A ribbon lake or loch is a long and narrow, finger-shaped 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,...

, usually found in a glacial trough. Its formation begins when 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...

 moves over an area containing alternate bands of hard and soft bedrock

Bedrock

In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...

. The sharp-edged boulder

Boulder

In geology, a boulder is a rock with grain size of usually no less than 256 mm diameter. While a boulder may be small enough to move or roll manually, others are extremely massive....

s that are picked up by the glacier and carried at the bottom of the glacier erode the softer rock more quickly by abrasion, thus creating a hollow called a rock basin. On either side of the rock basin, the more resistant rock is eroded less and these outcrops of harder rock are known as rock bars, which act as dams between which rainwater may accumulate after the retreat of the ice age

Ice age

An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

, filling up the rock basin and creating a ribbon lake.

A ribbon lake may also form behind a terminal or recessional 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...

, both of which also act as dams, enabling water to accumulate behind them.

A ribbon lake may also occur if a tributary glacier joins a main glacier. The increase in power can create a trough, which is filled with water from a river/meltwater to create a ribbon lake.

A ribbon lake is also one of a number of glacial landscapes. These include aretes, corries, rock lips, rock basins and terminal moraines.

Examples of ribbon lakes include: Windermere

Windermere

Windermere is the largest natural lake of England. It is also a name used in a number of places, including:-Australia:* Lake Windermere , a reservoir, Australian Capital Territory * Lake Windermere...

, Panguipulli

Panguipulli Lake

The Panguipulli Lake is one of the "Seven Lakes" in Panguipulli municipality, southern Chile. The lake is of glacial origin and it is enclosed by mountain ranges of the Andes, on all sides except the west, where the town of Panguipulli lies in the Chilean Central Valley. The lake is drained by the...

, Coniston Water

Coniston Water

Coniston Water in Cumbria, England is the third largest lake in the English Lake District. It is five miles long, half a mile wide, has a maximum depth of 184 feet , and covers an area of . The lake has an elevation of 143 feet above sea level...

, Lake Washington

Lake Washington

Lake Washington is a large freshwater lake adjacent to the city of Seattle. It is the largest lake in King County and the second largest in the state of Washington, after Lake Chelan. It is bordered by the cities of Seattle on the west, Bellevue and Kirkland on the east, Renton on the south and...

 and Wastwater.