11:00 AM - 1:00 PM
[MIS11-P01] The origin of sands on the Oki-no-hama Beach in Tosashimizu Geopark
Keywords:Tosashimizu Geopark, shell sands, granite
Tosashimizu Geopark is the 44th Japanese National Geopark, which was certified as a Japanese Geopark by the Japan Geopark Committee on September 25, 2021. Its area covers Tosashimizu City and its coastal waters in the southwestern part of Kochi Prefecture. The Tosashimizu Geopark Promotion Council, which is in charge of the management of this Geopark, has set 25 geosites, 5 eco-sites, and 4 cultural sites in order to clarify the geological and topographical heritage to be taken over to successors.
The "Oki-no-Hama" beach, one of the eco-sites, has many local information boards. The investigators for the new Geopark certification recommended to organize them as well as their description contents. In response to this point, we surveyed them again and found that not only the local information boards but also all the existing tourist information (100 Best Roads in Japan, Tourist destination information of Tosashimizu City, etc.) stated that sands of the Oki-no-hama beach originated from Cape Ashizuri. Examining the grounds for this description, we found that the Geological Survey Report (written by Professor Jiro Katto, Kochi University (at that time)) in the "Ashizuri National Park Candidate Site Basic Record" (December 1968) compiled by Kochi Prefecture when selecting a Japanese national park. It turned out that the Report was the starting point. After that, Prof. Katto changed his view as the sands originated from crashed coral and shells rather than granite in "Nature of Tosa" published in 1988 by the Kochi Prefectural National Holiday Prefectur Bureau (at that time). However, since this publication is not an academic one, it is not enough to correct the description of the tourisit information. Although Arita and Sudo (2006) observed the sands components as shells, shale, and sandstone on Chishitu News No620, there has seen a constant description as weathered granite even after the change of centuries.
The Secretariat of the Tosashimizu Geopark Promotion Council, as part of organizing the commentary on the topography and geology in the area, aims to provide an explanation with scientific basis of the origin of sands on the Oki-no-hama Beach, conducted analysis and evaluation in collaboration with the Kochi Core Research Institute, JAMSTEC and regarding institutes. After comparing with sands of other sandy beaches in the Tosashimizu Geopark area, some minerals originating from granite are found in the sand of the Oki-no-hama beach, but the main component is calcium carbonate from crushed coral and shells. By proactively disclosing this result, we will share this knowledge among the parties concerned so that it will be the first step to revise the "established theory" so far, and will encourage them to revise the explanation on information boards.
The "Oki-no-Hama" beach, one of the eco-sites, has many local information boards. The investigators for the new Geopark certification recommended to organize them as well as their description contents. In response to this point, we surveyed them again and found that not only the local information boards but also all the existing tourist information (100 Best Roads in Japan, Tourist destination information of Tosashimizu City, etc.) stated that sands of the Oki-no-hama beach originated from Cape Ashizuri. Examining the grounds for this description, we found that the Geological Survey Report (written by Professor Jiro Katto, Kochi University (at that time)) in the "Ashizuri National Park Candidate Site Basic Record" (December 1968) compiled by Kochi Prefecture when selecting a Japanese national park. It turned out that the Report was the starting point. After that, Prof. Katto changed his view as the sands originated from crashed coral and shells rather than granite in "Nature of Tosa" published in 1988 by the Kochi Prefectural National Holiday Prefectur Bureau (at that time). However, since this publication is not an academic one, it is not enough to correct the description of the tourisit information. Although Arita and Sudo (2006) observed the sands components as shells, shale, and sandstone on Chishitu News No620, there has seen a constant description as weathered granite even after the change of centuries.
The Secretariat of the Tosashimizu Geopark Promotion Council, as part of organizing the commentary on the topography and geology in the area, aims to provide an explanation with scientific basis of the origin of sands on the Oki-no-hama Beach, conducted analysis and evaluation in collaboration with the Kochi Core Research Institute, JAMSTEC and regarding institutes. After comparing with sands of other sandy beaches in the Tosashimizu Geopark area, some minerals originating from granite are found in the sand of the Oki-no-hama beach, but the main component is calcium carbonate from crushed coral and shells. By proactively disclosing this result, we will share this knowledge among the parties concerned so that it will be the first step to revise the "established theory" so far, and will encourage them to revise the explanation on information boards.