Fjords

A fjord forms where a glacier has eroded a valley below or near sea level and the sea later enters the valley. Ice flowing through an existing valley can abrade bedrock and remove loosened rock, deepening and widening the route into a glacial trough. After the glacier retreats, seawater floods the lower valley. The result is a long inlet connected to the sea, often with steep sides and a broad, U-shaped cross-section.

Fjord development is not a single, uniform process. Many fjord valleys were shaped and reworked during more than one glaciation. The strength and arrangement of the bedrock, the route and volume of flowing ice, and other landscape processes help determine a fjord's length, depth and form.

Many fjords have their deepest water in the middle or inner reaches, while the entrance is shallower. A shallow submarine ridge, or sill, may separate a deep basin from the open sea. This pattern can result from differences in how strongly glaciers eroded the valley along their route; it is common, not a rule that describes every fjord. Steep valley walls may continue far below the water surface, while waterfalls and hanging valleys occur where smaller tributary valleys meet the deeper main trough.

Fjords are not all identical. Their cross-sections, bends and depth profiles vary with local rock type, geological structures, ice flow and later modification. A study of fjord landscapes in southern South America found that their orientations commonly follow geological structures; the researchers proposed that successive glaciers widened and deepened these pre-existing routes. The example illustrates how ice erosion and bedrock can shape a landscape together.

Fjords are found along coasts that have experienced extensive glaciation. They occur in Arctic and Antarctic regions, as well as along the coasts of Norway, Greenland, Canada, Alaska, southern South America and New Zealand. Their presence is therefore not limited to Scandinavia, although Norway is especially well known for its fjord landscapes.

In southwestern Norway, Geirangerfjord and Nærøyfjord are recognized together as the UNESCO World Heritage property “West Norwegian Fjords – Geirangerfjord and Nærøyfjord.” UNESCO describes them as classic examples of fjord landscapes, with narrow, steep-sided rock walls, deep water, waterfalls, rivers, glaciers and surrounding mountains. They also illustrate how a geological landform can be part of a wider natural and inhabited landscape.

Because fjords expose deeply eroded valleys and preserve features such as rock basins, sills and glacial deposits, they provide evidence about past ice movement and landscape change. Mapping their shapes and the geological structures beneath them can help researchers reconstruct how glaciers used and modified valleys over successive glaciations. Fjords are consequently studied as part of glacial geomorphology and the history of formerly ice-covered regions, not only as coastal scenery.