著者

吉野 正敏

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.118, no.6, pp.1221-1236, 2009-12-25

参考文献数

60

被引用文献数

1 2

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&emsp;The global climate is known to have been relatively warm during the period from the 4th to 10th centuries, although there were slightly different fluctuation patterns locally and regionally. The present article addresses these differences, analyzing the results of previous studies. The warm period is known in Europe as the Medieval Warm Period.<br>&emsp;Evidence in Japan is also found from the 4th century to the 11th century. Because historical age divisions differ between Europe and Japan, the peak of the Warm Period from the 7th to the 10th century is classified as part of the ancient period in Japan. Therefore, the Warm Period in Japan has been proposed to be called the Nara-Heian Warm Period, Heian Warm Period or Little Climatic Optimum.<br>&emsp;Based on the water level changes of Lake Shinji in Shimane Prefecture, the present article discusses the warmer climatic conditions in the Heian Period. It also examines old agricultural settlements in the Tohoku District, northern Honshu. People came from Hokkaido or northern Honshu and cultivated rice in the northeastern-most part of Honshu in the 1st century B.C. It is thought that the effect of the warm current branch flowing along the Japan Sea Coast and emerging on the Pacific side through the Tsugaru Straight had an influence on the distribution of rice cultivation at this early stage.<br>&emsp;Finally, the article shows that the northward shift of the power front of the Central Government (Yamato Chotei) during the 7th to the 9th centuries occurred about 70-80 years earlier in Dewa, an ancient state on the Japan Sea side of Tohoku District, than in Mutsu, also an ancient state on the Pacific side. It is interesting to note, however, that the speed of the northward shift was almost the same on both sides, even though there were different political powers, situations and problems on either side. It is suggested that the northward shift was affected by the warming on the broader space scale.

著者

柳町 治

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.92, no.3, pp.152-172, 1983-06-25 (Released:2009-11-12)

参考文献数

50

被引用文献数

11 7

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The glacial landforms, consisting of cirques, troughs, moraines, etc., are widely distributed in the vicinity of Mt. Kisokomagatake (2, 956 m) in the northern part of the Kiso Mountain Range. They are obviously classified into the younger and fresh landforms and the older and dissected ones. The older ones are much more extensive than the younger ones. The author discussed the glacial fluctuations and chronology in the drainage basin of Nakagosho-gawa east of Mt. Kisokomagatake, where glacial landforms are well preserved, in order to clarify the developmental period of these two types of glacial landforms (Fig. 1). Geomorphological data (Figs. 2, 11 and 12), geological data (Figs. 3 and 5), sedimentological data (Figs. 710, and Tab. 1) as well as tephrochronological data (Fig. 4 and Tab. 2) were examined to this purpose.Since about 80, 000 years B. P., three stages of glacial advance were revealed in the drainage basin of Nakagosho-gawa. Consequently, they are included in the Last Glacial Age and are named, from older to younger, Nakagoshodani Stadial I, II and III, respectively. Glacial landform development during each stadial were quite different, as described below (Figs. 2 and 13) : 1. Nakagoshodani Stadial I (80, 000-45, 000 years B.P.) This stadial is characterized by the largest extension of glacier. Glacier, attained 100 m or more in maximal thickness, extended from the Senjojiki- and Gokurakudaira- Cirque to the east of Shirabidaira (1, 790-1, 600 m a.s.l.) over a horizontal distance of 2.5 to 3.0 km. Glacial snout was located approximately at 1, 550 m a.s.l.. This glacial advance resulted in the formation of large trough (HG) below the above-mentioned cirques as well as the deposition of till (S-1 gravel bed) at Shirabidaira. The total thickness of till composed of ablation and lodgement till amounted to 50 to 60 m. Besides, lateral moraines were formed at Shirabidaira.2. Nakagoshodani Stadial II (45, 000-30, 000 years B.P.) Though glacier extended to Shirabidaira again, glaciation was limited in extension and magnitude rather than that of the Nakagoshodani Stadial I. Glacier is inferred to have been a maximum thickness of 50 to 70 m. Only the upper part of the trough was further denudated resulting in the formation of relatively small trough (MG) through this glacial advance. Ablation till (S-2 gravel bed), 20 to 30 m in maximum thick, was deposited and formed lateral moraines at Shirabidaira. End and lateral moraines (a, b) were also formed on the thresholds of both the Senjojiki- and Gokurakudaira- Cirque, preceded and accompanied by the retreat of glacier from Shirabidaira.3. Nakagoshodani Stadial III (30, 000-10, 000 years B.P.) Glaciation was much more limited in extension and magnitude than that of the Nakagoshodani Stadial II. The glaciers descending from both the Gokurakudaira-Cirque and the northern half of the Senjojiki-Cirque excavated in the Nakagoshodani Stadial I and II, attained only a maximum thickness of about 20 m. The glacial snouts were at about 2, 290 m a.s.l.. The upper part of the trough, modified during the Nakagoshodani Stadial II, was further slightly denudated resulting in the formation of small trough (LG) through this glacial advance. The formation of lateral moraine (c) in the Senjojiki-Cirque was prior to that of the end and lateral moraines (d-o) in the trough. In the northwestern part of the SenjojikiCirque (A, B), glacier remained up to the latest stage.Judging from the investigation in the drainage basin of Nakagosho-gawa, it can be regarded that the older and younger glacial landforms obviously classified by the degree of dissection are relevant to the Nakagoshodani Stadial I and to Nakagoshodani Stadial III, respectively. Surface area and equilibrium-line altitude of glaciers, the altitude of glacial snouts, etc., during these two stadials are shown in Tab. 3.

