The interactions of tsunami and tides

Numerical modelling of palaeotsunamis requires a cross-disciplinary approach incorporating new software

development, sea-level change dynamics, tectonics, fluid dynamics, sedimentology and even archaeology. There

is a huge potential for this field to make a significant contribution to tsunami hazard assessment

by recreating and understanding past events. The interaction of tides with past events is key to interpreting the

sedimentary record they leave behind. Tidal dynamics affect past sea-level reconstructions, as well as the

maximum wave estimates from the sedimentary record. Here, the first reconstruction of the Storegga tsunami that

incorporates the effects of the tidal dynamics at the time is presented. The Storegga tsunami was caused by a

large (~3200 km3) submarine slide that generated waves of up to 40m on the Norwegian coast, 20m in the

Shetlands, before reducing to several meters along the UK coastline. It left behind a number of deposits as

widespread as Greenland and Denmark. The wave is recreated using up-to-date palaeobathymetric

reconstructions and the tsunami event is simulated in conjunction with tidal forcing. The slide is initiated at several

points in the tidal cycle to assess the effect it has on timing and wave run-up at key deposit sites along the UK

coast, as well as the Faroes and Norway. There are non-linear effects that act between the tsunami wave and the

tidal wave that mean the effects of tides cannot be simply added on afterwards. The work shows the need for a

range of disciplines to work together to fully understand past tsunami events, which in turn are crucial to

understanding future risk, even in regions that experience only infrequent events.