The World’s Biggest Mountain Range Begins In – Iceland?

There’s only one place in the world where you can walk along the world’s longest mountain chain.

It certainly may not feel like you’re doing so at the time. “It’s certainly spectacular, but – this?” you’ll think, as you walk down Almannagjá Gorge, deep in the heart of Iceland’s Thingvellir National Park. The walls of the gorge are severe-looking, but they’re not really that high, and the land around is soft and green. It’s ruggedly beautiful, for sure. But – this?

You’re more likely to hear about the gorge’s human history, as it’s the site of the world’s longest-running, ongoing parliament, the Alþing. The laws of the day would be read out by lawmakers standing up on these rocks, settling disputes, representing the interests of local families and trying to bring everyone together.

But Almannagjá is the place where the non-human world is coming apart at the seams. The walls of the gorge are different continents: one side is the North American tectonic plate, the vast slab of rock that underlays the whole of the United States and stretches westwards as far as Russia – and facing it across the gorge is the Eurasian Plate (everything east of Iceland, until it circles the globe and hits the North American Plate on the other side). That’s why there is a gorge in the first place. It’s because Iceland is unzipping itself.

In a few million years, Iceland may be hundreds of kilometres wider in both directions – or it’ll have split in two, or reared and sunk into the surrounding oceanic crust, or something much, much weirder. The only certainty here is that it won’t look anything like it does today.

Thingvellir National Park
Thingvellir National Park

Far below the Thingvellir National Park, rock is slowly pushing its way upwards, squirting up into that gap left between the Eurasian and North American plates as they creep apart. That pressure is filling the space between them with new rock, remaking Iceland from the bottom up – and pushing each continental plate away from its neighbour, at the rate of a few centimetres a year.

But it’s not just happening to Iceland.

If you know your way around a snorkel, you can follow the line of this baby mountain range as it runs southwest, into the astoundingly clear water at Silfra, where the rocky walls of each tectonic plate are on either side of you, and below is a fissure running down into darkness. But if you wanted to go further – well, you’ll need lights. And a submarine. And that rarest of things until very recently: a reliable map of the sea floor of the Atlantic.

Here we have two people in particular to thank – geologists Marie Tharp and Bruce Heezen, whose work overturned the common assumption that the floor of the Atlantic was mostly flat and featureless:

“Navy regulations meant Tharp couldn’t go out on the research vessels that Ewing and her other colleagues chartered. Even if she had, they would not have been hospitable places for women (one of the deep sea cameras Ewing took on his journeys was affectionately dubbed “The Pyrex Penis” due to its phallic appearance). Instead, she stuck to her drafting table, collaborating with geologist Bruce Heezen on a map of the ocean floor.

For years, Heezen collected the data while Tharp crunched the numbers and charted them out. It was thankless work in a time before computers; Tharp had to comb through an enormous pile of sonar soundings and plot out her measurements by hand. Still, she found inspiration in the very mystery of the task. “The whole world was spread out before me,” she recalled in a 1999 essay about the Lamont-Doherty Earth Observatory. “I had a blank canvas to fill with extraordinary possibilities … It was a once-in-a-lifetime – a once-in-the-history-of-the-world – opportunity for anyone, but especially for a woman in the 1940s.”

Then, something unexpected showed up on Tharp’s canvas: a huge valley in the middle of the gigantic ocean ridge she was mapping. It was so deep that she kept re-checking her calculations. If it was what she thought it was, she would have evidence of a rift valley inside a ridge at the bottom of the North Atlantic Ocean.”

– “Seeing Is Believing: How Marie Tharp Changed Geology Forever,” Erin Blakemore, Smithsonian Magazine

Lakes and Mountains in Thingvellir National Park
Lakes and Mountains in Thingvellir National Park

Nowadays, thanks to their data, we know it broadly looks something like this utterly beautiful NatGeo relief map from 1968. As is customary for relief maps, the vertical scale is exaggerated – but this map does convey the staggering magnitude of what we’re looking at. It’s a rift valley comparable to the Grand Canyon, but stretching for – how far? 

Answer: the Atlantic portion alone is about 16,000km – but it’s also connected to other oceanic trenches of a similar nature, creating a continuous chain running for a jaw-dropping 65,000km.