著者

棚井 敏雅

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.100, no.6, pp.951-966, 1991-12-05 (Released:2009-11-12)

参考文献数

64

被引用文献数

9 11

著者

吉田 明夫 青木 元

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.111, no.2, pp.212-221, 2002-04-25 (Released:2009-11-12)

参考文献数

26

被引用文献数

2

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We show that conspicuous seismic quiescence occurred in large areas along the coast of the Japan Sea before the 1891 Nobi, 1964 Niigata, 1983 Central Japan Sea, and 2000 Western Tottori Prefecture Earthquake. If we had noticed the quiescence that had appeared since the late 1980s along the northern coasts of Shimane, Tottori, and Hyogo Prefectures and had remembered the feature that a large earthquake in the coastal region of the Japan Sea is likely to be preceded by a widely extended seismic quiescence along the coast, we could have paid close attention to the focal region of the Western Tottori Prefecture Earthquake. We think the occurrence of seismic quiescence in a large area before a large earthquake implies that the preparatory process proceeds not only in the focal region, but in the circumferential areas as well.

著者

伊倉 久美子 太田 陽子

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.112, no.3, pp.394-405, 2003-06-25 (Released:2009-11-12)

参考文献数

23

被引用文献数

3 3

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Well-defined Holocene marine terraces are present continuously along the west coast of the Asahi Mountains. This area faces the Sea of Japan and is located east of the epicenter of the 1964 Niigata earthquake, which caused an uplift with considerable westward tilting of Awashima Island, located west of the epicenter. In contrast, the study area subsided at the time of the destructive 1964 earthquake, although the presence of Holocene and stage 5e or other marine terraces record the long-term uplift during the late Quaternary of this area (Ota, 1971). This paper describes the nature and the age of Holocene terraces, which had not been studied in detail, and discusses the uplift pattern and its tectonic significance.The Holocene marine terrace here is usually wave-cut platform with few beach deposits. At large river mouths, however, there are relatively wide and flat valley bottom plains, burying drowned valleys, and separated by sand dunes from the present beach. Radiocarbon age from the bottom of terrestrial deposits on marine deposits is 6.4 ka or slightly younger, and indicates that the emergence of Holocene terrace took place ca. 6 ka. The former shoreline height of the Holocene terrace ranges from 8 m to 4 m. Thus, the maximum uplift rate reaches 1.3 m/ka, which is larger than the uplift rate deduced from the Ml (stage 5e) terrace. The Holocene terrace is subdivided into two on the southern part of the Budo Mountains, where the uplift rate of Ml terrace is the maximum. The late Quaternary uplift of this area, deduced from marine terraces, is discordant with coseismic subsidence caused by the 1964 Niigata earthquake. This means that the uplift of this study area is not caused by seismogenetic fault for the 1964 earthquake. We cannot find the specific onshore active fault within or at both sides of the Budo Mountains and the Maya Mountains that was responsible for the coastal uplift. To interpret such a long-term uplift of the coastal area, we need to assume that offshore reverse active fault dipping eastward is repeatedly activated. Establishing the exact location, nature, and length of offshore faults is important to interpret the coastal uplift of this area.

