5:15 PM - 7:15 PM
[G01-P04] Learn about the origins of the valleys and ridges of the Tama Hills on a geo-walk in Ikutaryokuchi Park, Kawasaki City
Keywords: Tama Hills, valleys and ridges, Kawasaki city, Ikutaryokuchi Park, Kanagawa Prefecture, Geowalk
The hills located on the west side of the Musashino Plateau (Yamanote) across the Tama River have long been called the Tama Hills. This area is known for the large-scale residential development that took place during the Showa era, a period of rapid economic growth, as a commuter town on the outskirts of Tokyo. The topography of these hills is about 200,000 years older than the Musashino Plateau, and by understanding their origins, we can predict the future topography of the Musashino Plateau (Yamanote), which will be located in the center of Tokyo 200,000 years from now. In this presentation, we propose a geowalk through Ikuta Green Space, located at the eastern end of the Tama Hills, to learn about the origins of the valley and ridge topography.
The topographical surface around Ikutaryokuchi Park can be divided into the Tama II surface and the alluvial surface. The base of the Tama II surface is made up of the Iimura Formation of the Kazusa Group, on top of which the Oshinuma Formation (Tama II surface terrace constituent layer), a shallow marine deposit from 337,000 to 300,000 years ago (MIS 9), was deposited, which is thought to have subsequently emerged and formed a terrace (Kaizuka et al. (eds.), 2000). The terrace constituent layer (Oshinuma Formation) is covered by a series of Kanto Loam Formations, from the Tama II Loam Formation to the Tachikawa Loam Formation. The topographical characteristics of the area covered by the Kanto Loam Formation include the cliffs (”Kokuto”:valley heads) at the beginning of steep valleys caused by collapse, and the existence of “Yato”, a valley topography where the cliffs rise to a steep end at the valley heads. The reason for the steep cliffs at the valley heads is that there is a spring there, and the cliffs are constantly eroded and collapsed. Furthermore, valleys are formed by water flowing down from the head of the valley, and are an erosional landform that can only be created in land with the Kanto Loam layer, which has soft soil and is easily eroded.
The route we propose for the Ikutaryokuchi Park Geowalk is to start from (Stop 0) the East Gate Visitor Center, observe the geosites at Stops 1-14 along the promenade, and then return to (Stop 0) the East Gate Visitor Center. The distance traveled during this process is about 2.5 km, and the total time required, including observation time, is approximately 2.5 hours. (Stop 0) Depart from the East Entrance Visitor Center, (Stop 1) Observe the Iimuro Formation of the Kazusa Group exposed near the entrance to the Masugatayama Promenade, (Stop 2) Observe the Iimuro Formation of the Kazusa Group exposed along the Masugatayama Promenade, (Stop 3) Observe the lithological boundary between the Iimuro Formation and the Oshinuma Formation, (Stop 4) Observe the shallow-water strata indicated by the Oshinuma Formation, (Stop 5) Observe the lithological boundary between the Oshinuma Formation and the Kanto Loam Layer, (Stop 6) Observe the superposition of the Kanto Loam Layer in various stages, (Stop 7) View of the Musashino Plateau from the Masugatayama Observatory, (Stop 8) Observe the Tachikawa Loam Layer covering the ridge near Nanakusa Pass, (Stop 9) Observe the Tama II surface of the ridge near the West Entrance Satellite, (Stop 10) Observe the unconformity relationship between the Oshinuma Formation and the Iimuro Formation, (Stop 11) Observe the Masugatayama boring core display at the Kawasaki Municipal Science Museum, (Stop 12) the accident site of the Kawasaki Loam slope collapse experiment hidden near the back pond, (Stop 13) observe the valley head that remains in the west exit plaza behind the Taro Okamoto Museum of Art, (Stop 14) return via the Japan Open Air Folk House Museum to the east exit visitor center (Stop 0).
References: Kaizuka et al. (eds.), 2000, Topography of Japan 4, Kanto, Izu, and Ogasawara, University of Tokyo Press.
The topographical surface around Ikutaryokuchi Park can be divided into the Tama II surface and the alluvial surface. The base of the Tama II surface is made up of the Iimura Formation of the Kazusa Group, on top of which the Oshinuma Formation (Tama II surface terrace constituent layer), a shallow marine deposit from 337,000 to 300,000 years ago (MIS 9), was deposited, which is thought to have subsequently emerged and formed a terrace (Kaizuka et al. (eds.), 2000). The terrace constituent layer (Oshinuma Formation) is covered by a series of Kanto Loam Formations, from the Tama II Loam Formation to the Tachikawa Loam Formation. The topographical characteristics of the area covered by the Kanto Loam Formation include the cliffs (”Kokuto”:valley heads) at the beginning of steep valleys caused by collapse, and the existence of “Yato”, a valley topography where the cliffs rise to a steep end at the valley heads. The reason for the steep cliffs at the valley heads is that there is a spring there, and the cliffs are constantly eroded and collapsed. Furthermore, valleys are formed by water flowing down from the head of the valley, and are an erosional landform that can only be created in land with the Kanto Loam layer, which has soft soil and is easily eroded.
The route we propose for the Ikutaryokuchi Park Geowalk is to start from (Stop 0) the East Gate Visitor Center, observe the geosites at Stops 1-14 along the promenade, and then return to (Stop 0) the East Gate Visitor Center. The distance traveled during this process is about 2.5 km, and the total time required, including observation time, is approximately 2.5 hours. (Stop 0) Depart from the East Entrance Visitor Center, (Stop 1) Observe the Iimuro Formation of the Kazusa Group exposed near the entrance to the Masugatayama Promenade, (Stop 2) Observe the Iimuro Formation of the Kazusa Group exposed along the Masugatayama Promenade, (Stop 3) Observe the lithological boundary between the Iimuro Formation and the Oshinuma Formation, (Stop 4) Observe the shallow-water strata indicated by the Oshinuma Formation, (Stop 5) Observe the lithological boundary between the Oshinuma Formation and the Kanto Loam Layer, (Stop 6) Observe the superposition of the Kanto Loam Layer in various stages, (Stop 7) View of the Musashino Plateau from the Masugatayama Observatory, (Stop 8) Observe the Tachikawa Loam Layer covering the ridge near Nanakusa Pass, (Stop 9) Observe the Tama II surface of the ridge near the West Entrance Satellite, (Stop 10) Observe the unconformity relationship between the Oshinuma Formation and the Iimuro Formation, (Stop 11) Observe the Masugatayama boring core display at the Kawasaki Municipal Science Museum, (Stop 12) the accident site of the Kawasaki Loam slope collapse experiment hidden near the back pond, (Stop 13) observe the valley head that remains in the west exit plaza behind the Taro Okamoto Museum of Art, (Stop 14) return via the Japan Open Air Folk House Museum to the east exit visitor center (Stop 0).
References: Kaizuka et al. (eds.), 2000, Topography of Japan 4, Kanto, Izu, and Ogasawara, University of Tokyo Press.