Гренландын алслагдсан фьордод болсон хүчирхэг хөрсний гулсалтын улмаас дэлхий даяар 92 секунд тутамд чичиргээ мэдрэгджээ

In mid-September 2023, seismic stations around the world began picking up something that looked nothing like an ordinary earthquake. There was no sharp jolt, no sequence of tremors gradually dying away. Instead, the instruments recorded a steady pulse, repeating at precisely the same interval for hours, then days.

Sensors thousands of miles apart, from the Arctic to Antarctica, registered the same strange rhythm, which continued for more than a week before fading. Scientists initially had no explanation for it. Whatever was shaking the planet appeared to be coming from one of the Arctic’s most remote regions.

A Hum With No Obvious Source

The signal first appeared on September 16, 2023. Unlike earthquakes, which typically generate a jumble of seismic frequencies, it was remarkably clean: a monochromatic vibration at 10.88 millihertz, completing one cycle every 92 seconds. The frequency remained almost perfectly constant.

Seismologists classify such vibrations as very-long-period signals, far too slow for people to hear or feel directly. For up to nine days, the pulse traveled through the Earth, gradually losing strength without shifting its rhythm. Few recordings in modern seismology had looked quite like it.

Early calculations pointed toward East Greenland, a sprawling landscape of glaciers, mountains and deep fjords where monitoring equipment is scarce. Working out what had happened would require dozens of researchers from an international team, along with satellite imagery and observations collected in the field.

A Mountain Falls Into the Sea

At 12:35 UTC on September 16, a section of Hvide Støvhorn, a mountain peak rising roughly 1,200 meters (3,900 feet) above the water, gave way above Dickson Fjord in East Greenland. Rock broke loose and plunged toward the narrow inlet below, setting off a chain of events that would eventually be detected across the planet.

An estimated 25 million cubic meters (880 million cubic feet) of rock fell down the mountainside, sweeping up glacier ice and becoming a massive rock-ice avalanche. Its impact with the fjord generated a tsunami that climbed as high as 200 meters (650 feet) up the opposite slopes.

The scale of the destruction emerged in a study led by Kristian Svennevig of the Geological Survey of Denmark and Greenland, published in Science. The researchers reconstructed the collapse and the resulting tsunami using several lines of evidence. Along approximately 10 kilometers (6 miles) of the fjord, the water reached an average height of 60 meters (200 feet) on the surrounding rock walls.

The initial wave was enormous, but it did not account for nine days of steady seismic pulses. Something else was happening inside the fjord, and researchers needed to understand how the water had behaved after the avalanche struck.

Water With Nowhere to Go

In the open ocean, tsunami waves can travel outward and gradually disperse their energy. Dickson Fjord presented a different problem: its steep sides confined the water, while a sharp bend near the outlet restricted its escape toward the sea, as Angela Carrillo-Ponce and colleagues showed in The Seismic Record.

Instead of simply flowing away, the disturbed water began rocking back and forth. The motion developed into a seiche, a standing wave that forms when water oscillates inside a confined basin, rather like water sloshing from one end of a bathtub to the other. Computer simulations by Svennevig’s team indicated that the seiche reached a height of roughly 7 meters (23 feet).

With each oscillation, the water pressed against the fjord walls before swinging back and pushing again. Researchers calculated that the moving water exerted a peak oscillating force of approximately 500 billion newtons against the surrounding rock, setting the Earth’s crust vibrating and generating the recurring 92-second seismic signal.

The cycle continued for days, even as the water’s movement slowly weakened. Its persistence helped explain why instruments so far from Greenland had recorded what initially appeared to be an inexplicable seismic hum.

Seen From Orbit

The seismic records offered a convincing explanation, and the computer models backed it up. But there was still a missing piece: no instruments had directly captured the water moving inside the fjord. Confirmation eventually arrived from orbit, where a satellite was measuring changes in the height of Earth’s surface waters.

The evidence came from SWOT, a satellite built to measure surface elevations across oceans, lakes and rivers with exceptional precision. Its radar observations offered researchers a way to examine the water’s movement inside Dickson Fjord rather than relying entirely on seismic measurements and simulations.

In a study published in Nature Communications in June 2025, Thomas Monahan and colleagues examined SWOT radar observations to map the fjord’s water surface in two dimensions. The satellite data revealed a height difference of up to 2 meters (6.5 feet) between opposite sides of the fjord, with the surface tilt reversing as the trapped water swung in the other direction. The movement matched what the seismic models had predicted.

To reconstruct the wave’s earlier strength, the researchers combined the satellite observations with seismic recordings from Alert, a station in northern Canada. Their calculations put the seiche’s initial amplitude at approximately 8 meters (26 feet). Weather records and tidal models also helped rule out two more ordinary explanations, since neither wind nor tides could account for the oscillation.

A Slope Weakened From Below

The question of why the mountain collapsed led researchers back to the glacier supporting its lower slopes. Over time, that glacier had been thinning, gradually stripping away the support that helped hold the rock above it in place. Eventually, the mountainside could no longer sustain its own weight, a process Svennevig’s team identified as a glacial thinning-induced landslide.

Greenland had experienced destructive landslide tsunamis before. In 2017, a mountainside collapsed into Karrat Fjord in western Greenland, sending a wave into Nuugaatsiaq and destroying the village. But the September 2023 disaster marked the first documented large tsunami-generating landslide in East Greenland.

Nor was the September collapse the end of the activity at Dickson Fjord. On October 11, 2023, less than a month after the original event, another section of the same mountainside failed. The second landslide was smaller, but it again sent rock crashing into the water and produced a fresh seismic signal, recorded from the same remote stretch of Greenland’s coast.

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