Some lessons learned from the “tsunami-like” storm deposits from Typhoon Haiyan (2013) in the Philippines

Palaeotempestological studies provide a critical long-term context for understanding tropical cyclone variability beyond the short instrumental record, allowing past changes in typhoon frequency, magnitude, and coastal impact to be evaluated in relation to climate change. The exceptional sedimentary record produced by Typhoon Haiyan (locally Yolanda) in November 2013, offers a modern analogue that helps link projected intensification of tropical cyclones in warming tropical oceans to how extreme events may be preserved, and potentially misinterpreted, in the geological record. Haiyan, one of the strongest tropical cyclones on record, made landfall in the central Philippines and produced extreme storm surge and wave conditions that left sedimentary deposits closely resembling those of a tsunami. Post-storm field surveys documented extensive sand sheets extending onshore up to and exceeding 1km inland along parts of the Leyte and Samar coastlines that experienced severe inundation. These unusually far-reaching storm deposits occurred in coastal embayments and fringing reef settings where local hydrodynamic processes greatly amplified the surge and waves. In Leyte Gulf, funnel-shaped bathymetry and localised near shore dynamics from offshore winds caused the storm surge to steepen and reach ~5–6 m in height near Tacloban City, behaving much like a tsunami in its rapid flooding. Along exposed Pacific shorelines (e.g., Eastern Samar), incoming wave groups generated powerful infragravity-period oscillations (surf beat) that steepened into bore-like waves, overtopped a broad coral reef, and drove tsunami-like inland flooding. As a result of these processes, Haiyan’s overwash deposits exhibit a hybrid sedimentological signature with characteristics of both storm and tsunami deposits. For instance, boulders, multiple sand layers and coarse marine debris transported inland by successive wave bores were observed, which is atypical for ordinary storm deposits. Such infragravity wave influence and surge over-steepening make the Haiyan deposits a rare and anomalous case. Although they expand the known spectrum of cyclone-induced sedimentation, these deposits should probably considered outliers and should not be treated as representative “type” storm deposits. In fact, even under Haiyan’s extreme conditions, the sand sheets did not generally extend as far inland as those from large tsunami events, which remains a key distinguishing factor. Overall, the Haiyan example highlights how localised hydrodynamics and surf-beat processes can greatly exacerbate coastal flooding in embayments and reef-fringed coasts, and it underscores the need for caution when using Haiyan’s deposits as a model for storm-generated sedimentary records or sediment transport modelling.