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Marine conglomerates at high elevation on the flanks of ocean islands are usually interpreted as evidence of mega-tsunamis generated by volcano flank collapses, although their origin is sometimes debated (elevated littorals vs. tsunami). In this review, we introduce case studies of well-documented examples of tsunami conglomerates in Hawaii (Pacific Ocean), the Canary and Cape Verde Islands (Atlantic Ocean), and Mauritius Island (Indian Ocean). Other less-documented marine conglomerates are also presented as tsunami candidates. Then, we build a comprehensive picture of the general characteristics of these conglomerates and the different methods that can be applied to date them. Different perspectives of research are proposed, especially on the use of tsunami conglomerates as proxies for better constraining numerical models of ocean island flank collapses and associated tsunamis. We also discuss the possible links between volcano growth, flank instability, and climate.

Past coastal flooding events may be inferred from geomorphic and sedimentary archives, including particular landforms (e.g., beach ridges, washover fans), deposits (e.g., washover sediments in lagoons) or erosional features (e.g., erosional scarps within strandplains). In Giralia Bay, southern Exmouth Gulf (Western Australia), sandy ridge sequences in supratidal elevations form the landward margin of extensive mudflats. The formation of these ridges is assumed to be mainly driven by tropical cyclones (TCs), although their depositional processes need to be clarified. We investigated the supratidal sandy ridge sequence in Giralia Bay by carrying out process monitoring, geomorphological mapping by means of an unmanned aerial vehicle survey, as well as sedimentological and geochronological investigations and multivariate statistics. Based on the resulting data, this study aims at (i) identifying the most important driving processes to form the sandy ridges; (ii) establishing their chronostratigraphy; and (iii) understanding their significance for recording past TC activity. Trench excavations revealed sandy units that are interbedded with mud layers at the base, similar to the present distal mudflat sediments. On top, mud intercalations recede, and sand layers of varying grain size distribution dominate. In the upper part of the trenches, younger sediment layers onlap older ones documenting the stepwise seaward accretion of the ridges onto the mudflat While our data suggests that tidal processes have only limited effects on ridge activity, sediment transport, erosion and deposition seems to be driven by both TC-induced storm surges and high magnitude precipitation events causing surface discharge. Most accretionary sand units are thus assumed to represent events of morphodynamic activity during TC-induced flooding since the mid-Holocene. Ridge activity is recorded in a roughly decadal resolution and over historical as well as prehistorical/Holocene time scales. While th

Dating the transport/deposition time of supratidal coarse-clast deposits is difficult, limiting their value for inferring frequency-magnitude patterns of high-energy wave events. On Bonaire (Leeward Antilles, Caribbean), these deposits form prominent landforms, and transport by one or several Holocene tsunamis is assumed at least for the largest clasts. Although a large dataset of C-14 and electron spin resonance (ESR) ages is available for major coral rubble ridges and ramparts, it is still debated whether these data reflect the timing of major events, and how these datasets are biased by the reworking of coral fragments. As an attempt to overcome the current challenges for dating the dislocation of singular boulders, three distinct dating methods are implemented and compared: (i) C-14 dating of boring bivalves attached to the boulders; (ii) Th-230/U dating of post-depositional, secondary calcite flowstone and subaerial microbialites at the underside of the boulders; and (iii) surface exposure dating of overturned boulders via Cl-36 concentration measurements in corals. Approaches (ii) and (iii) have never been applied to coastal boulder deposits so far. The three C-14 age estimates are older than 40 ka, i.e. most probably beyond the applicability of the method, which is attributed to post-depositional diagenetic processes, shedding doubt on the usefulness of this method in the local context. The remarkably convergent Th-230/U ages, all pointing to the Late Holocene period (1.0-1.6 ka), are minimum ages for the transport event(s). The microbialite sample yields an age of 1.23 +/- 0.23 ka and both flowstone samples are in stratigraphic order: the older (onset of carbonate precipitation) and younger flowstone layers yield ages of 1.59 +/- 0.03 and 1.23 +/- 0.03 ka, respectively. Four coral samples collected from the topside of overturned boulders yielded similar Cl-36 concentration measurements. However, the computed ages are affected by large uncertainties, mostly d

Marine conglomerates at high elevation on the flanks of ocean islands are usually interpreted as evidence of mega-tsunamis generated by volcano flank collapses, although their origin is sometimes debated (elevated littorals vs. tsunami). In this review, we introduce case studies of well-documented examples of tsunami conglomerates in Hawaii (Pacific Ocean), the Canary and Cape Verde Islands (Atlantic Ocean), and Mauritius Island (Indian Ocean). Other less-documented marine conglomerates are also presented as tsunami candidates. Then, we build a comprehensive picture of the general characteristics of these conglomerates and the different methods that can be applied to date them. Different perspectives of research are proposed, especially on the use of tsunami conglomerates as proxies for better constraining numerical models of ocean island flank collapses and associated tsunamis. We also discuss the possible links between volcano growth, flank instability, and climate.

