Torque, Rotation, and Turbulence in Tsunami Bores

When a tsunami arrives a coast, it often breaks offshore and forms a bore. In my talk, I first address a fundamental question, how vorticity (fluid rotation) is generated and leads to the formation of a turbulent flow in a bore (defined as a quasi-steady broken water wave of an infinite wave length) propagating into a quiescent water of a uniform depth. Then, the similar question can be asked for some extended conditions, which includes backwash flow caused by the earlier tsunami runup, for example. Based on the fundamental considerations, we present some hypotheses for sediment-transport mechanisms in a tsunami runup zone.