The Strait of Magellan: what it is and where it is

What the Strait actually is

The Strait of Magellan is a sea passage, not a river, not a lake and not a channel in the ordinary sense of the word. It is a 611 km stretch of open water that runs north to south between the Chilean mainland on the west and the Tierra del Fuego archipelago on the east, and it connects the Pacific Ocean to the Atlantic. What makes it unusual is not the length but the shape: at its narrowest, at the Primera Angostura, it is about 3.1 km wide, and in its deepest basins it reaches about 1,080 m. That is a canyon with the width of a race track on top of it, and it is why the water out there behaves the way it does.

The reason it exists is geological. The Andes were pushed up along the western edge of South America and the glacial carving of the last ice age cut a channel between the continent and the islands that lay offshore. When the sea levels rose at the end of the last glacial period, about 11,000 years ago, the channel filled with water and became what it is now. The navigation that Magellan made in 1520 was the first time anybody had been through it, and it was not obvious: finding it was the hard part, and Magellan's fleet spent weeks in the strait going the wrong way before it found the right channel.

The three sections, from east to west

It helps to think of the Strait as three sections, because they behave differently and the tours treat them differently.

The eastern section opens into the Atlantic at the Boca Oriental, between Cape Virgenes on the Chilean mainland and Punta Dungeness on the Argentine side. This is the mouth Magellan's ships sighted on 1 November 1520. The Strait then narrows twice in quick succession — the Primera Angostura, the critical passage for anything over a certain size, and the Segunda Angostura — before opening out again into the wide central basin where Punta Arenas stands, on the Chilean shore.

The western section, past Cape Froward, closes down toward the Pacific Mouth at Cape Pillar, with Desolation Island forming the outer wall. Between them are the islands: Clarence, Dawson, the remnants of the archipelago that the 1881 boundary treaty later divided between two countries.

Why nobody found it for two centuries of looking

European ships had been sailing around the southern tip of South America for two hundred years before Magellan. What they were looking for was a passage, and the reasoning went: if a strait connects the two oceans, it must be somewhere around the continent's southern end, and it must be a short one. The Tierra del Fuego archipelago looked like an obvious place for it, and explorers sailed into it repeatedly, including in 1527 when the admiral of France's expedition pushed his way through what is now the Strait of Magellan and came out the other side — without realising it. Magellan was the first to cross it and the first to understand what he had crossed.

It took until 1578 to make sense of the geography, when a ship under Drake was driven south by a storm, discovered that the Pacific was open, and sailed home the other way round the continent. From that point the Strait was known to be the only sea passage between the two oceans that does not go through the Arctic — and it became, almost immediately, a strategic question as much as a navigational one. The 1881 treaty between Argentina and Chile fixed the border down the middle of the water and through the islands, which is why the archipelago is split between two countries today.

What it is like to be on it

The Strait is at roughly 53°S, which means the weather is doing a lot of the talking. The southern westerlies are the dominant force: they run around the Southern Ocean and arrive at this latitude with nothing to slow them down. In the austral summer, from December to February, the days are long and the light is generous. Through the spring the wind builds, and the general rule is that the Strait is windier in the shoulder seasons than in the middle of summer, which surprises people who think of Patagonia as a place where it is always cold.

The Atlantic side receives the heavier rain; the Pacific side is drier and the skies are clearer over the Chilean channels. Water temperature is a separate matter from air temperature, and on a small boat in the shoulder season the difference is felt immediately. None of this makes the region unpleasant. It makes it specific: this is a place where the trip is decided by the weather on the day, and where an operator who knows the water is worth more than an operator with a cheaper boat.

How to plan a trip around it

Three days is the minimum that does the region justice, and five is where it starts to feel generous. The usual shape is two days in Punta Arenas for the water — the fort, the penguin islands, the full navigation — and one or two in Puerto Natales for Torres del Paine, which is 110 km from the park gate against Punta Arenas' 250 km.

That shape works because the two cities do different things well. Punta Arenas is the departure point for everything that involves a boat, and it is the only city in the region with an international airport. Puerto Natales is the base for the park, and almost every Torres del Paine tour leaves from there. The two are 247 km apart along the shore, about three and a half hours by scheduled bus, and the road itself passes the same landmarks the boats pass at a distance.

If you only have time for one city, choose by what you want to see on the water — Punta Arenas — or by what you want to walk — Puerto Natales. Trying to do both properly needs three days minimum, and four is better.