18 also suggest convective upwelling of magmas to a shallower level beneath the volcanic edifice. We propose a magma-ascending model in which vesiculating magmas continuously ascend through the wall of subsided piston-like blocks.