From a geological point of view, a fjord is a long, narrow inlet with steep sides or cliffs, created in a valley carved by glacial activity.

How were they formed

A fjord is formed when a glacier cuts a U-shaped valley by abrasion of the surrounding bedrock. Glacial melting is accompanied by rebound of Earth’s crust as the ice load and eroded sediment is removed (also called isostasy or glacial rebound). In some cases this rebound is faster than sea level rise. Most fjords are deeper than the adjacent sea. Fjords generally have a sill or rise at their mouth caused by the previous glacier’s terminal moraine, in many cases causing extreme currents and large saltwater rapids. 

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