GEOMORPHOLOGICAL EFFECTS OF TSUNAMI RUN-UP AND BACKWASH

Geomorphological processes associated with tsunami run-up and backwash are highly complex. To date, most studies have considered the sedimen tology of palaeo-tsunamis while almost no detailed studies have been u ndertaken in areas known to have been affected by tsunamis in recent t imes. Research on contemporary tsunamis show that coastal landscapes m ay be greatly altered not only by direct tsunami run-up orthogonal to the shoreline, but also by episodes of vigorous backwash and by water flow sub-parallel to the coastline. The combined effect of these proce sses produces hitherto unrecognised coastal landforms that are dominat ed by the effects of high-magnitude erosion and deposition. Deposition of large boulders is also associated with severe tsunamis, while in a djacent areas run-up processes often result in the deposition of conti nuous and discontinuous sediment sheets. In many instances the upper l imit of sediment deposition lies well below the upper limit of wave ru n-up which is frequently marked by a well-defined zone of stripped veg etation and soil. The processes described have considerable implicatio ns for models of coastal evolution. It may even be the case that the e volution of particular stretches of coastline are dominated by such hi gh-magnitude low-frequency events.