9:15 AM - 9:30 AM
[ACG43-02] Sediment transport and geomorphological change due to tsunami and earthquake: a geological perspective
★Invited Papers
Keywords:Great East Japan Earthquake, numerical modeling, Sanriku Coast, Sendai Bay
This presentation discusses the roles of tsunamis and earthquakes in sediment transport and geomorphological changes in coastal areas, based on a literature review and some numerical simulations.
Tsunamis move large amounts of sediment from coastal zones to land or from land to coastal zones in an extremely short period of time. Our understanding of this phenomenon has been deepened through researches over the last 60 years. Based on previous researches that examined erosion and deposition of sediments due to the 2011 Tohoku-oki tsunami, tsunami-induced sediment transport can be understood macroscopically as material transfer from land to coastal zones and then to open sea. Indeed, on the Sanriku and the southern Sendai Bay Coasts, sediments delivered from beach erosion moved onto land, and the rest moved to coastal zones. On the other hand, transport of sediments from coastal zones to land is greatly affected by differences in geomorphological settings, sediment properties, and wave characteristics; this often inhibits developing a general understanding of the phenomena. A well-known pattern is erosion of beach ridge due to tsunami overwash, and inland transport of sand. In some regions, this type of sandy tsunami deposits account for much of coastal sedimentary sequences, and may have a major contribution to geomorphological development and environmental change of the coast. Tsunami-induced erosional topography on beaches are recovered by subsequent coastal sand drift, but traces can be preserved for a long time in the coastal geomorphology or sedimentary sequences. Exploring and evaluating tsunami-induced erosional topography using geological approaches is a new research theme in paleo-tsunami and earthquake studies.
Earthquakes often cause frequent slope failures in mountainous areas. In such case, growth of beach ridges is enhanced through the rise of riverbed and increase in the amount of sediment supply to coastal zones. Previous studies in New Zealand and Japan have demonstrated that formation ages of older beach ridges coincide with ages of earthquakes known from historical and geological records. The increase in sediment supply to coastal zones and the formation of beach ridges triggered by earthquakes is called the Seismic Driving, and has been discussed as one of the frameworks for paleoseismology. Although no attempt has not yet been made, quantitative evaluation of the Seismic Driving may be possible by coupling existing numerical models. Wide-area, long-term predictions of sediment transport across land and coastal zones are thought to help not only reconstruct the timing and size of past earthquakes but also deepen our understanding of sediment dynamics in coastal zones.
Tsunamis move large amounts of sediment from coastal zones to land or from land to coastal zones in an extremely short period of time. Our understanding of this phenomenon has been deepened through researches over the last 60 years. Based on previous researches that examined erosion and deposition of sediments due to the 2011 Tohoku-oki tsunami, tsunami-induced sediment transport can be understood macroscopically as material transfer from land to coastal zones and then to open sea. Indeed, on the Sanriku and the southern Sendai Bay Coasts, sediments delivered from beach erosion moved onto land, and the rest moved to coastal zones. On the other hand, transport of sediments from coastal zones to land is greatly affected by differences in geomorphological settings, sediment properties, and wave characteristics; this often inhibits developing a general understanding of the phenomena. A well-known pattern is erosion of beach ridge due to tsunami overwash, and inland transport of sand. In some regions, this type of sandy tsunami deposits account for much of coastal sedimentary sequences, and may have a major contribution to geomorphological development and environmental change of the coast. Tsunami-induced erosional topography on beaches are recovered by subsequent coastal sand drift, but traces can be preserved for a long time in the coastal geomorphology or sedimentary sequences. Exploring and evaluating tsunami-induced erosional topography using geological approaches is a new research theme in paleo-tsunami and earthquake studies.
Earthquakes often cause frequent slope failures in mountainous areas. In such case, growth of beach ridges is enhanced through the rise of riverbed and increase in the amount of sediment supply to coastal zones. Previous studies in New Zealand and Japan have demonstrated that formation ages of older beach ridges coincide with ages of earthquakes known from historical and geological records. The increase in sediment supply to coastal zones and the formation of beach ridges triggered by earthquakes is called the Seismic Driving, and has been discussed as one of the frameworks for paleoseismology. Although no attempt has not yet been made, quantitative evaluation of the Seismic Driving may be possible by coupling existing numerical models. Wide-area, long-term predictions of sediment transport across land and coastal zones are thought to help not only reconstruct the timing and size of past earthquakes but also deepen our understanding of sediment dynamics in coastal zones.