Orals: Mon, 28 Apr | Room G1
Coastal boulder deposits (CBD) are supratidal accumulations that can include clasts many metres in diameter. Emplaced by extreme waves (whether storms or tsunami) on high-energy rocky coasts, they take many forms, including isolated blocks, small clusters, and well organized coast-parallel ridges of imbricated clasts. CBD occur in many topographic settings, from low-elevation shore platforms to cliffs as tall as 50 m. CBD provide unique sedimentary archives that preserve a record of past high-energy wave events; but they remain poorly understood.
The study of CBD is very young. They were not on the research radar until work on Australian occurrences in the early 1990s (primarily by Jonathan Nott and Edward Bryant) asked whether these unusual deposits with their anomalously large clasts were due to extreme storm waves or tsunami. Their papers kickstarted wider interest, but progress was sluggish until the twin advances of accessible high-resolution satellite imagery and drone-based photogrammetry made it possible to perform longitudinal analyses of these slow-evolving features. The number of studies grew dramatically, from a few per decade in the 1990s to many per year in the past 15 years. But the overall number of studies is still low: about 10-30 new studies annually in recent years, totaling about 230 published papers since 2010. For comparison, there were almost 1500 papers on sandy beaches/coastal dune systems published last year alone.
The most significant breakthrough of the past three decades came from before-and-after studies of changes wrought by coastal storms, which revealed unanticipated power and bore-like uprush behaviour of coastal storm waves, and documented transport of boulders previously thought unmovable except by tsunami. This new knowledge forced a re-examination of the physics and hydrodynamics of wind-driven waves. Numerical modelling and wave tank experiments provided increased understanding of complex non-linear processes that can drive wave amplification in steep near-shore environments, helping explain how storm waves can impart forces necessary for transport of enormous boulders. Given that many CBD were originally interpreted to be of tsunami origin (based on clast size and inferred lack of storm wave power), these insights render many coastal boulder deposits open to re-analysis, particularly in areas prone to both tsunami and strong coastal storms.
But the most fundamental questions remain unanswered. For example, although several attempts have been made to provide an analytic relationship between boulder size and the characteristics of emplacing waves (e.g. wave height, bore velocity), the precision and predictive value of existing equations is limited at best. Therefore, increased experimental and theoretical analysis of near-shore hydrodynamics and breaking wave behaviour is a critical need. Furthermore, it remains impossible to definitively conclude whether coastal boulder deposits have been deposited by storm waves or tsunami in many cases, unless there are historical records or before-and-after observations, and more field exploration and measurement are required.
The bottom line is that after three decades of CBD research, we are still far from answering fundamental questions about these fascinating and enigmatic deposits. Many coastal boulder deposits remain undocumented, and there is much work to be done!
How to cite: Cox, R.: Coastal boulder deposit research three decades on: advances and outstanding questions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4578, https://doi.org/10.5194/egusphere-egu25-4578, 2025.
The Indian Ocean tsunami of 26 December 2004 had a devastating impact on Thailand's Andaman Sea coast, claiming more than 5,000 lives, causing widespread destruction and posing significant environmental challenges.
The event also left extensive tsunami deposits, documented at hundreds of sites by international post-tsunami field surveys conducted in the months and years that followed. In November 2024, two decades after the disaster, we revisited these sites to assess the long-term evolution of the post-tsunami landscape and the preservation of tsunami deposits. Our study covered a range of sites, from rapidly urbanising tourist centres to areas abandoned after the tsunami. The main findings relate to long-term coastal change, preservation of tsunami deposits, finding of younger storm deposits, and recommendations for future research in the area.
Intensive development of tourist infrastructure and housing was observed in areas such as Phuket Island, where wave heights were lowest. In contrast, abandoned areas inundated by higher tsunami waves showed new soil formation and vegetation growth in tsunami-inundated zones. Tsunami evacuation roads, memorials, vertical evacuation structures and information signs have been installed throughout the affected areas.
However, other ongoing hazards have been identified, such as coastal erosion, which continues along significant stretches of coastline, such as between Khao Lak and Nham Kem, with erosion rates exceeding 2 metres per year.
The preservation of tsunami deposits was assessed at several dozen sites. Tsunami deposits thicker than 10 cm and located on contrasting sedimentary substrates within depression-like terrains were relatively well preserved. However, soil development and post-depositional processes have significantly obscured their macroscopic internal structure. At other sites, tsunami deposits were absent or unidentifiable by visual inspection. Laboratory analyses are underway to determine whether sedimentological and geochemical signatures remain detectable where macroscopic evidence is absent. Boulder deposits left by the tsunami have either been relocated or show signs of ongoing karstification. In addition, post-2004 storm deposits have been documented, consisting of up to 1 metre thick layers of laminated sands extending tens of metres inland.
The study highlighted the need for further research into coastal hazards and long-term environmental change along the Andaman Sea coast. Despite progress, significant gaps remain in understanding the region's Holocene coastal evolution, the effects of sediment supply and climate change.
The area's anthropogenic history, including centuries of tin mining and its abrupt interruption - possibly related to palaeo-tsunamis - also warrants further investigation. Emerging concerns about critical resources such as sand and gravel need to be addressed alongside wider environmental and sustainability issues. Future research should therefore take a holistic, multi-hazard approach, integrating tsunami geology with studies of other geohazards such as storms, landslides, coastal erosion and saltwater intrusion. These efforts should also prioritise sustainable coastal development under increasing anthropogenic pressures, using interdisciplinary methodologies.
This research was funded by the Polish National Science Centre grant No. 2020/37/B/ST10/03677 (TSUNASTORM).
