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The World’s Most Incredible Undersea Tunnels

Written by Nicholas Suarez


The ocean – big, blue, beautiful, and a massive pain in the butt when it comes to getting around it. Having access to the coast is fantastic if you have a boat, but if all you have is, for example, a car, it’s more of an annoyance than anything else. For example, in the United States, the city of Seattle and Bainbridge Island are only a short ferry ride away. But if you have a crippling fear of the ocean and want to drive to it over land, it’s going to take around two hours and 90 miles of driving to reach it. If your fear of the ocean is particularly acute and you want to avoid the Tacoma Narrows Bridge – which, if you read our post on that, is probably understandable – then it would instead take you three hours and 146 miles.

You know what would solve this problem? A tunnel. A tunnel that runs under the ground, and under the water, allowing those with thalassophobia to breathe easy, knowing that, as opposed to having the ocean sit ominously beneath them, it’s instead just over their heads. Okay, maybe it won’t help them too much, but if you hadn’t guessed, this is a post about the world’s most incredible underwater tunnels.

Why Tunnels?

Before we get started, we should clarify that most “underwater tunnels” aren’t “underwater” in the sense of being built on the ocean floor. Instead, they’re drilled into the rock underneath the seabed. Some of them aren’t, however; stay tuned for more.

The next thing we should address is: why? What’s the practical reason for not just using a bridge, or a ferry? The answer is geography. Bridges can block off ships from accessing previously open waterways, while ferries require a lot of people working on them to, well, make them work. If there’s no crew to crew the ferry, then the ferry can’t ferry. That’s a brilliant sentence.

Underwater tunnels, then, are a solution with the best of both worlds. Like bridges, they work on their own, requiring only maintenance now and then, but they also leave the water far above them open to ships. It’s a win-win. This became especially appealing following the Second World War, when the car took over the Western world as the premiere mode of transportation.

So, the reasons, and the appeal, are clear. With that in mind, just how common are these underwater tunnels? Well, it depends on where you go, but let’s start with perhaps the most well-known one in the entire world.

The Chunnel


The Channel Tunnel is located in, big surprise, the English Channel. It’s a rail tunnel that connects the island of Great Britain with the European mainland on the other side, specifically France. It’s just over 50 kilometers (30 miles) long, and sits 75 meters (250 ft) below the water at its lowest point. It even has special trains for bringing your car along with you. We’ve already done a post on the Channel Tunnel, so we’ll keep things brief, but here’s the general summary.

The first ideas for the Channel Tunnel emerged in 1802, right at the beginning of the Napoleonic Wars. Sterling timing on that one, chief. But the idea floated around for a long time afterwards; it was even advocated for by Winston Churchill, of all people. It came back into style in the latter half of the 20th century, and was accepted by the British government. It began construction in 1988 before opening six years later.

The task was, by no means, an easy one. The tunnel didn’t need to just work – it needed to work perfectly, all of the time. So, how do you make an undersea tunnel, undersea-worthy? In the case of the Channel Tunnel, building the tunnel directly in the water was impractical, so instead, they tunneled underneath it. The drilling had to occur in a layer of chalk, which was the only part of the sediment conducive to tunnel building. From there, it was business as usual, building with concrete and rebar and drilling through the rocks at the proper angles until they came out the other side. Well, actually they dug from both sides at once and met in the middle, but… details.

That’s the short story of the Channel Tunnel; again, if you want more info, we did an entire episode on it. Still, it’s far from the only example of undersea tunnels, even in Europe. Indeed, there’s one region that seems to be absolutely infatuated with them. With that in mind, let’s go north and pay them a visit.

Nordic Models


Scandinavia is undeniably the world capital of undersea tunnels. To prove that, let’s start with the outer reaches of Scandinavia, specifically, the Danish Faroe Islands.

The Faroes are an archipelago in the middle of the North Sea, and importantly, they’re close enough to each other that it’s possible to connect them by bridge or by tunnel. Usually it’s a tunnel, because boats are pretty important to an island locality. Who’d have guessed.

