Article

4. The 1950-1951 Eruptions of Mt. Mihara, Oshima Volcano, Seven Izu Islands, Japan. : Part I. The 1950 eruption.

Authors:

伊豆大島三原山は,昭和25年7月16日中央火孔南縁より噴火を開始,漸次その活動規模を増大しつゝ連続的噴火を行い,9月23日噴火を休止,翌26年2月4日噴火を再開,4月1日まで,更に大規模な熔岩流出を伴った活動を継続した.ついで,噴火は,間歇的かつ爆発的になり,6月28日活動を停止した.本編では,昭和25年の噴火経過の観察を詳細に述べ,地形変化,噴出溶岩の温度,比熱の測定,噴出物の量(大約5千万噸)などについて記載した.

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Article

Mount Oyama Eruption: Analysis Using GPS Residuals Data

January 2002

On July 8th 2000, after a one week-long seismic crisis, the mount Oyama on the Miyake Jima island (Japan) explosively erupted. This first plume dispersed ashes over wide areas on the island. On August 18th 2000, another large explosion occured. The volcano plume, (the most important during all the eruption) reached an elevation of 15 km above sea level. We analysed the August 18th data of four ... [Show full abstract] permanent GPS stations located around the volcano. We processed the data using GAMIT software and we found anomalous residuals for the satellite-station rays crossing the plume. Theses residual values range from 0.5 to 1.5 cycle on LC (ionosphere-free) frequence (1 LC cycle 6.6cm). Performing a dynamic inversion of those residuals, we get a dynamic 3D information of the delays induced by the plume. Thoses delays can then be interpreted in terms of water and particule containt in the plume.

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Syn- and Post-caldera Eruptive History of Izu Oshima Volcano based on Tephra and Loess Stratigraphy

January 1996 · Journal of Geography (Chigaku Zasshi)

We reveal the detailed syn-and post-caldera eruptive history of Izu Oshima Volcano, Japan, by tephra and loess stratigraphy. Twenty-four tephra layers, which overlie the slope outside the caldera, show that 24 eruptions occurred since the formation of the caldera (about 1, 450 years ago). These eruptions are separated by 10-200 years clear dormant periods, which can be identified by eolian dust ... [Show full abstract] (loess) interbedded with tephra layers. The 24 eruptions can be classified into three types : 1) eruption with scoria and ash falls (12 eruptions), 2) eruption only with scoria falls (7 eruptions), and 3) eruption only with ash falls (5 eruptions). While tephra discharge mass of the type 1 is generally large (1.5×1010 to 7×1011 kg), that of the type 2 or 3 is small (0.6 ×109 to 1 ×1011 kg). The 1986 eruption is classified into the type 2. Debris avalanches, which occurred just before the caldera formation and covered almost all of the Izu Oshima island, demonstrate that the present caldera wall was formed by slope failure of an old edifice. The tephra-discharge stepdiagram, which shows a relationship between time and cumulative discharge volume / mass of magma, shows : 1) the average tephra-discharge rate is constant (92 kg/ s before the N1.0 eruption and 25 kg/s after the N1.0 eruption), showing an abrupt decrease of the rate at about the time of the N1.0 eruption, which occurred about 900 years ago and was the most voluminous eruption for the past 1, 450 years, 2) both before and after the N1.0 eruption, the type 1 eruption shows volume-predictability, that is, the discharge volume / mass of a next type 1 eruption can be predicted, 3) a type 1 eruption should occur sometime in the future again, and when it occurs, the discharge mass of tephra should attain to as much as 2×1011 kg or more.

Article

Geomorphic and sedimentary evidence of a gigantic outburst flood from Towada caldera after the 15ka...

January 2011 · Geomorphology

Kyoko S. Kataoka

This study reports on geomorphic and sedimentary evidence for a gigantic breakout flood from Towada caldera, Honshu Island, northeast Japan, as observed along the Oirase River downstream from the outlet of the caldera lake. A number of features of the Oirase River are inconsistent with its present discharge, including the occurrence of 1) hanging valleys and a horseshoe-shaped waterfall in the ... [Show full abstract] upstream gorge area, 2) boulder bars and scattered flood boulders, 3) a dry valley at a high elevation in the gorge, and 4) a large fan (the Sanbongi fan) in the downstream area of the river. The Sanbongi fan is composed of thick, lithic-rich hyperconcentrated flow deposits that include pumice clasts derived from the 15 ka Towada–Hachinohe ignimbrite and well-rounded meter-sized (and outsized) boulders derived from bedrock of welded ignimbrite. The deposits are entirely aggradational, with no major channels, indicating the absence of a major hiatus during sedimentation. The depositional facies also indicate that a single sheet-like flood event deposited the sediment within the Sanbongi fan area. Based on the age of the Sanbongi fan, the flood occurred between 15 and 12 ka, after eruption of the Towada–Hachinohe ignimbrite. The most probable water source for the flood is Towada caldera lake, as suggested by landforms and sediments along the lake outlet. A paleohydrological analysis indicates that at least 6 km3 of water was released from the caldera at a peak discharge of > 2 × 104 to 3 × 105 m3 s− 1 during the breakout flood. Although the Sanbongi fan was previously considered to be a “normal” alluvial fan that formed during a stage of low-stand sea level, the present results show that the formation of the fan was closely related to a catastrophic flood from Towada caldera rather than perennial fluvial activity, climate change, or a change in relative sea level.

