Block and boulder transport in Eastern Samar (Philippines) during Supertyphoon Haiyan

Authors / Editors: May, S. M., Engel, M., Brill, D., Cuadra, C., Santiago, J., Suarez, J. K., Reyes, M., and Brückner, H. Lagmay, Alfredo Mahar


ABSTRACT

Fields of dislodged boulders and blocks record catastrophic coastal flooding during strong storms or tsunamis and play a pivotal role in coastal hazard assessment. Along the rocky carbonate coast of Eastern Samar (Philippines) we documented longshore transport of a block of 180 t and boulders (up to 23.5 t) shifted upslope to elevations of up to 10 m above mean lower low water level during Supertyphoon Haiyan on 8 November 2013. Initiation-of-motion approaches indicate that boulder dislocation occurred with flow velocities of 8.9–9.6 m s−1, which significantly exceeds depth-averaged flow velocities of a local coupled hydrodynamic and wave model (Delft3D) of the typhoon with a maximum < 1.5 m s−1. These results, in combination with recently published phase-resolving wave models, support the hypothesis that infragravity waves induced by the typhoon were responsible for the remarkable flooding pattern in Eastern Samar, which are not resolved in phase-averaged storm surge models. Our findings show that tsunamis and hydrodynamic conditions induced by tropical cyclones may shift boulders of similar size and, therefore, demand a careful re-evaluation of storm-related transport where it, based on the boulder's sheer size, has previously been ascribed to tsunamis.


Published by: Earth Surface Dynamics , 2015 | Page Nos: 543-558
Link: https://www.earth-surf-dynam.net/3/543/2015/
Type of Publication: Journal Article