Tsunamis are notoriously hard to detect in the open ocean. Yet, in the summer of 2025, scientists witnessed one as it happened — live.
It began with the most powerful earthquake in nearly 15 years. In July 2025, an 8.8 magnitude quake struck off Russia’s Kamchatka Peninsula. The shockwaves unleashed a tsunami that sped across the Pacific at over 400 mph (644 km/h). Within minutes, alarms blared in communities across the ocean basin.
Millions of people were told to evacuate, including more than two million in Japan. But as the waves raced across the sea, they triggered something unexpected — ripples high above Earth’s surface.
An earthquake that moved the sky
The enormous motion of the ocean disturbed the atmosphere above it, disrupting satellite navigation signals. This interference allowed scientists to see the tsunami almost in real time.
By pure coincidence, the US space agency Nasa had just upgraded its disaster alert system, Guardian, with artificial intelligence. The update enabled the system to automatically alert researchers to major events.
Around 20 minutes after the Kamchatka quake, the Guardian system confirmed that tsunami waves were heading toward Hawaii. The warning arrived 30 to 40 minutes before the first waves reached shore.
Thankfully, the waves that hit Hawaii were only about 5ft (1.7m) high. Minor flooding occurred, but no serious damage followed. Much of the tsunami’s energy dissipated across the open ocean, and the largest waves struck uninhabited regions.
Those extra minutes of notice, though, could have saved countless lives if the disaster had been worse.
Listening to space to detect danger
This event proved that Nasa’s Guardian system can detect a tsunami long before it reaches the coast — simply by monitoring radio signals between orbiting navigation satellites and ground stations. The same technology can also detect volcanic eruptions, rocket launches and even nuclear tests.
“They were able to say, almost in real time, ‘there is a tsunami,’” says Jeffrey Anderson, a data scientist at the US National Center for Atmospheric Research. Anderson admits that when he first heard about the idea years ago, he thought it sounded “kind of crazy.”
The concept of using satellite signals to detect tsunamis dates back decades. A few scientists proposed it in the 1970s, but only in the 2020s did it become reality. In 2022, Anderson and researchers from Nasa’s Jet Propulsion Laboratory published details of the Guardian system.
Ripples that reach into space
A tsunami begins quietly in the open ocean, with waves often no higher than 10–50cm (4–20 inches). “It’s almost invisible while it’s travelling,” explains Yue Cynthia Wu, an ocean engineering researcher at the University of Michigan.
Yet these modest waves shift massive volumes of water. This motion displaces the air above, sending ripples into the ionosphere — a charged layer 30 to 190 miles above Earth. The ripples alter the number of electrons there, changing how radio signals travel.
“You have ionic reactions, temperature changes, everything gets out of balance,” says Michael Hickey, professor emeritus of physics at Embry-Riddle Aeronautical University.
Navigation satellites use dual frequencies to communicate with ground stations. When the ionosphere changes, the travel time of those signals shifts. By measuring the delay, Guardian can detect strange disturbances above Earth — clues that something big is happening below.
Turning noise into warnings
Engineers had long known that ionospheric changes affected GPS accuracy. Earth scientists realised they could use that same “noise” to detect natural disasters. “It’s smart people thinking outside the box,” says Anderson.
Researchers had already seen similar effects after major events. Hickey and his colleagues studied data from the 2011 Japan earthquake and tsunami, spotting vast ripples in the ionosphere above the region. The massive 2022 Tonga volcanic eruption also left visible traces in the sky.
But until 2025, no tsunami had been tracked in real time using this approach. During the Kamchatka event, the Guardian system followed the waves as they spread, while conventional buoys from NOAA’s DART network confirmed their height.
A new hope for early warning
Atmospheric tracking could allow scientists to spot tsunamis forming in the open ocean, long before they strike land. Such warnings could save lives and reduce false alarms.
The same technology can also confirm nuclear explosions. Ripples in the ionosphere even verified North Korea’s underground tests in 2009.
Traditional tsunami monitoring relies on seismometers and deep-ocean buoys. Those tools are useful but often slower and less comprehensive. “Minutes really matter for evacuation,” says Harold Tobin, a seismologist at the University of Washington. “Guardian’s early detections are a major advance for safety.”
Anderson adds that watching the ionosphere could help detect tsunamis triggered by landslides or other non-seismic events.
The next generation of sky watchers
Guardian may soon have company. “In Europe, we are developing our own system,” says Elvira Astafyeva of the Paris Institute of Planetary Physics. Her team plans to test it soon, aiming to monitor areas such as the Indian Ocean.
Hickey notes that tsunamis can also be detected through airglow — a faint light emitted by the upper atmosphere when disturbed.
Guardian itself remains a work in progress. Anderson says upcoming upgrades could let it forecast wave behavior automatically. “It would allow automated detection and prediction of where and when waves will strike,” he explains.
Every ten minutes, such a system could issue forecasts of a tsunami’s size, direction and landfall time.
Limitations and promise
Not all communities would benefit equally. Diego Melgar, an expert at the University of Oregon, notes that the ionosphere takes minutes to respond to a tsunami. For people close to the epicentre, that delay may be too long.
However, tsunamis can cross entire oceans. The 2004 Indian Ocean disaster took two hours to reach Sri Lanka and seven hours to reach East Africa. Systems like Guardian could provide vital warnings to distant coastlines in similar cases.
“If something’s travelling a long distance, it can absolutely save lives,” says Hickey.