How to cite: Szczuciński, W., Yawsangratt, S., Soisa, T., Kererattanasathian, V., and Saengsawang, S.: Twenty years after the Indian Ocean tsunami - Andaman Sea coast of Thailand revisited, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21917, https://doi.org/10.5194/egusphere-egu25-21917, 2025.
Understanding the North Sea Pleistocene succession requires identifying the sequence of glacial events and sea-level fluctuations. The presence of the Last Glacial Maximum is supported by numerous geomorphic evidence in the Shetland archipelago. However, the presence of older ice sheets and the dominance of a locally sourced ‘Shetland ice cap’ or an invasive Fennoscandian Ice Sheet over the islands is still debated. Microtextures of quartz grains originating from the North Sea tsunami deposits retrieved at four offshore sites in Dury Voe (E Shetland) were analysed. The results reveal a complex history of the North Sea Pleistocene succession evidenced in overlapping micro-scale features encountered on the surface of quartz grains – from the primary features indicative of the crystallisation of quartz grains to the last processes affecting the grains. The majority of grains represent well-crystallised euhedral silica crystals. This indicates that the studied quartz grains originated and were delivered by glaciers from a single source area rich in quartzite or quartzite sandstone. The surficial characteristics of the studied grains are dominated by the microtextures formed due to glacial and subaqueous processes, including palaeo-tsunami events. Glacially-originated microtextures include sharp angular features, such as large-sized (> 10 µm) conchoidal fractures with minor microtextures imprinted on their surface, parallel ridges, arc-shaped steps, linear steps and subparallel linear fractures. Mechanically-induced chattermarks were also observed. Subaqueous processes induce the smoothing of the grain surface and rounding of the grain edges and protrusions. Moreover, a microtexture induced by the oscillation movement of water and thus peculiar for coastal processes, i.e. V-shaped percussion cracks, was commonly observed on the grain surface. Tsunami events are evidenced by the presence of single, small-sized (< 5 µm) conchoidal fractures encountered on the most convex parts of the grains.
Based on the freshness and overlapping of glacial and subaqueous microtextures observed on the surface of the studied quartz grains, three glacial events followed by sea-level changes, including at least two tsunami events, were inferred in Dury Voe (E Shetland). A mineralogical homogeneity of the studied quartz grains denies the hypothesis suggesting that the Shetland archipelago was covered by the Fennoscandian ice sheet during the last glacial cycle. The studied quartz grains reveal a multi-cycle history of sediment redeposition with no sediment supply from outside the Shetland area (e.g. quartz grains from the Fennoscandian magmatic rocks) to the system. The prevailing nature of the Shetland Pleistocene glaciation was therefore dominated by the presence of a locally sourced ‘Shetland ice cap’.
The research was supported by The Belgian Science Policy Office (BELSPO); NORSEAT project - Storegga and beyond – North Sea tsunami deposits offshore Shetland Islands and The Polish National Agency for Academic Exchange (NAWA); BPN/BEK/2023/1/00319 project - Micro-scale perspective of tsunami events – traces recorded on quartz grains and coastal risk prediction.
How to cite: Górska, M. E., Woronko, B., Nahar, R., Costa, P., Van Daele, M., Dawson, S., Engel, M., Scheder, J., Heyvaert, V. M. A., and De Batist, M.: From glaciations to tsunami – a complex history of Shetlands recorded on the surface of quartz grains, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19495, https://doi.org/10.5194/egusphere-egu25-19495, 2025.
Understanding the evolution of coastal environments requires integrating evidence from both onshore coastal regions and shallow marine environments. The Shetland Islands offer a unique natural laboratory to investigate episodic impacts on the coastal environment through abundant well-preserved tsunami deposits. While numerous studies have identified tsunami deposits onshore in the Shetland Islands, offshore tsunami deposits remain underexplored. This study aims to reconstruct the stratigraphic history of these offshore environments by utilizing shallow seismic surveys, geomorphological analyses, and sediment core investigations.
Bathymetric data and sub-bottom profiles reveal a complex geomorphology characterized by bedrock exposures and isolated depressions that form sub-basins. Initial sedimentation filled these preexisting basins, and this was then overlain by shallow marine sediments that typically accumulated in mounded depocenters, suggesting a strong influence of bottom currents. Stratigraphic reconstruction across three study areas (Dury Voe, Basta Voe, and Sullom Voe) reveals a consistent pattern: moraine deposits associated with glacial till at the base, overlain by postglacial lacustrine or fluvial deposits near the shoreline, and transitioning into shallow marine deposits indicative of transgressive phases in deeper areas.
Within this sedimentary sequence, anomalous layers were identified in all three voes, marked by high-amplitude reflectors and contrasting characteristics, including coarser grain sizes and erosional boundaries, suggesting deposition by extreme wave events. Preliminary dating of these layers aligns with the Storegga tsunami (~8150 cal yr BP) and a Holocene tsunami event around 1500 cal yr BP.
These findings underscore the influence of local bathymetric conditions, sediment supply, and depositional configurations in shaping the distribution of offshore tsunami deposits in the shallow waters surrounding the Shetland Islands. This study contributes to a deeper understanding of Holocene coastal evolution and the geological record of extreme wave events. For instance, we reconstruct connectivity between onshore and offshore deposits and try to establish a model of how the offshore deposit changes with distance to the coast, and how the environmental factors influence this model.
How to cite: Nahar, R., Van Daele, M., Costa, P., Dawson, S., Engel, M., Scheder, J., Goovaerts, T., Heyvaert, V., and De Batist, M.: Holocene stratigraphy of the shallow offshore zones of the Shetland Islands: Insights into paleotsunami and paleoenvironment reconstructions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11445, https://doi.org/10.5194/egusphere-egu25-11445, 2025.