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Low Q Zone in Izu-Oshima Volcano Island, Detected by Attenuation of Volcanic Tremor

January 1985 · Papers in Meteorology and Geophysics

The Q-structure of Izu-Oshima Volcano Island has been studied based on the propagation characteristics of the isolated-type eruption tremor originated from the central crater, Mihara-crater. This kind of tremor has been known to occur at the time of a small Strombolian eruption at the crater. Temporary observation was carried out at thirty-nine points, using one portable seismometer. The ... [Show full abstract] frequency detected of the tremor is within the range lower than 30 Hz, and its maximum amplitude exists roughly at 3 Hz wave component. The propagation mode of higher than 5 Hz seismic wave of the tremor looks like that of the body wave. The high frequency body wave generated is considered to have been by the explosion sound at the crater or by high frequency vibration of the materials at the crater due to the volcanic explosion. Large attenuation of certain wave components has been observed on the eastern flank of the volcano. On the other hand, notable large power of 10 to 12 Hz wave component is observed to the WNW and ESE just outside of Mihara-crater. The former phenomenon seems to be by the influence of the coarse materials which form the eastern area of the volcano, which is the low Q-structure region. The latter phenomenon seems to be by the influence of new pyroclastic materials stratified in the atrio of Mihara-crater. © 1985, Japan Meteorological Agency / Meteorological Research Institute. All rights reserved.

Article

22. The 1950-1951 Eruptions of Mt. Mihara, Oshima Volcano, Seven Izu Islands, Japan. : Part II. The...

January 1970

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Geochemical Changes in Spring Water Associated with the 2000 Eruption of the Miyakejima Volcano, Jap...

April 2006 · Pure and Applied Geophysics

Water was sampled from eight springs and a lake in volcanic Miyakejima Island of Japan after the 2000 eruption. Major chemical and isotopic compositions of the water were analyzed. Significant increases of sulfate ion are observed in several springs where the thickness of ejecta exceeds 32 mm. A good relationship of Cl/S mole ratios between spring water and leachate of the ejecta is observed. ... [Show full abstract] Sulfur isotopic compositions of the spring water become close to that of leachate of the ejecta as time elapses after the eruption. Consequently the sources of the added sulfate ion in the spring water after the eruption are interpreted to be anhydrite and adhered sulfur of the ejecta.

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The 1962 Eruption of Miyake-sima, one of the Seven Izu Islands, Japan

January 1964 · Bulletin of Volcanology

Takeshi Minakami

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Full-text available

Shear Strength of the Volcanic Coarse-Grained Soil

January 1997

Japan is awarded with a total of about 144 volcanos distributed over the whole country from the south to the north. In Kyushu Island there are three main volcanos, namely Unzen, Sakurajima and Aso. The eruption of these volcanos has created the need to utilize these huge amounts of debris flow deposits as a construction material. In this paper, the physical and chemical properties of debris flow ... [Show full abstract] deposits of the Unzen and Sakurajima Volcanos are examined by a series of laboratory tests and the results are compared for the evaluation.of these debris flow deposits as a construction material

Article

The 1950-1951 Eruptions of Mt. Mihara, Oshima Volcano, Seven Izu Islands, Japan. Part II. The 1951 e...

January 1955

伊豆大島三原山の昭和26年の噴火は,第2期の活動[地震研究所彙報第32号,第3冊,昭和29年9月290-312頁]に続いて,同年4月2日以降6月28日に至る第3期の活動をもつて終つた.この第3期の活動の特徴は,三原火口内の新噴石丘に起つた間歇的の爆発性噴火と,同火口中央部の隆起丘(中央丘)及びその周辺に起つた著しい昇降変化とで,前年7月16日に始まつた,今回の噴火輪廻のうちの活動減退相を表わすものと考へられる.その経過から見ると,この活動は,更に3次,すなわち(1)4月2日-20日, (2)4月30日-5月7日, (3)6月9日-28日の各活動に分たれる.

Article

Volcano Miyake-jima and the 1962 eruption (in Japanese)

January 1963 · Journal of Geography (Chigaku Zasshi)

Akira SUWA

A flank eruption in a radial fissure took place at the basaltic volcano of Miyake-jima, one of the Seven Izu Islands, on August 24, 1962, after a repose of 22 years. The activity lasted only about 28 hours and the total volume of lava and ejecta is estimated to have been about 0.009 km3. But the islanders (population : 6359) became extremely uneasy and nearly 60 % of them sought safety on other ... [Show full abstract] islands of Japan, because swarms of severe earthquakes were felt on the island after the eruption.The writer intends here to sketch in broad outline the 1962 eruption and also the characteristics of the volcanism of Miyake-jima in pre-historic and historic times.

Article

The 1741 Oshima-Oshima Eruption: Extent and Volume of Submarine Debris Avalanche

February 2001 · Geophysical Research Letters

Oshima-Oshima is a small volcanic island southwest off Hokkaido in Japan Sea. The violent eruption on August 29, 1741 caused a sector collapse of the north flank. Very destructive tsunami with 2000 casualties was also documented, but the generation mechanism has been controversial; volume of subaerial sector collapse, about 0.4 km3, was considered too small to generate such a devastating tsunami. ... [Show full abstract] We compile and analyze recently-obtained swath bathymetry data around the island. The volcano is more than 2.3 km high from ocean bottom with its base diameter of 18 km. The total slide volume, both subaerial and submarine, is estimated as 2.4 km3, nearly an order of magnitude larger than the subaerial part. To the north of island, hummocky terrain of debris deposits extends in an area of 69 km2 with the total volume of 2.5 km3, a value similar to the total slide volume. It is one of the largest debris avalanches in historic time, and probably responsible to the tsunami generation.