Géosciences marines

GEOSCIENCES : Sedimentology, Géohazards, Coastal dynamics

Population growth in coastal areas increases their vulnerability to marine and geological hazards, exacerbated by climate change. 110 projects supported by the ANR have led to major advances in different sectors: modeling of sediment dynamics, monitoring of underwater risks (earthquakes, tsunamis), and assessment of coastal vulnerability. By combining physical, socio-economic data, and innovative tools (AI, sensors, satellite imagery), this research strengthens the alert and adaptation capacity of coastal territories, laying the foundations for more resilient management in the face of climatic and geological pressures.

Gilles Lericolais : Ifremer/SG Mer, Bruno Castelle : Univ Bordeaux

1) Scientific background:

The Earth’s population has reached 8.2 billion people in 2024, of whom more than 2 billion live near the coast and could reach 2.9 billion by 2050 according to the United Nations population estimates and projections report, 2024. This high population density along the coasts and the expected growth of complex critical infrastructure and ocean services in coastal regions lead to increasing levels of exposure and vulnerability to marine geohazards. Indeed, these coastal areas are subject to risks that can lead to severe impacts due to the high concentration of people and assets in exposed locations. In particular, climate-induced sea-level rise will exacerbate these risks during the 21st century.

A geohazard is a geological condition that represents – or has the potential to develop – a situation leading to uncontrolled damage or risk. The United Nations Office for Disaster Risk Reduction (UNDRR) defines intensive risk as disaster risk associated with low-probability, high-impact events, while extensive risk is disaster risk associated with high-probability, low-impact events. Dangerous marine geological events can occur at any time and the scientific community, the maritime industry and government agencies are called upon to cooperate to better understand and monitor the processes involved in order to mitigate the unpredictable damage that results.

The marine geoscience projects funded by ANR, whether for the understanding of sedimentary processes (sedimentary hydrodynamics) or on the understanding of geological risks, have increased knowledge on marine geohazards and therefore shed light on the measures needed to reduce our exposure and vulnerability to such events. This corresponds to one of the societal objectives of the United Nations Decade of Ocean Science for Sustainable Development (2021-2030), which advocates a safe ocean where lives and livelihoods are protected from ocean-related hazards.

Coastal regions are facing increasing risks from natural hazards such as coastal erosion, flooding, and submersion, which are being intensified by climate change. Rising sea levels, along with changes in storm frequency and intensity, pose serious threats to coastal communities, infrastructure, and ecosystems. Understanding, modelling, and predicting coastal evolution is therefore essential to developing effective adaptation strategies and mitigating future risks. Coastal change is, however, a complex problem driven by multiple nonlinear processes interacting with each other on a wide range of time and space scales. At small scales, waves, tides, and currents move the sediment through different modes and reshape the seabed. At larger scales, extreme events, sea-level fluctuations, and human interventions influence coastal evolution over days, decades to centuries. Because these nonlinear processes and feedback mechanisms, predicting future changes remains a major scientific challenge. Progress requires combining small-scale physical process studies, through laboratory experiments, upscaling and process-based modelling, with large-scale approaches such as reduced-complexity models and satellite remote sensing to track long-term shoreline change an large spatial scales. The accuracy of the models and remote sensing algorithms also heavily rely on high-quality, detailed, ground-truth data through intensive field measurements and long-term monitoring program.

Over the past 20 years, major scientific advances through ANR-funded projects have improved our understanding of sediment transport, feedback mechanisms, and the impacts of extreme events. Such processes can now be transformed into parametrisation into larger-scale models, which have been used in other ANR-funded projects to explore future changes, including under the effects of climate change. Satellite remote sensing also transformed the, large-scale multi-decadal, coastal science from a data poor to a data rich field, recently making possible data assimilation, application of machine and deep learning techniques and shoreline change assessments at global scale. Although limitations and knowledge gaps remain, these developments have led to better long-term projections and uncertainty assessments, providing valuable tools for engineers, policymakers, and coastal managers.

2) Main Contributions of the French Communities through ANR co-funding.