How to cite: Majewski, J. M., Szczuciński, W., Ismail, N., Jagodziński, R., Afrizal, T., and Asyqari, A.: Exploring Regional Variability in Paleotsunami Deposits: Evidence from Bengkulu and Lampung, Sumatra, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21851, https://doi.org/10.5194/egusphere-egu25-21851, 2025.
Extreme flow conditions occur frequently in the context of flash floods, storm surges and tsunamis; some of these natural hazards are strongly exacerbated by climate change, either through more energetic storms, more intense precipitation or increased sea levels around the global coastlines. Most of these extreme flow conditions manifest through a series of transient flow stages or transitions from transient to steady flows. Typically, the onset of these extreme flow conditions is rapid, characterized by a steep gradient of surface elevation and depth-averaged flow velocity, followed by less rapid rise of flow depth, and eventual plateauing with a steady-state condition of depth and velocity. In some cases, these flow characteristics are a combination of background extreme flow conditions, with overlapping singular bore-type waves riding on top of it. It has remained a challenge to obtain a good understanding as to which of these stages is the most severe with respect to marine or terrestrial ecosystems and infrastructure, such as residential houses, bridges, culverts or road dams. This work will hence address the challenge by utilizing a unique, and large-scale experimental facility, the large wave-current flume (LWCF) of Coastal Research Center in Hannover, Germany, to demonstrate the use of breaking solitary waves climbing up a compound beach (von Häfen et al. 2022), which eventually led to a broken-bore, emblematic of the early stage of extreme flow conditions addressed herein. The study aims at illustrating the hydrodynamics, and flow-structure-interaction, with the compound beach and with single beach front houses, approximated by geometric primitives, ultimately providing accurate benchmark datasets and insights into the flow dynamics, both for further analysis and as a training dataset for numerical modelling. Two large-scale physical model studies were conducted in the LWCF (300 × 5 × 7 m). Solitary waves, generated by a piston-type wave generator, propagate across a water body of 3.4 m water depth, subsequently breaking over a 1:15 slope and impacting a simplified coastal structure on a horizontal platform in a height of 3.6 m. In total, three simplified coastal houses (1 × 1 × 0.7 m) with varying levels of structural elevation are utilized to model the impact of structural elevation on flow dynamics (Krautwald et al. 2022). Few test runs on hydraulics-only conditions were also recorded. Using large-scale particle image velocimetry (PIV), insights into flow phenomena, vortex shedding at pile structures below elevated buildings, and distributed velocities are obtained. The study demonstrates that the recirculation zone for slab-on-grade structures extends up to 2 m (with a building length of 1 m) at a Reynolds number (Re) of up to 107. Furthermore, flow velocities increase for elevated structures compared to slab-on-grade structures up to 100% at a distance of 1 m downstream. Therefore, structural elevation serves as a method to decrease structural loads but should be carefully considered as a disaster mitigation strategy due to reduced flow sheltering effects in the light of requirements from local evacuation strategies, hydrodynamic loads on adjacent/downstream buildings and protection requirements of those buildings.
How to cite: Goseberg, N., Krautwald, C., and Brendel, A.: Extreme Flow Conditions Interacting With Coastal Structures: Large-Scale Physical Model Tests, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6199, https://doi.org/10.5194/egusphere-egu25-6199, 2025.
Onshore lithostratigraphic surveys were used to validate tsunami inundation models in Verde Lago (Algarve, Portugal). To validate numerical modelling, filed data was gathered including: sediment samples collected in eight trenches and three cores retrieved within the Late Holocene stratigraphic sequence. Furthermore, textural analysis and age-estimation of the main lithostratigraphic units was obtained. Five sequential lithostratigraphic units were identified and defined in the different cores and trenches.
A tsunami-related depositional unit was described within the medium-sand dominated sequence. It presented features commonly associated with tsunami sedimentological imprints (e.g. coarser unit, thinning inland; erosional contact). However, dating results indicate the deposit to be originated from a yet-unknown evet at app. 4500 yrs BP. Four tsunami-earthquake sources were simulated (i.e. Gorringe Bank, the Horseshoe Fault, the Marquês de Pombal Fault and a combined scenario that is the result of the combination of Gorringe and Horseshoe Fault). Tsunami generation and propagation and sediment transport modelling were conducted using Delft-3D, a numerical model extensively used to simulate tsunamis and storm events.
For the Gorringe Bank seismic source, a maximum value 2.4 m of water column near the coastline was recorded and a velocity 0.7 m/s, the maximum inundation extension recorded was 32 m. The Horseshoe Fault scenario, presented the greatest inundation extent in Verde Lago with a maximum extent of 845 m, it was also possible to observe that the water column was about 5.5 m, finally, a maximum flood velocity of about 2.8 m/s. For the Marquês de Pombal Fault a maximum water level of 3.75 m, and a flood velocity of 2.2 m/s was recorded, in this scenario, a maximum length of 390 m was recorded. For the Scenario 1, a maximum water level of 2.5 m was recorded, as well as a maximum velocity of 1.3 m/s, a maximum inundation extent of 195 m was recorded. From the results obtained, it was evident that the Horseshoe Fault scenario showed the best correspondence between the morphological changes along the perpendicular coastal stratigraphic profiles in Verde Lago and the hydrodynamic results.
This work is supported by the Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025, UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020) and LA/P/0068/2020 https://doi.org/10.54499/LA/P/0068/2020).
How to cite: Henriques, R., Costa, P., and Dourado, F.: Numerical Modelling of a Tsunami impinging Verde Lago, Algarve, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5832, https://doi.org/10.5194/egusphere-egu25-5832, 2025.
