Washover deposits formed by overwash are important deposits for evaluating the stratigraphy and evolution of coastal environments. Examination of preserved washover fans can provide a palaeotempestological record that inform past and recent coastal risk with a view to predicting future coastal risk. The recognition of past washover deposits in coastal systems requires detailed knowledge of the internal structure of recent deposits including washover fans. We used very high frequency Ground Penetrating Radar and satellite imagery to examine the internal architecture of the 31st December 2011 Cyclone Thane surge-generated washover deposit on the beach that blocked the Thenpennai River at Thazhamkuda, near Cuddalore in Tamil Nadu Province, southeastern India. Cyclone Thane overwash overtopped the beach and deposited sediments on the contemporary beach and behind the beach within the former channel of the blocked river. The modern washover fan thus contains sediments that are preserved subaqueously and subaerially. We demonstrate that the internal architecture of the fan at Thazhamkuda is largely controlled by the pre-existing topography, and erosional and depositional processes as the cyclone washed sediment inland. At the landward margin of the fan, terminal foreset bedding is preserved and is likely to be one of the only features that can discriminate storm over tsunami deposits.

Turbid coral reefs experience high sedimentation and rapid light attenuation. However, local environmental conditions vary considerably across time and space influencing benthic reef communities and their depth distributions. Sediment fluxes and the hydrodynamic drivers of turbidity on reefs remain poorly quantified despite their control on coral ecology. Field measurements are required to assess long-term water quality change and the environmental thresholds of turbid coral communities. Here, we present a one-year time series of sediment flux and hydrodynamic conditions on turbid reefs in Singapore. Our results show strong seasonality in turbidity related to synoptic forcing, with peaks occuring during the Southwest Monsoon, and gross sedimentation rates ranging from 9.8 to 39.6 mg cm-2 d-1. Elevated turbidity was associated with increased siliciclastic silt inputs, which decreased during the subsequent inter-monsoon period. This transition was accompanied by reduced current velocities and the deposition of finer silt particles on reefs. Heterogeneity in sediment stress was observed to have a strong influence on coral cover across reefs. Our findings show the dynamic nature of equatorial turbid reefs over scales of hours to weeks, where corals must tolerate substantial fluctuations in turbidity and sedimentation. Field measurements demonstrate the complexities of defining quantitative thresholds for nearshore environments and highlight the need for expanded geographic datasets to improve our understanding of reef habitats under terrestrial influence.

Volcanic meteo-tsunamis (VMTs) are rare, devastating phenomena first recognised after the 1883 Krakatau eruption in Indonesia and recently quantified following the 2022 Hunga Tonga-Hunga Ha’apai volcanic eruption in the Kingdom of Tonga. While most studies have focused on their fast-moving leading waves, little attention has been given to their trailing free waves, which have been shown in the past to represent a major hazard. We conducted high-resolution simulations of VMTs in the South China Sea, examining their characteristics in Singapore, Manila, and Hong Kong. Our results show a clear separation between forced leading and free trailing waves in large shallow-water areas, confirmed by spectral analysis, which revealed characteristic periods for both types of waves. Temporal gaps between the arrivals of forced and free waves correlate with the continental shelf extent and local bathymetry. These gaps have significant implications for designing VMT early warning systems, and advancements in tsunami hazard assessment.

Estimating coastal erosion by a tsunami is essential for land use planning, assessing hazards for current structures (e.g., coastal nuclear power plants), and for paleotsunami reconstruction. Such estimations are currently available only for sandy beaches, using sand sediment transport models, which are not applicable to gravel beaches, which are the most common beach type in high-latitude settings. This study extended the one-dimensional cross-shore XBeach-G model to account for two-dimensional gravel transport by a tsunami. First, this study confirmed that the extended XBeach-G model can simulate a time series of waveforms of solitary waves during laboratory experiments. The proposed model was then applied to gravel transport by the 2011 Tohoku-oki tsunami at Koyadori, Japan, and found that the simulation results were consistent with observations of gravel deposits in previous studies. It was revealed that infiltration and exfiltration have an impact on morphological change caused by a tsunami on gravel coasts. In the simulation, inundation depth over land by the tsunami increased due to groundwater exfiltration, which increased the onshore deposition volume of gravel tsunami deposits. The groundwater flow calculation has not been incorporated so far for tsunami modelling, but this is important for modelling tsunami inundation at gravel beaches and gravel sediment transport by a tsunami. However, choosing appropriate values for the sediment friction factor and multiplier in the equation for gravel transport is more critical to reproducing the deposition of gravel sediments by a tsunami because these parameters are more sensitive than the parameter of groundwater flow. Although the presented model has been developed for tsunami simulation on any gravel beach, further testing and validation are recommended.

