地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
115 巻 , 2 号
選択された号の論文の11件中1~11を表示しています
  • 五反田 克也, 福澤 仁之
    2006 年 115 巻 2 号 p. 125-135
    発行日: 2006/04/25
    公開日: 2009/11/12
    ジャーナル フリー
    In order to construct past biome distributions on Kyushu Island, we compiled fossil pollen data that record vegetation changes during the past 20, 000 years. Age models estimated using 14C dates and/or Tephrochronology allowed the data digitized from published pollen diagrams to be compiled in 1000-year intervals from 20, 000 years ago to the present day.
    We applied a method for identifying biomes from Japanese modern pollen data (Gotanda et al., 2002) to the fossil pollen data set. We obtained 20 biome maps that show the spatial changes in biome distribution through time. During the Last Glacial Maximum, Kyushu Island was covered with cool-mixed forest, and therefore the climate was estimated to be about 7°C cooler than the present. After 17, 000 yr BP cool-mixed forest retreated and warm-mixed forest migrated northward in western Kyushu. In eastern Kyushu, warm-mixed forest had not yet become established, and temperate deciduous forest started grewing. The appearance of warm-mixed forest in eastern Kyushu was delayed until 7, 000 yr BP This late appearance suggests that the refugia of warm-mixed forest during the Last Glacial Maximum not only existed in Yaku Island and southern Kyushu, but also on the Koshiki Islands in western Kyushu. Warm-mixed forest spread over the Kyushu Island, and its maximum coverage occurred at 4, 000 yr BP, which is much later than the interpreted climatic optimum at 6, 000 yr BP. This time lag may reflect the fact that winter temperature at 6, 000 yr BP was too cold for warm-mixed forest to grow and only became warm enough by 4, 000 yr BP.
  • 高屋 康彦, 廣瀬 孝, 青木 久, 松倉 公憲
    2006 年 115 巻 2 号 p. 136-148
    発行日: 2006/04/25
    公開日: 2009/11/12
    ジャーナル フリー
    The results of three laboratory experiments in a batch (closed) system were reexamined to elucidate the influence of some factors related to the dissolution characteristics of limestone;Experiment A : an experiment in which the samples (200 g in weight) crushed to fragments with three kinds of grain size (coarse : a diameter of 45-32 mm; medium : 16-8 mm; and fine : 2-1 mm) were treated with distilled water under various solid/liquid ratios (0.25, 0.5, and 1) over 960 hrs (40 days); Experiment B : an experiment in which clay-size powder sample (1.00 g in weight) or a block sample (3.54×3.54×20 mm3) was treated with distilled water (50.0 mL) over 417 hrs (ca. 17 days); Experiment C : an experiment in which a block sample (5.0×5.0×40.0 mm3) was treated with distilled water (250.0 mL) at various temperatures (5, 50, and 75°C) over 2164 hrs (ca. 90 days). Electric conductivity (EC) of aqueous solution, as an index of solute concentration, was measured.
    Experimental results showed that (1) surface area of crushed samples and temperature influence the dissolution rate less than solid/liquid ratio, (2) the dissolution rates at the initial stage of reaction are influenced by both physical property of rock (porosity) and water temperature, and (3) the rate-determining step at the initial stage is a mass transport process (e.g., diffusion of ions in solution). Therefore, it is necessary for the continuous dissolution of limestone to prompt the transport of dissolved materials. In other words, a condition for it is to send water undersaturated with respect to carbonate minerals into the rock surface by stirring a solution in a batch (closed) system experiment.
  • 早川 由紀夫, 前嶋 美紀, 宮永 忠幸, 長井 隆行, 湯浅 (佐藤) 成夫, 新井 雅之
    2006 年 115 巻 2 号 p. 149-171
    発行日: 2006/04/25
    公開日: 2009/11/12
    ジャーナル フリー
    Asama Volcano repeatedly erupted in 2004. Six major eruptions were identified, each of which discharged more than 10, 000 tons of ash, lapilli, and bombs from the summit crater. Five were single Vulcanian explosions including the first eruption on 1 September. They are common in Asama, as thousands of Vulcanian explosions occurred in the last century. However, the series of eruptions from 14 to 18 September was unusual for Asama. It was an ash eruption. An eruption plume of a few kilometers high intermittently rose above the summit crater for the first two days. It was sustained by the morning of 16 September. From the plume, sand-sized micropumice and free-crystals continuously showered down at Karuizawa, 10 km SE from the source. It was observed for the first time since the notorious 1783 eruption that the juvenile was dominant among fallout. This makes a remarkable contrast to preexistent material by Vulcanian explosions. In the evening, a small amount of ash (1-0.1 g/m2) reached as far as Tokyo, 150 km from source. Incandescent bombs ejected from the summit crater were seen from the slopes until midnight. The maximum range traveled by the bombs in 2004 was 2.2 km. It was measured at the NW flank for the 1 September explosion and also at the W flank for the 23 September explosion. In total, 3.7 × 108 kg of ash, lapilli, and bombs were ejected from the crater in 2004. This is no more than 8 % of new lava, which was emplaced on the crater floor in the middle of September. An Internet forum is a useful tool for risk communication during a volcanic crisis. Thousands of messages were posted on three boards of a forum during the 2004 crisis. They described detonations, ash fallout, and other unrests of Asama. Some of them were posted ahead of not only television news but also official Volcano Information issued by Japan Meteorological Agency. Although Internet forums are very helpful for volcano risk communication, readers must use caution to distinguish the false from the true.
