抄録
A strong earthquake hit eastern Japan on March 11th, 2011 and it lasted for 6 minutes. It triggered huge tsunami and the tsunami damaged not only houses and residents but also farmlands. There are several types of interactions between the tsunami and the farmlands. If there was a muddy (sometimes contains sulfidic materials) and/or sandy deposit under the shallow seawater or in the nearshore zone, it was transported inland. Pyrite was found in the sulfur-rich muddy deposits. There are narrowly eroded places along a road and a ridge where tsunami fell down from these micro-high sites. Moreover, the plow layer soil was lost at least partly. Thus, the deposits on the farmlands are the mixtures of the eroded plow layer soil and transported materials from the nearshore zone. The chemical interactions include the exchange reaction between Na+ in seawater and exchangeable cations in the plow layer soil, and precipitation of gypsum (CaSO4 .2H2O) as well as halite (NaCl) when the soils dry. Debris of various materials and halite, at least, must be removed to restore the damaged farmlands.
