Dieter Kelletat

Sedimentologic and geomorphologic tsunami imprints worldwide: a review

Abstract Tsunami events with extreme effects on sedimentary transport or considerable alterations of the coastal configuration are rather rare regarding human history, but considering geological timescales they occur frequently. At least 100 megatsunami in different parts of the world have been recorded in the past 2000 years—but presumably far more have failed to be noticed during historical times and are not mentioned either in written or oral ancient records. Therefore, the topic of paleotsunami requires inevitable sedimentological and geomorphological research. However, field research concerning paleotsunami is astonishingly rare within the scientific approach and only 5% of the existing tsunami literature is related to this subject. Future efforts in paleotsunami research should focus on the geological evidence of these mega-events to clarify their contribution to coastal forming processes. This paper reviews the state-of-the-art knowledge of sedimentologic and geomorphic imprints of tsunami along the worlds coastlines in order to highlight the need for more detailed studies of paleotsunami depositional and geomorphological traces.

Paleo-Tsunami Relics on the Southern and Central Antillean Island Arc

Abstract Three Holocene tsunami events that struck the islands of Aruba, Curaçao, and Bonaire around 450–500 YBP, 1,500 YBP, and 3,500 YBP resulted in extensive deposits of coarse sediments and boulders along the coastal zone. The tsunami waves approached the islands from an easterly direction. We investigated paleo-tsunami imprints on the islands of Grenada, St. Lucia, and Guadeloupe to locate the source area of those three events. However, along the Caribbean coastlines of the islands, no evidence for Holocene tsunami impacts have been found. Instead, tsunami relics of Middle Pleistocene age are incorporated into tephra depositions of these volcanic islands. At least one Holocene tsunami event is preserved in the form of bimodal accumulations and boulder deposits along the east coast of Guadeloupe, indicating that the tsunami hit the island from the open Atlantic ocean. Radiocarbon dating yielded an age of about 2,400–2,700 years YBP for the event.

Wave‐Emplaced Coarse Debris and Megaclasts in Ireland and Scotland: Boulder Transport in a High‐Energy Littoral Environment

Many coastlines of the world, particularly those at higher latitudes and those located in tropical cyclone belts, are regularly battered by strong storm waves. Drowning of low‐lying areas by storm surges and storm floods has been thoroughly recorded; however, storm deposits at rocky shorelines or on cliffs have been underrepresented in the literature. This article presents observations of extraordinary wave deposits along the high–wave energy coastlines of western Ireland and the northern Scottish isles and discusses possible wave event types and time windows of the processes responsible. We used archaeological, geomorphological, and geochronological disciplines to compare our findings with earlier results published for these areas and to contribute to the debate on whether large clasts found well above sea level and/or a considerable distance inland were deposited by storms or by tsunamis.

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.

ESR Dating of Coral Reef Terraces on Curacao (Netherlands Antilles) with Estimates of Younger Pleistocene Sea Level Elevations

Abstract A sequence of at least three Late and Middle Pleistocene coral reef terraces (Lower Terrace, Middle Terrace I and II), which are uplifted up to 45 m a.s.l., is conserved on Curaçao. The less uplifted Lower terrace (elevation 6 to 12 m above sea level) consists of two different coral reef formations: the Hato unit and the underlying Cortalein unit. The discontinuity between these two superimposed units is typically marked by a strong difference in the degree of weathering. Samples of coral in growth position were collected from the Lower Terrace (Hato and Cortalein unit) and the Middle Terrace I. ESR ages indicate a Last Interglacial age of the Hato unit of about 122 ky BP, and a correlation with the Last Interglacial sea level maximum (stage 5e). The ESR age of the underlying Cortalein unit is about 216 ky BP (stage 7). Palaeo sea level calculations imply a correlation with the youngest of three Penultimate coral reef terraces located on the island of Barbados, which was uplifted more strongly than the island of Curaçao. No equivalents of older Penultimate Interglacial coral reefs and of the Interglacial stage 9 were found. Middle Terrace I could be at least as old as stage 11 (approx. 400 ky BP), however, it could also be more than 500 ky old.

Submarine slides on volcanic islands ¿ a source for mega-tsunamis in the Quaternary

Slope instability and mass movements on volcanic islands may generate large magnitude tsunamis. During the Quaternary, tsunamis originating from volcanic islands have significantly impacted the world’s coastlines. However, research has only recently begun to analyse the effects of tsunamis in coastal environments. This paper overviews the distribution, magnitude, recurrence interval, and age of large submarine slides on volcanic islands and their potential for the generation of mega-tsunamis during the Quaternary.

Holocene sea levels along the Andaman Sea coast of Thailand

For the Malay-Thai Peninsula several sea-level curves for the younger Holocene, based on field evidence as well as on hydro-isostatic modelling of a far-field site, have been published. The general assumption is a rapid rise to a mid-Holocene maximum up to +5 m above present sea level, followed by a constant or oscillating regression. However, from the Andaman Sea coast of Thailand, which was affected by the 2004 tsunami, only isolated observations are available regarding Holocene sea levels. Thus, the timing and magnitude of the Holocene highstand as well as the course of the regression remain to be defined. As several palaeotsunamis could be detected in the meantime it is important to know the related sea levels as exactly as possible to judge the energy, inundation width and potential wave height of these events. Therefore, fixed biological indicators from the rocky coasts of the Phang-nga Bay and Phuket, as well as morphological indicators from beach-ridge and swale sequences along the exposed west coast (Ko Phra Thong) were studied, to gain information about the Holocene sea-level development in this region. While oyster and coral data from the Phang-nga Bay and Phuket document a Holocene maximum of +2.6 m at 5700 cal. BP, the ridge crests and swale bases in the northwest of the study area point to maximum heights of +1.5–2.0 m above the present level around 5300 years ago. During the last 3000 years, to when the largest part of the Holocene palaeotsunami deposits from Thailand was dated, relative sea levels (RSL) in both areas did not exceed +1.5 m.

