Ride a jet ski through a re-creation of an Alaska mega-tsunami with the help of science

By Ella Nilsen, Sam Hart, CNN

(CNN) — The world’s second-tallest tsunami wave on record tore through the remote Tracy Arm fjord in Alaska last August, leaving immense destruction in its wake.

Luckily, there were no people nearby. But in its aftermath, scientists immediately went to work, piecing together what happens when a mountainside collapse kicks off a mega-tsunami and no one is around to see it.

This is how it happened: On August 10, at 5:30 in the morning, an entire mountainside at the mouth of the receding South Sawyer glacier detached, falling into the ocean and producing a monster wave. At its peak, the wave raced up over 1,500 feet on the opposing wall of the fjord — a height taller than Kuala Lumpur’s twin Petronas towers.

The mega-tsunami wreaked havoc across the landscape, stripping forests down to bare rock, ripping trees out by their roots and hurling boulders.

It also produced a seismic vibration so strong it shook the entire planet for days. Only the second time that an effect like this has been recorded anywhere, it was caused by trapped energy from the wave sloshing around in the fjord for days following the initial event.

In the months following the tsunami, a dozen scientists from the US, Canada and Europe have been doing “detective” work, attempting to “re-create this hazards cascade,” said Daniel Shugar, a geomorphologist and professor at the University of Calgary. The group published their findings in the journal Science on Wednesday.

Scientists see the fingerprints of climate change all over this event and several others like it that have occurred in recent years. Many of them have been linked to retreating glaciers, as melting ice destabilizes the mountains and land that had been covered for centuries.

“As the climate is changing, as glaciers are retreating, we are likely going to see more of these kinds of events in high latitude environments in the Arctic and the sub-Arctic,” Shugar said.

“I can barely believe it”

Even for scientists who study these kinds of disasters, the awe-inducing destruction and power of the Tracy Arm mega-tsunami is hard for the human brain to comprehend.

The mountainside that slid off to produce the skyscraper-size wave was, itself, more than 3,200 feet tall — higher than the world’s tallest building. Today, the mountainside looks bare, as though the 370 million metric tons of rock were scooped out as they slid into the ocean below, leaving a concave scar.

When tsunami modeler and researcher Patrick Lynett traveled with a team to the site of the landslide months later for field work, he was left in awe by the disaster’s magnitude.

“I saw it in real life, and I can barely believe it,” said Lynett, a professor at the University of Southern California.

It may seem odd that such a disaster left no injuries or deaths. But the sheer height of tsunami waves doesn’t always correspond with the number of fatalities. Counterintuitive as it might be, the deadliest tsunamis in the world happened with much smaller waves than either Tracy Arm or the 1958 Lituya Bay tsunami — the current record-holder for biggest wave. (Lituya Bay killed between 2 and 5 people, sources differ.)

Landslide-induced tsunamis can best be thought of as a big splash set off by many tons of rock falling into deep water, often in narrow channels like mountain fjords. Just like when you throw a big rock into a river, the splash happens quickly. Colossal as it was, the Tracy Arm wave happened in just 45 seconds to a minute.

Earthquake-caused tsunamis may have waves that are shorter in height, but they are much longer both in the length of a wave, and the period of time the wave lasts — 20 to 30 minutes, as opposed to one minute. That helps explain why the 2004 tsunami in the Indian Ocean and the 2011 earthquake and tsunami in Japan were so much more deadly.

“It may not go up as high vertically, but there’s a tremendous amount of water,” Lynett said. “It can flood much further inland, because it just keeps coming.”

Scientists have been vexed by the problem of how to communicate the sheer size of a wave like the one in Tracy Arm in a way that feels real — so they recreated it in a video game. Lynett admitted it’s an unconventional approach for a group of engineers to take.

“It’s not our goal to do graphic artistry,” he said. But putting people in an immersive environment to experience the tsunami without the deadly consequences of being there in person turned out to be the best way to help people grasp the scale.

“If you can have them experience that disaster digitally, they will recall it as something close to the real event,” Lynett said. “It’s much better than reading about it.”

Enter the jet ski.

The videogame shows the perspective of the landslide and tsunami wave from the point of view of someone riding a jet ski — trying to outrun a towering wall of water before quickly being overwhelmed by it.

Lynett said the point is public education in a tangible way, raising awareness for people who live in coastal Alaskan communities, as well as tourists flocking to see its glaciers.

