Hidden Tsunami Threat to Anguilla, Saint Martin and Saint Barthélemy Revealed by New Simulations

The sun-drenched islands of the Anguilla Bank — Anguilla, Saint-Martin/Sint Maarten and Saint-Barthélemy — draw millions of visitors each year with their turquoise bays and low-lying shorelines. Yet those same gentle landscapes are precisely what makes the archipelago acutely vulnerable to one of nature’s least expected hazards in the Caribbean: tsunamis. A new open-access study published in the journal Natural Hazards by Jean H. M. Roger of Earth Sciences New Zealand and Mélody Philippon of Géosciences Montpellier presents the first dedicated numerical assessment of earthquake-related tsunami hazard for this densely populated island group, combining roughly 500 years of historical records with modern fault characterization and high-resolution wave simulations.

The researchers begin from a sober demographic observation. Low-elevation coastal zones cover only about two percent of the planet’s land surface but held ten percent of the world’s population in 2000, and in the Caribbean roughly seventy percent of people live in large coastal cities. Population density on the Anguilla Bank is striking: around 160 inhabitants per square kilometre on Anguilla, about 500 on Saint-Martin/Sint Maarten and some 530 on Saint-Barthélemy. On these flat forearc islands, there is often no high ground within a reasonable walking distance, so even a modest tsunami could trap residents and tourists on narrow coastal strips between the open sea and shallow salt ponds.

Although the Caribbean accounts for only about five percent of global tsunami records — roughly seventy of the 1,540 events catalogued by NOAA — the region’s history is far from quiet. The infamous Lisbon earthquake of 1 November 1755, with an estimated moment magnitude of 8.5 off the Iberian Peninsula, sent destructive waves across the Atlantic that reached the Lesser Antilles about ten hours later. Contemporary documents describe several-metre waves and inundations throughout the arc. On Saint Martin, historical compilations report a run-up of 4.5 metres and a dramatic sea withdrawal: a sloop anchored in roughly 4.6 metres of water was reportedly left lying dry on her broadside. A second, lesser-known transatlantic event followed on 18 November 1755, when the Cape Ann earthquake in Massachusetts apparently produced a sea withdrawal and a six-foot return wave at Saint Martin’s harbour, as recorded in a letter by Professor Winthrop.

The most destructive regional tsunami struck on 18 November 1867, after a magnitude 7.2 earthquake ruptured a 50-kilometre segment of a fault along the northern border of the Virgin Islands basin. Waves reached several metres — up to about ten metres — in the U.S. Virgin Islands within fifteen minutes and were reported from Puerto Rico to Grenada. In the Anguilla Bank, damage was documented in Saint Martin and Saint Barthélemy, where the 2.1-metre-deep Carenage was left dry, vessels were stranded and then swept adrift, and one schooner was carried by currents at a rate of ten knots before being secured hours later. Beyond these three documented events on the bank, geological evidence points to older, pre-colonial tsunamis: boulders transported up to six metres above sea level on Saint Martin, sediment cores from Etang Guichard recording five extreme-wave events over the past 3,500 years with a 300-to-400-year recurrence, and a regionally extensive inundation dated to roughly 1200–1500 years before present identified on Anegada, Saint Thomas and Scrubb Island.

To translate this history into forward-looking hazard estimates, the team built twelve rupture scenarios. Seven (S01 to S07) represent local upper-crustal faults mapped around the Anguilla Bank from high-resolution bathymetry and seismic reflection profiles, selected for their ability to produce magnitude greater than 6 earthquakes and for their near-complete azimuthal coverage of the archipelago. Fault dimensions were converted into moment magnitudes, rupture areas and coseismic slips using the empirical scaling relationships of Wells and Coppersmith, Leonard, and Thingbaijam, with fault dips and slip directions constrained by seismic profiles and seismotectonic data. Three further scenarios reproduce historical events: the 1755 Lisbon source (S08), the 1867 Virgin Islands rupture (S09) and the 1843 Guadeloupe earthquake (S10), the largest known event in the Lesser Antilles at an estimated magnitude 8.5. Two final scenarios (S11 and S12) relocate that 1843 megathrust rupture northward along the subduction interface — one beneath the Anguilla Bank region and one in the Puerto Rico subduction zone — to test how source position controls impact.

The simulations were run with COMCOT, the Cornell Multi-grid Coupled Tsunami model, which solves linear and non-linear shallow-water equations on a system of nested grids. Three grid levels were used: a 2-arcminute grid of the North Atlantic built from GEBCO bathymetry, an intermediate 15-arcsecond grid over the northeastern Caribbean, and a finely resolved 3.75-arcsecond grid — about 115 metres — covering the Anguilla Bank itself, assembled from the HOMONIM and Litto 3D datasets offshore and SRTM topography on land, all referenced to local mean sea level. Seafloor displacement for each scenario was computed with Okada’s elastic dislocation model, and inundation was activated on the two inner grids with Manning’s friction coefficients of 0.013 for the seabed and 0.0025 for land. Local and regional scenarios were propagated for ten hours; the Lisbon teletsunami was tracked for thirty-six.

