Satellite captures the first detailed look at a giant tsunami

Summary

When a magnitude 8.8 earthquake ripped through the Kuril-Kamchatka subduction zone on July 29, 2025, it launched a Pacific-wide tsunami – and a rare natural experiment.NASA and the French space agency’s SWOT satellite happened to pass overhead. The satellite captured the first high-resolution, spaceborne swath of a great subduction-zone tsunami.Instead of a single neat crest racing across the basin, the image revealed a complicated, braided pattern of energy dispersing and scattering over hundreds of miles. These are details that traditional instruments almost never resolve.The results go well beyond a pretty picture. They suggest the physics we use to forecast tsunami hazards – especially the assumption that the largest ocean-crossing waves travel as largely “non-dispersive” packets – need a revision.Satellites transform tsunami mappingUntil now, deep-ocean DART buoys have been our best open-ocean sentinels: exquisitely sensitive, but sparse, each giving a time series at a single point.SWOT maps a 75-mile-wide swath of sea surface height in one pass. This lets scientists see the tsunami’s geometry evolve in both space and time.“I think of SWOT data as a new pair of glasses,” said study lead author Angel Ruiz-Angulo of the University of Iceland. “Before, with DARTs we could only see the tsunami at specific points in the vastness of the ocean.”“There have been other satellites before, but they only see a thin line across a tsunami in the best-case scenario. Now, with SWOT, we can capture a swath up to about 120 kilometers (75 miles) wide, with unprecedented high-resolution data of the sea surface.”From eddies to a tsunamiNASA and the French space agency CNES launched SWOT in December 2022 to survey surface water around the world.Ruiz-Angulo and co-author Charly de Marez had been poring over its data for ocean eddies when the Kamchatka event hit. “We had been analyzing SWOT data for over two years understanding different processes in the ocean like small eddies, never...