Scientists have made the first direct observations of a strange seismic event that shook the world for nine consecutive days in 2023 and confirmed its cause: two “mega-tsunamis” that sloshed around an East Greenland fjord.
The signal was initially a mystery to scientists, but ground and satellite imagery traced the likely culprit to landslides in the fjord.
Now, the theory has been confirmed by a new satellite that tracks water on the surface of the ocean.
This study shows how we can leverage the next generation of satellite Earth observation technologies to study these processes.”
SWOT data taken above the fjord during the two mega-tsunamis revealed two cross-channel slopes moving in opposite directions between it, confirming their presence.
In 2023, two “mega-tsunamis” sloshed around an East Greenland fjord, causing a strange seismic event that rocked the world for nine days in a row. Scientists have now made the first direct observations of this event.
For nine days in September 2023, the enormous waves—one of which was 650 feet (200 meters) high, or roughly half the height of the Empire State Building—entered Dickson Fjord in East Greenland and rocked back and forth, sending seismic waves that echoed through the earth’s crust.
Scientists were first baffled by the signal, but satellite and ground imagery identified the likely cause as landslides in the fjord. Following the melting of a glacier behind the fjord due to climate change, these landslides released the waves, also referred to as seiches. Nevertheless, there was no concrete proof of these seizures.
The theory has now been validated by a new satellite that monitors ocean surface water. The results were released in the journal Nature Communications on Tuesday, June 3.
“Climate change is giving rise to new, unseen extremes,” said Thomas Monahan, the lead author of the study and a University of Oxford graduate student for engineering science. “In remote locations like the Arctic, where we have limited access to physical sensors, these extremes are changing the fastest. This study demonstrates how we can investigate these processes using the newest satellite Earth observation technologies. “,”.
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In satellite altimetry, scientists typically use radar pulses sent from orbit to the ocean’s surface to measure the height of tsunami waves based on the time it takes for the pulses to return.
However, satellites cannot measure the variations in water height in confined areas like those inside the fjord because of their long coverage gaps and the fact that their instruments can only measure what is beneath them.
The scientists used data from the new Surface Water and Ocean Topography (SWOT) satellite, a collaboration between NASA and CNES, the French space agency, to verify the seiches’ existence. The satellite was launched in December 2022 and maps 90% of the ocean’s surface using a device known as the Ka-band Radar Interferometer (KaRIn).
KaRIn measures water levels with a resolution of up to 8.2 feet (2.5 m) along a 30-mile (50 km) arc by triangulating the return signals of radar pulses using two antennae placed across a boom on either side of the satellite. This technique yields previously unheard-of accuracy.
Two cross-channel slopes traveling in opposing directions between the fjord were confirmed by SWOT data taken above it during the two mega-tsunamis. In addition to weather and tidal readings, seismic observations taken thousands of miles away allowed the researchers to reconstruct the waves and establish a clear connection between them and the enigmatic seismic signals.
In the statement, co-author Thomas Adcock, an engineering science professor at the University of Oxford, said, “This study is an example of how the next generation of satellite data can resolve phenomena that has remained a mystery in the past.”.
He went on to say, “We will be able to get new insights into ocean extremes such as freak waves, storm surges, and tsunamis.”. However, we will need to be creative in interpreting our new findings and apply both machine learning and our understanding of ocean physics to make the most of these data. “.