And in that sense, the Faroes are pretty well off. Nearly every island in the archipelago is either connected, or being connected by current projects, the most notable of which is the Eysturoyartunnilin, which is also known by the earlier name of… that.[NS1]  The Eysturoy Tunnel, as it’s known in English, is the largest undersea tunnel in the Faroes, connecting the two largest and most populous islands. It also has the distinction of having the world’s first undersea roundabout. Fancy.

They’re not done, either. There’s currently a tunnel under construction to connect the second-southernmost island to the rest of the archipelago, as well as a proposed project to connect that island, Sandoy, to the most southern island, Sudoroy. These, when completed, would probably make the Faroes one of the most tunnel-happy places, per capita, in the entire world. But it has some stiff competition in that arena – in its own neighborhood, no less.

We’re still technically in Denmark with this next one, but we’re moving to Denmark proper, specifically the Oresund Strait, between Denmark and Sweden. Here, a bridge was built across the strait to connect the two countries, but interestingly, the bridge dives down partway across the strait, turning into an undersea tunnel. And this, unlike the Channel Tunnel or later examples, is “properly” undersea; it’s a so-called “immersed tube”, built in a trench dug directly out of the seabed and then reinforced with a huge amount of concrete, made in onshore drydocks in 55,000 ton segments.

Why do it this way? Well, it’s cheaper than digging under the ground itself. It’s also more safe to construct, since they’re usually prefabricated on land and then dropped into place in the water. This was how the Drogden Tunnel, as it’s called, was built. Lastly, if there’s no seismic activity to speak of, then you generally only have to worry about sufficiently waterproofing the tunnel.

The Drogden tunnel may soon have company. There’s currently a project, in its earliest stages, to connect the northern coast of Germany with the Danish island of Lolland with the same immersed tube tunnel design. It was first proposed as a bridge as far back as 2000, and has since spent some time in development hell as it was pushed back several times. But it is, as of now, under construction, meaning one may soon be able to drive directly from Lubeck to Copenhagen over the Fehrman Belt.

But all of this rather pales in comparison when we move one space over from Denmark and Sweden to the country of Norway, the queen of tunneling under the sea. Norway has more than thirty subsea tunnels, with several more proposed or under construction. Why does Norway, of all places, have so many tunnels?

The answer lies, once again, in geography. The vast majority of Norway consists of mountains, fjords, and hundreds upon hundreds of islands. Extremely pretty, as anyone who’s been there can attest, but for anything practical it’s something of a hindrance. That means if someone wants to get somewhere, usually their only option is by boat. Or it was, at least, until Norway decided to start connecting.

The first undersea tunnel that Norway opened was the Vardø Tunnel in 1983, connecting the small island village of, take a guess, Vardø, to the Norwegian mainland. It’s a cute little town, and the easternmost town in Norway – further to the east, in fact, than even St. Petersburg or Istanbul. Geography is weird like that.

After that, it was off to the races. Dozens of tunnels went up in the next few decades, including the Ryfast, a tunnel system with the distinction of being both the world’s longest and deepest subsea tunnel. Running from the city of Stavanger, Norway’s fourth-largest city, under the nearby Hogsfjord, the Ryfast stands at 14.3 kilometers (8.9 mi) long and reaches as far down as 292 meters (958 ft) below sea level. When it was completed, this tunnel broke the records for both of these measurements, which at the time were held by subsea tunnels that were… also built in Norway. Norway just loves these things.

But, like the Faroes, they aren’t done yet. There’s a project underway to construct another tunnel under the same fjord as the Ryfast, further along the coast, which would make the Hogsfjord similar to the Faroes as one of the most tunnel-happy places in the world. In addition, Norway is currently experimenting with a new way of designing subsea tunnels, namely one that doesn’t have to be drilled underneath the water or lie on the seabed.

