Tsunami versus Infragravity Surge: Comparison of the Physical Character of Extreme Runup

Abstract

Recent observations of energetic infragravity (IG) flooding events, such as those in the Philippines during Typhoon Haiyan, suggest that IG surges may approach the coast as breaking bores with periods of minutes: a very tsunami‐like characteristic. Energetic IG waves have been observed in various locations around the world and have led to loss of lives and damages to property. In this study, a comparison of overland flow characteristics between tsunamis and energetic IG wave events is presented. In general, whenever the tsunamis and energetic IG waves have similar runup, tsunamis tend to generate greater flow depths and longer flood durations than IG. However, flow velocities and Froude number are larger for IG primarily due to bore‐bore capture. This study provides a statistical and physical discriminant between tsunami and IG, such that in areas exposed to both, a proper interpretation of overland transport, deposition, and damage is possible.

Systematic Review Shows That Work Done by Storm Waves Can Be Misinterpreted as Tsunami-Related Because Commonly Used Hydrodynamic Equations Are Flawed

“…We now know that such categorical statements are inappropriate. Tsunami flows commonly have Fr < 2, with values well below 1 in many cases (Matsutomi et al, 2006;Nandasena et al, 2013;Tang and Weiss, 2015;Montoya et al, 2017;Chen et al, 2018;Montoya and Lynett, 2018). Likewise, storm waves generate onshore flows that are supercritical: Fr > 1 is not uncommon (e.g., Tsai et al, 2004;Kuiry et al, 2010), and increasing numbers of studies show that wave overwash can have Fr > 2 (Holland et al, 1991;Matias et al, 2014Matias et al, , 2016.…”

Extreme long waves over a varying bathymetry

“…They could also represent infragravity waves (IGWs) or storm surges in terms of wave periods. IGWs and long storm surges are highly energetic and can magnify runup amplifications (Montoya & Lynett 2018). But the wave amplitudes and the bathymetry used in the present paper are not representative of such waves.…”

The origins of marine and non-marine boulder deposits: a brief review

“…They contrast this with the Lower Miocene tsunamite of the Matheson Formation, New Zealand, which covers some 80,000 m × 5800 m. 2) compares the principal characteristics of coarse grained tsunami deposits with those of a large storm such as those from northeast Atlantic storms, and other mechanisms. The combined wave energy associated with storms and many tsunamis can be similar (Montoya and Lynett 2018) so that distinguishing between these two types of deposit depends more on those aspects of their internal structure that reflect the wave period (Table 2). The principal geological features that distinguish such deposits are that tsunami deposits have generally poorer sorting, structures that reflect several inundations and imbrication caused by both run-up and backwash.…”