The northern coast of the South China Sea (SCS) is a densely populated and economically important area. Despite the absence of any tsunamigenic events in the last century in this region, their occurrence on a much longer timescale remains largely unknown. Given the catastrophic consequences a potential tsunami event could bring, we aim to bridge this research gap by conducting high-resolution sedimentological, geochemical, and geochronological analyses on two well-preserved offshore sedimentary columns, B01 and D02, from the northern SCS, at depths of -27 and - 46 m, respectively. Using statistical methods, we identified two anomalous sediment units, each 30 to 40 cm thick, in both columns. These units are dominated by coarse-grained, poorly sorted sediments with a normally graded sequence. Each unit is rich in biogenic debris, devoid of parallel or crossbedding, and has a unique set of elemental and isotopic signatures. They contain allochthonous biological species and record a disordered age-depth pattern. Such observations are indicative of the sudden input of marine components, suggesting an instantaneous high-energy event. The median calibrated ages, measured by accelerator mass spectrometry (AMS), from shell and foraminifera in the anomalous units, return the mixed ages of 4454-842 cal. yr BP and 2098-840 cal. yr BP, respectively. Shell and foraminifera above and below the anomalous units define AMS 14C ages of 951-779 cal. yr BP, with a median age of 868 cal. yr BP. Our data collectively point to a tsunami event at 868 cal. yr BP, equivalent to the North-Song Dynasty of 1000 years ago. This age pattern is consistent with reported tsunami events in and around the SCS, also compatible with historical accounts describing a "tidal overflow in Eastern Guangdong and Eastern Fujian at AD1067-1068" in Chinese documents. Combined with available data, the ca 868 cal. yr BP tsunami event in the SCS likely originated from the joint interaction of earthquakes induced by the Manila Subduction Zone and the Littoral Fault Zone, along with related landslide activities within the northern SCS.

This study examines ground penetrating radar (GPR) records of beach ridge stratigraphy as a proxy for reconstructing regional sea-level and tsunami histories in the tropics. We present topographically corrected GPR profiles on a prograded coast in Phra Thong Island, Thailand where we 1) identify downlap points marking the boundary between foreshore / beachface and upper shoreface facies and use this as past sea-level marker and 2) identify ‘cut and fill’ packages in the upper fill that we infer to be records of past erosion and recovery following repeated tsunami events. Optically Stimulated Luminescence (OSL) dates collected at locations slightly offset from the same profile line were incorporated to create the temporal record. The shore-normal GPR record shows ~0.82 m fall in the sea-level between 2659±139 years BP to 367±27 years BP that is consistent with other proxy based sea-level curves obtained in the region. The early part of the record (before ~2600 years) presents a period of rapid progradation and relatively stable sea level conditions. From ~2600 years BP to ~2200 years BP the record shows a steeper fall in sea level followed by a relatively stable to slightly falling phase between ~2200 years BP and ~550 years BP. Finally, for the seaward side, between ~550 years BP and ~350 years BP, the record indicates falling relative sea-level. The cut and fill packages suggest that Phra Thong has experienced 5 tsunami events in the last 2600 years including two events in close succession around 500 years ago that are recorded in the most landward part of the sequence. This study confirms that the study of tropical beach ridge systems using GPR and OSL techniques can be highly effective for reconstructing regional sea-level trends and tsunami histories through the Common Era and beyond.

