Whispers of Tsunami

Tsunamis are notoriously difficult to spot on the open ocean as they race towards shore. But in the summer of 2025, scientists watched one unfold as it happened.

It was the most powerful earthquake anyone had seen for nearly 15 years. It struck off the far eastern coast of Russia's Kamchatka Peninsula in July 2025 – an 8.8 magnitude quake that also triggered a tsunami with waves racing outwards at more than 400mph (644km/h). Within minutes, alarms sounded in communities around the Pacific Ocean.

Millions people were ordered to evacuate in the tense hours that followed, including at least two million in Japan alone. But as the wave propagated out across the ocean, it triggered something other than just fear – it created ripples in Earth's atmosphere.

The ocean, moving up and down across such a vast area, was disturbing the atmosphere above it and messed with global satellite navigation signals. But this disturbance also allowed scientists to spot the tsunami almost in real-time.

Purely by chance on the previous day, US space agency Nasa had added an artificial intelligence component to a disaster alert system called Guardian, enabling it to flag major events to scientists automatically. Roughly 20 minutes after the Kamchatka earthquake happened, tsunami-watchers knew that waves were heading for Hawaii, 30 to 40 minutes before they arrived.

The reason why navigation satellite signals can register a tsunami is because of the up-and-down motion of the sea. When a tsunami begins to form in the open ocean, its waves may not be very high – perhaps between 10-50cm (4-20 inches). "It's almost invisible while it's travelling in the open ocean," says Yue Cynthia Wu, a researcher in marine engineering at the University of Michigan who specialises in ocean wave dynamics.

This undulation, however, occurs on a gigantic scale, moving extremely large amounts of water at once. This movement displaces the air above it, which disturbs the atmosphere higher up, creating ripples in the layer of charged particles that form the ionosphere some 30 to 190 miles above the Earth's surface. The ripples alter the number of electrons present in parts of the ionosphere.

"You have ionic reactions, you change the temperatures, it gets out of whack," says Michael Hickey, professor emeritus of physics at Embry-Riddle Aeronautical University, in Daytona Beach, Florida, who has studied these atmospheric waves.

Navigation satellites use dual frequencies to communicate with ground stations on Earth, so increases in the number of electrons in the ionosphere can cause unusual delays in the time it takes for these two signals to arrive. By measuring those delays, systems such as Guardian can detect whether something weird is going on in the ionosphere.

GPS engineers already knew that signals got disturbed in this way – they have to adjust for this "noise" to ensure that navigation systems remain accurate. But it was Earth scientists who realised all that noise could be used to detect tsunamis.

"It's smart people thinking outside of the box," says Anderson.

In recent years, researchers have been able to see the fingerprints of tsunamis and volcanoes in data from the ionosphere. Hickey and colleagues retrospectively studied the impact of the 9.1 earthquake that struck off the northeast coast of Japan in 2011, which triggered a tsunami. "[We] saw the rings," recalls Hickey, referring to giant, outward-spreading ripples in the ionosphere above Japan that could be visualised using electron count data.

The enormous volcanic eruption in Tonga in 2022 also made a significant impression on the ionosphere, which scientists later analysed in detail.

But no major tsunami event had ever been tracked in real time using such methods – until the Kamchatka earthquake this year. Although forecasts of the tsunami were produced using the National Oceanic and Atmospheric Administration's DART tsunami detection system that uses buoys moored to the ocean floor, the Guardian system allowed the waves to be followed as it happened.

- Author: Chris Baraniuk, BBC

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