日本に広く分布するローム層の特徴とその成因(<特集>堆積物による火山噴火史研究)  [in Japanese] Characteristics of Japanese Loam, and its Eolian Origin(<Special Section>Volcanic History and Eruptive Deposits)  [in Japanese]

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Abstract

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.

Journal

  • BULLETIN OF THE VOLCANOLOGICAL SOCIETY OF JAPAN

    BULLETIN OF THE VOLCANOLOGICAL SOCIETY OF JAPAN 40(3), 177-190, 1995

    The Volcanological Society of Japan

References:  47

Cited by:  24

Codes

  • NII Article ID (NAID)
    110003041611
  • NII NACSIS-CAT ID (NCID)
    AN10512786
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    0453-4360
  • NDL Article ID
    3624097
  • NDL Source Classification
    ZM44(科学技術--地球科学--海洋・陸水・火山)
  • NDL Call No.
    Z15-101
  • Data Source
    CJP  CJPref  NDL  NII-ELS  J-STAGE 
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