Fault-bounded sag pond sediment records are commonly found to be excellent archives of palaeoearthquakes and more rarely, they can provide robust evidence of local environment and climate change. We examined the sedimentary and geomorphological record of the Aksay Pond within the Karachingar Valley along the southern margin of the Altai Mountain Range in northwestern China. This pond is associated to a shutter ridge resulting from cumulative deformation associated with successive earthquakes along the Fuyun Fault, including the most recent 11 August 1931 Mw7.9 earthquake. However, detailed chronology based on 14 C Accelerator Mass Spectrometry, 210 Pb and 137 Cs dating suggests that only deformation related to the 1931 earthquake have been preserved at the pond site. A small wedge of sediments comprising cobble and gravel sized clasts are separated by two palaeosoil deposits suggesting that very minor sediment could accumulate prior to 1931. In the northern part of the pond, sediment was deposited predominantly from a colluvial fan that has periodically been mobilised from the steep mountain slopes to the east. In the southern part of the pond we find that the dry climate of the region has experienced periodic storms that have resulted in the deposition of 11 fining upwards packages formed by remobilised and deposited sand to mud-sized sediments within the pond. Associated with these fining upward cycles are two colluvial wedges that emanate from the fault scarp. The upper wedge is dated at approximately 1986 CE and coincides with a high precipitation event recorded at the Fuyun Meteorological Station in 1986. The middle wedge may be related to an earlier high precipitation event, but due to challenges in obtaining accurate ages, cannot be verified. Alternatively, these two colluvial wedges could coincide with minor ca. Mw5 earthquakes in the region. Importantly, these wedges are not associated with large scale rupturing similar to the 1931 earthquake. Based on the sedimentary and geomorphological evidence of the Aksay Pond, we propose a model for the sequential formation of sag ponds highlighting the influence of both climatic and tectonics processes.

Surface currents influence ship navigation, coastal heat transfer and sediment transport, and thus necessitate robust models that can reliably predict surface current behaviour. However, our ability to make predictions over long time scales are commonly hampered by a lack of long observational datasets. Remote sensing technologies, which include satellite altimetry and high-frequency radar, are often used to measure global surface currents. However, their ability to reveal insights on ocean dynamics at a regional scale remain limited by restrictions related to space-time sampling. Here, we explore the use of AIS data as a means to derive surface currents in the Sunda Shelf Region in equatorial southeast Asia. Firstly, we apply nearest-neighbour interpolation to map relevant AIS information, that includes the ship’s speed over ground, course over ground and heading, onto a grid with a spatial resolution of 100m and an hourly temporal resolution. Next, we applied a gradient descent approach to derive surface currents at the positions of the ships. We then implement a generative model on PyTorch to reconstruct surface currents in the region. The model performance is evaluated by comparing to observational data from drifters and drifting buoys. Lastly, we employed wavelet analysis, a type of nonstationary spectral analysis, to examine the dominant frequencies or periods where surface currents are strong. Our pilot study highlights the potential of AIS data as a credible alternative to traditional methods of measuring surface currents in data scarce areas.

Climate-induced hazards exert uneven impacts on communities. However, conventional risk models rarely consider these disparities, which are critical for informing risk reduction decisions. Instead, they quantify risk solely based on the value of assets at risk, without accounting for how communities are differentially exposed and vulnerable to particular hazards. This has significant consequences for low-income populations, who tend to suffer most from disasters. Our study introduces an equity-sensitive framework that considers inequities in exposure and vulnerability, demonstrating how these inequities compound into well-being risks. We apply this framework in a large-scale study of coastal flooding and sea-level rise risk in the Philippines, highlighting both quantitative and spatial variations in asset and well-being risks. Findings indicate that accounting for income-driven inequities yields a more comprehensive understanding of coastal flood risks across groups. This framework is adaptable for other hazards and contexts, and aims to promote more equitable disaster risk reduction outcomes.

