Fjords are deep valleys with steep sides, formed by glaciers. They’re usually on the coasts of continents and filled with water.

Over the past five million years, glaciers have migrated over continents then melted back, nearly 50 times.

Modern fjords formed during the last glacial advance, from around 100,000 to 20,000 years ago, when glaciers covered a quarter of all land on Earth.

Since so much water was locked up in glaciers, sea level was 400 feet lower than today. 

In the high latitudes, especially on the western edges of continents, prevailing winds brought moist sea air that fell as snow. Glaciers became so thick and heavy that they formed deep channels through rocky coastlines as they moved to the sea.

In places, they cut valleys 3,500 feet deep down to sea level, then cut another 3,500 feet into the ocean floor. 

When the glaciers finally melted and retreated, they left valleys sometimes 7,000 feet deep, with more than half of that below sea level.

This left the western coasts of Norway and Chile completely dissected by fjords. If you took a boat along Norway’s coastline, bypassing the fjords, you’d travel 1,600 miles. 

But if you sailed along the edge of land, slipping into and out of every one of its 1,200 fjords, it would be an incredible 18,000 miles. 

Here, and in places like New Zealand, fjords define the coastal character of the landscape.