[M-ZZ52] 地質と文化

[MZZ52-03] 北海道東部太平洋側の特異な地質基盤に起因する植生・気候・文化・産業

*平野 直人¹、山本 順司² (1.東北大学東北アジア研究センター、2.九州大学理学研究院)

The Nemuro Peninsula and Habomai-Shikotan Islands, in the northeasternmost part of Japan, are located in front of the Kuril Trench, where the Pacific plate is sinking into the deep Earth mantle. This process creates magma, which erupts along volcanic chains parallel to the Kuril Trench axis, such as the Kuril Islands, Shiretoko Peninsula and central Hokkaido Island, called “volcanic arcs”. Areas on the side of oceanic trench from the volcanic arc, called “forearcs”, are generally below the sea level in nonvolcanic areas. Nevertheless, on-land situations of the Nemuro Peninsula and Islands are peculiar, making them unique environments in the world. This study defines environments where the forearc is located in front of the Pacific plate through the point of view in geoscience, ecology, and social science of the Nemuro area. Such geological peculiarity have ever created unique inshore fisheries, kelps ecology, and Ainu culture in the region. According to our analysis, the formation of the areas is caused by the peculiar geology of the Nemuro Peninsula and Habomai Islands, where volcanic rocks have erupted on a submarine sedimentary rock layer deposited during the Late Cretaceous (approximately 70 Ma ago). The areas are protected by the hard volcanic rocks against the present costal erosion. Furthermore, the Late Cretaceous volcanic rocks near oceanic trenches occurs the on-land situation in spite of forearc setting of Nemuro, where the geological setting plausibly makes a unique topography and environment. The area shows a characteristic low-land plateau without any mountain ranges surrounded by coastal cliffs of a few to ten meters in height, which has controlled the unique climate, vegetation, industry, and social culture.