9 days, every 90 seconds: Greenland megatsunamis that triggered global earthquake were real

Scientists have successfully observed for the first time two megatsunamis that shook the world for nine days in 2023. The global seismic signal was recorded every 90 seconds. It was only after a year that the cause was revealed to be two megatsunamis in a remote East Greenland fjord. However, it was merely a theory till now, as no proof of the event had been found. Even a Danish vessel that visited Greenland three days after the first seismic signal did not see the megatsunami waves.

Now, using the new Surface Water Ocean Topography (SWOT) satellite, launched in December 2022, scientists have captured evidence of the Greenland megatsunamis, according to observations made using the SWOT satellite published in Nature Communications.

Waves got caught in a narrow inlet in Greenland

In September 2023, a glacier in Greenland, bearing the brunt of global warming, triggered two landslides. The waves that were unleashed got caught in between a fjord - a long, narrow sea inlet formed by a glacier and steep sides or cliffs.

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The sky-high water swayed in this inlet, resulting in standing waves, also known as seiches. This movement resulted in mysterious seismic signals that were recorded across the world, every 90 seconds for nine days. They were again reported a month later.

Oxford researchers interpreted satellite altimetry data using the new technique. They measured the time a radar pulse took to travel from a satellite to Earth's surface and back again to deduce the height of Earth's surface, including that of the ocean.

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Satellite captured the megatsunamis

Conventional satellite altimeters failed to capture any evidence of the megatsunami because their technology could not spot the differences in water height needed to spot the waves. However, the SWOT has two antennas mounted on a 10-meter boom on either side which enables it to measure ocean and surface water levels with great accuracy along a 50 kilometre wide area.

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Elevation maps of the Greenland Fjord showed "cross-channel slopes with height differences of up to two meters" at the time the megatsunamis hit. They also moved in opposite directions, proving that the water caught there moved back and forth.

The study authors said that climate change is driving quick shifts in remote areas, like the Arctic. Satellites like SWOT can help them record these. Lead author Thomas Monahan of Oxford said, "Climate change is giving rise to new, unseen extremes.

These extremes are changing the fastest in remote areas, such as the Arctic, where our ability to measure them using physical sensors is limited."

"This study shows how we can leverage the next generation of satellite earth observation technologies to study these processes."