著者
早川 由紀夫 由井 将雄
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.28, no.1, pp.1-17, 1989-05-31 (Released:2009-08-21)
参考文献数
23
被引用文献数
22 or 0

The eruptive history of the Kusatsu Shirane volcano is well described by means of 14 beds of key tephra and intercalating loess soil. Three eruptive stages are recognized. During early or middle Pleistocene the Matsuozawa volcano was formed; this is the first stage. The second stage was initiated by effusion of the Horaguchi lava, which was followed by eruptions of the Oshi pyroclastic flow, older lava flows, 3P pumice fall, and Yazawahara pyroclastic flow. Brown loess soil about 10m thick covering these deposits indicates that a dormant period of more than 100, 000 years followed this stage. The summit area upheaved about 400m or more against the foot of the volcano during this period, as is suggested by the extraordinarily steep (6.1°-3.0°) surface of the Oshi ignimbrite plateau. The third stage, which started about 14, 000 years ago, is the formation of three pyroclastic cones on the summit and contemporaneous effusion of the younger lava flows, e. g. the Kagusa lava of 7, 000 years ago and the Sessyo lava of 3, 000 years ago. In historic times, phreatic explosions have frequently occurred on the summit crater, Yugama. This means that the present belongs to the third stage. It is unlikely that eruptions of the third stage are caused by cooling of the magma chamber which was active in the second stage. The activity of the third stage seems to denote arrival of a new magma chamber at shallow depth.
著者
早川 由紀夫 野村 正弘
巻号頁・発行日
2011-04-28 (Released:2011-08-05)

福島第一原発の2011年3月事故によって大気中に放出された放射性物質は、短軸5km程度の楕円形をした霧のひとかたまりとして、地表から数十mまでの高さを速さ2~6m/sでゆっくり移動した。放射性物質の大量放出は大きく分けて3回あった(3月12日、15日、20-21日)。放射性物質はグローバルに広がったが、その6割が日本列島上に降り注いだ。大気中に放出されたセシウム総量は1京1000兆ベクレル。チェルノブイリ原発事故の1/12だった。原発事故に際して、以上の地学的知見をインターネットを利用してツイッターやブログですみやかに発信し、広く情報共有した。
著者
小山 真人 早川 由紀夫
出版者
公益社団法人 東京地学協会
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.105, no.2, pp.133-162, 1996-04-25 (Released:2009-11-12)
参考文献数
50
被引用文献数
17 or 0

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 (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.
著者
早川 由紀夫
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.40, no.3, pp.177-190, 1995-07-31
参考文献数
47
被引用文献数
24 or 0

Loam is an international scientific term, however, it has been used in a peculiar way in Japan. Japanese loam is a massive, brown, weathered rock unit composed of silt, clay, sand and occasional lapilli. It extensively covers coastal terraces, river terraces, ignimbrite plateaus and other uplands around volcanoes. Loam is not a product of soil forming process operated beneath the earth surface against rock bodies ; but it is a sediment accumulated slowly on the earth surface. Small-magnitude volcanic eruptions play a very minor role for the sedimentation. An eolian reworking process of pre-existing fine-grained deposits by the wind plays a major role. This is proved by following facts : 1) loam has accumulated even during the time when no ash-fall was observed ; 2) a volcano infrequently erupts explosively and the intensity of ash fallout is far lower than the sedimentation rate of loam ; it is about 0.1 mm/year ; 3) loam is hardly thickening toward a volcano. Very small particles carried from continental China by the westerlies at a high altitude are contained in loam, however, in the area around volcanoes their contribution is little for the formation of loam compared with eolian dust carried from nearby bare grounds by local winds at a low altitude. Loam does not accumulate all the year round. Just before and during fresh verdure, occasional strong winds pick up fine particles into the air from a bare ground which is dried up by a high-angle sunlight and high-temperatures. Eventually fine particles will settle down in vegetation. The most favorable season for loam deposition is April to May, in which more than half of an annual amount is achieved. It is convenient and practical to define a single eruption by a tephra layer which is not interbedded with loam. The thickness of loam can be used for the quantitative measurement of geologic time intervals, in years to thousands years, on certain conditions. Lithology of Japanese loam and the mechanism of sedimentation are identical to those of loess in other areas, such as China, northern Europe, northern America and New Zealand. There is no reason to hesitate to designate Japanese loam loess.
著者
早川 由紀夫 古田 貴久 小山 真人
巻号頁・発行日
2003 (Released:2003-04-01)