Tidal flats, marshes, and mangroves in deltaic areas are important for biodiversity, carbon storage, and coastal flood protection. Those delta wetlands are threatened to collapse due to drowning in response to sea-level rise and subsidence. To prevent degradation, it is essential to quantify the resilience of tidal wetlands to high impact disturbances such as hurricanes, especially in densely populated river deltas characterized by high rates of sea-level rise and subsidence. Here, we show how resilience indicators rooted in dynamical systems theory can be devised using NDVI remote sensing data as input, which enables to identify relatively vulnerable wetlands in coastal areas worldwide. Specifically, the recovery rate after disturbances allows to quantify how large a disturbance a system can tolerate prior to reaching a critical threshold or tipping point, and shifting to a degraded state. We first test our methodology by hindcasting known tidal marsh collapse triggered by hurricanes. We then continue to map current-day tidal marsh resilience in several data-sparse river deltas. Finally, we interpret the resulting resilience maps using datasets of various physical forcing factors. While in-situ observations remain essential to determine site-specific thresholds for marsh collapse, our method based on globally available remote sensing and coastal oceanography data provides guidance for coastal protection efforts.
How to cite: van de Vijsel, R. C., Jonathans, T., Ashton, A. D., Ganju, N. K., and Hoitink, A. J. F.: Anticipating tidal marsh collapse in river deltas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9641, https://doi.org/10.5194/egusphere-egu25-9641, 2025.
Posters on site: Tue, 29 Apr, 08:30–10:15 | Hall X3
Coastal monitoring is a rapidly evolving field essential for understanding meteorological and marine conditions, which in turn supports the development of effective strategies for managing coastal areas. This necessity is increasingly critical given the challenges posed by climate change, rising sea levels, and extreme weather events. Among the tools available, video surveillance, combined with advanced machine learning and computer vision techniques, has emerged as a powerful method. It offers detailed spatial and temporal data, essential for analyzing tidal phases, wave parameters, and storm dynamics across extensive geographic areas.
In this study, we propose an innovative integration of optical flow techniques with video analysis to accurately quantify wave motion parameters. Optical flow, which evaluates object displacement between video frames, is applied to determine wavelength, wave height, and flow velocity. This approach is particularly suited for storm conditions where traditional methods face logistical and financial constraints. Our method enables high-precision, real-time measurements vital for analyzing coastal processes during extreme events. To ensure reliability, the results are cross-validated with in situ instrument data and verified through environmental reconstructions using point clouds and ground control points. This dual-validation strategy minimizes video distortions and enhances measurement accuracy, aligning optical flow results with physical realities.
The proposed system has been tested in a controlled environment at the Coastal Engineering Laboratory of the University of Palermo. A two-dimensional laboratory flume simulated different coastal conditions, ranging from calm waters to storm-like scenarios, ensuring the robustness and adaptability of the methodology. By leveraging optical flow techniques with video surveillance, this approach promises a transformative impact on coastal monitoring, providing continuous, automated, and cost-effective data collection even in remote or inaccessible locations. It offers a scalable alternative to conventional methods, which often demand expensive installations and extensive manpower. The potential of this method to deliver high-quality real-time data, represent a significant advancement in coastal management and environmental monitoring.
How to cite: Sabato, G., Scardino, G., Kushabaha, A., Ciraolo, G., Scala, P., Manno, G., and Scicchitano, G.: Optical Flow for Wave Characterization in a 2D Water Flume Using Video Analysis: A Cutting-Edge Tool for Coastal Monitoring, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-424, https://doi.org/10.5194/egusphere-egu25-424, 2025.
Coastal boulder deposits (CBD) are geomorphic signatures of past extreme wave events (EWEs) such as storms and tsunamis. CBD can be used to reconstruct EWEs if the link between local wave climatology and boulder transport is understood. This proxy of wave data is important for building records in regions where wave data are sparse and for coastal hazard management. This study is focused on storm-driven coastal boulder transport along the west coast of Ireland.
We monitored coastal boulder motion at four sites on Inishmaan, Ireland over two winters (2022/23 and 2023/24). We manually relocated most study boulders to supra-tidal positions closer to the shoreline where they were more likely to be mobilized during storms. The boulders were instrumented with accelerometers to capture the timing of orientation changes, while pressure sensors were deployed on the supratidal platforms to record onshore wave conditions. Site characterization and distance measurements were conducted using uncrewed aerial vehicles (UAVs) for Structure-from-Motion (SfM) processing to create Digital Terrain Models (DTMs). Additionally, traditional ground surveys—measuring boulder axes and GPS locations—were augmented with iPhone LiDAR to estimate boulder volumes. Other methods included, 3D printing for sensor housing and Apple Airtags for boulder tracking.
Our results indicate that boulder transport occurs almost exclusively during storm events coinciding with high tide. We also found that transport was more likely for boulders on low-roughness platforms compared to those constrained by geomorphic features such as grykes, boulder ridges, or platform steps.
Our findings suggest that some boulders are mobilized annually, with isolated boulders being particularly susceptible to storm-driven transport. These results have implications for interpreting preservation potential in the context of coastal hazard assessments. Ongoing numerical modeling will enhance our understanding of regional wave climatology associated with these transport events.
How to cite: Spero, H., Bourke, M., Berke, M., Cullen, N., Herterich, J., Westerink, J., Tejaswi, A., and Kennedy, A.: Annual Mobility of Coastal Boulder Deposits During Storm Events: Inishmaan, Ireland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2017, https://doi.org/10.5194/egusphere-egu25-2017, 2025.
