Scientists uncover “unprecedented” vibration that lasted 9 days after tsunami

In September last year, a glacier melted. The melting triggered a massive landslide, which triggered a 200-meter-high mega-tsunami in Greenland. And then something inexplicable happened: a mysterious vibration shook the planet for nine days.

Last year, dozens of scientists around the world tried to figure out what this vibration was.

Now they have an answer, according to a new study published in the journal Science — one that provides yet another warning that the Arctic is entering “uncharted waters” as humans push global temperatures ever higher.

Some seismologists thought their instruments were broken when they began picking up vibrations in the ground in September, said Stephen Hicks, a study co-author and seismologist at University College London.

It wasn’t the rich orchestra of high tones and rumbles you’d expect from an earthquake, but more of a dull hum, he told CNN . Earthquake signals tend to last minutes; this one lasted nine days.

He was perplexed, saying this was “completely unprecedented.”

Seismologists traced the signal to eastern Greenland, but were unable to pinpoint a specific location. So they contacted colleagues in Denmark, who had received reports of a tsunami triggered by a landslide in a remote part of the region called Dickson Fjord.

The result was a nearly year-long collaboration between 68 scientists from 15 countries, who analyzed seismic, satellite and ground data, as well as tsunami wave simulations to solve the puzzle.

The result was a nearly year-long collaboration between 68 scientists from 15 countries, who analyzed seismic, satellite and ground data, as well as tsunami wave simulations to solve the puzzle.

What happened is called “cascading risk” Svennevig said, and it all started with man-made climate change.

For years, the glacier at the base of a massive mountain nearly 4,000 feet (1,210 meters) high above Dickson Fjord has been melting, as have many glaciers in the rapidly warming Arctic.

As the glacier thinned, the mountain became increasingly unstable, until it finally collapsed on September 16 last year, dumping enough rocks and debris into the water to fill 10,000 Olympic-sized swimming pools.

The subsequent mega-tsunami — one of the largest in recent history — triggered a wave that was trapped in the narrow, winding fjord for more than a week, bouncing back and forth every 90 seconds.

The phenomenon, called “seiche” refers to the rhythmic movement of a wave in an enclosed space, similar to water splashing back and forth in a bathtub or glass. One scientist even tried (and failed) to recreate the impact in his own bathtub.

Although seiches are well known, scientists had no idea they could last so long.

“If I had suggested a year ago that a seiche could persist for nine days, people would have shaken their heads and said that’s impossible,” said Svennevig, who compared the discovery to suddenly finding a new color in the rainbow.

It was this seiche that created seismic energy in the Earth’s crust, scientists discovered.

This may be the first time scientists have directly observed the impact of climate change “on the ground beneath our feet,” Hicks said. And no place was immune: The signal traveled from Greenland to Antarctica in about an hour, he added.

Global warming and melting ice

No one was injured in the tsunami, though it devastated centuries-old cultural sites and damaged an empty military base. But that stretch of water is on a commonly used cruise route. If anyone had been there at the time, “the consequences would have been devastating,” the study authors wrote.

East Greenland had never experienced a landslide and tsunami like this before, Svennevig said. It shows that new areas of the Arctic are “coming into line” for these types of weather events, he added.

As the Arctic continues to warm — in recent decades, the region has warmed four times faster than the rest of the world — mega-tsunamis triggered by landslides could become more common and deadly.

In June 2017, a tsunami in northwest Greenland killed four people and swept away homes. The threat extends beyond Greenland, Svennevig said; similarly shaped fjords exist in other regions, including Alaska, parts of Canada and Norway.

What happened in Greenland last September “once again demonstrates the ongoing destabilization of large mountain slopes in the Arctic due to amplified climate warming,” said Paula Snook, a landslide geologist at the Western Norway University of Applied Sciences who was not involved in the study.

Recent rock avalanches in the Arctic, as well as in alpine regions, are “an alarming sign,” she told CNN . “We are thawing soil that has been in a cold, frozen state for many thousands of years.”

There is still much research to be done on rock avalanches, which are also affected by natural processes, warned Lena Rubensdotter, a researcher at the Geological Survey of Norway who was also not involved in the study.

However, she added, it is “logical to assume that we will see more frequent rockfalls on permafrost slopes as the climate warms in Arctic regions.”

The discovery of natural phenomena behaving in seemingly unnatural ways highlights how this part of the world is changing in unexpected ways, Svennevig said. “It’s a sign that climate change is pushing these systems into uncharted waters.”

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This content was originally published in Scientists uncover “unprecedented” vibration that lasted 9 days after tsunami on the CNN Brasil website.

Source: CNN Brasil

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