Factors responsible for the limited inland extent of sand deposits on Leyte Island during 2013 Typhoon Haiyan

Abstract

Previous geological studies suggest that the maximum inland extent of storm‐induced sand deposits is shorter, but their thickness is larger, than those of tsunami‐induced sand deposits. However, factors that determine the maximum extent and thickness of storm deposits are still uncertain. We conducted numerical simulations of storm surge, waves, and sediment transport during Typhoon Haiyan in order to understand the distribution and sedimentary processes responsible for storm deposits. Numerical results showed that wave‐induced currents slightly offshore were strong, but attenuated rapidly in the inland direction after wave breaking. Therefore, sediments were not transported far inland by waves and storm surge. Consequently, the maximum inland extent of storm deposits was remarkably shorter than the inland extent of inundation. We also revealed that vegetation (roughness coefficient) and typhoon intensity greatly affect the calculation of maximum extent and thickness distribution of storm deposits. As the duration of wave impact on a coast is relatively long during a storm (hours, compared to minutes for a tsunami), sediments are repeatedly supplied by multiple waves. Therefore, storm deposits tend to be thicker than tsunami deposits, and multiple layers can form in the internal sedimentary structure of the deposits. We infer that limitation of the sand deposit to within only a short distance inland from the shoreline and multiple layers found in a deposit can be used as appropriate identification proxies for storm deposits.

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

“…Generally, scientists assume that wind wave-driven runup cannot reach those limits (e.g., Cox et al, 2018). Furthermore, geologists characterize deposits based on the hydrodynamic differences between tsunamis and storm, which create distinctive sedimentary patterns (Mamo et al, 2009;Switzer & Jones, 2008;Tuttle et al, 2004;Watanabe et al, 2017Watanabe et al, , 2018. Nevertheless, recent observations of apparent infragravity (IG) dominated flooding during storm and swell events appear very tsunami-like due to the generated extreme runup (Roeber & Bricker, 2015).…”

Redeposition of volcaniclastic sediments by a tsunami 4600 years ago at Kushima City, south‐eastern Kyushu, Japan

“…This is because, in some cases, it is possible that such deposits might also be explained by unusually large‐scale storm surges (e.g. Morton et al ., ; Pilarczyk et al ., ; Soria et al ., ; Watanabe et al ., , ). In this study, it is also difficult to determine whether PL‐b was formed by a past tsunami or storm surge based solely on its distribution and sedimentological characteristics.…”

Paleo-tsunami history along the northern Japan Trench: evidence from Noda Village, northern Sanriku coast, Japan

“…We performed a numerical simulation of wave propagation and run-up using a combination of Delft-3D (Deltares 2011) and SWAN (Booij et al 1999) software. The numerical method followed Bricker et al (2014) and Watanabe et al (2017). When using Delft-3D and SWAN, the hydrodynamic model repeatedly passes the water level and current fields to the wave model, which then calculates the wave field considering currents and storm surges (Bricker et al 2014).…”

“…Numerical methods can be used to distinguish deposits formed by tsunami and other extreme wave events. For instance, the inundation distance of storm waves is known to be generally shorter than that of tsunami waves because of the difference in wavelength (e.g., Morton et al 2007;Watanabe et al 2017). Therefore, in a lowland sedimentary environment, the distance that event deposits can be transported will differ for storms and tsunamis.…”