The Arctic is warming nearly four times faster than the globe. The drastic consequences of climate change are observed in high mountain areas located within the Arctic coast. This is where permafrost degradation and slope destabilization occur, which can be a direct cause of large-scale landslides. Masses of soil, rocks and sediments reaching the coast cause the formation of tsunami waves, which, reaching the other side of the fjord or strait, destroy infrastructure or affect the development of the coastal zone. An example of this is the Vaigat Strait in western Greenland, where tsunami waves have been observed for several decades. In the last dozen years, the intensity of this phenomenon has increased, which was a direct consequence of, among others, the destruction and displacement of the town of Qullissat on Disko Island. The research in the GLAVE project attempted to read the record in sediments located in areas flooded by tsunami waves. For this purpose, the commonly known GPR method was used, but with the use of a modern GPR set consist of the Mala Ground Explorer and 450 MHz shielded antenna, which provides high-resolution radar data. The 2D/3D profiles were supplemented with information from trenches and shallow boreholes made at the intersection of the profile lines. Preliminary results indicate that each tsunami wave reaching the opposite coasts of the Vaigat Strait leaves behind evidence in the form of specific sedimentological structures. The interpretation of the obtained new GPR data supported by information from possible dating can indicate contemporary and historical tsunami episodes. The conducted GPR studies can support landslide monitoring conducted in threatened areas and more accurately predict the threat from the occurrence of sudden tsunami waves to the environment and the local community.
How to cite: Senderak, K., Sobczyk, A., Kasprzak, M., Szczypińska, M., Kostrzewa, O., and Strzelecki, M.: Reflection of landslide tsunami in sediment structures: the new GPR data from coastal zone of the Vaigat Strait, West Greenland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6178, https://doi.org/10.5194/egusphere-egu25-6178, 2025.
The impact of extreme wave events, such as hurricanes and tsunamis, has resulted in the displacement of large coastal boulders along various coastlines worldwide. Several coastal boulders have been studied along the Mediterranean coasts to assess the wave flow capable of causing their dislodgment. In particular, recent extreme wave events, primarily associated with the occurrence of Mediterranean hurricanes, have led to the dislodgment of multiple boulders under different pre-setting transport conditions (subaerial/submerged, joint-bonded, cliff-edge). These movements have been recorded by surveillance cameras located along the coasts, providing direct evidence of boulder displacements under well-defined transport conditions. A detailed understanding of the pre-setting transport conditions and types of movements (sliding, overturning, saltation) is crucial for evaluating the theoretical wave flow needed to initiate boulder transport. In this study, a comparison was performed between theoretical wave flow and computed wave flow, utilizing numerical models of incipient motion formulas along with the recorded data obtained through computer vision techniques. Morpho-topographic surveys were conducted at different times on a rocky coast in southeastern Sicily (Italy), which experienced boulder dislodgments during various impacts of Mediterranean hurricanes. Terrestrial Laser Scanning (TLS) and Structure from Motion (SfM) techniques were used to assess the dimensional parameters of the coastal boulders. Subsequently, numerical models based on incipient motion formulas were applied to determine the theoretical wave flow required to initiate boulder movement. To compute the wave flow impacting during a given storm event, we applied computer vision techniques to analyze video recordings from surveillance cameras that captured the moments of boulder movement. The video recordings were automatically georeferenced using Ground Control Points extracted from TLS and SfM data to obtain a planar view of the wave propagation with adjusted perspective wrapping. Optical Flow was then applied to the georeferenced video recordings in order to compute the wave flow during these movements. The comparison between computed and theoretical flow provided useful insights for sensitivity analysis of friction, drag, and lift coefficients, thereby improving the accuracy of the force assessments in the incipient motion formulas.
How to cite: Scardino, G., Nandasena, N. A. K., and Scicchitano, G.: The computer vision techniques and numerical models for the assessment of wave flow during coastal boulder movements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3076, https://doi.org/10.5194/egusphere-egu25-3076, 2025.
Sedimentary ancient DNA (sedDNA) is emerging as a powerful tool for studying storm and tsunami deposits, offering novel insights into past events and their ecological impacts. By analyzing sedDNA from microbial communities preserved in known tsunami and storm-deposited sediments, researchers can distinguish between these deposits and non-overwash sediments. This method has been successfully applied to sites impacted by the Palu tsunami in 2018, where we distinguish between tsunami and non-tsunami deposits in different geological settings and to the deposits of the 2004 Indian Ocean Tsunami and subsequent storm events, demonstrating significant differences in microbial communities (Yap et al., 2021). Despite challenges related to sample preservation and data interpretation, the integration of sedDNA with traditional methods holds promise for enhancing our understanding of sedimentary processes and ecological shifts associated with catastrophic natural events. Combining sedDNA with traditional sediment analysis can provide a more comprehensive understanding of past environmental events. Furthermore, sedDNA has shown potential longevity in tsunami deposits (Yap et al., 2023), preserving microbial community signatures for up to several millennia.
Yap, W., Switzer, A. D., Gouramanis, C., Marzinelli, E., Wijaya, W., Yan, Y. T., ... & Lauro, F. M. (2021). Environmental DNA signatures distinguish between tsunami and storm deposition in overwash sand. Communications Earth & Environment, 2(1), 129.
Yap, W., Switzer, A. D., Gouramanis, C., Horton, B. P., Marzinelli, E. M., Wijaya, W., ... & Lauro, F. M. (2023). Investigating geological records of tsunamis in Western Thailand with environmental DNA. Marine Geology, 457, 106989.