著者

神津 俶祐

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.24, no.11, pp.754-764, 1912-11-15 (Released:2010-10-13)

著者

志保井 利夫

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.62, no.2, pp.84-94, 1953

著者

小河 正基

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.124, no.1, pp.1-30, 2015-02-25 (Released:2015-03-11)

参考文献数

133

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Great advances on observational studies of terrestrial planets including our own Earth since the 1990s suggest that we should fundamentally revise our view on the evolution of planetary interiors. It has been implicitly assumed that the mantle of a terrestrial planet evolves quasi-statically due to heat extraction by mantle convection. Tomographic studies on the Earth's mantle together with geologic studies, however, show that the overturn time of mantle convection is on the order of a billion years, which is comparable to the age of the Earth. So the evolution of the Earth's mantle is a dynamic process and the quasi-static model of mantle evolution is no longer tenable. Images of terrestrial planets recently sent from spacecraft suggest that the evolution of terrestrial planets depends systematically on their size, and that the evolution of the Earth should be understood in the context of this systematic relationship. The finding of super-Earths implies that we must figure a way to infer the evolution of these planets from limited information, such as the planetary mass, radius, and the composition of the atmosphere, on the basis of studies on terrestrial planets in our solar system. Geologic studies on Archean continents older than 2.5 billion years show that the tectonic regime of early Earth is qualitatively different from that of modern Earth, so the magmatism-mantle convection system in the Earth must have experienced a regime-transition at some point in its history. More dynamically oriented models of mantle evolution would be useful for predicting how the Earth's mantle evolved at its earliest stages on the basis of observations of other celestial bodies such as the Moon, where the old surface is still preserved. Further refinement of seismic studies on the Earth's interior combined with studies on the properties of mantle materials under high pressures are crucial to improve our understanding of the history of the Earth's interior.

著者

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.5, pp.819-833, 2011-10-25 (Released:2012-01-17)

参考文献数

20

被引用文献数

4 9

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Geopark is a beneficial tool for regional development that makes use of characteristic natural and cultural resources, such as landform, rocks, animals, and plants, as well as human history, culture, and traditions in an area. Geopark as a system includes promoting regional development based on integrating three fundamental elements of geopark activity, i.e., conservation, education, and geotourism. Itoigawa Geopark was designated a member of the Global Geopark Network with assistance from UNESCO on 22 August 2009. Itoigawa is a small city with a population of about 48,000 located on the coast of the Japan Sea close to mountains. Following its recognition, the citizens of Itoigawa became aware of the international excellence of the nature and culture of the city and developed pride in their hometown. Consequently, work began to construct a new community by promoting the region based on the geopark system. The awareness of the citizens generated the spontaneous ideas and actions needed to construct a comfortable life with good health, education, and economy in the city. Local governments, such as those of cities, towns, and villages, especially in rural areas, have been looking for ways to promote their regions because of Japan's weak economy over the past twenty years. The geopark is expected to be a useful tool for achieving significant regional development in rural areas.