The coastlines of the world with Google Earth: understanding our environment

Introduction: Oceans and Coastlines 1 The Oceans 1.1 Extent, Origin and Topography 1.2 Sediments in the Oceans 1.3 Physics and Chemistry of Ocean Waters 1.4 Life in the Oceans 1.5 Movements in the Ocean: Currents, Waves and Tides 1.6 Changing Sea Levels 2 Coastal Landforms and Landscapes 2.2 Ice Cliffs, Calving Glaciers and Sea Ice 2.3 Structural Dominated Coastlines 2.4 Volcanic Coasts 3 Coastlines Dominated by Ingression of the Sea into older Terrestrial Landforms 3.1 Ingression in Rocky Glacial Landscapes 3.2 Ingression in Sedimentary Glacial Landscapes 3.3 Ingression into Fluvial Landscapes 3.4 Ingression into Karst Landforms 3.5 Ingression into Eolian Landforms 3.6 Permafrost Coastlines with Ingression 4 Destructive Coastline 4.1 Bioerosion 4.2 Tafoni and Tessellated Pavements 4.3 Cliffs and Shore Platforms 5 Sedimentary Coasts 5.1 Introduction - The beach and its features 5.2 Foreshore Features and Tidal Flats 5.3 Spits and Tombolos 5.4 Barriers, Barrier Islands and Lagoons 5.5 Beach Ridge Systems and Cheniers 5.6 Coastal Dunes 5.7 Marine Deltas 6 Coasts Dominated by Organisms 6.1 Marine Plants - Algae and Seagrass 6.2 Marine Plants - Mangroves 6.3 Coral Reefs 6.4 Other organic hardgrounds 7 Coasts as Archives of the Past 7.1 Geologic archives in coastal environments 7.2 Coastal Geoarchaeology 8 Coasts at Risk 8.1 Coastal Natural Hazards - Storms and Tsunamis 8.2 Sea Level Rise - The unavoidable and uncertain future of our coasts 8.3 Man-made Coastlines Epilogue Index 3 Coastlines Dominated by Ingression of the Sea into older Terrestrial Landforms 3.1 Ingression in Rocky Glacial Landscapes 3.2 Ingression in Sedimentary Glacial Landscapes 3.3 Ingression into Fluvial Landscapes 3.4 Ingression into Karst Landforms 3.5 Ingression into Eolian Landforms 3.6 Permafrost Coastlines with Ingression 4 Destructive Coastline 4.1 Bioerosion 4.2 Tafoni and Tessellated Pavements 4.3 Cliffs and Shore Platforms 5 Sedimentary Coasts 5.1 Introduction - The beach and its features 5.2 Foreshore Features and Tidal Flats 5.3 Spits and Tombolos 5.4 Barriers, Barrier Islands and Lagoons 5.5 Beach Ridge Systems and Cheniers 5.6 Coastal Dunes 5.7 Marine Deltas 6 Coasts Dominated by Organisms 6.1 Marine Plants - Algae and Seagrass 6.2 Marine Plants - Mangroves 6.3 Coral Reefs 6.4 Other organic hardgrounds 7 Coasts as Archives of the Past 7.1 Geologic archives in coastal environments 7.2 Coastal Geoarchaeology 8 Coasts at Risk 8.1 Coastal Natural Hazards - Storms and Tsunamis 8.2 Sea Level Rise - The unavoidable and uncertain future of our coasts 8.3 Man-made Coastlines Epilogue Index

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.

Shoreline changes and high-energy wave impacts at the leeward coast of Bonaire (Netherlands Antilles)

Supralittoral coarse-clast deposits along the shores of Bonaire (Netherlands Antilles) as well as increased hurricane frequency during the past decade testify to the major hazard of high-energy wave impacts in the southern Caribbean. Since deducing certain events from the subaerial coarse-clast record involves major uncertainties and historical reports are restricted to the past 500 years, we use a new set of vibracore and push core data (i) to contribute to a more reliable Holocene history of regional extreme-wave events and (ii) to evaluate their impact on shoreline evolution. Multi-proxy palaeoenvironmental analyses (XRF, XRD, grain size distribution, carbonate, LOI, microfossils) were carried out using nearshore sedimentary archives from the sheltered western (leeward) side of Bonaire and its small neighbour Klein Bonaire. In combination with 14C-AMS age estimates the stratigraphy reflects a long-term coastal evolution controlled by relative sea level rise, longshore sediment transport, and short-term morphodynamic impulses by extreme wave action, all three of which may have significantly influenced the development of polyhaline lagoons and the demise of mangrove populations. Extreme wave events may be categorized into major episodic incidents (c. 3.6 ka [?] BP; 3.2–3.0 ka BP; 2.0–1.8 ka BP; post-1.3 ka [?] BP), which may correspond to tsunamis and periodic events recurring on the order of decades to centuries, which we interpret as severe tropical cyclones. Extreme wave events seem to control to a certain extent the formation of coastal ridges on Bonaire and, thus, to cause abrupt shifts in the long-term morphodynamic and ecological boundary conditions of the circumlittoral inland bays.