Medieval tsunami revealed by giant coral blocks in the Caribbean
New scientific research has just shed light on a geological event that is as spectacular as it is forgotten: a tsunami of exceptional magnitude that is believed to have struck the Caribbean at the end of the 14th century.
Anegada Island
The study, recently published in Geophysical Research Letters, relies on a remarkable natural indicator: massive coral boulders torn from the reef and hurled several hundred meters inland on Anegada Island, in the British Virgin Islands, at the northern end of the Lesser Antilles arc. Silent witnesses that, six centuries later, tell a story human archives never recorded.
Researchers from IPGP discovered these corals during a field mission on Anegada. They mapped them precisely to obtain information on their distribution—an essential dataset for constraining tsunami models. They then sampled the coral surfaces to accurately date their death using Uranium-Thorium techniques in two laboratories (CEREGE in France and HISPEC in Taiwan).
These corals provide geological evidence of a major tsunami that struck the Caribbean before the arrival of Christopher Columbus and long before the first written accounts of natural disasters in the region, which only begin in the mid-17th century. The tsunami was generated by an earthquake with a magnitude greater than 8. Thanks to highly precise dating, researchers can now conduct targeted historical searches in archives from coastal cities lining the Atlantic—across the United States, Canada, Europe, and Africa. Given the scale of the event, the waves almost certainly crossed the entire ocean basin, hitting these shores hours after the earthquake.
Corals displaced by colossal force
On the island, researchers identified dozens of coral boulders up to 2 meters in diameter, now lying in areas never reached by the sea—not even during the most violent storms. Their very presence indicates they were transported by a phenomenon of extraordinary power.
To determine their age, scientists used uranium-isotope dating. The result: all corals died between 1381 and 1391, before Columbus’ arrival in the region and the earliest historical records.
A major earthquake as the likely origin
By combining geological data with wave-propagation models, the authors suggest that an earthquake with a magnitude above 8—either along a fault within the subducting American plate or at the subduction interface in the Puerto Rico Trench—was responsible for the corals’ demise. The quake would have generated tsunami waves powerful enough to rip living corals from the reefs surrounding the island. These boulders were then carried far inland before the sea retreated and left them behind.
A geological memory
The traces left in the field bear witness to a rare and powerful event, one capable of reshaping coastal landscapes over the long term.
This large medieval tsunami most likely crossed the Atlantic and struck the coasts of Canada, Europe, or Africa. Being able to date it with such precision will make it possible to search for this event effectively in historical archives. The study highlights how geological records can reveal major events that occurred before written history or in regions where populations were sparse or dispersed.
The long history of coastal hazards
Beyond the discovery itself, this work is a reminder that regions exposed to subduction zones or active faults can experience, even at very long intervals, large-scale tsunamis. The diversity of methods used—isotopic dating, field observations, modelling—makes it possible to reconstruct the dynamics of ancient events and refine our understanding of coastal hazards.
This is precisely the goal of the work carried out over several years in the Caribbean by IPGP: identifying and characterizing on land and at sea the active faults that could rupture and generate a tsunami; studying the functioning and seismic cycle of the subduction zone; and searching for the geological and historical traces of past earthquakes and tsunamis, from the coastline down to the deep seafloor. The aim is to rebuild the history of past catastrophic events in order to better prepare for future earthquakes.
This study therefore represents a major step forward. This previously unknown medieval tsunami—revealed by coral boulders scattered and preserved in the landscape for centuries—offers a rare window into the natural history of the Caribbean, a history in which the sea sometimes reaches far farther inland than we imagine.
(HISPEC), High-Precision Mass Spectrometry and Environment Change Laboratory, National Taiwan University
