An Evaluation of Boulder Deposits along a Granite Coast Affected by the 2004 Indian Ocean Tsunami Using Revised Hydrodynamic Equations: Batu Ferringhi, Penang, Malaysia

Abstract

A field survey of wave-transported granite boulder deposits occurring at Batu Ferringhi on the north coast of the island of Penang, Malaysia, was undertaken to evaluate whether the boulders had more likely been transported by storm waves or by the 2004 Indian Ocean tsunami. Field measurements of boulder dimensions, imbrication, and depositional position in relation to the tidal frame (using a local intertidal biozonation) were collected from seven boulder groups. Revised hydrodynamic equations for wave height and flow velocity for subaerial and submerged boulders were employed, as well as formulas for joint-bounded pretransport settings. Under subaerial pretransport settings, five of the boulder groups could have been transported under local storm wave conditions. A joint-bounded setting would have precluded the transport of three of the boulder groups by the 2004 tsunami event; otherwise all seven groups could have been transported by this tsunami event under subaerial or submerged pretransport settings. This event is known to have fatally affected this coastline, and, although it is very likely that there have been other historic tsunami events within the region, based on evaluation of the boulder deposits presented here, there is no evidence to suggest that any wave event of a magnitude higher than the 2004 tsunami, be it tsunami or storm wave, has been experienced along this coastline.