Glacial cirque: what it is and how it is formed

A glacial cirque is a semicircular depression that has very inclined walls and is formed in the accumulation zone, the highest part of a glacier where it snows and the presence of very low temperatures keeps the snow in solid form, feeding the glacier. Its shape is due to the process of basal erosion, bottom drag and the fragmentation of the rocks of the walls generated by the freezing of water between cracks, fractures and pores. When the ice is no longer present, glacial lakes usually form.

Glacial cirques are important climate indicators, since their formation, size and conservation depend directly on temperature and precipitation conditions. Being closely linked to snow accumulation and melting, circuses allow us to study past and current climate changes.

Glacial cirques originate from the progressive expansion of depressions on mountain slopes, which can be associated with fluvial or volcanic processes or mass movements, such as landslides. When these depressions fill with snow, they begin to expand through processes such as freezing and thawing, chemical weathering, and seasonal melting.

The growth of the glacial cirque occurs when the thickness of the accumulated snow is sufficient for glacial ice to form due to compaction. Once the glacier develops, it widens and deepens the cirque through subglacial abrasion and erosion at the base and headwalls. In addition, cirques can continue to grow due to regressive erosion of the head wall, caused by the action of frost, thawing and mass movement.

As the cirques expand and merge, they transform the original interfluvial topography, creating an Alpine-style structure of sharp ridges, characterized by ridges and horns. More often, these elements make up the highest and upper areas of glacial valleys, and even some river valleys. They can occur as isolated formations or as part of a broader alpine landscape, where cirque glaciers have advanced beyond their initial limits to give rise to more extensive valley glaciers.

• High valleys of Aragón and Gállego, Spanish Pyrenees: in this site 206 glacial cirques have been identified that have great morphometric variability and topographic situations. Studies have shown that some environmental variables such as altitude, exposure and lithology influence the shape and size of cirques, but their control over them is quite limited.
• Snowdonia Glacial Cirques in the United Kingdom: The formation of this cirque dates back to the last Ice Age. It features a U-shaped valley with steep cliffs surrounding a glacial lake. Currently, the site functions as an educational center for geology students.
• Martial Glacier, Tierra del Fuego, Argentina: north of the city of Ushuaia in Argentina in the Martial Mountains, is the Martial Glacier, whose front is located about 1,000 meters above sea level. This constitutes the most important source of fresh water in the city. It is currently the subject of monitoring, since it has lost much of its surface due to global warming.
• Frébouze Glacier, Italy: this cirque-type glacier has an area of ​​11 km² and is located within the Gray Alps in the Mont Blanc massif. Unfortunately, like other glaciers in the world, it is receding.
• Pla de l’Estany, in Comapedrosa, Andorra: it is located within the communal natural park of the Compadrosa valleys in Andorra, Spain. It is a wide and deep glacial cirque with a large slope. It is one of the most accessible in the region, since it can be reached on foot or even on horseback.
• Glacial cirques of the Cordillera Blanca, Peru: in the Cordillera Blanca, located in the north of the Peruvian Andes, there are numerous glacial cirques that give rise to imposing lagoons of glacial origin. These cirques are fed by mountain glaciers, which are shrinking due to climate change. Some of the best-known lagoons, such as Laguna 69, are a popular tourist destination, although they are also the subject of scientific studies on glacial retreat.
• Cirque de la Meije, French Alps: it is a glacial cirque of great prestige, especially among mountaineers, due to its complex orography and the difficulty of access to its summits. This cirque is formed by the La Meije glaciers, and is famous for its impressive landscape, which includes large cliffs, sharp peaks and a mountain glacier that has been receding since the mid-20th century.

Now that you know what a glacial circle is, discover the largest glaciers in the world.

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