Glacier valley: what it is, how it is formed and examples

A U-shaped glacial valley is a type of valley that is formed by the action of moving glaciers, since they can advance and retreat, dragging rocks and material with them. They are generally U-shaped in width and depth and often have features such as moraines and glacial lakes.

1. Glacial movement

The glacier begins to move influenced by gravity and the slope towards lower heights. This movement, facilitated by a layer of meltwater at the base and by internal deformation of the ice, begins to form the valley over thousands and millions of years.

2. Valley erosion

As the glacier advances, it erodes the terrain through two main processes:

• Abrasion: Rocks and sediment trapped in the ice scrape and polish the valley’s rock surface, creating striations and grooves.
• Plucking: the ice adheres to the rocks of the bed and, when moving, tears off fragments that are incorporated into the glacier.

These processes transform “V” river valleys into wider and deeper “U” glacial valleys.

3. Transport and deposition of sediments

The glacier transports the eroded materials and deposits them in different areas as it retreats. These accumulations are known as moraines and are classified according to their location as lateral (along the edges of the glacier), central (formed by the union of lateral moraines of converging glaciers) and terminal (located at the final end of the glacier, marking its maximum extension).

4. Formation of the glacial valley

The result of this set of processes is a glacial valley with distinctive characteristics such as a “U” shape, steep walls and secondary valleys that form waterfalls.

• Glacial cirque: it is the area of ​​birth of the glacier, where the largest amount of snow accumulates and is later transformed into ice. It is usually in the shape of enormous circular basins and is located at high mountain levels.
• Moraines: accumulations of tills, that is, rock fragments of various sizes dragged by the glacier. Its size depends on the load of materials transported by the glacier.
• Hanging valleys: These are tributary valleys that flow into the main valley from a higher level. They were formed by smaller glaciers and, when the ice disappears, they remain “hanging” (hence their name) on the walls of the main valley. They usually have waterfalls.
• Glacial lakes (circus lakes or tarns): are lakes that form in depressions excavated by the glacier or where water was retained after the retreat of the ice. Generally, they are frequent in glacial cirques or behind terminal moraines.
• Sheep rocks: These are rocky outcrops polished and rounded by the abrasion of ice. They show a smooth face (upstream) and an abrupt one (downstream), which indicates the direction of the glacial flow.
• Glacial striations: striations are grooves produced by the abrasion and drag of fragments transported by the glacier. They indicate the direction of the glacier when it has retreated.

Here is a list of ten glacial valleys present around the world:

• Yosemite Valley in California, United States.
• Leh Valley, Ladakh, northwestern Indian Himalayas.
• Malyovitsa Valley, Rila Mountain, Bulgaria.
• Valley of the Río de las Vueltas, province of Santa Cruz, Argentina.
• Alerce and Manso Valleys of Monte Tronador, Río Negro province, Argentina.
• Lauterbrunnen Valley, Switzerland.
• Glencoe Valley, Scotland.
• Khumbu Valley, Nepal.
• Chamonix Valley, France.
• Valley of the chambers, Venezuela.

• Formation: a glacial valley is formed by the action of the movement of a glacier that drags with it different types of sediments, while a river valley is formed by the erosion and sedimentation caused by a river or stream over time.
• Process: the glacier acts abrasively on the terrain, carving and wearing away the rocks and sediments through which it passes, creating moraines, striations, among other structures. On the other hand, the water course shapes the terrain through erosion and sediment deposition processes.
• Shape: Glacial valleys have a characteristic U shape due to deeper and wider erosion compared to river valleys. River valleys are typically “V”-shaped in their upper reaches and may become wider and “U”-shaped or meander-shaped in lower reaches.
• Characteristics: glacial valleys are typical in high mountain areas or cold latitudes where conditions allow the accumulation of ice over the years and the subsequent formation of glaciers. On the contrary, river valleys are common in areas of plains, wide valleys, or transition zones, and have continuous development by the flow of river water.

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