100-foot tsunami silently strikes Alaska fjord after rock as big as 40,000 Olympic-sized swimming pools crashes into sea

Something truly astonishing happened in Alaska on Sunday. A mega-landslide and tsunami struck the Tracy Arm south of the city of Juneau. An Alaska seismologist said that the region had been hit by "hundreds or thousands of very small" earthquakes for several hours before the landslide, and the tsunami waves were likely 100 feet in areas near the source. However, no one knew about this event for hours after it happened. The remote event was not reported until a trio of kayakers woke up to waves crashing inches away from their camps on Harbor Island, an uninhabited islet in Holkham Bay. At this point, two of Southeast Alaska’s most-visited fjords, Tracy Arm and Endicott Arm, converge. They had pitched their tents far from the high tide line.

Also Read: 'Waves of Destruction': Top 10 deadliest tsunamis that shook the Earth in last 500 years

A huge chunk of a mountain collapsed into sea in Alaska

But on Sunday morning, Sasha Calvey was woken up by the sounds of crashing waves. She was shocked to see that all of their gear was gone, and their kayaks were in different places, on a cliff, in a tree, and one floating a quarter mile offshore. They alerted the Alaska state seismologist, Michael West, who noted that seismometers across North America were indeed rattled. West says it seems like the "side of a mountain" collapsed into the water, triggering tsunami waves, leading to the water levels rising. He believes tens or hundreds of millions of cubic meters of rock and debris tumbled down the mountain.

Also Read: 'Ryo Tatsuki was right': 8.7 earthquake in Russia sets social media abuzz with Japan's Baba Vanga's prophecy

Rock the size of “a couple of football fields” crashed into the sea in Alaska

This event, near the end of Tracy Arm, where South Sawyer Glacier reaches tidewater, triggered a truly colossal tsunami. “We're talking about a cube of rock, that is, you know, a couple of football fields on each side,” West told Alaska Public. A photo taken by Nick Heilgeist, one of the kayakers who was rescued, shows an island in the fjord with all vegetation submerged, except for a lone tree. West says more analysis and studies are required to understand what happened and the aftermath of the landslide, but going by the pictures, the tsunami wave "was at least 100 feet tall in some areas near the source."

Also Read: Why tsunamis are so dangerous—and what actually causes them | WION Explains

The waves continued to splash around for hours. A tide gauge in Juneau picked up the movement and fluctuations of around a foot several times were recorded in the hours after the landslide. West said that a series of small tremors were recorded before the bigger slide. “Modest earthquakes, but hundreds or thousands of very small ones. This landslide had a very clear precursory sequence, and that is not something we have often observed," he said.

Also Read: Russia earthquake: No, the tsunami has not left Beluga Whales stranded

The earthquakes were not automatically detected since the region is outside of the Earthquake Centre’s recently expanded landslide detection coverage. The landslide signal was detected not only by nearby seismic stations, but also by stations located 1,000 km away. This proves that the landslide was a truly mammoth "rare geologic event", which West says scientists around the world will study for years to come.