As we’ve said, Norway’s geography consists of fjords, long stretches of water situated between mountains. Some of those fjords are simply too deep to practically build a tunnel on or under them. The most salient culprit is the Sognefjord, the largest and deepest fjord in Norway that essentially forces Norwegians on opposite sides of it to either take the ferry or pound sand. Or snow, in this case.

But some people believe that, with a little ingenuity, this can be overcome. The idea is to create a suspended undersea tunnel – essentially, one that floats underneath the water. Such a project has actually been proposed by the Norwegian Public Roads Administration, projecting it to cost around 25 billion USD. Adjusting for inflation, that’s about the same cost as the Channel Tunnel, which, when it was proposed, was the most expensive construction project in history. So yeah, a lot of money.

Whether such a project actually gets built is another matter. To start with, it’s an untested theory; a floating tunnel, at least not one on this scale, has never been built before. Second, there isn’t much reason why an old-fashioned suspension bridge can’t be built in its place. Granted, the bridge would be enormous – even taller than the Eiffel Tower – and also vulnerable to storms that occasionally strike the Sognefjord, but it’s certainly doable. In any event, the project is still in the planning stages, and it may or may not result in yet another undersea tunnel for Norway’s collection.

So, that about does it for Europe’s undersea tunnels, but Europe isn’t the only place in the world to have invested so heavily in such infrastructure. With that said, let’s head to the other side of the continent, to East Asia.

Concrete Coasts


When it comes to underwater tunnels in Asia, the big two contenders are China and Japan. This makes sense – Japan is an archipelago, making underwater infrastructure a useful investment, and China just likes building infrastructure in general, for better and for worse.

Let’s start with Japan. The most notable tunnel they have is the Seikan Tunnel, which is a 53 kilometer (33.5 mile) railway tunnel that connects the main island of Japan, Honshu, with the northern island of Hokkaido. Through this tunnel, someone can catch a train from Tokyo all the way to Sapporo, without stopping to get on a boat mid-journey.

This tunnel, like the Channel Tunnel, has a long history. It was first mulled as an idea in the early 20th century, but only gained serious attention after World War II, when Japan lost its empire and needed to basically rebuild the entire country from scratch. Further pressure was put on when a number of passenger ferries sank in 1954 during a typhoon, resulting in the deaths of many passengers.

Surveys were carried out following this instance, and the groundwork was laid. Work officially commenced in 1971, seventeen years after the 1954 typhoons, and the tunnel officially opened in 1988, another seventeen years later. What lovely symmetry. The tunnel stood as a symbol of post-war recuperation, and the accomplishment was so impressive that other countries took note. Later that year, a Japanese company would formally be brought on to help with the construction of the Channel Tunnel, providing expertise in the creation of the boring machines that would dig through the ground.

Lastly, there is China. As we’ve said, China loves its infrastructure, having the largest high-speed rail network of any country on Earth. But recently China has been looking to expand that infrastructure further, and one of the targets is water. To that end, they’ve constructed several underwater tunnels, particularly on the coastline for large cities such as Shenzhen.

Last year, however, they went a step further. Just before the turn of the New Year, China officially opened the Taihu Tunnel, currently its longest underwater tunnel at 10.8 kilometers. It’s a highway tunnel, meaning its for cars, and it runs under the appropriately-named Lake Taihu, China’s third largest freshwater lake. As China continues to urbanize and more Chinese people are able to afford their own cars, it seems likely that China will invest more into infrastructure to ensure that cities are travelable. The Taihu Tunnel will not be the last.


And, for the most part, that’s the overview of the world’s many underground, underwater tunnels. There’s some we didn’t mention, like the Maastunnel in the Netherlands which is basically the only reason traffic in Rotterdam isn’t unbearable. On the other side of the Atlantic, America has a few underwater tunnels, going underneath its many rivers, such as Hampton Roads in Virginia’s part of the Chesapeake Bay, or the Massachusetts Bay Outfall, which… well, that one’s a sewage outlet. But hey, technically correct, at least.

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