The Bay of Bengal is a well-known hotspot for cyclone formation. Multiple recent cyclones, such as the Odisha Super Cyclone in 1999 and Cyclone Fani in 2019, along with a series of historical cyclones, have severely impacted the east coast of India, particularly the coastal regions of Odisha and West Bengal States. However, the existing cyclone record from the area is insufficient for multi-decadal recurrence analysis, rarely extending beyond last few decades. Hence, understanding and integrating historical, prehistorical, and geological cyclone records from the area can provide information on the social, economic, and environmental impacts of cyclones. This information will aid in planning response strategies and implementing policies to mitigate cyclone effects. This study investigates the geological record of cyclones buried in the prograded beach systems near Konark in Odisha over the past few hundred years. Shore-normal ground penetrating radar (GPR) reflection profiles were collected using the 250 and 500 MHz antennas of the pulseEKKO PRO GPR system. Sediment cores and excavated faces were analysed along the same GPR lines, and optically stimulated luminescence ages provide a chronological framework over the last 300 years. Processed GPR profiles exhibit a number of high-angle erosional surfaces. These surfaces were likely caused by erosion during severe cyclones in the region, spanning at least the last three centuries. Eight such erosional surfaces were identified from the GPR profile near Konark. Trench and core data from the swales also highlight several distinctive layers rich in heavy minerals, possibly the result of repetitive cyclones in the area. One prominent sand layer gives an interim age of 150 years, likely linked to a late 19th century washover event. The data presented in this study indicate that geological records can be used to build a long-term cyclone record for the area. Given the increasing population density in the region, a comprehensive cyclone record can provide valuable insights into the changes in frequency and intensity over the long term, which can be used to inform decision-making processes for coastal management and development.

Holocene marine records provide key insights into environmental changes associated with changing relative sea-levels under interglacial conditions. However, most Holocene records are found in the mid to high latitudes, and there is a lack of records in the tropics. Here, we present a multi-proxy record from a sediment core GRBH03 from the Kallang River Basin in Singapore, spanning from 9.1 to 1.2 cal kyr BP. Three sedimentary units and five foraminiferal assemblages were recognised, reflecting the successive environmental change during the early Holocene marine transgression and subsequent coastal progradation. A depositional hiatus of similar to 5.8 to 1.2 cal kyr BP and shell layer formed during this period may be associated with falling sea level after the mid-Holocene highstand. Stratigraphic interpretation, anchored by the Marina South Member (MSM), identifies Transgressive and Highstand Systems Tracts in the Kallang River Basin, though evidence for Falling Stage and Lowstand Systems Tracts is limited. From GRBH03, an abrupt increase in sedimentation rate from 8.4 to 8.2 cal kyr BP, with simultaneous increase in Fe/Ca and decrease in delta C-13(OM) values, may reflect drier conditions linked to the 8.2 ka climate anomaly. These findings highlight the combined influence of relative sea-level and climate variability on depositional processes in tropical coastal systems and provide valuable analogues for anticipating coastal responses to future environmental change.

Supplementary File 3. Data table for LA-ICP-MS U-Pb zircon analysis and zircon morphology observation of sample ES13-255 (Palu Formation).

The South China Sea (SCS) coastlines are particularly vulnerable to tsunamis due to rapid urbanization and dense infrastructures. However, whether the SCS has experienced ocean-wide tsunamis is still under debate. Some geological records from the offshore islands inside the SCS imply a regional tsunami event may have occurred approximately 1000-yr-ago. We address these questions for the first time using forward numerical simulations in the SCS: what source could be responsible for such deposits, how the deposits were formed and at what conditions do the deposits could be preserved? Here, we assume the validity of the tsunami deposit hypothesis and use the forward model COMCOT-SED to investigate if these tsunami deposits can be linked to potential seismogenic tsunami sources inside the SCS, including megathrust earthquakes (Mw8.8-9.2) from the Manila subduction zone (MSZ) and the 1918 Mw7.5 Nan'ao earthquake from the Littoral Fault Zone (LFZ) in the northern continental shelf of the SCS. We also utilize a reported tsunami deposit from Qing'ao Embayment, Nan'ao Island, China, to exemplify the deposit formation process in a typical barrier-low coastal plain system. Quantitative analysis suggests large earthquakes from the MSZ may account for the reported geological deposits. The full-rupture earthquake scenario could best explain the depositions if such extreme case is geophysically and geologically plausible. If not, earthquakes (similar to Mw 9.0) covering the northern (16-23.5 degrees N) or southern portion (14-19 degrees N) of the MSZ could also be suitable candidates. Such great earthquakes can generate large tsunami waves (>7 m) that inundate the Qing'ao Embayment, transporting sediments and leaving tsunami deposits in low-lying areas. Conversely, tsunamis triggered by nearshore earthquakes in the LFZ cannot cause deposition in Qing'ao Embayment. The barrier-low coastal plain system is well-suited for preserving tsunami deposits, which remain unaltered by subsequent tsunami waves. Our findings offer a quantitative reference for paleo-tsunami research in the SCS and enhance global understanding of the tsunami deposition process in barrier-low coastal plain systems.

