1,000-ft ‘mega-tsunami’ could wipe away large regions of US. When is it coming?

A “mega tsunami”, nearly 1,000 feet high, could destroy a large part of the United States, scientists have warned.

They say this could happen if a powerful earthquake hits the Cascadia Subduction Zone.

This warning comes from a new study by researchers at Virginia Tech, published in the ‘Proceedings of the National Academy of Sciences’.

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The study says the quake could make parts of the coastline sink by up to 6.5 feet, which would make the tsunami even more damaging.

In this explainer, we look at what a mega tsunami is, what the study has found, and which areas are most at risk.

Here’s a look:

What is a mega-tsunami?

Mega-tsunamis are not like regular tsunamis, which usually produce waves only a few feet high. These waves can reach hundreds of feet in height.

They are caused by major underwater events, such as powerful earthquakes, landslides, volcanic eruptions, or even meteor strikes.

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Unlike ordinary tsunamis, mega-tsunamis can push several miles inland with huge force. They can destroy coastal barriers and leave little time for people to escape.

Though rare, such events have happened in the past and could be very dangerous if they hit areas where many people live.

What does the recent study say?

The new study by geoscientists at Virginia Tech, published in the Proceedings of the National Academy of Sciences, says there is a 15 per cent chance of a magnitude 8.0 earthquake striking the region in the next 50 years.

Such a powerful quake could sink coastal areas by as much as 6.5 feet and could wash away major cities like Seattle and Portland, Oregon.

The areas at risk include Alaska, Hawaii and parts of America’s West Coast, if the earthquake happens along the Cascadia Subduction Zone, a fault line that runs from northern Vancouver Island to Cape Mendocino in California.

In that case, waves from a mega-tsunami could rise as high as 1,000 feet, putting millions of lives at risk.

Scientists said this kind of earthquake would strike suddenly, “within minutes,” offering no time for people to adapt or prepare, unlike changes caused by climate.

Tina Dura, lead author of the study and assistant professor at Virginia Tech’s Department of Geosciences, said in a statement, “The expansion of the coastal floodplain following a Cascadia subduction zone earthquake has not been previously quantified, and the impacts to land use could significantly increase the timeline to recovery.”

The study found the worst damage would likely occur in southern Washington, northern Oregon and northern California.

Alaska and Hawaii are also at risk, despite being further from the fault, due to their own history of earthquakes and volcanic activity.

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Cascadia subduction zone: What is it?

The Cascadia Subduction Zone is one of the most active earthquake zones in North America, with experts warning of a strong chance of another major quake in the coming decades.

This fault stretches around 700 miles, from northern California to British Columbia, and lies roughly 70 to 100 miles off the Pacific coast.

Over the past 10,000 years, there have been 43 recorded earthquakes along this fault.

The last known quake here struck on January 26, 1700. It was believed to be around magnitude 9.0, causing the coastline to sink and a tsunami to form and crash onto land, according to the Oregon Department of Emergency Management.

The department says Oregon could face another earthquake of magnitude 9.0 or more, along with a tsunami up to 100 feet high hitting the coast.

If such a quake occurs, people near the shore could feel five to seven minutes of shaking, with the force reducing the further inland it reaches.

Alaska, Hawaii and the West Coast: Why these regions are vulnerable

In 1958, a powerful earthquake in Alaska’s Lituya Bay triggered a massive landslide, sending millions of tons of rock into Gilbert Inlet.

The rock, about 2,400 feet by 3,000 feet in size and weighing up to 90 million tons, created the tallest wave ever recorded, a 1,719-foot mega-tsunami that swept across the bay.

Alaska remains highly prone to landslides due to its rugged landscape and frequent earthquakes, Daily Mail reported. Climate change is making this risk worse by melting glaciers, which weakens slopes and loosens rocks.

Meanwhile, Hawaii also faces a history of mega-tsunamis, caused by the collapse of volcanic slopes. Around 105,000 years ago, a 1,000-foot wave hit the island of Lanai, leaving marine fossils high up on its mountains.

The islands’ volcanoes grow by layers of lava, but these can become unstable and break apart, especially during eruptions or earthquakes. When large sections of rock fall into the ocean, they can trigger huge waves that threaten nearby islands.

Hawaii’s steep terrain makes these events especially dangerous.

Along the West Coast, a magnitude 9 earthquake on January 26, 1700, struck the Cascadia Subduction Zone.

It caused a mega-tsunami that wiped out the village of Pachena Bay within 30 minutes, with no survivors.

Scientists are working to improve early warning systems and evacuation plans, the report said. But earthquakes, landslides, and volcanoes continue to make these regions highly vulnerable.

As history shows, melting glaciers in Alaska , unstable volcanoes in Hawaii, and major quakes along the West Coast could all lead to deadly waves once again.