河川と混濁流のつくるクレバススプレイ堆積物の違い：数値実験による検討

抄録

Crevasse splay landforms are lobate landforms formed on flood plains when levees fail due to river flooding. Crevasse splays are one of the major fluvial geomorphological elements and have long been studied for their geomorphological characteristics and sedimentary facies because they provide a record of past inundation disasters. Similar to fluvial deposits, crevasse splay deposits are also found in submarine fans. Crevasse splay deposits are generally massive sandy deposits that, depending on their size, can be good reservoirs for hydrocarbons. Hence, understanding their development pattern and three-dimensional morphology are important issues in resource exploration. Observations of fluvial geomorphology suggest that the direction of development of the crevasse splay is extremely diverse. Recently, Kato et al. (in review) revealed through flume experiments that this diversity is a function of the developmental stage of splays. Although the river crevasse splay initially develops downstream, the crevasse channel diverges as sedimentation progresses, and the splay gradually acquires a radial shape. While the study of fluvial crevasse splays has progressed, the shape development process of similar landforms in submarine fans has been little studied. Therefore, this study examined the morphological differences in crevasse splay deposits formed by rivers and turbidity currents. We developed the 2DH models of rivers and turbidity currents and conducted experiments with the breached levee on the channel. As a result, while river-derived splay deposits tend to elongate downstream, those formed by turbidity currents exhibited upstream elongation or radial configurations. This variance can be attributed to the dissimilar forces driving these processes. River flow, characterized by the substantial pressure force of the main channel, generates downstream elongation in resultant splay deposits. Conversely, the weaker pressure force in turbidity currents causes these density flows to follow local topography, forming upstream elongation.The significance of this research extends beyond its core findings, hinting at broader implications for our understanding of depositional environments.