2-1 Scientific progress; cutting edge science

Today, the expansion of economic activities is driven by a combination of population growth, rising incomes, diminishing natural resources, responses to climate change and pioneering technologies. The “blue economy” thus encompasses established ocean industries as well as emerging and developing activities that are reshaping and diversifying maritime industries (OECD, 2016). These activities include offshore renewable energy, communications, maritime cruise tourism, offshore aquaculture, marine biotechnology and bioprospecting, seabed mining, aggregate extraction, ocean monitoring, control and maritime surveillance. Other activities for which there are not yet established markets include carbon sequestration, coastal protection, waste disposal and biodiversity conservation and restoration.

ANR participates in the European Partnership for a Sustainable Blue Economy. The objective of this Partnership is to accelerate the transformation towards a climate-neutral, sustainable, productive and competitive blue economy. This is to restore the health, resilience and services provided to ocean populations by promoting climate-neutral, sustainable and productive economic activity. Such objectives cannot reach without encompassing geohazards.

Marine geohazards related to seabed processes include earthquakes (the most destructive earthquakes to affect humanity have occurred at sea), landslides, volcanic eruptions and associated tsunamis. Marine geohazards can also include rapid changes on the seabed such as the migration of submarine dunes (bedforms), seabed liquefaction and gas migration that can lead to local overpressure in sediments and potential submarine landslides. To date, most geohazards occurring on the seabed are unknown, poorly characterized and difficult to monitor (with current technology).

Hazards are intimately linked to risk. A risk is the probability that an event resulting in loss of life, injury, or destruction or damage to property could occur to a system, society, or community within a given time frame. A risk is therefore determined as the product of three factors: hazard, i.e. the probability that a given event will occur within a given time; exposure, i.e. the human lives and the quantity and value of property exposed to the hazardous event; and vulnerability, i.e. the amount of damage the event will cause to the exposed property. The main marine geological hazards are coastal erosion, seawater intrusion, earthquakes, submarine landslides, subsidence, tsunamis, dissociation of natural gas hydrates, seabed sand waves, shallow gas, overpressure strata, gas chimneys, mud volcanoes, and mud diapirism.

The advancement of deep-sea exploration activities, uncertainties about the consequences of climate change, recent global catastrophic events (e.g. the 2004 Indian Ocean and 2011 Japanese tsunamis) correlated with the increase in human population density in coastal regions of the world are responsible for the increased importance and awareness related to marine geohazard research. Specific threats to society related to marine geohazards are the loss of land near the coast, the devastation of coastal areas by tidal waves generated by landslides and the destruction of marine facilities, (e.g. communication cables, pipelines).
ANR funded projects collectively bridge gaps between fundamental processes and practical applications, from small-scale sediment transport in turbulent flows to large-scale coastal evolution under varying climatic scenarios. A major scientific breakthrough in sediment transport has come from projects like SHEET-FLOW, WEST, 2-phaseSEDEXPn, and RUPTURE, which have refined our understanding of sediment dynamics under high-energy conditions. These projects focused on the complex fluid-particle and particle-particle interactions that occur during sediment transport, particularly under energetic flows and during extreme events like storms and hurricanes. SHEET-FLOW, for example, has advanced two-phase sediment transport models, incorporating acoustic instrumentation to measure velocity and sediment concentration at turbulent scales, revealing the key role of sheet flows in sediment dynamics. Similarly, WEST has provided new insight into sediment transport during recovery phases, focusing on accretion and bed slope adjustments after storms, with has implications for coastal resilience. The 2-phaseSEDEXPn and RUPTURE projects further refine our understanding of turbulence-induced sediment transport, using new ultrasound and hydro-acoustic techniques to measure sediment fluxes in turbulent flows. These advancements have significantly improved sediment transport models, allowing for more accurate predictions of bedform evolution and coastal erosion.