The Palu Formation, previously known as the Celebes Molasse in the Palu area, is understudied and was previously considered to be associated with the Pliocene collision between an Australian-derived microcontinent (Banggai Sula) and the eastern margin of Sundaland (West Sulawesi). Here, we present sedimentological, heavy mineral and zircon geochronological data to provide insights into sediment provenance and to elucidate Neogene tectonic activity in Sulawesi. These analyses suggest that the Pleistocene Palu Formation comprises synorogenic alluvial fan to braided river deposits that record the rapid uplift of metamorphic and granitoid rocks in the Neck and west Central Sulawesi. The Palu Formation is characterized by predominant granitoid and metamorphic clasts and heavy mineral assemblages dominated by pyroxene, amphibole and garnet. Detrital zircons record youngest grain ages of c. 2.5 and 3.0 Ma with a significant Pliocene age population and subsidiary Eocene, Cretaceous, Jurassic and Late Triassic age peaks. Rapid uplift and erosion associated with mountain building shaped the topography and influenced the evolution of Palu River networks. Supplementary material: Complete location, heavy mineral and detrital zircon geochronology datasets are available at https://doi.org/10.6084/m9.figshare.c.7033388 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Modern and geological records of storm sedimentary deposits preserved on siliciclastic coastlines are important archives to evaluate the past and current magnitude and impacts of storms. Examination of modern storm deposits also offers the opportunity to evaluate the similarities and differences between storm and other coastal overwash processes and hazards.We examined the stratigraphy and sedimentary characteristics of the 31st December 2011 Cyclone Thane and underlying coastal units from 14 pits from six sites from the coastal zone of Tamil Nadu Province, southeast India. We analysed the grain size parameters, grain shape, and heavy mineral proportions of each deposit in high resolution and examined the sedimentary structures of each unit. For the first time, we use Bayesian factors to quantitatively evaluate the similarities and differences between the storm sedimentary deposits and other co-located coastal sedimentary deposits. At several sites, the storm deposits differ in several parameters from the underlying coastal deposits, but at some locations, distinguishing between different depositional units cannot be achieved. In comparing the storm deposits from the different sites, mean grain size results in the most coherent pattern with closely located sites having similar mean grain size, and more southerly sites being finer grained. The other measured parameters show a far less coherent pattern with adjacent sites often preserving larger differences than more distal sites attesting to very local hydrodynamic variations during sediment deposition. As with the sedimentary parameters, the sedimentary structures formed during sediment deposition preserved at each site are highly variable. To date, the presence of terminal foresets at the landward edge of washover fans remains the only diagnostic feature of storm deposition, but that this feature is not ubiquitous across all storm deposits. Our findings demonstrate the spatially heterogeneous nature of storm sediment deposition and the challenges of identifying storm deposits in coastal siliciclastic sequences. The use of Bayesian statistical approaches also offers a robust method for evaluating and discriminating between coastal sediment deposits that has many advantages over traditional frequentist approaches. This method can easily be applied to other sedimentary depositional environments.

