Peter Squire

Beach ridge systems: archives for Holocene coastal events?

Holocene coastal evolution has been extensively studied by workers from various earth science disciplines, particularly sedimentologists and geomorphologists. Some of these studies have focused on the history of regional sea-level changes in various ocean basins and the mechanisms – such as eustasy, glacio-isostasy, sediment compaction, neotectonics and climatic forces – involved in such changes. Although beach ridges have been used to identify steps in coastal evolution, only in a few cases have beach ridge systems been investigated with respect to event histories (for example, cyclones and tsunamis). Beach ridge systems, however, belong to the most promising geo-archives for the study of climate change and sea-level variations over the Holocene, as well as for deciphering event histories. This paper presents examples of some studies in this field, in relation to a global overview of beach ridge systems and their morphological characteristics.

Coastal hazards from tropical cyclones and extratropical winter storms based on holocene storm chronologies

Aware of past and future climate changes, the question arose whether modern instrumental data adequately reflect the chronology of tropical cyclones and extratropical winter storms for the period of the present eustatic sea level highstand (approx. the past 6,000 years). For pre-instrumental times, geological and sedimentological methods have been applied at geo- and bioarchives such as coastal marshes, lagoons, washover features or beach ridges, showing a frequency of strong cyclones roughly every 100–300 years, which is in contrast to the high number of major cyclones recorded recently. Many of these palaeotempestological records are discontinuous or contain hiatuses and it may be difficult to evaluate whether these sections of the record represent quiet phases without major cyclones or simply erosion or fluctuations in the ability of an archive to record the signature of cyclones. Manifold questions are still unanswered: as the potential number of former cyclones may be stored in landforms and sediments, how can the intensity of these cyclones be identified? Is the crest height of beach ridges a good indicator for storm surge heights, air pressure, and cyclone categories? This paper reviews important achievements in palaeotempestology and discusses open questions of cyclone distribution, frequency and energy (i.e., hazard potential) in the last few decades and reconstructions of these parameters back into Mid-Holocene times.