Past coastal flooding events may be inferred from geomorphic and sedimentary archives, including particular landforms (e.g., beach ridges, washover fans), deposits (e.g., washover sediments in lagoons) or erosional features (e.g., erosional scarps within strandplains). In Giralia Bay, southern Exmouth Gulf (Western Australia), sandy ridge sequences in supratidal elevations form the landward margin of extensive mudflats. The formation of these ridges is assumed to be mainly driven by tropical cyclones (TCs), although their depositional processes need to be clarified. We investigated the supratidal sandy ridge sequence in Giralia Bay by carrying out process monitoring, geomorphological mapping by means of an unmanned aerial vehicle survey, as well as sedimentological and geochronological investigations and multivariate statistics. Based on the resulting data, this study aims at (i) identifying the most important driving processes to form the sandy ridges; (ii) establishing their chronostratigraphy; and (iii) understanding their significance for recording past TC activity. Trench excavations revealed sandy units that are interbedded with mud layers at the base, similar to the present distal mudflat sediments. On top, mud intercalations recede, and sand layers of varying grain size distribution dominate. In the upper part of the trenches, younger sediment layers onlap older ones documenting the stepwise seaward accretion of the ridges onto the mudflat While our data suggests that tidal processes have only limited effects on ridge activity, sediment transport, erosion and deposition seems to be driven by both TC-induced storm surges and high magnitude precipitation events causing surface discharge. Most accretionary sand units are thus assumed to represent events of morphodynamic activity during TC-induced flooding since the mid-Holocene. Ridge activity is recorded in a roughly decadal resolution and over historical as well as prehistorical/Holocene time scales. While th

Dating the transport/deposition time of supratidal coarse-clast deposits is difficult, limiting their value for inferring frequency-magnitude patterns of high-energy wave events. On Bonaire (Leeward Antilles, Caribbean), these deposits form prominent landforms, and transport by one or several Holocene tsunamis is assumed at least for the largest clasts. Although a large dataset of C-14 and electron spin resonance (ESR) ages is available for major coral rubble ridges and ramparts, it is still debated whether these data reflect the timing of major events, and how these datasets are biased by the reworking of coral fragments. As an attempt to overcome the current challenges for dating the dislocation of singular boulders, three distinct dating methods are implemented and compared: (i) C-14 dating of boring bivalves attached to the boulders; (ii) Th-230/U dating of post-depositional, secondary calcite flowstone and subaerial microbialites at the underside of the boulders; and (iii) surface exposure dating of overturned boulders via Cl-36 concentration measurements in corals. Approaches (ii) and (iii) have never been applied to coastal boulder deposits so far. The three C-14 age estimates are older than 40 ka, i.e. most probably beyond the applicability of the method, which is attributed to post-depositional diagenetic processes, shedding doubt on the usefulness of this method in the local context. The remarkably convergent Th-230/U ages, all pointing to the Late Holocene period (1.0-1.6 ka), are minimum ages for the transport event(s). The microbialite sample yields an age of 1.23 +/- 0.23 ka and both flowstone samples are in stratigraphic order: the older (onset of carbonate precipitation) and younger flowstone layers yield ages of 1.59 +/- 0.03 and 1.23 +/- 0.03 ka, respectively. Four coral samples collected from the topside of overturned boulders yielded similar Cl-36 concentration measurements. However, the computed ages are affected by large uncertainties, mostly d

Coasts worldwide experience considerable population pressure and the demand for reliable hazard management, such as of tsunamis, increases. Tsunami hazard assessment requires information on long-term patterns of frequency and magnitude, which are best explained by inverse power-law functions. In areas with a short historical documentation, long-term patterns must therefore be based on geological traces. The Caribbean tsunami hazard is exemplified by >80 events triggered by earthquakes, volcanic activity, or mass wasting within the region or in the far-field during the last 520 years. Most of these tsunamis had regional or local impacts. Based on two numerical hydrodynamic models of tsunamis spawning at the Muertos Thrust Belt (MTB) and the South Caribbean Deformed Belt (SCBD), which are two scenarios only marginally considered so far, we show that pan-Caribbean tsunamis can also be taken into account. We furthermore review almost 60 sites for possible geological evidence of tsunamis in the Caribbean including fine-grained subsurface deposits and subaerial coarse clasts, and re-evaluate their implications for tsunami hazard assessment against state-of-the-art models of onshore sediment deposition by tsunamis and extreme storms. The records span the mid- to late Holocene, with very few exceptions of Pleistocene age. Only a limited number of reliable palaeotsunami records with consistent and robust age control were identified, hampering inter-island or interregional correlation of deposits of the same event. Distinguishing between storm and tsunami transport of solitary boulders is very difficult in most cases, whereas those clasts arranged as ridges or incorporated into polymodal ridge complexes, which line many windward coasts of the Caribbean, can mainly be attributed to long-term formation during strong storms, overprinting potential tsunami signatures. The quantification of tsunami flooding parameters such as flow depth, inundation distance or flow velocities, by