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.26, no.7, pp.565c, 1914

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.23, no.7, pp.510a-510a, 1911

著者

佐藤 暢 熊谷 英憲 根尾 夏紀 中村 謙太郎

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.117, no.1, pp.124-145, 2008-02-25 (Released:2010-02-10)

参考文献数

60

被引用文献数

3 5

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Mid-ocean ridge basalt (hereafter, MORB) is a final product of melt generated from the partial melting of mantle peridotite, following reaction with mantle and/or lower crustral rocks, fractionation at a shallower crust and other processes en route to seafloor. Therefore, it is difficult to estimate melting processes at the upper mantle solely from any investigations of MORB. In contrast to the restricted occurrence of peridotite of mantle origin in particular tectonic settings (e.g., ophiolites, fracture zones, or oceanic core complexes), the ubiquitous presence of MORB provides us with a key to understanding global geochemical variations of the Earth's interior in relation to plate tectonics. In fact, MORB has been considered to show a homogeneous chemical composition. In terms of volcanic rocks from other tectonic settings (e.g., island arc, continental crust, ocean island), this simple concept seems to be true. However, recent investigations reveal that even MORB has significant chemical variations that seem to correspond to location (Pacific, Atlantic, and Indian Oceans). These observations suggest that the mantle beneath each ocean has a distinct chemical composition and an internally heterogeneous composition. In this paper, global geochemical variations of MORB in terms of major and trace element compositions and isotope ratios are examined using a recently compiled database. The compilation suggests that MORB has heterogeneous compositions, which seem to originate from a mixture of depleted mantle and some enriched materials. Coupled with trace element compositions and Pb-isotope ratios, there seems to be at least two geochemical and isotopic domain of the upper most mantle: equatorial Atlantic-Pacific Oceans and southern Atlantic-Indian Ocean. Material (melt and/or solid) derived from plume, subducted slab, subcontinental crust, or fluid added beneath an ancient subduction zone is a candidate to explain the enrichment end-member to produce heterogeneous MORB. Because MORB is heterogeneous, using a tectonic discrimination diagram that implicitly subsumes homogeneous MORB or its mantle sources should be reconsidered. Further investigations, particularly of off-axis MORB, are needed to understand the relationship between heterogeneous compositions of MORB and geophysical parameters (e.g., degree of melting, temperature, spreading rate, crustal thickness, etc). In addition, the role of the MOHO transitional zone should be investigated to interpret the chemical characteristics of MORB.

著者

小坂 丈予 小沢 竹二郎 松尾 禎士 平林 順一 大隅 多加志

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.94, no.6, pp.551-563, 1985-12-25 (Released:2009-11-12)

被引用文献数

5 5

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The temperature of fumarolic gas ranged from 100 to 128 °C. These gas usually contained few HCl and SO2, and contained a small amount of H2S. These facts indicated that acidic gas components were absorbed into the aquifer during the cause of ascent. Hot springs may be classified into three types according to their chemical composition : 1) volcanic thermal water type ; 2) sea water type ; and 3) type of mixture of 1 and 2.δD and δ18O of waters collected from this island are high. The rocks from Iwo-jima are all trachy andesite with the SiO2 content of 54-58 %, and with the Na2O+K2O content of 9-10 %.

著者

零丁

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.11, no.7, pp.512-514, 1899

著者

鹿園 直建 荒川 貴之 中野 孝教

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.123, no.3, pp.323-342, 2014-06-25 (Released:2014-07-03)

参考文献数

26

被引用文献数

2 6

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Water samples (number of samples = 52) were collected from the vicinity of the southern foot of Mt. Fuji, central Japan, and were analyzed for major elements (Si, Al, Fe, Mg, Ca, Na, K, Cl-, HCO3-, NO3-, etc.) and other chemical properties (pH, EC, ORP, etc.). The results show that major element concentrations increase with decreasing elevation, particularly at a low-elevation site. In the Yoshihara area, located at the southwestern foot, anion and cation concentrations vary widely and increase from west to east. In this area, water samples with a high total concentration tend to contain a high NO3- concentration, suggesting NO3- pollution of the groundwater. By contrast, in the southeastern area, NO3- pollution was not recognized. Based on nitrogen isotopic and ionic concentration data, the high NO3- concentration in the southwestern area is considered to be due to inorganic fertilizer (e.g. (NH4)2SO4) used at tea farms. Analytical results show two groundwater flows in a high-elevation area along the Urui River and in the direction from a high-elevation site at the southwestern foot toward Susono City, and that they mix together at a low-elevation site. In the southeastern foot area, two groundwater flows derive from a high-elevation site on Mt. Fuji along the Gotenba mudflow and the Mishima lava flow. The latter groundwater mixes with groundwater derived from Ashitaka and the Hakone mountains.

