Observations of extreme wave runup events on the U.S. Pacific Northwest coast

Abstract

Abstract. Extreme, tsunami-like wave runup events in the absence of earthquakes or landslides have been attributed to trapped waves over shallow bathymetry and long waves created by atmospheric disturbances. These runup events are associated with inland excursions of hundreds of meters and periods of minutes. While the theory of radiation stress implies that nearshore energy transfer from the carrier waves to the infragravity waves can also lead to very large runup, there have not been observations of runup events induced by this process with magnitudes and periods comparable to the other two mechanisms. This work presents observations of several runup events in the U.S. Pacific Northwest that are comparable to extreme runup events related to trapped waves and atmospheric disturbances. It also discusses possible generation mechanisms and shows that energy transfer from incident waves to bound infragravity waves is a plausible generation mechanism. In addition, a method to predict and forecast extreme runup events with similar characteristics is presented.