How to cite: Switzer, A., Yap, W., Lauro, F., and Majewski, J.: Unlocking the Secrets of Past Coastal Catastrophes : Using sedimentary ancient DNA (sedDNA) to investigate Storm and Tsunami Deposits, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7829, https://doi.org/10.5194/egusphere-egu25-7829, 2025.
Coastal boulders have been identified as significant markers for the assessment of extreme wave conditions and forces in past events, thus providing crucial insights into the dynamics of coastal hazards. This study examined a coastal boulder field located near Pounta in the Gulf of Laconia (Southern Peloponnese, Greece). The boulders were studied in terms of their lithology, geometrical shape, distribution by UAV imagery, and axis orientation along the coast. 3D LiDAR measurements in combination with rock density analysis were carried out to calculate their masses. The investigation was achieved through open-access methodologies, encompassing readily accessible LiDAR recording technology, with the objective of substantiating the replicability of such studies. An essential aspect of the study involved the detailed specification of previously published data for the region, providing correct locations and characteristics of the boulders, besides employing high-resolution field data and refined analytical techniques for the estimation of wave heights and velocities.
We mapped and analyzed >250 boulders along a ~600 m-long coastal stretch with the furthest inland boulders being located at ~200 m at 6-7 m asl. Boulders were imbricated and show overturning marks (e.g., rock pools) indicating transport during an extreme wave event. Some boulders are deposited on the bedrock, while further inland located boulders are partly embedded in sand-grade sediments, indicating joint transport and deposition of boulders and sediments. Preliminary results from UAV mapping show grouping of boulders based on differences in size and potentially by different events (e.g., AD 1303 Crete earthquake). The largest imbricated boulders (~3.3 t) have been moved a few meters inland, while smaller boulders (up to several hundred kilograms) were transported further inland.
With reference to the existing literature, we found that the volume analyses carried out overestimated the masses of the coastal boulders, thus calculated wave energies to transport or even move boulders were erroneous. We updated existing mathematical approaches to calculate the properties of the waves transporting the analyzed boulders by adding the properties of the transport medium itself that sets the boulder in motion. An approach to take this into account is implemented here for the calculation, accordingly affecting the studied wave energies of historic high-energy events (i.e., storm surges or tsunami).
The study area is characterized by complex coastal geomorphology by staircase-like raised marine terraces, which is susceptible to effects brought by sea-level rise and is particularly sensitive to hazards triggered by extreme wave events. The absence of protective infrastructure in this area necessitates the crucial role of studies that investigate the potential hazard of extreme wave events in coastal risk assessment.
How to cite: Louis, K. J., Bellanova, P., Justen, S., Kautz, G., Houbertz, S., Arianoutsou, A., Papanikolau, I., and Reicherter, K.: Coastal Hazard Assessment through 3D Mesh Analysis of Coastal Boulder Deposits from Extreme Wave Events in Greece, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19938, https://doi.org/10.5194/egusphere-egu25-19938, 2025.
Extreme meteorological events, such as medicanes, are increasingly recognized as key drivers of geomorphic transformation along rocky coastlines. This study explores the response of coastal boulder deposits in Malta to Medicane Helios, focusing on detachment, displacement, and the role of localized geomorphic vulnerabilities.
Medicane Helios, originating over the North African coast, intensified as it traversed the central Mediterranean, reaching Malta on February 9–10, 2023. Its passage was marked by torrential rainfall, gale-force winds, and intense wave energy that reshaped the coastal landscape. While studies often generalize the effects of such storms, this research emphasizes micro-scale interactions between wave energy and specific geomorphic features, including solution hollows and structural joints.
Field observations and aerial surveys using unmanned aerial vehicles (UAVs) were conducted pre- and post-event, providing data for 3D terrain models. The analysis revealed significant movement of boulders, including rotational displacement and intertidal reconfiguration, previously unreported during other extreme events in the region. The findings highlight not just the physical redistribution of clasts but also newly exposed erosional features, such as abrasion marks and scree accumulations.
By drawing parallels with other medicanes, the study underscores the increasing vulnerability of Mediterranean coastal zones to intensified storm impacts. These results emphasize the necessity of integrating localized geomorphic assessments with broader climate models to develop effective coastal defence strategies. The outcomes have broader implications for understanding the resilience of coastal systems to future climatic stressors.
How to cite: Gauci, R., Causon Deguara, J., and Inkpen, R.: The role and impact of medicanes on coastal boulder dynamics: a preliminary case-study from the Maltese Islands. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19371, https://doi.org/10.5194/egusphere-egu25-19371, 2025.
The northwestern coast of Sal Island, Cape Verde Archipelago, features an almost continuous rocky shoreline, regularly impacted by powerful Atlantic waves exceeding 4 meters in height and 20 seconds in period. The most striking geomorphic feature of this coast is a prominent boulder ridge perched atop the rocky cliff, situated 10 to 15 meters above sea level and extending 80 to 100 meters inland. The ridge contains boulders with diameters exceeding two meters, raising intriguing questions about its origin: Is the boulder ridge a product of modern wave action? Was it formed during the Last Interglacial, when relative sea levels were 4–8 meters higher than today? Or does it record a single, catastrophic tsunami event? To address these questions, we conducted high-resolution topographic mapping using Unmanned Aerial Vehicles (UAVs). This topographic data was used as a base for hydrodynamic modeling with XBeach. The modeled flow velocities were compared against the location and elevation of the boulder ridge, while the highest flow velocities were cross-validated with empirical equations of incipient motion for the largest boulders in the area.
