Seismic Signals Reveal Secrets of Greenland's Fjords

On September 16, 2023, a strange seismic noise shook the world. This noise, called a seismic signal, was like a loud whisper from deep within the Earth that lasted for nine whole days. A month later, it decided to show up again, but this time it was a little quieter and shorter, lasting only a week. Scientists quickly got to work, scratching their heads and checking their data to find out what was going on.

#A Big Splash in Greenland

The scientists guessed that these odd noises were linked to some huge landslides in East Greenland. These landslides had caused massive waves, called mega-tsunamis, to splash around in a fjord. A fjord is just a fancy word for a deep, narrow sea or lake, usually surrounded by tall cliffs. In this case, the fjord was doing some serious sloshing because of the landslides.

But here’s the kicker: while many scientists had theories based on computer models and numbers, nobody had actually seen or measured these giant waves, or seiches, directly-until now! Thanks to a cool satellite mission called Surface Water Ocean Topography (SWOT), a group of scientists was finally able to get a glimpse of what was happening.

#The Satellite Comes to the Rescue

SWOT is like a superhero in the sky, gathering loads of data about how the ocean surface changes. It can measure the height of ocean waves more precisely than your friend who's really into surfing. The scientists used this data to check whether the weird Seismic Signals were indeed caused by the seiches in the fjord.

After ruling out other possible reasons for the strange signals, they confirmed that these seismic noises were indeed linked to the seiches formed by the mega-tsunamis. They even figured out that the initial height of the wave was about 7.9 meters-impressive for a wave that doesn’t have to share the ocean's stage with any boats!

#The Climate Factor

The scientists noted that extreme events like these are becoming more common due to climate change. The warming planet affects how our rivers and seas behave. In remote places like the Arctic, where there aren’t many measurement tools, scientists find it tricky to study these changes. They rely on mathematical models that can simplify things too much, which sometimes leads to errors.

The signals from the seismic events were also a reminder of how quickly things can change in nature. Just a month later, another landslide triggered another wave of seismic noise on October 11, 2023. It wasn't as strong as the first one, but still surprising to the scientists.

#A Detective Story Unfolds

To understand the seismic signals better, scientists turned to the combination of data from both the satellite and seismic sensors stationed in the area. They found that the seismic waves were behaving just as they expected based on their models of the seiches. However, they also noticed that estimating the initial height of the seiches was no small feat. Different studies had come up with different numbers, ranging anywhere from 2.6 to 8.8 meters.

In essence, the scientists became detective-analysts, using different methods and data to try to solve the mystery of the seiches. They looked at charts, analyzed graphs, and crossed their fingers for some solid conclusions.

#The Fjord: A Dramatic Setting

Now, let’s talk about Dickson Fjord, where this whole drama was unfolding. It’s a stunning place tucked away in East Greenland, surrounded by glaciers. That means it’s not just chilly; it’s freezing most of the year. The fjord gets covered in ice for most of that time, only showing its true colors when things warm up in the summer.

The fjord stretches about 38 kilometers long and has widths varying from 2.5 to 3.2 kilometers. It’s deep too-ranging from 150 meters to 700 meters. This impressive backdrop only adds to the story of how nature can throw a tantrum; a good reminder to respect its power.

#The Landslide Connection

The two mega-tsunamis that triggered these seismic signals came from landslides caused by the melting glaciers. As the ice melted away, it weakened the ground, leading to rocks and ice tumbling into the water below. The scientists documented these landslides and the waves they created.

For the first event, they saw waves around 200 meters high at the slide’s location, and 60 meters high spread across the fjord. The second event wasn’t quite as dramatic, but there were still noticeable waves, causing some damage.

#A Workout for the Scientists

The scientists had their work cut out for them. They had to analyze tons of data from different sources, including satellites and ground sensors, to create a clear picture of what was happening. They used various techniques to process the data, filtering out noise and distractions.

They even used something called machine learning, which might sound like something out of a sci-fi movie, but it's just a smart way of analyzing data using computers. It helped them make sense of the measurements they gathered.

#Ruling Out Other Causes

Even with the evidence pointing to seiches, the scientists had to make sure nothing else was at play. They considered other things that could cause the strange slopes seen in the fjord, such as tides and wind-driven circulation.

Using advanced data analysis, they checked for the influence of tides and found that they could not be the source of the noise. They also ruled out the impact of wind fluctuations, which might push water around but wouldn’t create the same kind of standing waves that they were seeing.

#The Satellite's Fine-Tuning

One important aspect of the SWOT mission was its ability to measure ocean surface height at a very fine scale. Instead of just looking straight down like traditional satellites, SWOT could scan the water surface from the side, getting a broader view. This allowed scientists to spot variations in the water level that matched the predictions made by their models.

By carefully comparing the seismic data to the satellite observations, the scientists were able to estimate the initial amplitude of the seiches with greater accuracy. They found that the slopes observed from the satellite data corresponded nicely with the seismic measurements.

#The Conclusion: A Seiche in Action

This scientific adventure brought the team to an important conclusion: the persistent seismic signals originated from seiches in Dickson Fjord. They even managed to estimate the maximum cross-channel slope, a measure of the height of the seiche, using the data from both the satellite and ground sensors.

Ultimately, their findings confirmed that the first seismic signal was indeed linked to the gigantic waves caused by the mega-tsunamis. And there you have it-a mystery solved with a mix of satellite data, seismic science, and a good dose of teamwork.

#The Takeaway

What’s the big lesson here? Nature is constantly changing, and these changes can have dramatic effects, especially in our remote and fragile environments. Understanding how these events happen is crucial, especially as climate change continues to impact our planet.

Moreover, the importance of tools like SWOT cannot be overstated. Such satellites can give us invaluable insights into extreme events that would be otherwise difficult to measure, enabling scientists to stay one step ahead of nature’s surprises.

It's a wild and captivating story, filled with twists and turns. Who knew that a simple seismic signal could lead to so much excitement and discovery? For those of us not directly involved in these scientific adventures, it’s a reminder of how much is still out there in our world, waiting to be uncovered!