Coasts worldwide experience considerable population pressure and the demand for reliable hazard management, such as of tsunamis, increases. Tsunami hazard assessment requires information on long-term patterns of frequency and magnitude, which are best explained by inverse power-law functions. In areas with a short historical documentation, long-term patterns must therefore be based on geological traces. The Caribbean tsunami hazard is exemplified by >80 events triggered by earthquakes, volcanic activity, or mass wasting within the region or in the far-field during the last 520 years. Most of these tsunamis had regional or local impacts. Based on two numerical hydrodynamic models of tsunamis spawning at the Muertos Thrust Belt (MTB) and the South Caribbean Deformed Belt (SCBD), which are two scenarios only marginally considered so far, we show that pan-Caribbean tsunamis can also be taken into account. We furthermore review almost 60 sites for possible geological evidence of tsunamis in the Caribbean including fine-grained subsurface deposits and subaerial coarse clasts, and re-evaluate their implications for tsunami hazard assessment against state-of-the-art models of onshore sediment deposition by tsunamis and extreme storms. The records span the mid- to late Holocene, with very few exceptions of Pleistocene age. Only a limited number of reliable palaeotsunami records with consistent and robust age control were identified, hampering inter-island or interregional correlation of deposits of the same event. Distinguishing between storm and tsunami transport of solitary boulders is very difficult in most cases, whereas those clasts arranged as ridges or incorporated into polymodal ridge complexes, which line many windward coasts of the Caribbean, can mainly be attributed to long-term formation during strong storms, overprinting potential tsunami signatures. The quantification of tsunami flooding parameters such as flow depth, inundation distance or flow velocities, by

A sediment record of three alluvial sites along the east- and northeast oriented shore of Bonaire (Netherlands Antilles) provides evidence for the recurrence of several extraordinary wave impacts during the Holocene The interpretation of onshore high-energy wave deposits is controversially discussed in recent sedimentary research However It represents a powerful tool to evaluate the hazard of tsunami and severe storms where historical documentation is short and/or fragmentary A facies model was established based on sedimentary and geochemical characteristics as well as the assemblage and state of preservation of shells and shell fragments Radiocarbon data and the comparison of the facies model with both recent local hurricane deposits and global tsunami signature types point to the occurrence of three major wave events around 3300 2000-1700 and shortly before 500 BP Since (i) the stratigraphically correlated sand layers fulfill several sedimentary characteristics commonly associated with tsunamis and (ii) modern strong hurricanes left only little or even no sediment in the study areas they were interpreted as tsunamigenic However surges largely exceeding the energy of those accompanying modern hurricanes in the southern Caribbean cannot entirely be ruled out The results are partially consistent with existing chronologies for Holocene extreme wave events deduced from supralittoral coarse clast deposits on Aruba Bonaire and Curacao as well as overwash sediments from Cayo Sal Venezuela (C) 2010 Elsevier B V All rights reserved

A sediment record of three alluvial sites along the east- and northeast oriented shore of Bonaire (Netherlands Antilles) provides evidence for the recurrence of several extraordinary wave impacts during the Holocene The interpretation of onshore high-energy wave deposits is controversially discussed in recent sedimentary research However It represents a powerful tool to evaluate the hazard of tsunami and severe storms where historical documentation is short and/or fragmentary A facies model was established based on sedimentary and geochemical characteristics as well as the assemblage and state of preservation of shells and shell fragments Radiocarbon data and the comparison of the facies model with both recent local hurricane deposits and global tsunami signature types point to the occurrence of three major wave events around 3300 2000-1700 and shortly before 500 BP Since (i) the stratigraphically correlated sand layers fulfill several sedimentary characteristics commonly associated with tsunamis and (ii) modern strong hurricanes left only little or even no sediment in the study areas they were interpreted as tsunamigenic However surges largely exceeding the energy of those accompanying modern hurricanes in the southern Caribbean cannot entirely be ruled out The results are partially consistent with existing chronologies for Holocene extreme wave events deduced from supralittoral coarse clast deposits on Aruba Bonaire and Curacao as well as overwash sediments from Cayo Sal Venezuela (C) 2010 Elsevier B V All rights reserved