  • 石原 肇
    2006 年 115 巻 2 号 p. 172-192
    発行日: 2006/04/25
    公開日: 2009/11/12
    ジャーナル フリー
    In June 2000, an eruption was first observed on Miyakejima, a volcanic island in the Pacific Ocean administratively belonging to Tokyo Metropolitan Prefecture, and located 180 km south of central Tokyo. The 2000 Miyakejima eruption and resultant events had the following characteristics. Volcanic ashes covered the whole island, and disastrous mudflows occurred at various locations, especially after rain. Since late August on the same year, large quantities of volcanic gases containing hazardous sulfur dioxide have continued to be released. As a result, on September 2, 2000, all of the inhabitants were ordered to evacuate the island. Mudflows have decreased considerably, but the problem of sulfur dioxide has not yet been completely solved.
    This report aims to clarify the process of disaster prevention by the related authorities for the extended evacuation and restoration of Miyakejima. Actions were taken specifically according to changes in the quantities and the concentrations of volcanic gases containing sulfur dioxide. Among these, some safety measures were taken against the volcanic gases, including those that made overnight stays on the island possible. Considering how safety measures have varied over time during the past four or five years, it is possible to establish the following four periods of disaster avoidance.
    1) Period of Physical Avoidance During this period it was impossible to precisely grasp the specific characteristics of the volcanic gases, and the quantity of volcanic gases was too great to be measured. In consequence, the on-site disaster measures headquarters had to be moved offshore, and later to Kouzushima 30 km west of Miyakejima.
    2) Period of Chemical Avoidance-Chemical desulphurization equipment was installed in most of the public and semi-public buildings, which were designated clean houses, to receive residents in an emergency.
    3) Period of Forecasting Avoidance-Index of sulfur dioxide concentration was defined separately according to short-or long-term influence on human health. Focusing attention on this, judgments on safe areas were based on whether the sulfur dioxide concentration had decreased to the benchmark level, and some areas considered to be under a long-term influence were established. In areas under a short-time influence, a few residents were permitted to return (overnight stay permitted) provided at least one room was provided with desulphurization equipment as in the case of minshuku (pensions).
    4) Period of Institutional Avoidance-With the increasing use of observation systems and information transmission systems, and the establishment of a new evacuation act (provision of clean houses, etc), it became possible for returning inhabitants to stay overnight in their houses without desulphurization equipment, with the exception of two control areas where the sulfur dioxide concentration remained high.
  • 千葉 晃
    2006 年 115 巻 2 号 p. 193-207
    発行日: 2006/04/25
    公開日: 2009/11/12
    ジャーナル フリー
    The object of this study was to obtain the geographical distribution of minimum temperatures in northeastern Japan during winter using ten-minute Automated Meteorological Data Acquisition System (AMeDAS) readings. The area under analysis included the Hokkaido and Tohoku districts, as well as north of 37 North Latitude in Niigata Prefecture. Within this area there are 332 observation sites from which data were collected. Data were obtained from AMe-DAS, which records data every ten minutes. The observation period covered the months of January and February from 1998 through 2003. There were a total of 355 days of readings. For each station, seventy-one of the days from this period were extracted for an analysis of lowest temperature, being a 20 percent representation of the data. In this paper, the author defines minimum temperature as not being a record low but rather above a rank of six from data taken between 00 : 10 and 09 : 00 Japan Standard Time.
    The time at which minimum temperatures were most frequently observed was 06 : 50, with a frequency of 4.49%. The time at which minimum temperatures were observed least was 01 : 40, with a frequency of 1.14%. From 07 : 20, the frequency decreases abruptly.
    Using a Correspondence Analysis, the author classified the data into four types according to time and geographical distribution.