著者

町田 洋 新井 房夫

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.88, no.5, pp.313-330, 1979

被引用文献数

53 27

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The eruptions of the Daisen Valcano (35&deg;22'N, 133&deg;33'E) were mainly rhyodacitic and of the paroxysmal type, producing several extensive sheets of tephra. The Kurayoshi pumice (DKP, for short), one of the excellent Late Pleistocene markers arising from the Daisen valcano, is rhyodacitic in composition with abundant hornblende and orthopyroxene crystals and relatively small amount of biotite. Its identification can be made from the above mentioned mineral assemblages as well as from the characteristic refractive index of orthopyroxene (&gamma;=1.703-1.708) and of hornblende (n<SUB>2</SUB> = 1.673-1.682) and the specific crystal habit of orthopyroxene. This pumice-fall deposit occurs on marine and fluvial terraces in the San'in and Hokuriku districts facing the Japan sea and extends eastward beyond the Northern Japan Alps to north Kanto plain as a thinner discontinuous layer. Stratigraphic relation with the dated tephra layers in north Kanto indicates that the pumice was probably deposited between about 47, 000 and 45, 000 years ago. That is, this pumiceous deposit is found at the intermediate horizon between Yunokuchi Pumice (UP, slightly younger than 49, 000 YBP) and Hassaki Pumice (HP, 40, 000-44, 000 YBP) in north Kanto, about 500 km far from the Daisen.<BR>Daisen Kurayoshi Pumice wonld be particularly valuable for establshing chronological framwork as a fundmental time-marker in arears where no suitable markers have yet been documented. Moranic deposit of the Murodo glacial advance at Mt. Tateyama, Northern Japan Alps, is mantled by this marker and overlies the Raicho-dai pumice-fall deposit, products of the earliest stage of volcanic activity of Tateyama III, which is correlated with the Omachi EPm deposit approximately 60, 000 years old. Distribution of these two unreworked tephras indicates that major valley glaciers had nearly disappeared by the times of these initial tephra falls. The glacial advance at Mt. Tateyama, the most extensive of the advances during Last Glacial age, therefore, apparently culminated between about 55, 000 and 50, 000 years ago. On the other hand, a filltop terrace repesented by Uwadan terrace along the River Joganji flowing from Mt. Tateyama, is covered by DKP and is nearly younger than the pyroclastic flow deposit of Tateyama III. Accumulation of the river of Uwadan stage is, therefore, simultaneous and probably associated with the Murodo glacial advance.

著者

矢野 桂司

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.121, no.4, pp.586-600, 2012-08-25 (Released:2012-09-03)

参考文献数

24

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This paper presents a brief history of geography in the United Kingdom, how it was institutionalized, referring to external impacts on research and teaching. Although geography has a long history in the United Kingdom as an intellectual activity, extending back to the Age of Exploration in the late 16th century, it has only been institutionalized as an academic discipline in universities since the end of the 19th century. Geography was established as a discipline offering an integrated study of complex reciprocal relationships among human societies and physical components of the Earth. By the early 1960s, quantitative and theoretical revolutions were having considerable impacts not only in the United States but also in the United Kingdom. Since then, geography has become a popular subject in elementary and secondary education, as well as higher education, in the UK. Although spatial science expanded rapidly in the 1960s, and continued to do so in the early 1970s, it never became part of the mainstream of human geography. Some fundamental critiques of the positivist approach led to the emergence of humanistic geography and radical geography. The following decades were turbulent for human geography—exciting but confusing—in part because human geographers were busy exploring new ideas. Then, the GIS revolution occurred in the late 1980s in the USA and the UK, which greatly affected geography. Around the same time, as new aspects of social and cultural geography came to be sufficiently established, differences between spatial science and new social and cultural geography became apparent. By the end of the 20th century, geography was firmly established in UK universities. Geography is taught to a large number of students and attracts many applicants to universities. However, changes in funding regimes and school curricula have influenced education and research. One major change in UK geography in the 1990s can be found in its research orientation. Previously, geography was an integrated area of study, based on physical and human geography, and its focus was on how much a university department could cover in terms of disciplines. However, after a new funding regime, called Research Assessment Exercise (RAE), was introduced, all geography departments came to be graded according to the quality of their research. External assessments of both research through the RAE and teaching through QAA have greatly affected how geography is practiced. Although UK geography remains an apparently successful and vibrant intellectual discipline, it might have suffered from fragmentation. Like all disciplines, geography has become fragmented and diversified in recent decades, because of its greater breadth and depth of knowledge. Based not only on substantive but also on epistemological and methodological differences, it is usually divided into physical and human geography. Moreover, human geography can be distinguished by the two major approaches of spatial analysis and social theory. This is because geography has become a community of sub-communities and individual departments, responding to research and teaching assessments. Despite fragmentation, geography in the United Kingdom continues to develop in the university and school systems, and has a substantive international reputation for the quality of its scholarship.

