Block and boulder transport in Eastern Samar (Philippines) during Supertyphoon Haiyan
- 1Institute of Geography, Universität zu Köln, Albertus-Magnus-Platz, 50923 Cologne, Germany
- 2Project NOAH (Nationwide Operational Assessment of Hazards), Department of Science and Technology, Quezon City, Philippines
- 3National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon City 1101, Philippines
- 4Marine Science Institute, University of the Philippines, Velasquez St., Diliman, Quezon City 1101, Philippines
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.