Subaqueous, asymmetric sand waves are typically observed in marine channel/canyon systems, tidal
environments, and continental slopes exposed to strong currents, where they are formed by current
shear resulting from a dominant unidirectional flow. However, sand-wave fields may be readily
observed in marine environments where no such current exists; the physical processes driving their
formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs) induced
by tides can produce an effective, unidirectional boundary “current” that forms asymmetric sand waves.
We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that
ISWs formed at the interface between intermediate and surface waters are refracted by topography.
Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave
field is due to refraction of such ISWs. Combining field observations and numerical modelling, we
show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing
bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom
topography matches the observed deflection of the sand waves; and predicted migration rates of sand
waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure
of continental margins and it represents a promising link between the geological and oceanographic
communities
