Fjords: ice-carved inlets, not river deltas
Deep glacial troughs flooded by the sea, found only at formerly glaciated, high-latitude coastlines
What it is
A long, narrow, deep sea inlet with steep rock walls, in mountainous high-latitude coasts.
How it forms
Past glaciers cut river valleys into deep U-shaped troughs, later flooded by rising seas.
The sill
A shallow underwater ridge at the mouth, marking weaker glacial erosion or deposited debris.
Not a ria
A ria is a drowned river valley, shallower and V-shaped, never deepened by ice.
What a Fjord Is, and How It Forms
Must KnowCarved by Ice, Not by Rivers
- A fjord is a long, narrow, deep inlet of the sea, with steep rock walls on either side. It forms in mountainous coastal regions at high latitudes.
- During past ice ages, glaciers carved existing river valleys into deep, U-shaped troughs. When the ice melted and sea levels rose, seawater flooded these troughs, creating a fjord.
- Glacial erosion cuts much deeper and wider than a river ever could. This is why a fjord’s floor often lies well below sea level. An ordinary river-carved inlet is never cut this deep.
- Fjords occur only in formerly glaciated, high-latitude coastal regions. Major examples include Norway, New Zealand, Chile, Alaska, Greenland, and British Columbia in Canada.
Q1. True or False: A fjord is a long, narrow, deep glacially-carved sea inlet, not a shallow river delta.
Q2. True or False: Fjords form when seawater floods a valley that was previously deepened by glacial erosion.
Think it through, before reading on. A river also carves valleys over time. So why does only glacial erosion, and not river erosion, produce a deep inlet like a fjord?
Show the explanation
A river cuts downward slowly and only along a narrow channel, leaving a shallow, V-shaped valley. A glacier, by contrast, is a massive moving body of ice that scours the entire valley floor and walls at once, carving a much deeper, wider, U-shaped trough. When sea levels later rise and flood that trough, the result is deep enough to sit well below sea level, which an ordinary river-cut valley never reaches. This is exactly why a fjord is called glacially-carved, not river-carved, even though a river valley is often where the glacier started.
The Sill, Hanging Valleys, and Notable Fjords
Good to KnowThe Sill, and the World’s Deepest Fjord
- Many fjords have a shallow underwater ridge, called a sill, at their mouth. It marks where the glacier’s erosive power weakened, or where it deposited debris, leaving the inner fjord deeper than the entrance.
- Sognefjord is Norway’s longest and deepest fjord, running about 205 km inland and reaching over 1,300 m deep in places. It is the country’s best-known example.
- Milford Sound in New Zealand is technically a fjord, not a true sound. It was carved by glacial action, not by a river valley later flooded by the sea.
- Fjords combine dramatic vertical relief with calm, deep water. Sheer rock walls often rise over 1,000 m straight from the water, frequently laced with waterfalls, producing some of the world’s most photographed coastal scenery.
Q3. True or False: The shallow underwater ridge near a fjord’s mouth, marking weaker glacial erosion, is called a sill.
Q4. True or False: Sognefjord, running about 205 km inland and exceeding 1,300 m deep, is Norway’s longest and deepest fjord.
Hanging Valleys and a Look-Alike Landform
- Where a smaller tributary glacier met a larger trunk glacier, the trunk glacier cut its valley far deeper. This left the tributary valley “hanging” above the main fjord floor, and its stream now falls as a waterfall into the fjord below.
- Norway’s Geirangerfjord and Nærøyfjord, both part of the West Norwegian Fjords, are inscribed as a UNESCO World Heritage Site. Their scenery draws both scientific interest and major tourism revenue for Norway.
- A fjord is easy to confuse with a ria, a drowned river valley formed purely by rising sea levels, without any glacial carving. Rias are typically shallower and more V-shaped, since they were never deepened by ice, unlike the article on hard, resistant rock that lets fjord walls stand as steep cliffs.
Q5. True or False: Hanging valleys sit above the main fjord floor because the trunk glacier cut its valley far deeper than the smaller tributary glacier could.
Remember the pairing. Glacial erosion, flooded by rising seas, equals a fjord. River erosion alone, flooded by rising seas, equals a ria instead.
Quick Q&A
What carves a fjord’s deep trough?
A glacier, during a past ice age, cutting far deeper than a river ever could.
What is a sill?
A shallow underwater ridge at a fjord’s mouth, where glacial erosion weakened or debris was deposited.
Which is Norway’s longest and deepest fjord?
Sognefjord, about 205 km inland and over 1,300 m deep.
How is a ria different from a fjord?
A ria is a drowned river valley, shallower and V-shaped, never carved by ice.
Previous Year Question
PYQUPSC Mains 2023, GS Paper I, Q6
- How Fjords Form — and Why They’re So Picturesque asked candidates to explain the glacial process behind fjord formation and why these coastlines draw such scenic appeal.
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