当初は、CDなどのメディアで配布して学校内LANで使う火山教材を作成しようとしたが、回線やマシンスペックの性能向上が予想したより早く、インターネット上にコンテンツを置いて学校や家庭からユーザーにアクセスしてもらっても私たちの目的を十分達成することができるようになった。そのため予定を変更して、ユーザーにとって使いやすく、私たちにとって配布と更新が容易なポータルサイト「火山の教室」を作成した。http://vulcania.jp/school/ポータルサイトには、「子どものページ」への入り口と「先生のページ」への入り口がある。「子どものページ」は、「ニュース」「火山の学習」「火山がいっぱい」「電子掲示板」「リンク」からなる。「先生のページ」は、「ニュース」「授業素材」「研究レポート」「電子掲示板」「リンク」からなる。児童生徒と教諭はそれぞれのページを利用する。ただし他方のページを開くことを禁じてはいない。教諭は、授業で使う教材をここから選び出す。インターネットに接続して使っても良いし、手元に保存しておいてオフラインで使っても良い。児童生徒は、調べ学習などに利用する。作成したコンテンツのおもなものは、次のとおりである。・ウェブ紙芝居(おはなし編):「マグマのしんちゃん(鳥海山)」、「赤い岩のかけら(浅間山)」・ウェブ紙芝居(立体地形編):浅間山、阿蘇カルデラ、富士山・弁当パックで立体模型:各地の火山と震源分布・地震波シミュレーション:地震波形、縦波と横波、地震観測シミュレーション・生きている火山:噴火動画とライブカメラ・フィールド火山学:火山と噴火の体系的写真解説・見学案内:浅間山、草津白根山、富士山、伊豆大島
著者
早川 由紀夫
出版者
東京大学地震研究所
雑誌
東京大学地震研究所彙報 (ISSN:00408972)
巻号頁・発行日
vol.60, no.4, pp.507-592, 1986-03-31

The eruptive activity of Towada Volcano is documented by the tephrostratigraphic study. More than 20 eruptive episodes are described in detail with isopach maps and isograde maps of maximum pumice size, maximum lithic size, and median diameter for the individual fallout deposits. The activity of the volcano started about 200,000 years ago along the NE-SW trending line crossing the present lake Towadako and relatively small-scale volcanoes were formed. A caldera 11km×11km wide was formed as a result of several eruptive episodes during the period about 55,000 to 13,000 years ago, three of which included voluminous pyroclastic flow eruptions. The post-caldera activity occured at a rate of one eruptive episode every 1,000 to 2,000 years and a stratovolcano and two lava domes were formed in the caldera. The latest eruptive episode was dated 1,250 y B. P. by the radiocarbon method. Rocks of Towada Volcano cover a wide range from basaltic andesite to rhyodacite (SiO2 : 51-70wt.%) with phenocrysts of plagioclase, augite, hypersthene, and magnetite with occasional olivine. Horn-blende is characteristically found in the pyroclastic deposits of 13,000 years old and in some earlier deposits. Volumes, V, of two plinian deposits are determined by the crystal method : 6.7km3 for the Chuseri deposit and 2.2km3 for the Nambu deposit. Then an empirical formula, V=12.2 TS, is obtained for the practical volume estimation, where T is the thickness of an isopach and S is the area enclosed by the isopach. Application of the formula to the fallout deposits of Towada Volcano suggests that the total magma erupted during the past 55,000 years amounts to 1.5×1017g. This corresponds to the discharge rate of dense rock equivalent to 1.1km3 per thousand years. The cross-wind range, Rc, of the pyroclasts of a given size may be a good indicator of the maximum height reached by the pyroclasts in the eruption column. It is found that the Rc is relatively large for those deposits whose erupted masses are relatively large. The dispersal of a fallout deposit is also seriously affected by winds. A plausible solution of the eruption condition for the Nambu deposit is that 4mm size lithic fragments reached the maximum height of 15km in the eruption column, then they were detached from the column and displaced by winds having an average velocity of 30m/s. After a 20 min flight, they fell upon the ground 48km east of the source. Whole-deposit grain size populations are determined for the Chuseri and Nambu plinian deposits. The Chuseri population is similar to the New Zealand examples. However, the Nambu population is distinctly coarser than the others.
著者
小林 哲夫 早川 由紀夫 荒牧 重雄
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.28, no.2, pp.129-139, 1983-07-01
被引用文献数
6 or 0

