Generation of ripple-size internal waves on a fluidized seafloor (The Ephemeral Ripples)

Ripples produced on a fluidized seafloor have been observed in the field as well as in the laboratory. Because of their dynamic properties, they are s ometimes referred to as transitional or ephemeral ripples, as they have bee n observed to go through cycles of forming and disappearing on the time sca le of an individual wave period. The ripples also appear to go through a co mplex evolutionary sequence, occasionally leading to the spectacular evens of sediment bursting from the seafloor. During bursting, loads of fluidized sediment will be ejected upward into the water column - in the form of int ense sand plumes. Reproducing these ripples in the laboratory revealed that these ripples are actually a standing subharmonic internal wave on the wat er-sediment interface, produced by the water wave propagating above through an instability mechansim. In this paper an inviscid theory for the initial excitation of these dynamic ripples on a fluidized seafloor is presented.