Fjord

A fjord is a long, narrow sea inlet. It features steep sides or high cliffs within a valley. These valleys were created by former glaciers. Once the ice melted, the ocean moved in to fill the space.

This process makes them the glacial equivalent of rias. Rias are drowned river valleys flooded by rising seas. Fjords are found in many cold regions. They exist on the coasts of Antarctica and the Arctic.

They also appear on landmasses in both the northern and southern hemispheres.

The formation of a fjord follows a specific geological sequence. It begins with a glacier moving through a pre-existing valley. These original valleys often had gently sloping floors. The glacier uses ice segregation and abrasion to carve the bedrock. Abrasion is the scraping of rock by the moving ice. This process creates an overdeepened, U-shaped valley.

When the glacier retreats, the valley ends abruptly at a trough. If the ocean floods this deep trough, a fjord is born. In some places, the land rises after the ice disappears. This is called isostasy, or glacial rebound. This happens because the heavy weight of the ice is removed.

Fjords possess unique physical structures like sills and hanging valleys. A sill, or shoal, is a rocky area at the fjord's mouth. This occurs because the glacier's erosion rate decreased as it reached the sea. It can also be formed by a terminal moraine.

Sills often cause extreme currents or saltwater rapids. For example, Saltstraumen in Norway has very strong tidal currents. Another feature is the hanging valley. This is a tributary valley that sits higher than the main valley.

It forms when a smaller glacier flows into a larger one. These high valleys often create waterfalls that drop into the fjord.

Scientific understanding of fjords has evolved over many years. In the 19th century, Jens Esmark introduced a major theory. He proposed that glaciers created these deep inlets. He argued that thick ice once covered much of Northern Europe.

Not everyone agreed with him at first. John Walter Gregory argued that fjords had a tectonic origin. He believed glaciers played almost no role in their formation. However, later research rejected his views. The presence of rocky thresholds and overdeepened basins proves the glacial origin. These features are the strongest evidence for Esmark's theory.

Fjords are massive and can be much deeper than the open sea. The Sognefjord in Norway is a famous example. It reaches great depths well below sea level.

The scale of these systems is truly enormous. Norway has nearly 1,200 fjords along its coast. This creates an extremely complex coastline. This complexity is linked to the coastline paradox. The coastline is very long, but only if you exclude the fjords. The physical layout of these waters also creates skerries. Skerries are small, rocky islands or reefs.

They often form where ice-scoured channels meet the coast.

Life in the fjord is shaped by complex water movements. In winter, surface and deep waters often mix due to wind and cooling. In summer, rivers bring fresh water into the inner fjord. This creates a layer of brackish water on the surface. Brackish water is a mix of fresh and salt water.

This layer can block the circulation of deep, salty water. If the deep water does not mix, it can lose oxygen. This makes the seabed unsuitable for many animals. However, some fjords are very productive. Nutrient-rich meltwater can drive blooms of phytoplankton. These tiny organisms are the base of the food web.

Deep-sea ecosystems also thrive in these dark environments. In 2000, scientists discovered coral reefs in Norwegian fjords.

These reefs host thousands of lifeforms. They include plankton, anemones, fish, and even sharks. These species are adapted to high pressure and total darkness. In New Zealand, a layer of fresh water allows corals to grow shallower. This allows tourists to view them via underwater observatories. These biological systems make fjord coasts vital fishing grounds. The study of these communities remains an active area of research.