大隅降下軽石堆積物は, 約22, 000年前に鹿児島湾最奥部で起こった一連の巨大噴火の最初期のプリニアン噴火の産物である.灰白色の軽石と遊離結晶および少量の石質岩片からなる本堆積物は, 全層にわたってほぼ均質な見かけを呈するが, 多くの場合, 上方に向かって粒径がやや大きくなる逆級化層理を示す.層厚分布図(Fig.3)と3種の粒径分布図(軽石の平均最大粒径・石質岩片の平均最大粒径・堆積物の中央粒径;Figs.5, 6, 7)は, いずれも本堆積物の噴出火口が姶良カルデラの南縁, 現在桜島火山の位置する地点付近にあったことを示している.分布軸は火口からN120°E方向に伸びるが, 分布軸から60 km以上離れた地点にも厚く堆積している.又, 堆積物は分布軸の逆方向すなわち風上側にも20 km以上追跡できる.分布軸上で火口から30 km離れた地点での層厚は10 mに達するが, 40 km地点より遠方は海域のため層厚値は得られない.そのため噴出量の見積もりには多くの困難が伴うが, すでに知られている他のプリニアン軽石堆積物の層厚-面積曲線(Fig.4)にあてはめて計算すると, 総体積98 km^3(総重量7×10^<16>g)が得られ, 本堆積物は支笏-1軽石堆積物(116 km^3)に次ぐ最大規模のプリニアン軽石堆積物であることがわかる.3種の粒径分布図から得られる粒径-面積曲線(Fig.8)は, 噴出速度・噴煙柱の高さ・噴出率などで示される噴火の「強さ」を比較する上で有効である.それにより, 大隅降下軽石噴火の「強さ」はけっして例外的なものではなく, プリニアン噴火の平均あるいはそれをやや上回る程度であったことが判明した.
著者
早川 由紀夫
出版者
公益社団法人 東京地学協会
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.108, no.4, pp.472-488, 1999-08-25 (Released:2009-11-12)
参考文献数
94
被引用文献数
3 or 0
著者
鈴木 毅彦 早川 由紀夫
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.29, no.2, pp.105-120, 1990
被引用文献数
15 or 0

