Mysterious 650-foot mega-tsunami recorded by satellites

 Mysterious 'mega-tsunamis' sends seismic waves worldwide for nine days 

A new satellite has captured the first direct evidence of a mysterious nine-day seismic signal that shook the world in 2023. Scientists have made the first direct observations of a strange seismic event that shook the world for nine consecutive days and confirmed its cause: two "mega-tsunamis" that sloshed around an East Greenland fjord. Greenland’s eastern edge rarely causes a stir. Then, with no warning, seismic instruments across the world lit up at the same time with a slow, steady rhythm which lasted for nine full days. The pulse rose and fell every ninety-two seconds. The rumble was far too soft for people to feel, but strong enough to rattle bedrock from Alaska to Australia. No typical earthquake behaves that way. Scientists soon linked the signal to Greenland’s Dickson Fjord, a narrow inlet hemmed in by 3,000-foot cliffs on each side. Fresh satellite images showed a new scar where a section of mountain had vanished. Something colossal had struck the water and set the fjord in motion.

The gigantic waves, one of which measured 650 feet (200 meters) high, or about half the height of the Empire State Building, entered East Greenland's Dickson Fjord and rocked back and forth for nine days in September 2023, sending seismic waves reverberating through the planet's crust. The signal was initially a mystery to scientists, but ground and satellite imagery traced the likely culprit to landslides in the fjord. These landslides unleashed the waves, known as seiches, following the climate-change-induced melting of a glacier behind the fjord. However, no direct evidence of these seiches was found. On 16 September, 2023, more than 25 million cubic yards of rock and ice, enough to fill 10,000 Olympic-size pools, broke loose and plunged into Dickson Fjord. The impact hurled up a mega-tsunami wave, reaching about 650 feet high. The surge barreled down the two-mile corridor, bounced off the headland, and tore back again, wrecking roughly $200,000 in equipment at an empty research post on Ella Island. Water did not calm after the first pass. Instead, it began rocking from wall to wall. Computer models later showed the surface rising as much as 30 feet, then sinking the same amount in a steady rhythm that pressed on the seafloor like a giant piston.

The mystery drew seventy-plus researchers from forty-one institutions. “When we set out on this scientific adventure, everybody was puzzled and no one had the faintest idea what caused this signal,” said Kristian Svennevig of the Geological Survey of Denmark and Greenland. “All we knew was that it was somehow associated with the landslide. We only managed to solve this enigma through a huge interdisciplinary and international effort.” Now, the theory has been confirmed by a new satellite that tracks water on the surface of the ocean. Field teams measured fresh gouges high on the cliffs, while supercomputers recreated the avalanche’s path and the fjord’s response. “It was exciting to be working on such a puzzling problem with an interdisciplinary and international team of scientists,” said Robert Anthony of the US Geological Survey. “Ultimately, it took a plethora of geophysical observations and numerical modeling from researchers across many countries to put the puzzle together and get a complete picture of what had occurred.” Conventional radar altimeters see only a thin line beneath each spacecraft. By contrast, the Surface Water and Ocean Topography (SWOT) mission launched in December 2022 maps a 30-mile-wide swath with 8-foot resolution. “Climate change is driving the emergence of unprecedented extremes, particularly in remote regions like the Arctic, where our ability to monitor conditions using traditional physical sensors is limited,” explained Thomas Monahan of the University of Oxford. “SWOT represents a breakthrough in our ability to study oceanic processes in areas such as fjords, places that have long posed challenges for earlier satellite technologies,” Monahan continued. This study highlights how next-generation Earth observation satellites can transform scientific understanding of these dynamic environments. “This study demonstrates how advanced satellite data can finally illuminate phenomena that have eluded us for years,” remarked Professor Thomas Adcock, also from Oxford. “We’re now gaining new insights into oceanic extremes like tsunamis, storm surges, and rogue waves. To fully harness the potential of these new datasets, we’ll need to push the boundaries of both machine learning and our understanding of ocean physics,” Adcock concluded.

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 shows how we can leverage the next generation of satellite Earth observation technologies to study these processes. Glacier ice once buttressed the failing slope, but warming air and ocean water have eaten away at that natural brace. “Climate change is shifting what is typical on Earth, and it can set unusual events into motion,” Gabriel noted. Similar instability elsewhere triggered a deadly tsunami in Karrat Fjord in 2017 which destroyed eleven houses and claimed four lives. Though no passengers were present last year, the episode highlights rising risks as Arctic travel grows. Authorities are now reviewing early-warning options which combine satellite feeds with real-time seismic data. Seismic stations normally record frantic scribbles during earthquakes. This time, the trace formed smooth peaks spaced a minute and a half apart and barely weakened over the better part of two weeks. No seiche had ever produced such a persistent global signature. One modeling group pegged the slosh at about 8½ feet; a second group estimated 23 to 30 feet. The disagreement stemmed from different assumptions about Dickson fjord’s shape, but both sets of simulations agreed on the source: the landslide-driven wave.

Typically, scientists study the movements of tsunami waves using a method called satellite altimetry, in which radar pulses are sent to the ocean's surface from orbit to measure a wave's height based on the time it takes for the pulses to return. But because satellites have long gaps in coverage and their instruments can only measure what's beneath them, they are unable to measure the differences in water height in confined areas like those within the fjord. “It was a big challenge to do an accurate computer simulation of such a long-lasting, sloshing tsunami,” said Alice Gabriel of UC San Diego’s Scripps Institution of Oceanography. To confirm the existence of the seiches, the scientists turned to data captured by the new Surface Water and Ocean Topography (SWOT) satellite, a joint project of NASA and CNES, France's space agency. Launched in December 2022, the satellite uses an instrument called the Ka-band Radar Interferometer (KaRIn) to map 90% of the water across the ocean's surface. KaRIn works by using two antennae mounted across a boom on each side of the satellite to triangulate the return signals of radar pulses with unprecedented accuracy, measuring water levels with a resolution of up to 8.2 feet (2.5 m) along a 30-mile (50 kilometers) arc.

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. Seismic observations made thousands of miles away, alongside weather and tidal readings, further enabled the researchers to reconstruct the waves and conclusively link them to the mysterious seismic signals. Researchers are now combing through seismic archives looking for similar slow pulses, which may uncover other natural disasters from the past that evaded detection. “This shows there is stuff out there that we still don’t understand and haven’t seen before,” said Carl Ebeling of Scripps. “The essence of science is trying to answer a question we don’t know the answer to – that’s why this was so exciting to work on.” Every new discovery will refine models of how slope failure, fjord geometry, and water depth interact. Better forecasts could one day provide critical minutes of advance warning for ships and settlements in high-latitude waters. Even the quietest corners of the planet deserve a closer listen. "This study is an example of how the next generation of satellite data can resolve phenomena that has remained a mystery in the past," Thomas Adcock, a professor of engineering science at the University of Oxford, said. "We will be able to get new insights into ocean extremes such as tsunamis, storm surges and freak waves," he added. "However, to get the most out of these data we will need to innovate and use both machine learning and our knowledge of ocean physics to interpret our new results."