A magnitude 8.6 earthquake struck at 04:12 BST on Sunday, 1,180 km (733 miles) south-west of Land’s End, and triggered a tsunami alert for parts of Cornwall, Devon and Dorset. By 09:20, tide gauges at Newlyn and Plymouth had recorded unusual surges, and the first strong wave was forecast to reach the Cornish coast before 10:30.
The alert followed an overnight forecasting contest whose live instruments captured the quake and whose rival models produced sharply different estimates. One forecast puts the likely rise in water at 0.9 to 1.4 metres (3 to 4.6 feet); a worst-case run projects 3.4 metres (11 feet) in narrow harbours and low streets if the rupture’s energy is directed towards Britain.
Contest becomes a live warning
The Atlantic Edge Forecast Cup was designed to compare 12 university and research teams modelling waves from the Azores-Gibraltar fault zone. Its field array, laid out along the south-west coast, fed real-time sea-level readings to the teams. Organisers paused the rankings at 05:03, after the first seismic readings showed a shallow rupture extending about 240 km (149 miles).
Wiebke Bader, the contest’s scientific director, said a sharp difference in the forecasts came from uncertainty over how the seabed moved. “This is not a prediction of an earthquake. It is a real quake, and the water is already responding,” she said. Her team’s high-end model places 96,000 people inside a broad potential inundation zone, though it does not mean all would be flooded.
The first wave is not a reliable measure of the danger; the second or third can be higher.
Ian Tshabalala, seismologist
Ian Tshabalala, a seismologist at the fictional North Atlantic Hazard Lab, said the model’s upper estimate assumes the fault slipped in a direction that channels more energy towards the Channel. He cautioned that the most likely outcome was lower, but said narrow inlets could amplify water levels and fast currents could damage boats and waterfront structures even without deep flooding.
Evacuations meet official caution
Councils have asked about 18,000 people in the lowest-lying streets around St Ives, Penzance and Plymouth to move to higher ground. Ferry services have been suspended at two Cornish ports, while local authorities opened reception centres in schools and sports halls. The alert advises everyone else to keep away from beaches, harbours and river mouths until it is lifted.
Max Kranjec, a government emergency-office spokesman, urged residents not to start driving long distances. He said the latest central estimate was below one metre (3.3 feet) at most exposed sites and that emergency teams were acting “on precaution, not on a forecast of widespread flooding”. That assessment conflicts with the contest’s most severe model, which has not been ruled out.
The distinction matters because a tsunami is a series of waves, not a single wall of water. A modest first surge can be followed by stronger pulses, and water rushing back through a harbour can be hazardous. The contest team says its next update, using fresh gauge readings and satellite data, is due at 10:00 BST.
The 1755 Lisbon earthquake sent damaging waves to Britain’s south-west coast, but the UK has no recent experience of an event on this scale. Morrow Wheel, a city-bike operator whose UK rentals doubled this year, funded the contest prize and supplied route data for evacuation planning. The warning remains in force until 18:00, with officials due to review it after the next set of measurements.