Five distinctive tephra beds (A<sub>1</sub>Pm-A<sub>5</sub>Pm), carrying abundant biotite and quartz crystals, are widely distributed in central Japan. They are here collectively called Omachi APms or APms in short, and are petrographically identified by high refractive indices of hornblende (n<sub>2</sub>=1.685-1.696) and orthopyroxene (γ=1.728-1.737). One bed of the APms is found as far as 239km from the presumed source, Momisawadake in the Hida Mountains, where it is 4cm thick and composed mainly of silt-sized glass. No proximal deposit made up of coarse pumice fragments is found owing to unfavorable preservation of the mountainous landscapes; however, the eruption style is supposed to be of plinian type based on analyses of grain size along the dispersal axis.<br>Assuming that the accumulation rate of loess soil has been constant at each locality, the age of APms is estimated 0.24-0.33 Ma by the overlying soil thickness. Moreover, in the south Kanto district, one of the APms is intercalated between two well-established marker-tephra: GoP (0.25-0.30Ma) and TE-5 (0.35-0.40Ma). It is very likely that the age of APms is 0.30-0.35Ma. The time interval between A<sub>1</sub>Pm and A<sub>5</sub>Pm eruptions is estimated to be less than 0.05Ma, because the thickness of the soil layer intercalatcd between APms does not exceed 106cm at any locality.<br>The Omachi APms are found on the flanks and slopes of many volcanoes in central Japan, such as Azumaya, Yatsugatake, Kusatsu Shirane, and Takahara. They are also found among deposits forming fluvial terraces in north Kanto. The significance of APms as Middle Pleistocene time-markers will be established hereafter.
著者
早川 由紀夫
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.38, no.6, pp.223-226, 1993-12-20
被引用文献数
4 or 9
著者
早川 由紀夫 藤根 久 伊藤 茂 Lomtatize ZAUR 尾嵜 大真 小林 紘一 中村 賢太郎 黒沼 保子 宮島 宏 竹之内 耕
出版者
公益社団法人 東京地学協会
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.120, no.3, pp.536-546, 2011-06-25 (Released:2011-09-06)
参考文献数
11

Two wood trunks, one charred and 75 years old and the other not charred and more than 199 years old, were collected from Hayakawa ignimbrite of Niigata Yakeyama Volcano. They were investigated using the radiocarbon wiggle-matching method to determine the age of the eruption. The result was 1225-1244 cal AD (95.4%), which is over 200 years younger than previous estimates. The eruption, including the Hayakawa ignimbrite, was the largest during the volcano's life period of 3000 years. Co-ignimbrite fallout KGc ash has been found at many archaeological sites spreading on the eastern flanks of Myoko Volcano and the Takada Plain. The age obtained here will provide a useful time constraint for archaeologists and volcanologists studying this area.
著者
早川 由紀夫 小山 真人
巻号頁・発行日
2005 (Released:2005-04-01)

中学1年で学ぶ「大地の変化」のうち、火山に関する部分の学習プログラム(全9時間)をつくって授業実践した。1時間目:火山噴火とは2時間目:火山噴出物とマグマ3、4時間目:火山の形、溶岩の色、噴火の様子とマグマ5時間目:火山がつくる地形・地層と人間生活6、7時間目:火成岩と鉱物8時間目:火山の災害と恵み9時間目:火山について調べよう当初計画していた地震と地層については、教材をいくつか作成するに留まり、学習プログラムをつくるまでには至らなかった。作成した火山学習プログラムには、ITを利用したデジタル教材を多用した。デジタル教材はリアルでわかりやすい表現を可能にしただけでなく、これまでできなかった新しい表現方法も生み出した。しかし、デジタル教材だけで学習プログラムを作成してもよい授業ができないことがわかった。従来のアナログ教材にも捨てがたい長所がある。古くからある教材に工夫を加えて使ったり、独創的なアイデアで新しい教材を開発するなどしてアナログ教材も使い続けるべきである。両者を併用して、バランスの取れた学習プログラムを作成するのが望ましい。本研究で新規作成あるいは改良した教材のうち主なものは次のとおりである。アナログ教材:コーラ噴火、減圧発泡、カルメ焼き、弁当パック立体模型、かざんきっずデジタル教材:カシミール3D、ウェブ紙芝居(立体地形編、自然史編、おはなし編)、噴火勤画、かざんくいず、噴火カタログ、噴火史料データベース、浅間山の北麓地質図、浅間山の火山灰を測ろう、オーロラカメラ、地震波シミュレーション
著者
早川 由紀夫
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.36, no.3, pp.357-370, 1991-10-15 (Released:2017-03-20)