    In type I, there is no prominent overall peak of frequency, but the frequency increases slightly after 07 : 30. This type I was distributed along the eastern coast of the Hokkaido and Tohoku districts, as well as within Aomori prefecture. The type most closely identified with sunrise time (06 : 20 07 : 30) was located in the basins of inland areas in Hokkaido, Iwate, and Fukushima prefectures (type II). Pre-sunrise times were defined as 04 : 40 to 06 : 10 (type III). This type was distributed along the eastern coast of Hokkaido and the Pacific Ocean coast. Data from before 04 : 30 are classified as type IV. Type IV has a small peak in temperature variation before 01 : 00. Type I has a small peak after 07 : 30. These two types can be seen along the coast of the Sea of Japan. Types II and III are related to sunrise time. In these areas there is frequent radiative cooling and a good probability of a clear sky throughout the night. Types I and IV have less relation to sunrise time.
  • 近藤 久雄, 遠田 晋次, 奥村 晃史, 高田 圭太
    2006 年 115 巻 2 号 p. 208-220
    発行日: 2006/04/25
    公開日: 2009/11/12
    ジャーナル フリー
    The East Matsumoto Basin faults (EMBF) consist of the northern segment of the Itoigawa-Shizuoka Tectonic Line active fault system (ISTL), central Japan, and extend for ca. 30 km along the eastern margin of the Matsumoto Basin. The faults have been considered to be eastdipping reverse faults, which were re-activated sometime after the tectonic inversion event during the middle Miocene in central Japan. However, we found geomorphic evidence of strikeslip movement on the EMBF, such as systematic left-lateral offsets of abandoned channels and scissoring vertical offsets on the fan surface, which were probably formed during the Nara era. These offsets were measured as left-lateral displacements of 6 to 7 m with a slight vertical component, and were probably formed in association with the most recent faulting event of EMBF. In this case, the style and the amount of slip per event are comparable with those of the neighboring Gofukuji fault, which has one of the highest probabilities of seismic risk calculated among active faults on land in Japan. These refined geomorphic features indicate that the principal slip component on the southern portion of EMBF is not merely dip-slip but left-lateral slip, taking account of the cumulative vertical displacement inferred from uplifted hills since Miocene to Plio-Pleistocene at the eastern side of the fault traces. These facts and presumptions are consistent with the deformation pattern around the ISTL revealed by recent continuous GPS observations. In addition, these new findings allow us to understand that the subsidence in the Matsumoto urban district can be explained as a pull-apart basin related to a 1.5-km-wide left-step between the EMBF and Gofukuji faults. Su8rface geometry, style, and amount of faulting of both faults suggest that this left-step does not seem to be a significant enough segment boundary of the ISTL to arrest rupture propagation. Thus, the portion between the southern EMBF and Gofukuji fault is appropriately a single fault segment.
  • 松本 至巨, 尾方 隆幸, 内川 啓
    2006 年 115 巻 2 号 p. 221-235
    発行日: 2006/04/25
    公開日: 2009/11/12
    ジャーナル フリー
    The Northern Japanese Alps (Chubusangaku National Park) has experienced a dramatic increase in the number of visitors since the boom referred to as “the Japanese hundred mountains”. The Ushiro-Tateyama Range, located in the northernmost area of the Japanese Alps, provides various alpine landscapes such as cirques, asymmetrical ridges, patterned ground, perennial snow patches and alpine plant communities. Data from 6922 trekkers indicate that the distribution of mountain huts and accessibility to trails control their trekking courses, and that the trekkers concentrate in three mountain areas : Shirouma-mountain area, Goryu-mountain area and Kashima-mountain area. These areas are divided by a landform called kiretto, where a col with steep rockwalls lies along a main ridge, operating as a natural obstacle. Such a concentration suggests that human impacts on mountain geoecosystem occur locally, but intensively.
  • 井上 正澄
    2006 年 115 巻 2 号 p. 236-242
    発行日: 2006/04/25
    公開日: 2009/11/12
    ジャーナル フリー
    Anticlinal theory, in combination with reflection seismic surveys, has been a powerful paradigm in petroleum exploration, and its application has dramatically increased oil discoveries and production since the end of World War II. However, the peak oil theory claims that oil production will peak soon (or has already peaked), and will then decline. The ultimate recoverable resources, production capacity, and future price of petroleum are examined, and the possibility of a new exploration paradigm is discussed.
  • 鈴木 毅彦, 丸山 茂徳, 長谷川 均, 西村 昭
    2006 年 115 巻 2 号 p. 243-247
    発行日: 2006/04/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 早川 由紀夫
    2006 年 115 巻 2 号 p. Plate1-Plate2
    発行日: 2006/04/25
    公開日: 2009/11/12
    ジャーナル フリー
  • 早川 由紀夫
    2006 年 115 巻 2 号 p. Plate3-Plate4
    発行日: 2006/04/25
    公開日: 2009/11/12
    ジャーナル フリー
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