2025 Close Call

We all know what a tsunami is, right?  Big-a$$ wall of water like what hit several countries December 26, 2004 after an offshore earthquake – that one was 30 meters tall and killed 226,000 and change. Wiki – Tsunami  Heck of a Boxing Day present to the world.

Now, tsunamis essentially come from a only few sources – an earthquake can cause one, or something like a volcanic explosion can trigger one. However, if a big chunk of land slides into water – look out. The water gets pushed away rapidly, and depending on many factors such as depth and width of the body of water, it can get pretty hairy.

Let’s wander to the Tracy Arm – a fjord (meaning its depth exceeds its width) southeast of Juneau. Last August a chunk of slope slid into the water.

Using imagery and digital elevation models from before and after the slide, the researchers estimate that at least 2.26 billion cubic feet of earth collapsed, resulting in a loss of about 500 feet of coastline. They think the rupture likely extended even farther below the water’s surface but lack the bathymetry data to prove this.

“The resulting tsunami reached more than 1,500 feet up the side of the fjord and sloshed back and forth like bathtub water, creating a seismic ‘ringing’ that could be detected around the world for up to 36 hours.”

For those of us a little slow on math, that means the wall of water was just under 1/3 MILE high. And this is a fjord that gets lots of tourist traffic, tour boats, etc. How many fatalities?

Zero.

The wave knocked vegetation and topsoil off the walls of the fjord, but at roughly 0530 in the morning, no tourists were upwater (is that even a word?)  of the wave. No fatalities at all.

Alaska seems to get lucky like that – the tallest tsunami on record was at Lituya Bay in 1968. Five killed, but that one was a couple hundred feet.

“The largest tsunami wave ever recorded broke on a cool July night in 1958 and only claimed five lives. A 1,720 foot tsunami towered over Lituya Bay, a quiet fjord in Alaska, after an earthquake rumbled 13 miles away.

“This massive tremor triggered around 30.6 million cubic meters of rock to fall 3,000 feet into the Lituya Glacier, causing a torrent of displaced water to rear up and form a monstrous wave which, miraculously, only killed five people.”  Surfer

Hopefully we’ll stay lucky. (More so than the 437 folks killed in the 2018 Sunda Strait tsunami caused by a collapse of the flank of Anak Krakatau. You should remember that one.)

Oh, and if you want to know where the potential is for an even larger tsunami? Urban legend says a Canary Island volcano, Cumbra Vieja, could dump 350 cubic kilometers of land into the Atlantic in one shot, and the resultant tsunami hitting our East Coast 8 hours later would be 160 feet tall and reach 12 miles in land. New York, Boston, DC, Miami… okay, you’re tempting me – but the actual odds of a meta-tsunami staying intact across thousands of miles of ocean, continental shelf edges, etc. are so far past minimal – Jane Fonda would probably get the veteran’s vote first. Mark that one right up there with the “Yellowstone Caldera blowing”.

Category: Reality Check, Science and Technology