“As engineers, we can build things really strong, and we can make them survive the events,” he said. “It’s not just how strong you can build things, it’s really training people how to understand and react.”

Danger to cruise ships

But the main reason scientists do this geologic detective work is to understand why exactly landslides of this magnitude happen. Every piece of new information can help them try to reduce the risk going forward, when the next one strikes, Shugar said.

“I certainly hope that we don’t get a repeat event this summer, but it’s entirely possible,” he said. “As hazard scientists, as disaster scientists, we want to minimize the risk to people and infrastructure from these events.”

While no one died in Tracy Arm and similar Alaskan tsunamis have so far happened in remote areas, there’s a real risk the next one won’t be as casualty-free. It’s not a theoretical worry; Alaska is teeming with cruise ships and tour boats promising a close-up view of hulking glaciers.

The Tracy Arm mega-tsunami happened early enough in the morning that none of these boats were around. But that was pure luck; the fjord is a popular spot for cruise ships and tour boats that bring ice-chasing tourists up close to snap pictures of shrinking and calving glaciers — more than 20 boats per day have visited in past years, including large cruise ships carrying up to 6,000 passengers and crew.

In fact, a National Geographic Venture cruise ship moving slowly towards the glacier was about 15 miles away from the event when it occurred. They saw white water washing up on the surrounding walls of the fjord and felt “strong currents … from many different directions,” according to email correspondence from the ship’s captain to a researcher.

“All of the curves of the fjord up near the glacier must have reduced the height of the wave and force just enough, though still very powerful, which is probably why we are still floating and not smashed into the wall of the fjord,” Captain Thomas Morin of the National Geographic ship wrote. The fjord bends, combined with the ship being far enough away and in deep water, were key factors that saved them.

At least three major cruise lines have since announced that they are suspending routes into the Tracy Arm fjord this year, swapping the route for the nearby Endicott Arm fjord. Experts say these precautions are necessary, but caution other areas could be prone to similar events.

Last year’s mega-tsunami was a “good wake up call” to the cruise industry, other marine vessels and policymakers, Shugar said.

“These risks are real,” he said. “It’s only a matter of time, I think, before one of these near misses turns into a real disaster.”

Slow-moving landslides are rampant across Alaska, where scientists have mapped more than 1,000 instances. Some are moving literal inches; others more than 10 feet per year. Sometimes, like in the case of Tracy Arm, they fail spectacularly and dangerously.

Scientist Bretwood Higman is the foremost Alaska expert on tracking these types of landslides, and is worried by the evidence he sees that catastrophic failures seem to be happening more frequently — both in Alaska and other countries, including Greenland.

“When we look back over the last couple 100 years, we see one of these happening about every 20 years,” said Higman, co-founder and executive director of nonprofit Ground Truth Alaska. But in the second-to-last decade, that number had increased to two, and in the last decade it was six such events.

“We have what seems to be a ten-fold increase,” Higman said. Despite the results being based on limited data, he said, “I think that pattern is real.”

Still, there’s a lot that scientists don’t know about how to predict future giant landslides or the tsunamis they could cause. Tracy Arm, in fact, still poses a bit of a mystery despite the work done to recreate the event. Besides nearly imperceptible seismic tremors that preceded the August landslide, “there were no obvious signs in the months to years prior that this slope was prone to failure,” Shugar said. Other steep mountain slopes in Alaska are moving down to the water faster than this one appeared to be.

The federal government and the state of Alaska are largely flying blind when it comes to tracking these types of landslides.

There is only one — Barry Arm, 60 miles east of Anchorage on the Alaska coast — that is continuously monitored by the federal US Geological Survey. Others in the area are checked periodically from satellites or aircraft. The Trump administration’s federal layoffs and budget cuts last year winnowed some the teams on the lookout, especially in Alaska’s heavily visited national parks.

In addition to informing policymakers and expanding research resources to find out more about the genesis of these events, scientists say more public awareness that these events are even happening is key. And if it takes a virtual jet ski to make that happen, so be it.

“We can never remove the risk of something calamitous happening,” Shugar said. “I think that the onus is not just on the cruise ship industries or the policymakers, but also on the individual citizens” to understand the potential dangers involved with a cruise ship trip or a backpacking expedition in the rugged wilderness near receding glaciers and sloping mountains.

These areas, he said, are “never going to be risk free.”

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