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

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 (ISSN:04534360)

巻号頁・発行日

vol.45, no.4, pp.209-216, 2000-08-28 (Released:2017-03-20)

参考文献数

10

被引用文献数

1

---

The Ito ignimbrite, the product of a big eruption at Aira caldera about 24,500 y B. P., is distributed very extensively around the caldera in south Kyushu. The region within about 70 km from the center of the caldera was the previously known extent of distribution of the ignimbrite. Recent field research revealed, however, Iocal but extensively-scattered distribution of the ignimbrite in many places beyond the previously known extent of distribution northwest to northeast of the caldera. The farthest site of distribution of the ignimbrite is located about 90 km north of the caldera, indicating that the Ito pyroclastic flow originally spread at least 20 km farther than the previously known extent. The ignimbrite in the remote region is characteristically fine-grained compared with the one near the source. Both pumice and lithic fragments in the ignimbrite decrease, as a whole, in size with distance from source. However, the size of lithic fragments increases in the mountainous area beyond 70 km from source. This is because lithic fragments were incorporated into the pyroclastic flow from local land surface probably due to increased turbulence of pyroclastic flow during the passage on the irregular basal relief. The most remote ignimbrite, at a site 90 km from source, attains to about 35 m in thickness and contains abundant lithics of 5-15 cm in diameter, suggesting that the Ito pyroclastic flow spread farther beyond.

著者

徳永 徹 横山 勝三

出版者

The Association of Japanese Geographers

雑誌

地理学評論 (ISSN:00167444)

巻号頁・発行日

vol.52, no.3, pp.111-125, 1979-03-01 (Released:2008-12-24)

参考文献数

36

被引用文献数

5 5

---

伊豆新島向山火山の生成過程(生成史)は,噴火様式の差異ひいては堆積物や地形の特徴に基づいて,I期:ベースサージ(base surge)丘の生成,II期:大峯火砕丘の生成,III期:向山溶岩円頂丘の生成の3期に大別される.これら一連の火山活動の推移は,噴火の経過(火山体の成長)に伴うマグマの噴出環境の変化に呼応したものと考えられる.すなわち,向山の噴火活動は海底噴火で始まったが,火山体の成長につれてマグマと海水との接触が次第に妨げられ,ついには遮断されるに至った.これに伴って,噴火活動は,ベースサージを伴った強烈なマグマー水蒸気噴火から,ベースサージを伴わない爆発的噴火,さらに溶岩の噴出へと移行した.その結果,ベースサージ丘・火砕丘・溶岩円頂丘で構成される単成複式火山が生成した.

著者

横山 勝三 Shozo YOKOYAMA

出版者

日本地形学連合

雑誌

地形 = Transactions, Japanese Geomorphological Union (ISSN:03891755)

巻号頁・発行日

vol.34, no.4, pp.303-311, 2013-10-25

---

阿蘇カルデラの外輪山には多数の安山岩質岩塔(トア)が見られる.その多くは,きわめて強く帯磁しており,その強い磁性はクリノメーターを使って容易に捉えられる.この強く帯磁した岩石すなわち磁石石は,落雷の影響で生じたと思われる.これらの磁石石(トア)の上面には風化穴(weathering pit,ナマ)がみられるものがある.一方,落雷の近年の報道には,花崗岩やコンクリートなどの建造物に損傷を与えた事例がある.また,いくつかの空港の滑走路上に落雷で小孔が生じた事例も報告されている.このような落雷の破壊力から判断すると,落雷で岩石表面に孔が生じる可能性はきわめて高い.これらのことから,磁石石上の風化穴は,落雷による最初の小孔(initial depression)の形成から始まったと考えられる.Numerous tors of andesite are found on the somma of Aso caldera, Kyushu, Japan. Many of them are very strongly magnetized as can be detected easily by a geologic compass. Such strongly magnetized rocks, namely lodestones, are presumed to have been formed by the effect of lightning strike. Weathering pits are found on some of the top surfaces of the lodestone tors. According to the recent reports, there are examples of lightning strikes which damaged constructions of granite and concrete. Also, pits on runways formed by lightning strikes have been reported from some airports. Judging from the destructive power of lightning strikes, it is highly probable that pits are formed on rock surfaces by lightning strikes. Thus, it is interpreted, from these, that the weathering pits on the lodestones started from initial depressions formed by lightning strikes.

著者

西山 賢一 横田 修一郎 横山 勝三

出版者

日本地形学連合

雑誌

地形 (ISSN:03891755)

巻号頁・発行日

vol.25, no.3, 2004-07-25

著者

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 (ISSN:04534360)

巻号頁・発行日

vol.45, no.4, pp.209-216, 2000-08-28

被引用文献数

1

---

The Ito ignimbrite, the product of a big eruption at Aira caldera about 24,500 y B. P., is distributed very extensively around the caldera in south Kyushu. The region within about 70 km from the center of the caldera was the previously known extent of distribution of the ignimbrite. Recent field research revealed, however, Iocal but extensively-scattered distribution of the ignimbrite in many places beyond the previously known extent of distribution northwest to northeast of the caldera. The farthest site of distribution of the ignimbrite is located about 90 km north of the caldera, indicating that the Ito pyroclastic flow originally spread at least 20 km farther than the previously known extent. The ignimbrite in the remote region is characteristically fine-grained compared with the one near the source. Both pumice and lithic fragments in the ignimbrite decrease, as a whole, in size with distance from source. However, the size of lithic fragments increases in the mountainous area beyond 70 km from source. This is because lithic fragments were incorporated into the pyroclastic flow from local land surface probably due to increased turbulence of pyroclastic flow during the passage on the irregular basal relief. The most remote ignimbrite, at a site 90 km from source, attains to about 35 m in thickness and contains abundant lithics of 5-15 cm in diameter, suggesting that the Ito pyroclastic flow spread farther beyond.