This presentation is a contribution to the WARMCOASTS project, which has received funding from the European Research Council under the European Union's Horizon 2020 research and innovation programme (grant agreement n. 802414)
How to cite: Rovere, A., Ramalho, R. S., Casella, E., Vieira, G., Barile, C., Scardino, G., Nandasena, N. A., and Scicchitano, G.: Boulder ridges in Sal Island, Cape Verde: imprint of tsunamis, modern storms, or Last Interglacial wave deposits?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5613, https://doi.org/10.5194/egusphere-egu25-5613, 2025.
This paper provides a detailed study of coastal boulder deposits (CBD's) that were recently discovered along the southern Istrian coasts at Premantura, and on the nearby islet of Fenoliga. Additional observations have also identified CBD's at the Brijuni archipelago 20 km's to the northwest. The northern Adriatic Sea is a semi-enclosed basin, limiting the number of storm wave capable of the detachment, transport, and deposition of large boulders. However, despite this constraint extensive CBD's are evident.
A multidisciplinary approach was used to investigate the sites including geological and geomorphological surveys, together with the use of an Uncrewed Aerial Vehicle (UAV), digital photogrammetric analysis and swim surveys. Measurements of boulder position, elevation, size, shape and density were carried out recently at the two sites.
We recognized and mapped approximately 950 clasts at Premantura and 592 clasts at Fenoliga. At Brijuni several observations have identified that some blocks periodically appear and disappear following severe storm events. Furthermore, we carried out multitemporal monitoring activities at the Premantura test site, identifying the movement of a dozen of blocks primarily during the extreme low pressure Mediterranean storm Vaia in 2018.
Biogenic marine carbonate encrustations observed on 14 boulders in Premantura suggest the infra- and sublittoral zones as source areas, while for other boulders a subaerial origin is hypothesised. Local topography, together with the stratified limestone bedding planes and dense joint pattern constitute the predisposing factors for boulder size and detachment.
How to cite: Devoto, S., Ceccotto, F., Corradetti, A., Hastewell, L., Mantovani, M., and Furlani, S.: A multidisciplinary approach for the investigation of coastal boulder deposits in southern Istria (north Croatia), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7064, https://doi.org/10.5194/egusphere-egu25-7064, 2025.
The Japanese archipelago has been subjected to the threat of tsunamis throughout the Holocene. The catastrophic 2011 Tohoku-oki tsunami demonstrated that tsunami hazard assessment in Japan was underestimated, i.e. in wave heights and inundation depths. Paleotsunami studies can provide a deeper understanding of historical tsunami events and deliver crucial information about the frequency, magnitude, and characteristics of past tsunamis, enabling better preparedness for future events. This study focuses on the eastern coast of Hokkaido in the Tokachi region, an area with documented historical tsunami impacts (such as from the Tokachi-oki earthquakes in 1843 CE, 1952 CE, and 2003 CE).
We analyzed 1.5 m-long sediment profiles using an integrated approach combining sedimentological and organic geochemical analyses. At least five distinct tsunami deposits were identified in the stratigraphy and preliminarily dated by volcanic ashes of Mount Tarumae volcanic eruptions, e.g., the 1739 CE (Ta-a), the 1667 CE (Ta-b) and the 2500 cal. BP (Ta-c). These deposits are characterized by distinct sand layers that exhibit landward thinning patterns typical of tsunami deposits intercalated with peats. The application of organic geochemical proxies (e.g., n-alkanes, fatty acids, polycyclic aromatic hydrocarbons and hopanes) allows us to trace tsunami inundation beyond the sand deposits, providing a more comprehensive understanding of the depositional characteristics of these paleotsunamis and the contents of organics.
Our findings contribute to a more comprehensive understanding of the maximum inland extent of these paleotsunamis and demonstrate the effectiveness of multi-proxy approaches in identifying and characterizing these events. This research enhances our understanding of tsunami recurrence intervals, sediment transport processes and inundation patterns along the eastern Hokkaido coast, providing valuable input for regional tsunami hazard assessments and coastal management strategies.
How to cite: Decker, J., Bellanova, P., Nishimura, Y., Schwarzbauer, J., and Reicherter, K.: Paleotsunami deposits from coastal sediments in Hokkaido, Japan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19749, https://doi.org/10.5194/egusphere-egu25-19749, 2025.
The application of hydrodynamic models serves as a fundamental benchmark in coastal engineering applications. Specifically, the evaluation of coastal flooding and surface runoff constitutes essential research topics that can inform intervention strategies. Coastal regions, particularly those near river mouths, are severely impacted by flooding during extreme wave events. In addition, these areas have undergone severe erosional processes, resulting in significant land-use loss. This study employed hydrodynamic models to evaluate coastal flooding using Delft3D and XBeach, as well as to assess surface runoff employing HecRas, focusing on the coastal regions surrounding the mouth of the Ofanto River in Apulia, Italy. This coastal area features an alluvial plain with salt marshes extending up to 2 kilometers inland. A Digital Elevation Model (DEM) was generated from LiDAR data provided by the former Italian Ministry of the Environment, with bathymetric data sourced from the Italian National Hydrographic Institute. Meteorological and marine parameters were extracted from observational data collected by tide gauges operated by the Istituto Superiore per la Ricerca e Protezione Ambientale (ISPRA), as well as from reanalysis products from ERA5 and Copernicus. The hydrodynamic models were forced using the meteorological and marine parameters from a storm that occurred in November 2019. Results from the models indicated extensive coastal flooding in the backdune areas, illustrating dune breaching and surface runoff, with water levels exceeding 2 meters in elevation. The application of hydrodynamic models enhances the prediction of flooding surfaces and elucidates the morphodynamic processes, particularly in low-lying coastal regions impacted by strong storm events.