The recent progress of physical volcanology is reviewed focusing on studies on volcaniclastic flows and their deposits. Pyroclastic flows are high-particle-concentration, laminar currents with gas as a continuous phase. Pyroclastic surges are low-particle-concentration, turbulent currents with gas as a continuous phase. Lahars are flows of debris with liquid water as a continuous phase. Debris avalanches are catastrophic landslides in which a continuous phase is absent or plays no role for the motion. Owing to the upward gas flow, fluidization processes operate in pyroclastic flows. Flow behavior and resultant deposits are remarkably different depending the degree of fluidization, because it effectively reduces the yield strength of the flow. However, the distance traveled is slightly affected by the degree of fluidization. It is determined mainly by the mass incorporated at the source or by the velocity acquired when it wes initiated.
著者
早川 由紀夫 井村 隆介
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.36, no.1, pp.p25-35, 1991-04
被引用文献数
4 or 0

The eruptive history of Aso volcano for the past 80,000 years is revealed by tephrochronology and loess-chronometry. Around the Aso caldera is a thick accumulation of loess, which is intercalated with numerous Aso tephra layers of limited dispersal as well as three widespread tephra layers of known age that are good marker horizons ; the Akahoya ash (6.3 ka), the Aira-Tn ash (22 ka), and the Aso-4 ignimbrite (70 ka). Loess-chronometry is based on the assumption that, in the Aso region, the accumulation rate of loess has been constant as 12 cm/ky from 80 ka to the present. Most of tephra layers after the caldera-forming Aso-4 eruption are composed of volcanic sand or scoria lapilli of basaltic andesite composition. However the 27 ka Kusasenri dacite (SiO_2 = 67%) pumice is a conspicuous exception. The large volume of 5.85 km^3 (bulk) and wide dispersal of this pumice suggests that it is a product of plinian eruption. From October 5 to the end of November 1989, the Nakadake crater of Aso volcano was in eruption. Ash was uninterruptedly emitted from a 500-1,000 m high eruption column coming out of the crater. The average discharge rate of ash was 5 × 10^7 kg/day. The total mass of ash discharged during the two months reached 3 × 10^9 kg. The penultimate eruption in recent history was June-August 1979, when 7.5 × 10^9 kg of ash was discharged. Outside the Aso caldera, the thickness of the 1989 ash is less than 1 cm. It is almost impossible to detect an old ash layer of thickness about 1 cm in a loess cross section, suggesting that sedimentary records 10 km away from a volcano are insufficient to reconstruct past eruptions smaller than 10^<10> kg. Eruptions smaller than 10^<10> kg can be determined only from proximal deposits. The history of eruptions of Aso volcano over the last few thousand years is tentatively determined from cross sections 2-4 km west of the Nakadake crater. After a 580-1,250 year dormant period, Aso volcano became active about 1,780 years ago. From then, small eruptions each with 10^9-10^<10> kg ash discharge have been repeated 48-88 times up to the present. The duration of each eruption was a few months, and the dormant interval between eruptions averaged 20-37 years.
著者
早川 由紀夫
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.36, no.3, pp.357-370, 1991-10-15
被引用文献数
4 or 0

The recent progress of physical volcanology is reviewed focusing on studies on volcaniclastic flows and their deposits. Pyroclastic flows are high-particle-concentration, laminar currents with gas as a continuous phase. Pyroclastic surges are low-particle-concentration, turbulent currents with gas as a continuous phase. Lahars are flows of debris with liquid water as a continuous phase. Debris avalanches are catastrophic landslides in which a continuous phase is absent or plays no role for the motion. Owing to the upward gas flow, fluidization processes operate in pyroclastic flows. Flow behavior and resultant deposits are remarkably different depending the degree of fluidization, because it effectively reduces the yield strength of the flow. However, the distance traveled is slightly affected by the degree of fluidization. It is determined mainly by the mass incorporated at the source or by the velocity acquired when it wes initiated.
著者
早川 由紀夫 由井 将雄
出版者
Japan Association for Quaternary Research
雑誌
第四紀研究 (ISSN:04182642)
巻号頁・発行日
vol.28, no.1, pp.1-17, 1989
被引用文献数
5 or 0