The results reveal a strongly source-dependent hazard. The pure strike-slip scenario S01 produces little more than 30 centimetres of wave amplitude, consistent with the small tsunamis that followed recent large strike-slip earthquakes elsewhere in the region. In contrast, six of the seven local fault scenarios push coastal amplitudes above 30 centimetres, at least one location above 1 metre, and five of them above 2 metres somewhere along the coast. Scenario S05 emerges as the most impactful, with maximum amplitudes of 2 to 5 metres at some coastal sites, waves exceeding 2 metres on the northern coast of Saint Martin and more than 2 metres at Saint-Barthélemy’s low-lying, northeast-facing Baie de Saint-Jean. The bank’s numerous submarine canyons play a decisive role, focusing wave energy onto the flanks of canyon heads while sheltering the areas directly in front of them — a pattern well documented in other ocean basins.

The historical scenarios tell a subtler story. The 1755 Lisbon simulation produces generally modest impacts, with amplitudes above 30 centimetres in bays near the populous towns of Marigot and Sandy Ground and between 0.5 and just over 1 metre at Nettlé Bay and Great Bay, but the modelled wave fails to enter Simpson Bay Lagoon and falls far short of the reported 4.5-metre run-up. The authors suggest the historical observation may be erroneous, misattributed to another island, or that the current 115-metre grid resolution cannot fully capture coastal shoaling and refraction. The 1867 Virgin Islands scenario produces 0.3-to-1-metre offshore amplitudes, overtops the Sandy Ground spit and floods parts of the east coast, while the 1843 megathrust scenario drives amplitudes above 1.5 metres along most of Saint Martin and about 2 metres inside Simpson Bay Lagoon. When the same rupture is shifted northward (S11), it generates the largest amplitudes of all twelve cases — 2 to 5 metres along nearly every coast of the archipelago.

Currents prove as consequential as wave heights. Previous studies identify 1.5 metres per second as the threshold at which tsunami flows become dangerous to people and navigation, and experiments show an adult can begin sliding backward in only 26 centimetres of water at 1.8 metres per second. The Lisbon scenario stays mostly below this threshold around Saint Martin, with localized hotspots off Pointe du Bluff, Pinel Island and in Great Bay. The 1867 event pushes speeds to or beyond the threshold at those same sites plus Marigot, Baie de Grand Case and Baie de l’Embouchure, while the 1843 scenario exceeds it along nearly the entire coastline. Conversely, zones of low current speed — below 0.5 metres per second — could serve as sheltering anchorages during a tsunami alert. Overlaying the simulations on satellite-derived building footprints shows that Saint Martin’s largest urban centres sit either within modelled flood zones or directly facing high-amplitude, high-current areas.

The authors stress that their twelve scenarios are a preliminary, deliberately limited set: alternative rupture geometries, uncharacterized faults and non-seismic sources such as submarine landslides and volcanic eruptions could produce larger waves. The steep slopes flanking the Anguilla Bank on both its Caribbean and Atlantic sides are candidates for future collapse, and the nearby volcano Saba represents a direct threat, with at least 47 flank-collapse events identified along the Lesser Antilles Arc, 15 of them within the last 12,000 years. Tsunami management plans for Saint Martin and Saint Barthélemy are still under construction, and the study argues that horizontal evacuation along limited coastal roads should be supplemented with vertical shelters. It also calls for an expanded monitoring network: the northern Lesser Antilles currently hosts only a handful of working sea-level gauges, the Saint Martin gauge has delivered no usable signal since February 2020, the planned Gustavia station was never completed, and the nearest deep-ocean DART buoys lie roughly 630 to 750 kilometres away — leaving these idyllic islands, for now, largely blind to the next approaching wave.

Subject of Research: Earthquake-related tsunami hazard assessment for the Anguilla Bank Archipelago in the northern Lesser Antilles using historical data, fault characterization and numerical tsunami simulation.

Article Title: Tsunami hazard in the Anguilla Bank Archipelago, Lesser Antilles: historical data, fault characterization and numerical simulation

Article References: Roger, J. H. M., & Philippon, M. (2026). Tsunami hazard in the Anguilla Bank Archipelago, Lesser Antilles: historical data, fault characterization and numerical simulation. Natural Hazards, 122(19), Article 636. https://doi.org/10.1007/s11069-026-08367-4

Image Credits: AI Generated

DOI: 10.1007/s11069-026-08367-4

Keywords: tsunami hazard, Anguilla Bank, Lesser Antilles, Caribbean, numerical modelling, COMCOT, earthquake, subduction zone, Saint Martin, Saint Barthélemy, crustal faults, natural hazards