How to cite: Carbone, F., Scardino, G., Scicchitano, G., Iacobellis, V., Damiani, L., Malcangio, D., Sannicandro, R., Fernandez Momblant, T., and Anfuso, G.: Hydrodynamic models for coastal flooding and surface runoff assessments along the coast of Ofanto River (Apulia, Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9992, https://doi.org/10.5194/egusphere-egu25-9992, 2025.
The climate crisis represents a significant threat to the Mediterranean regions, with potential repercussions on the environment, economy (e.g. tourism) and society. Rising global temperatures are responsible not only for the melting of glaciers and resulting rise in sea level, but also for the increasing temperature of the oceans. Future scenarios projected by the Intergovernmental Panel on Climate Change (2021) for the Mediterranean basin indicate a sea level rise of about 0.3 meters by 2050, with a potential doubling by 2100 with respect to 1900. In terms of temperature, an increase of between 2 and 5 degrees Celsius is expected with respect to 1900. These climate changes are capable of generating extreme weather events, including tropical-like cyclones and extratropical cyclones. While an increase in the frequency of these events has not been observed, there has been an increase in their intensity. . The impact of these events on coastlines can lead to coastal erosion, habitat loss, flooding of urban and agricultural areas and salinisation of aquifers, which, in turn, can affect availability of freshwater, safety risks and significant economic losses.
In this study, the potential impact of a Mediterranean hurricane (known as a medicane) was modelled in relation to future sea-level rise scenarios along the east coast of Sicily. In particular, the study considered the potential impact on a selection of pocket beaches that are of significant natural and tourist interest. Such beaches are particularly vulnerable due to their susceptibility to significant alterations in sediment deposition and erosion, especially during events such as medicanes. In the most extreme cases, these beaches can be completely lost. Due to their nature, once lost these beaches do not recover naturally. In order to model the future medicanes' scenarios that are likely to impact the east coast of Sicily, the Medicane Apollo (2021) was consider as a benchmark. The intensity parameters (as mean sea-level pressure and wind speed) of the Medicane Apollo were extracted from reanalysis products of ERA5. Subsequently, the Delft3D software was used to simulate significant wave heights and water levels, taking into account both the forcing conditions that occurred during the Medicane Apollo and the future conditions predicted for 2050 and 2100 by the IPCC (2021). XBeach was used for the modelling of coastal flooding in the proximity of nearshore zones of the pocket beaches. The Sicilian pocket beaches represent an important tourist attraction and it is crucial to preserve them. This work can contribute to the assessment of the vulnerability of the pocket beaches to extreme weather events, providing useful information aimed at developing strategies for their protection.
How to cite: Monforte, P., Sittoni, L., and Imposa, S.: Modelling evaluation of the impact of Medicane Apollo on pocket beaches in the context of climate change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5549, https://doi.org/10.5194/egusphere-egu25-5549, 2025.
Climate change and sea-level rise are crucial global effects in the coming decades. This study aims to estimate the future effects of sea storms on low-lying coastal areas, by using an integrated approach using advanced modeling tools and technologies that include in the analysis the anthropic impacts and coastal subsidence. The approach wants to analyze past storm surges, sea level changes, and shoreline displacements to model future coastal variations due to the increasing frequency and magnitude of extreme events related to climate change.
We focus on the Volturno coastal plain, which is one of the largest and most populated coastal areas along the mid-Tyrrhenian Sea in Italy. The area is mostly exposed to meteo-marine forcings in the sector between 180° and 280° N, therefore major storm surges registered by the nearby National Network’s wave buoy were analyzed for this sector, to evaluate the coastal effect of the main flooding that occurred in the last 35 years. Peak Over Threshold methodology was used for this evaluation by considering events with a minimum significant wave height greater than 1,50 meters and a minimum duration of 12 hours. The selected storms were then divided into 5 categories, based on their power index (Dolan R., Davis R.E., 1992). Numerical simulations of two storms for each category were carried out on a coastal sector with high social, touristic, and naturalistic values, between the Volturno and Regi Lagni rivers. The topographic base used for hydrodynamic modeling has been extracted by analyzing a set of LiDAR surveys collected by the Italian Ministry of the Environment at 2 m of resolution. The elevation data have been converted into the RDN2008/UTM 32-33 coordinate system above sea level elevation (geoid-related height) to create a revised DEM of the coastal zone, validated through multiple GPS surveys carried out in 2024. The DEM of the underwater coastal sector was created by interpolating data from a single beam survey.
The calculation of the shoreline displacement rates shows that during 1954-2003, the coastal sectors of the Volturno River mouth retreated at a velocity >10 m/y. After 2004, thanks to the construction of two submerged breakwaters, this trend inverted with a total accretion of the beach of about 100 meters in 20 years. Nevertheless, the hydrodynamic simulation results allowed the estimation of flooded areas, also considering the three more probable IPCC–AR6 predictive scenarios of sea level rise until 2150. Storms with a return time of 10–25 years reach the dune toe for 80% of the total length. In the sector protected by the breakwater, such events tend to overtop the dune flooding the back dune system area which is part of the WWF natural reserve “Oasi dei Variconi”. According to our procedure, in the future, with a sea-level rise to 1.1 m, not only will such effects increase, but also their return period will be reduced to 5-20 years. Finally, the extreme event that occurred in 1999 will shorten its return period from 50 to 25-30 years.
How to cite: Fasciglione, G., Benassai, G., Di Luccio, D., Florio, A., Mattei, G., Mucerino, L., Trippanera, D., Aucelli, P. P. C., and Anzidei, M.: Erosive effects of sea-storms, human pressure, and sea level rise on Volturno coastal plain (mid-Tyrrhenian area): present to future coastal hazard, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11116, https://doi.org/10.5194/egusphere-egu25-11116, 2025.