This makes it, by far, the longest mountain range on our planet, which we’ll never see because it’s covered in kilometres of seawater, making it arguably one of the least accessible places on Earth.

(This isn’t idle hyperbole, and I’m including the ends of the earth here. Yes, Antarctica’s Transantarctic Mountains are terrifyingly inhospitable, being not too far away from where the coldest temperature ever recorded on our planet – minus 89.2°C – was measured in July 1983. But in instant lethality, that’s small potatoes compared with what would happen to you in a split-second were you to step outside your submarine into an Abyssal Zone, with more than 4,000 metres of seawater pressing down on you.)

And don’t let Almannagjá Gorge fool you: these are mountains down here, on a scale you’d instantly acknowledge as mountainous if you could see it. The reason the Navy regulated Tharp and Heezen’s work was because mapping the sea floor was of vital importance to the military – not just to thwart potential incursions by Russian submarines, but to stop things like this happening:

“In 2005, the nuclear attack submarine USS San Francisco suddenly stopped dead in its tracks. The ship’s crew were thrown about, some over distances of 20 feet, and the majority of the 137-member crew suffered one injury or another—including one that would later prove fatal. Further inspection would explain what happened, and reveal that the submarine’s bow looked like a crushed soda can. USS San Francisco had run into an undersea mountain.”

– “15 Years Ago, a U.S. Navy Submarine Ran Into a Mountain,” Kyle Mizokami, Popular Mechanics

The Southern part of the Almannagjá Rift
The Southern part of the Almannagjá Rift

The biggest of these ‘sea mounts’ is just south of the Azores. It rises 4.5km (around 14,800 feet) from the sea floor to almost reach the surface of the Atlantic, with a summit that’s just 270 metres deep. For comparison: it’s about the size of Spain’s Gran Canaria, with an elliptical plateau covering 1,500 square km.

And despite that size, it was only discovered for the first time in 1927.

Another example, far to the south of Iceland where the floor of the Mid-Atlantic Trench is over 5 kilometres deep, and jinks west into a colossal transform fault, where the vast ocean plates to the north & south are slowly grinding past one another. On its corner is the mountain known as the Atlantis Massif (no connection to the famous legend). It’s around 16 km across, and climbs over 4,200 metres – which gets its summit to within 700 metres of the sea surface, rising all the way from the bottom of the Mid-Atlantic Ridge.

These are just numbers, so let’s make this real: that’s the same size as Washington State’s Mount Rainier, it’s one of the highest mountains in the US with its summit height of 4,392m.

If you put Rainier and this monster of a seamount next to each other, they’d look all of a pair. It’s just huge.

So, down the centre of the Atlantic runs this chain of newly-minted mountains, on a scale that would boggle our minds if we could ever see it (which is unlikely, to say the least).

Rock walls of Almannagjá Fault
Rock walls of Almannagjá Fault

 And 16,000 km to the south, at a latitude beyond the southernmost tips of South America, Africa and New Zealand, is Bouvet Island. This is a horrifyingly bleak place: 93% glacier-locked, bitterly cold and exposed, and hugely uninhabited since absolutely forever. But it’s also where the Mid-Atlantic Ridge ends, at the triple-boundary between the Africa, South American & Antarctic plates. 

As I wrote for CNN Travel a while back:

“Its cliffs are sheer. It’s almost entirely covered by a glacier. In winter, its seas are pack ice. And its nearest neighbor is Antarctica, 1,000 miles to the south. In short, idyllic. Reaching Bouvet: the entire island is a nature reserve – so unless you can make a compelling case for visiting, you’ll be blocked by Norwegian authorities. Get permission, and it’s now a simple matter of finding a research vessel, quickly mastering a valuable skill such as arctic geological surveying or marine biology and then getting someone to land you via helicopter. (There are no ports or harbors.) If all else fails, try becoming an amateur radio enthusiast: In 1990, a multinational expedition of operators spent 16 days on the island.”

And to think, it all started with a delightful stroll in the sunshine down a picturesque gorge in Iceland. That’s travel for you: you never know where these things will lead.


Wheel & Anchor will be circumnavigating Iceland in June 2024 on the Ms Seaventure – and taking a trip inland to see the continent-parting wonders of Thingvellir National Park in person. Download the tour’s brochure here.


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