著者

早川 由紀夫

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.107, no.3, pp.444-457, 1998-06-25 (Released:2009-11-12)

参考文献数

18

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ハワイ島はハワイ諸島最大の島で, 群馬県と埼玉県を合わせたくらいの面積をもつ。活発に噴火を続けるキラウエアのほか, 歴史時代に噴火記録があるマウナロアとフアラライ, 4,205mの山頂まで車で行くことができるマウナケア, 山頂近くまで深い谷に刻み込まれたコハラ, の5火山からなる火山島である (図1) 。ハワイ・ホットスポットの火山活動を観察するのに最適の島だ。オアフ島のホノルルから直行便が, 東海岸のヒロと西海岸のコナへ毎日数便飛んでいる。私たちはキラウエアに近いヒロへ飛ぶことにしよう。アメリカのレンタカーは一週間単位で借りると割安だから, ハワイ島に7泊する旅行計画を立てるとよい。40ドルの乗り捨て料金を負担すれば, ヒロ空港で借りた車をコナ空港に返すこともできる。実際, 私は11人の仲間といっしょに1997年12月24日にヒロ空港に降り立ち, 南回りで移動して, 12月31日早朝コナ空港から帰国の途についた。この火山見学案内は, そのときの体験と, 過去3回の私自身のハワイ島旅行経験 (1983年, 1987年, 1991年) に基づいて執筆したものである。出発当日に旅行代理店の倒産を知らされるという困難を克服して, 9日間の旅行を実り多く, しかも楽しく終えることができたのは, 旅行に参加した群馬大学教育学部学生と卒業生みなさんの力による。なお, 旅行参加者全員の分担執筆による体験記をウェブページ (http://www.edu.gunma-u.ac.jp/~hayakawa/fieldguide/p/US/HI/hawaii 97.html) で公開している。これから現地に行く人に利用していただけたら幸いです。

著者

守田 康太郎

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.73, no.6, pp.377-384, 1964-12-30 (Released:2009-11-12)

著者

西尾 嘉朗 佐野 有司

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.109, no.4, pp.636-645, 2000-08-25 (Released:2010-11-18)

参考文献数

24

被引用文献数

1

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Based on δ 13C values and CO2/ 3He ratios of North Fiji Back-Arc Basin basalt glasses, wediscuss the carbon geochemical cycle in the subduction zone. Among the North Fiji Back-ArcBasin basalt glasses, there is a close correlation among CO2/ 3He ratios, δ 13C value, and143Nd/ 144Nd ratios. The CO2/ 3He ratios and the δ 13C values of North Fiji Basin basalt maybe attributed to binary mixing between the mantle component (low-CO2/ 3He, high-δ 13C, andhigh-143Nd/ 144Nd) and the subducted (recycled) component (high-δO2/ 3He, low-δ13C, and low-143Nd/ 144Nd). From a simple mass balance calculation, it is derived that the subductedend-member (recycled carbon) has 70% carbonate and 30% organic matter in origin.Assuming that complete decomposition of the subducted organic matters has occurred, most (about 90%) carbonates are not decomposed, because the amounts of subducting carbonatesand organic matters throughout the North Fiji subduction zone are estimated in a ratio of20: 1. This suggests that carbonate can be transported into the mantle through the subduction zones.