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[MZZ44-P01] Life and geological background on a karst plateau in Niimi City, Okayama Prefecture
Keywords:lime stone, karst, doline, cave
Large scaled karst plateaus composed of Permian accretionary complex are scattered throughout southwestern Japan. These plateaus are mainly composed of limestone, and are characterized by extensive grassland with numerous karrenfelds and dolines, and large-scale limestone caves underground. The magnificent scenery has become a tourist destination and has been designated as a national park and geopark.
Atetsudai located in northwestern part of Okayama Prefecture, is one of them, but it is mainly used for residential land and farmland and has not been developed into a tourist site. This report shows the location of residential areas, culture and industry in Atetsudai, and describes its geological and topographical background.
Atetsudai is a flat surface at an altitude of 400m to 500m that belongs to the Kibi Plateau in the Chugoku region, and many unique topography such as dolines, karrenfelds, and karst valleys can be seen on the plateau. The geology of Atetsudai is not composed of a single limestone body, but rather repeated layers of limestone and other accretionary complex composed of chert, basalt, sandstone and mudstone. Therefore, large-scale underground caves have not developed and the formation of depressed dolines is rare. Most dolines are solution basins with downstream suction holes and those with particularly large suction hole-type caves are formed as continuations of valleys from other geological regions.
Characteristics of Atetsudai as a place of living is that most of the residential area and farmland are located in limestone areas, while other accretionary complex areas are mainly forests. Some of the villages, although small, have been formed within the doline. Fruit trees such as peaches and grapes are cultivated on the well-drained slopes of the doline, while a stream flows at the bottom of the doline, and small rice paddies are also grown there. Houses have also been built at the bottom of the doline. Also, the water from the stream flows laterally from the suction hole in the wall of the doline.
From the above, it is thought that the geological structure of Atetsudai developed a doline with a horizontal suction hole on the ground surface, which led the people of the Atetsudai area to use the doline and make the limestone area their place of life. In the suction-hole type caves near the village, there are many limestone caves that are worshiped, such as Himesakakanachiana Shrine, which has a limestone cave as its object of worship, and Rashomon, which is said to have been a training ground for Shugendo. It became a place for Since ancient times, Atetsudai, which lacks water, has actively cultivated leaf tobacco, buckwheat, vegetables such as daikon radish using the black soil that covers the plateau, and fruit trees, and in recent years, grapes for wine have been actively cultivated. became. Furthermore, from 2021, guided geotourism will begin to be offered, centering on Rashomon, a natural bridge formed by the cave-in of the ceiling of a suction-hole-shaped limestone cave. Although it was never able to become a major tourist destination, learning that people have lived with this kind of geology has given rise to a sense of pride in the area, which is leading to activities to convey this feeling.
Atetsudai located in northwestern part of Okayama Prefecture, is one of them, but it is mainly used for residential land and farmland and has not been developed into a tourist site. This report shows the location of residential areas, culture and industry in Atetsudai, and describes its geological and topographical background.
Atetsudai is a flat surface at an altitude of 400m to 500m that belongs to the Kibi Plateau in the Chugoku region, and many unique topography such as dolines, karrenfelds, and karst valleys can be seen on the plateau. The geology of Atetsudai is not composed of a single limestone body, but rather repeated layers of limestone and other accretionary complex composed of chert, basalt, sandstone and mudstone. Therefore, large-scale underground caves have not developed and the formation of depressed dolines is rare. Most dolines are solution basins with downstream suction holes and those with particularly large suction hole-type caves are formed as continuations of valleys from other geological regions.
Characteristics of Atetsudai as a place of living is that most of the residential area and farmland are located in limestone areas, while other accretionary complex areas are mainly forests. Some of the villages, although small, have been formed within the doline. Fruit trees such as peaches and grapes are cultivated on the well-drained slopes of the doline, while a stream flows at the bottom of the doline, and small rice paddies are also grown there. Houses have also been built at the bottom of the doline. Also, the water from the stream flows laterally from the suction hole in the wall of the doline.
From the above, it is thought that the geological structure of Atetsudai developed a doline with a horizontal suction hole on the ground surface, which led the people of the Atetsudai area to use the doline and make the limestone area their place of life. In the suction-hole type caves near the village, there are many limestone caves that are worshiped, such as Himesakakanachiana Shrine, which has a limestone cave as its object of worship, and Rashomon, which is said to have been a training ground for Shugendo. It became a place for Since ancient times, Atetsudai, which lacks water, has actively cultivated leaf tobacco, buckwheat, vegetables such as daikon radish using the black soil that covers the plateau, and fruit trees, and in recent years, grapes for wine have been actively cultivated. became. Furthermore, from 2021, guided geotourism will begin to be offered, centering on Rashomon, a natural bridge formed by the cave-in of the ceiling of a suction-hole-shaped limestone cave. Although it was never able to become a major tourist destination, learning that people have lived with this kind of geology has given rise to a sense of pride in the area, which is leading to activities to convey this feeling.