Key takeaways
- A fjord is a glacial valley drowned by rising sea level, which is why it is so much deeper than a river valley.
- Where the glacier lost power it dumped its load of rock, leaving a shallow bar that traps cold water in the basin behind.
- These mountains are worn roots of the Caledonian range, raised by a continental collision hundreds of millions of years ago.
- Relieved of the weight of ice, the whole coast is slowly rebounding upward, which is measurable today.
What a fjord actually is
The word gets applied loosely to any dramatic inlet, and the precise meaning is worth having because it explains the landscape you are driving through. A fjord is a valley cut by a glacier and subsequently flooded by the sea. Ice made it; water only moved in afterwards.
That distinction produces a shape you can read from the road. A river erodes downward at the lowest point of its channel, producing a V. A glacier is a mass of ice hundreds of metres thick that grinds the whole valley floor and both walls simultaneously, producing a broad U with steep sides and a flat bottom. Once you have noticed the difference you cannot stop seeing it.
Why they are so deep
Because a glacier has no reason to stop cutting at sea level. It is driven by its own weight and it keeps grinding downward as long as it is moving, which means fjord basins routinely lie hundreds of metres below the surface, often considerably deeper than the open shelf just outside the mouth.
The ice here was thick. During the last glacial maximum the whole of northern Scandinavia lay under an ice sheet, and the valleys you see were being deepened by something that dwarfed any glacier alive today. What retreated left the troughs behind, and as the ice melted worldwide, sea level rose and filled them.
A glacial valley meeting the sea on the coast west of Tromso
The sill at the mouth
Every classic fjord has one and it is the detail that makes fjords behave unusually. A glacier carries an enormous load of ground rock, and where it finally lost momentum it dropped that load in a bar across the mouth of the valley. The result is a fjord that is deep inside and shallow at its entrance.
That geometry has real consequences. Cold, dense water is trapped in the basin behind the sill and exchanges only slowly with the open sea, so the depths of a fjord are a cold, dark, stable environment year round. It also means the sheltered water inside is unusually calm, which is why this coast could be settled and worked at all.
Rock much older than the ice
It is easy to assume the mountains and the valleys are the same age. They are not, and the gap is enormous. The rock here belongs to the Caledonian range, thrown up when continents collided several hundred million years ago in an event that also raised the Scottish Highlands and the Appalachians, which were then part of the same chain.
What stands today is the worn stump of something once far higher, ground down over hundreds of millions of years. The ice arrived comparatively recently and carved valleys into that ancient stump. Two processes, unimaginably far apart in time, working on the same rock, and the landscape you are looking at is the sum of both.
U-shaped
The signature of a glacial valley. A river cuts a V by wearing at its lowest point; ice scours the floor and both walls at once.
When the ice left
Recently, in geological terms. The great ice sheet began retreating from this coast around fifteen to twenty thousand years ago and the process took millennia, with the sea flooding in behind it as global sea level rose.
That is why the landscape looks raw. There has not been time for weathering to soften the shapes the ice left, so the valleys are still recognisably glacial, the rock is still bare in places and the soil is thin. Compared with the rounded, wooded country of southern Europe, northern Norway looks like a landscape that was finished last week.
The land is still rising
This is the part people find hardest to believe and it is straightforwardly measurable. An ice sheet kilometres thick pressed the crust downward beneath it. When that weight was removed the crust began to rebound, slowly and steadily, and it has not finished.
The evidence is visible if you know to look for it. Flat terraces above the current shoreline are old beaches, cut by the sea when the water stood higher relative to the land, and now stranded well above it. Farms and settlements occupy them because they are the only flat ground on a steep coast. The land is still coming up at a few millimetres a year.
Why this is not a sea loch
Scotland has drowned glacial valleys too, and calls them sea lochs; so do New Zealand, Chile, Greenland and Canada under other names. The physical process is the same and there is no meaningful geological distinction.
What sets Norway apart is scale and quantity. The ice here was thicker and lasted longer, the rock was hard enough to hold the shapes it was cut into, and the coastline is long enough that the result runs to thousands of individual fjords. The word itself is Norwegian and it travelled with the landform, which is a reasonable summary of who did this best.