Beyond sediment transport, several projects have focused on the long-term evolution of coastlines, particularly in response to climate change and storm events. Projects like VULSACO and SHORMOSAT offer a broader understanding of coastal systems and their vulnerability to climate change. VULSACO, for instance, has developed vulnerability models for sandy coastal areas, assessing both short-term storm impacts and long-term erosion trends under future climate scenarios. The integration of socio-economic factors into these models has provided a more holistic view of coastal vulnerability. COASTVAR, focusing on tropical coastlines in West Africa and Vietnam, has employed innovative observational tools like drones and video imagery, as well as 3D coupled models, to study wave-induced circulation and surf-shelf exchanges. This research has significantly advanced our understanding of the hydrodynamics and sedimentary processes in these regions, which had received little attention by the scientific community so far. SONO has tackled the key role of beach-dune systems in coastal resilience. By studying dune evolution in response to human management and climate change, SONO has integrated geomorphological, ecological, and hydrodynamic data to develop a new coastal dune modelling framework. This research was used to improve coastal management practices in southwest France and beyond, especially in areas where dunes serve as vital buffers against storm surges and erosion. SHORMOSAT has made breakthrough advancements in large-scale shoreline change modelling by integrating satellite-derived data and improving shoreline models. This project has focused on understanding how shoreline changes are influenced by factors such as sea-level rise, wave conditions, coastal structures, and by addressing projections uncertainties.

Together, these projects highlight a significant advancement in our understanding of coastal dynamics, emphasizing the interactions between natural processes and human influences. They have not only expanded the fundamental scientific knowledge of coastal systems but have also provided practical tools for coastal zone management and planning. For example, the integration of numerical models with satellite observations in SHORMOSAT and GLOBCOASTS offers unprecedented opportunities for global coastal monitoring, while the development and/or improvement of process-based models in COASTVAR, CHIPO or KUN-SHEN helps anticipate future changes in coastal systems under various climatic conditions. Overall, these projects contribute to a more integrated understanding of coastal systems, particularly in the context of climate change

2-2 Innovation for private enterprises, for science policy, for the citizen with a focus of coastal communities

The ANR projects' results address Challenge 6 (Improve multi-hazard early warning services for all ocean and coastal hazards of geophysical, ecological, biological, meteorological, climatic and anthropogenic origins, and integrate community preparedness and resilience) of the UN Decade of Ocean Science for Sustainable Development (2021-2030). This is realised by presenting how to increase public authorities’ awareness of marine geohazards and frame marine geohazards in administrative management rules.

For a safe and sustainable use of the seabed, public authorities and policy makers responsible for coastal and maritime management and planning must be aware of the importance of marine geohazards. National and local government agencies responsible for coastal communities and infrastructure are well aware of land-based natural hazards, but the potential of offshore threats remains largely unknown. The reasons for this lack of attention are: 1) technologies to highlight marine geohazards are relatively new; and 2) until a decade ago, the use of the seabed was limited and there was little need to manage submerged territories. Similarly, public awareness of natural marine hazards is often low, even though the two very large tsunamis that hit Asia in 2004 (Indonesia) and 2011 (Japan) demonstrated how real marine geohazards can be and that they are not “a thing of the past”. It is therefore necessary that marine geohazards be included as natural hazards in all policies related to risk mitigation and land management.

By blending fundamental research on coastal dynamics with practical tools for coastal management and forecasting, ANR-funded projects provide a comprehensive approach to addressing the challenges faced by coastal communities worldwide. With rising concerns over climate change, coastal areas, particularly sandy beaches, are highly vulnerable to erosion, submersion, and extreme weather events. Projects like VULSACO, SHORMOSAT and COASTVAR have advanced the understanding of how human activities, such as urbanization and tourism, exacerbate these vulnerabilities. By integrating socio-economic factors into physical models, these projects are helping coastal managers anticipate the impacts of future storms and sea-level rise, informing adaptation strategies that are both scientifically sound and socially relevant. The integration of public and private stakeholders has also fostered collaborative solutions for beach restoration, and for instance coastal dune management in SONO contributing to more resilient coastal ecosystems. Furthermore, the development and application of advanced monitoring systems like drones, UAV surveys, and satellite imagery, as seen in GLOBCOASTS and SHORMOSAT, can now provide unprecedented data for making informed decisions.

Methodological breakthrough

The lack of an appropriate policy framework to guide the management of marine geohazards is a specific obstacle to the management of these risks. Due to the novelty of tools for detecting and quantifying marine geohazards, national and international legislation is often poorly defined. Local land management agencies should be required to translate scientific knowledge on marine geohazards into regulatory guidelines or restrictions to be applied, and to co-develop with civil protection agencies (or other similar bodies) emergency measures.

