A tarn is a mountain lake

Lake

A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

 or pool, formed in a cirque

Cirque

Cirque may refer to:* Cirque, a geological formation* Makhtesh, an erosional landform found in the Negev desert of Israel and Sinai of Egypt*Cirque , an album by Biosphere* Cirque Corporation, a company that makes touchpads...

 excavated by a glacier

Glacier

A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

. A moraine

Moraine

A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...

 may form a natural dam

Dam

A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...

 below a tarn. A corrie may be called a cirque.

The word is derived

Toponymy

Toponymy is the scientific study of place names , their origins, meanings, use and typology. The word "toponymy" is derived from the Greek words tópos and ónoma . Toponymy is itself a branch of onomastics, the study of names of all kinds...

 from the Old Norse

Old Norse

Old Norse is a North Germanic language that was spoken by inhabitants of Scandinavia and inhabitants of their overseas settlements during the Viking Age, until about 1300....

 word tjörn meaning pond. Its more specific use as a mountain lake emerges as it is the commonly used term for all pond

Pond

A pond is a body of standing water, either natural or man-made, that is usually smaller than a lake. A wide variety of man-made bodies of water are classified as ponds, including water gardens, water features and koi ponds; all designed for aesthetic ornamentation as landscape or architectural...

s in the mountainous areas of Northern England

Northern England

Northern England, also known as the North of England, the North or the North Country, is a cultural region of England. It is not an official government region, but rather an informal amalgamation of counties. The southern extent of the region is roughly the River Trent, while the North is bordered...

, particularly Cumbria

Cumbria

Cumbria , is a non-metropolitan county in North West England. The county and Cumbria County Council, its local authority, came into existence in 1974 after the passage of the Local Government Act 1972. Cumbria's largest settlement and county town is Carlisle. It consists of six districts, and in...

. Here, it retains a broader use, referring to any small lake or pond, regardless of its location and origin.

In Scandinavian languages a tjern or tjärn, tärn or tjørn is a small natural lake, often in a forest or with vegetation close around it or growing into the lake.

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