17:15 〜 18:45
[MIS20-P11] Numerical modeling for the tsunami erosional Landforms: A case study of the 2011 Tohoku-oki Tsunami on Osuka coast, Hachinohe, Japan
キーワード：津波、侵食、土砂移動、砂丘、シミュレーション
Tsunamis cause significant topographic changes. Especially, tsunami deposition is highlighted by geologists during last few decades because tsunami deposits can be a useful tracer of paleotsunamis to know their recurrence intervals and sizes. On the other hand, tsunami erosional features and process have not been well studied. This is because tsunami erosion has been reported at some limited area and it has been believed that tsunami erosion may have less preservation potential than that of tsunami deposits.
In the case of the 2011 Tohoku-oki tsunami, the distribution and characteristics of the deposits have been well clarified (e.g., Goto et al., 2021). Indeed, sediment sources and formation processes of the tsunami deposits have been well revealed. Meanwhile, the erosion landforms have been less examined than depositions. Udo et al. (2012) and Tanaka et al. (2012) examined erosion landforms by using aerial/satellite images and revealed in detail where erosion occurred. However, causes and processes of erosion have not yet been clarified.
Meanwhile, a numerical simulation has been applied to the topographic change caused by the 2011 Tohoku-oki tsunami by using sediment transport model (e.g., Sugawara et al., 2014). However, although numerical simulation has been applied to tsunami erosion to elucidate sources of tsunami deposits, it has not been applied to clarify the erosional process.
This study performed numerical simulation of the tsunami erosion/sedimentation in order to understand the processes to create tsunami erosional landforms. The target area is the Osuka coast in Hachinohe City, Aomori Prefecture, Japan, where Imura et al. (2023) have demonstrated depositional and erosional features in detail.
As a result, we found that the places where erosion landforms were formed in the simulation were consistent with reality. This indicates that numerical simulation can reproduce tsunami erosion well. Our results imply that the places where erosion landforms were formed were controlled only by (micro-)topography. We further revealed that coastal erosion was occurred during supercritical flow condition, which can be characterized by shallow but high-speed flows with a high Froude number (>1). Such flow condition occurred when the seawater brought by the run-up wave returned to the sea by overtopping the dune and continued for more than an hour. We therefore suggest that long-lasting seaward supercritical flow condition was the key to form spectacular erosion landforms at the Osuka coast.
Our results can improve not only countermeasures against future tsunamis but also our understanding about erosional landforms formed by paleotsunamis.
In the case of the 2011 Tohoku-oki tsunami, the distribution and characteristics of the deposits have been well clarified (e.g., Goto et al., 2021). Indeed, sediment sources and formation processes of the tsunami deposits have been well revealed. Meanwhile, the erosion landforms have been less examined than depositions. Udo et al. (2012) and Tanaka et al. (2012) examined erosion landforms by using aerial/satellite images and revealed in detail where erosion occurred. However, causes and processes of erosion have not yet been clarified.
Meanwhile, a numerical simulation has been applied to the topographic change caused by the 2011 Tohoku-oki tsunami by using sediment transport model (e.g., Sugawara et al., 2014). However, although numerical simulation has been applied to tsunami erosion to elucidate sources of tsunami deposits, it has not been applied to clarify the erosional process.
This study performed numerical simulation of the tsunami erosion/sedimentation in order to understand the processes to create tsunami erosional landforms. The target area is the Osuka coast in Hachinohe City, Aomori Prefecture, Japan, where Imura et al. (2023) have demonstrated depositional and erosional features in detail.
As a result, we found that the places where erosion landforms were formed in the simulation were consistent with reality. This indicates that numerical simulation can reproduce tsunami erosion well. Our results imply that the places where erosion landforms were formed were controlled only by (micro-)topography. We further revealed that coastal erosion was occurred during supercritical flow condition, which can be characterized by shallow but high-speed flows with a high Froude number (>1). Such flow condition occurred when the seawater brought by the run-up wave returned to the sea by overtopping the dune and continued for more than an hour. We therefore suggest that long-lasting seaward supercritical flow condition was the key to form spectacular erosion landforms at the Osuka coast.
Our results can improve not only countermeasures against future tsunamis but also our understanding about erosional landforms formed by paleotsunamis.