AbstractWe examined how variations in the horizontal resolution of bathymetry influence the behavior of modeled tsunamis at shallow depths nearshore. This was done using the Cornell Multi-grid Coupled Tsunami Model (COMCOT) to simulate tsunamis with resampled bathymetric data at resolutions of 5, 10, 20, 30, 40, 50, 100, 200, and 300 meters, derived from 1-m resolution NOAA coastal LiDAR data sets (at water depths of less than or equal to 30 m) and soundings. In total, we utilized 1,080 data sets, comprising 9 resolutions across 30 sets at 4 different sites. In addition, we included the 15-arc second grid ($$\sim$$ ∼ 455 m) 2021 GEBCO data for comparison. We initiated a 5-m high tsunami wave offshore and propagated it towards the coast, then used the resulting maximum wave heights for each resolution to quantify the differences across varying resolutions. Using the 5 m bathymetry as the reference model, we observed that data sets with 10–50 m resolutions can reproduce tsunamis reasonably well. The maximum heights are overestimated by less than or equal to 5% or underestimated by less than or equal to 10%, and the first wave arrival time is $$\sim$$ ∼ 10% earlier than expected. Coarser bathymetries show an increasing trend of height underestimation, with the GEBCO model underestimating it by as much as 70%. Coarser bathymetry models have more variable first wave arrival time, with waves arriving up to 20% later or up to 10% earlier than expected. Overall, a reasonably accurate result can be achieved using a bathymetric resolution in the 10 m–50 m range, and is achievable with reasonable computational efficiency (at least 80% faster than simulations using the 5 m model on high-performance computing). This study highlights the importance of shallow bathymetry data quality in the numerical modeling of tsunami propagation.

Sand is a vital ingredient for modern structures and to meet demand, a substantial volume of sand is extracted illegally from riverbeds globally. The Vietnamese Mekong Delta is one of the largest delta in Asia and it has a long history of riverbed sand mining. We quantified the illegal sand mining rate in this major sand mining hotspot, as the difference between the actual volume of sand mined and the allowable rate of sand extraction set by the provincial government. The volume of illegally mined sand decreased from 16.7 Mm 3 /yr in 2013 to 15.5 Mm 3 /yr in 2018-2020. An increase in the allowable rate of sand extraction from 11.5 Mm 3 /yr to 15.1 Mm 3 /yr reduced the volume of illegally mined sand. We recommend that scientific research should be conducted to assess the allowable rates of sand extraction and the volume of sand reserve.

Abstract Seaports are vulnerable to extreme sea level events. Beyond physical damage, any port inoperability affects trade flows in and out of the affected port and disrupts shipping routes connected to it, which then propagates throughout the port network. Here, we propose an approach to assessing tsunami risk to ports and the global port network. We leverage on the topological properties of the global liner shipping network and centrality measures to quantify the potential impacts of a Manila Trench earthquake-tsunami under both present and future sea levels. We find that a Manila Trench tsunami could potentially damage up to 11 ports at present-day conditions and 15 ports under rising sea levels. Port closure could exceed 200 days and cause greater disruption to shipping routes than historical tsunami events. We also find that sea level rise is likely to result in uneven changes in tsunami heights spatially and hence, uneven impacts on the global port network.

Instrumental sea-level records are insufficient to understand the response of sea-level changes to global temperature on centennial timescales. Sea-level histories spanning at least the Common Era have not been widely studied in Southeast Asia. This period is crucial for providing a pre-industrial context to understand sea-level change with climate. Linking sea-level change to climate change is proxy dependant, with most proxies only providing decadal to centennial scale resolution of both sea level and climate. This study examines the efficiency of beach ridge stratigraphy as a proxy for reconstructing regional sea-level histories in the tropics. We present topographically corrected Ground Penetrating Radar (GPR) profiles from a prograded coast in Phra Thong Island, Thailand, where we identify downlap point marking the boundary between the foreshore and shoreface subzones and use this as a past low-tide marker. The low-tide markers were corrected (considering the tidal range) and then connected to approximate the past sea level. Optically Stimulated Luminescence (OSL) samples collected at locations slightly offset from the shore-normal GPR profile line were incorporated to create a relative sea-level record. Overall, the shore-normal GPR record shows a similar to 1.06 m fall in sea level between similar to 2660 and similar to 370 years ago. The study also highlighted stepwise fluctuations in sea level that were not identified in previous studies. Between similar to 2600 and similar to 2200 years ago, the record indicates a steep fall in sea level, followed by a phase of relatively stable to slightly falling sea level between similar to 2200 and similar to 550 years ago. Finally, for the seaward side, between similar to 550 and similar to 350 years ago, the record indicates an accelerating sea-level fall. This study confirms that the investigation of tropical beach ridge systems using GPR and OSL techniques can be a highly efficient and effective means for reconstructing regional sea-level trends throughout the Common Era and beyond.