There is a need to integrate marine monitoring infrastructures such as the European Multidisciplinary Seabed and Water Column Observatory (EMSO) and all other long-term monitoring of high-risk areas with seabed mapping and geohazard research.

Permanent seafloor observatories continuously collect environmental data at a fixed location, while mapping seafloor geohazard characteristics will provide spatially continuous but time-accurate data. Since seismic, acoustic and chemical signals from the seafloor can travel tens of kilometres, a comparison between detailed geohazard characteristic maps and observatory signals will allow us to understand the evolution of geohazard phenomena such as mass loss, volcanic eruptions, fault activity and gravitational flows over time, and potentially to define precursors.

New technologies should facilitate long-term in situ monitoring combined with geohazard studies in surrounding regions to identify long-range signals. Dedicated marine geohazard field laboratories should be established at targeted sites to concentrate research, facilities and in situ modelling.

The projects have also introduced methodological breakthroughs that enhance our ability to predict, model, and manage coastal dynamics. CHIPO, for instance, has innovated by combining longshore and cross-shore processes into unified models, filling a gap in the study of beach morphodynamics. By initiating the development of a new generation of reduced-complexity shoreline models, complementary to traditional process-based models, CHIPO reduced simulation errors while providing cost-effective solutions for long-term shoreline predictions. Similarly, SHEET-FLOW and RUPTURE have made advancements in sediment transport modelling by resolving two-phase flow interactions, which are essential for accurately simulating sediment fluxes during turbulent conditions. The use of cutting-edge hydro-acoustic techniques and advanced sediment transport models in RUPTURE represents a significant leap in understanding fine-scale sediment transport dynamics. Additionally, the innovative data assimilation techniques developed in SHORMOSAT and GLOBCOASTS are setting new standards for global coastal monitoring, enabling more precise predictions of shoreline change and coastal evolution. These methodological advancements not only allowed enhanced scientific knowledge, but also provide practical tools and data for the scientist community as well as coastal managers.

3) Research perspectives.

The perspectives to be considered today for moving towards a more in-depth assessment of marine risks involve scientific research on marine geohazards, which is essential for understanding the characteristics, magnitude and recurrence intervals of events (i.e. how often they occur in the same place). For example, the magnitude of an earthquake that a fault can generate depends on its geometric characteristics and its relationship with deeply rooted active geological structures; the tsunamigenic potential of a volcano depends on the explosiveness of its past eruption(s) and the stability of its flanks. Sedimentary movements linked to ocean currents or sea-level rise generate risks on marine or coastal infrastructures. The magnitude of the geohazard is very different if an area is subject to storms or landslides every year, once every ten years, once a century or once a millennium. Scientific studies on marine geohazards therefore focus on: 1) the identification of past geohazard events and the assessment of their frequency, as well as 2) the monitoring of current active processes that may evolve into a marine geohazard.

Recently, the development of mathematical models for hazard definition, geotechnical measurements, field and laboratory data collection, and event dating has gradually increased. These tools can be applied to understand the formation and mechanisms of marine geohazards and their consequences, but also to develop warning systems before these disasters.

A challenge for future coastal research is improving the integration of multiple data sources and models to enhance predictions and better understand coastal change. Combining satellite observations with machine learning and deep learning algorithms represents a promising direction for refining our ability to forecast future coastal changes on a wide range of time and space scales. Such integration could improve understanding of coastal dynamics over large spatial scales, accounting for both natural variability and human influence, and offer more reliable projections of coastal evolution. Another issue in advancing coastal research is the quantification of uncertainties in model outputs. While progress has been made in the frame of recent ANR-funded projects, there remains a need to better understand the sources of uncertainty and how these propagate through the models. Future research should focus on improving uncertainty quantification methods, particularly in relation to the effects of climate change and human activities, to tackle where uncertainties can be reduced, and to generate more accurate predictions. The integration of human influences, such as coastal structures, beach nourishment, and land use, as well as biotic-abiotic interactions in certain environments, remains underexplored. Another important avenue for future research is the development of innovative, cost-effective monitoring and modelling tool, to enhance real-time monitoring of coastal systems, allowing for rapid response to extreme events and improving long-term coastal planning