2021 Volume 130 Issue 2 Pages 261-287
Using miscellaneous local reports on tsunami disasters and related subjects, the location/relocation histories of three settlements situated on the tsunami-prone mid-Sanriku Coast are retraced, and differences in the selective use of geomorphic resources by the settlements are discussed based on the retraced histories and original geomorphological investigations. On the coast, piedmont gentle slopes and small coastal lowlands have been generally used for the locations of fishing and farming settlements. Of course, coastal lowlands provide the settlements with convenient location for both fishing and farming activities, but they are very sensitive to tsunami hazards, while piedmont gentle slopes adjacent to the lowlands are almost free from tsunami. Although the undulating surface forms of piedmont gentle slopes requires artificial transformation for the use as flat housing lots, the transformation works were not so hard even when earthmovers were not available, because they are composed of unconsolidated rubbly deposits or grus, which are the products of morphogenetic processes under changing climatic and sea-level conditions since the mid-Pleistocene in the zone of granitic rocks. Three neighboring coastal hamlets, Oura, Funakoshi, and Tanohama, suffered repeated tsunami hazards in 1896, 1933, 1960, and 2011. Oura continued to be located on near-coast piedmont gentle slopes for more than 150 years with the additional use of adjacent coastal lowlands as paddy fields. Funakoshi moved from the beach to adjacent piedmont gentle slopes after the severe damage caused by the 1896 tsunami with continuing to use lowlands behind the beach as wet paddies. Tanohama, also damaged severely by the same tsunami, rejected the relocation from beach to the land prepared artificially on adjacent piedmont gentle slopes after the tsunami, and used the prepared land not for dwelling but upland farming. After the 1933 tsunami, which damaged Tanohama again, it moved to the already-prepared land, but many houses were built again on the beach and suffered damage from the 1960 tsunami. During the 2011 tsunami, both total number and ratio of damaged houses were highest in Tanohama and were rather low in the other two hamlets. Inhabitation in the lowland was legally prohibited after the 2011 tsunami and new public housing lots were constructed on piedmont gentle slopes around the existing settlements. The three hamlets thus showed differential location/relocation behavior to the same tsunami hazards and differential selection in the use of two-types of landform for dwelling, fishing, and farming. This was the result of a different cognition or evaluation of given geomorphic resources by the respective hamlets under respective living conditions. Cognition is interpreted as being highly influenced by the proportions of fishing and farming in livelihood, as well as changing contents of fishing, in each tsunami-sensitive hamlet. After the 2011 tsunami, all the three hamlets are located on the piedmont gentle slopes under the new regulation. Follow-up observations of newly constructed housing sites with transformation of piedmont gentle slopes are required to further understanding of the use of geomorphic resources under the changing living conditions of the hamlets.