A newly published study says a major North Sea earthquake triggering an underwater landslide could push a 3.1-metre (10-foot) surge against the coast near Den Helder, with the first waves arriving in 38 minutes. The scenario is not an imminent forecast, but the researchers warn that Dutch emergency planners have no specific alert protocol for a tsunami generated close to shore.
The findings appeared on Wednesday, 7 October, after a court in The Hague ruled last month that the infrastructure ministry must release seabed survey records it had kept restricted. Researchers say the newly available measurements helped them identify a steep, unstable slope in the central North Sea and model how a slide there could move water towards the Netherlands.
A short warning window
The team ran 240 simulations using different earthquake strengths, seabed shapes and slide volumes. In its most severe credible scenario, a magnitude 7.1 quake triggers the movement of about 6 cubic kilometres (1.4 cubic miles) of sediment; water reaches Texel in 38 minutes, Scheveningen in 52 and Rotterdam’s outer harbour in 71.
At the coast, the model produces a peak water level of 3.1 metres (10 feet) near Den Helder, 2.4 metres (7.9 feet) at Scheveningen and 1.6 metres (5.2 feet) at the entrance to Rotterdam harbour. Those figures describe the rise above the normal tide in the simulation, not a wall of water travelling across the North Sea.
Koen Thomas-Ramos, a marine geophysicist with the Utrecht-based North Sea Seismology Group and a lead author, said the study could not say when such a chain of events might happen. “The risk is small, but the response time is smaller still. If the earthquake is offshore, you cannot wait for a second confirmation before warning the coast,” he said.
The risk is small, but the response time is smaller still.
Koen Thomas-Ramos, marine geophysicist
The authors do not calculate a reliable annual probability. They say the fault’s past activity is too poorly recorded to support one, and caution that their largest wave depends on a combination of rare events. The North Sea is not a subduction zone, where one tectonic plate dives beneath another and can generate the planet’s largest earthquakes.
Warning plans under pressure
A court filing shows the case was brought by Henk Bolsonel, a former Zeeland provincial executive who argued that coastal hazard data should be public. The court ordered the ministry to release the survey records, but did not rule on tsunami risk. Researchers say they began their analysis after the data became available.
The ministry said there was “no immediate danger” and that existing dikes and coastal defences were built to withstand severe conditions. Spokeswoman Eliza Nedelcu said officials would ask the national flood authority to review the findings before considering changes to public alerts. She said no evacuation was being planned.
Berta Moravčík, a coastal engineer at the Delta Coastal Observatory who did not contribute to the research, said the study justified a review, not panic. The Dutch coast is protected by an extensive system of dunes, barriers and dikes, but the model raises a practical question: whether authorities could issue a clear warning and move people away from exposed waterfronts in time.
The researchers want the government to test a dedicated tsunami message through the national alert system and assess whether 12 coastal municipalities need evacuation routes for a fast-onset surge. The proposed review is expected to begin this winter. No public warning has been issued, and the study says nothing can reliably identify a date for the scenario.