The eruptive history of the Kusatsu Shirane volcano is well described by means of 14 beds of key tephra and intercalating loess soil. Three eruptive stages are recognized. During early or middle Pleistocene the Matsuozawa volcano was formed; this is the first stage. The second stage was initiated by effusion of the Horaguchi lava, which was followed by eruptions of the Oshi pyroclastic flow, older lava flows, 3P pumice fall, and Yazawahara pyroclastic flow. Brown loess soil about 10m thick covering these deposits indicates that a dormant period of more than 100, 000 years followed this stage. The summit area upheaved about 400m or more against the foot of the volcano during this period, as is suggested by the extraordinarily steep (6.1°-3.0°) surface of the Oshi ignimbrite plateau. The third stage, which started about 14, 000 years ago, is the formation of three pyroclastic cones on the summit and contemporaneous effusion of the younger lava flows, <i>e. g.</i> the Kagusa lava of 7, 000 years ago and the Sessyo lava of 3, 000 years ago. In historic times, phreatic explosions have frequently occurred on the summit crater, Yugama. This means that the present belongs to the third stage. It is unlikely that eruptions of the third stage are caused by cooling of the magma chamber which was active in the second stage. The activity of the third stage seems to denote arrival of a new magma chamber at shallow depth.
著者
早川 由紀夫 荒牧 重雄 白尾 元理 小林 哲夫 徳田 安伸 津久井 雅志 加藤 隆 高田 亮 小屋口 剛博 小山 真人 藤井 敏嗣 大島 治 曽屋 龍典 宇都 浩三
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.29, pp.S208-S220, 1984-12-28

Stratigraphy and thickness distribution of the pyroclastic fall deposits formed during the eruption of Miyakejima volcano on October 3-4, 1983, were studied immediately after the deposition. Of the total mass of 20 million tons erupted, 8.5 million tons were ejected as basaltic scoria to form a complex set of air-fall deposits east of the fissure vents. One million tons of the latter were ejected from the upper fissures as fire-fountain products. The rest was the product of phreatomagmatic explosions which occurred in the lower fissures where ground water chilled the magma to form dense scoria blocks which devastated villages. Explosion craters and a tuff ring were formed along the N-S trending lower fissures. Account of the general distribution of the deposits, nature of the constituents, mutual stratigraphic correlation and correlation with observed sequence are given.
著者
早川 由紀夫 中島 秀子
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.43, no.4, pp.213-221, 1998-08-31
被引用文献数
4 or 0

The 1108 eruption of Asama is the largest among numerous eruptions of the volcano during the Holocene. The magnitude is twice as large as that of the notorious 1783 eruption, which killed about 1,400 people. It is also the oldest written eruption of Asama. Chuyuki, which was written in Kyoto, 300 km SW of Asama, describes that the eruption started on September 29, 1108, by the Julian calendar, and that fields of rice and other crops were severely damaged. Many fatalities are strongly suspected by the distribution of the Oiwake ignimbrite, but no description is given for human loss in Chuyuki. A thin pumice layer intercalated between the 1108 scoria and the 1783 pumice can be correlated to a record of Pele's hair-fall in Kyoto in 1596. As many as 800 fatalities at the summit in 1598 described in Todaiki cannot be true. Tenmei Shinjo Hen'iki, which describes that a number of villages along the Jabori River were swept away by hot lahars in 1532, is not a contemporary document. It was written in the late 18th century. Fifteen fatalities at the summit in 1721 can be true. After the 1783 eruption, Asama had been relatively quiet for 100 years. During the early and middle 20th century, Asama had been very active with a peak of 398 times vulcanian explosions in 1941. About 30 Iives were lost at the summit, in the 20th century, by 12 explosions among the total about 3,000 explosions.