A crag (sometimes spelled cragg, or in Scotland craig) is a rocky hill or mountain, generally isolated from other high ground.

Origin

Crags are formed when a

glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...

passes over an area that contains a particularly resistant rock formation (often

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

, a

volcanic plug A volcanic plug, also called a volcanic neck or lava neck, is a volcano, volcanic object created when magma hardens within a Volcanic vent, vent on an active volcano. When present, a plug can cause an extreme build-up of high gas pressure if risi ...

or some other

volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

structure). The force of the glacier erodes the surrounding softer material, leaving the rocky block protruding from the surrounding terrain. Frequently the crag serves as a partial shelter to softer material in the wake of the glacier, which remains as a gradual fan or ridge forming a tapered ramp (called the tail) up the leeward side of the crag. In older examples, or those latterly surrounded by the sea, the tail is often missing, having been removed by post-glacial erosion.

Examples

Examples of crag and tail formations include: * Castle Rock (the crag, site of

Edinburgh Castle Edinburgh Castle is a historic castle in Edinburgh, Scotland. It stands on Castle Rock (Edinburgh), Castle Rock, which has been occupied by humans since at least the Iron Age. There has been a royal castle on the rock since the reign of Malcol ...

) and the

Royal Mile The Royal Mile () is the nickname of a series of streets forming the main thoroughfare of the Old Town, Edinburgh, Old Town of Edinburgh, Scotland. The term originated in the early 20th century and has since entered popular usage. The Royal ...

(the tail), in

Edinburgh Edinburgh is the capital city of Scotland and one of its 32 Council areas of Scotland, council areas. The city is located in southeast Scotland and is bounded to the north by the Firth of Forth and to the south by the Pentland Hills. Edinburgh ...

, Scotland * Salisbury Crags and

Arthur's Seat Arthur's Seat (, ) is an ancient extinct volcano that is the main peak of the group of hills in Edinburgh, Scotland, which form most of Holyrood Park, described by Robert Louis Stevenson as "a hill for magnitude, a mountain in virtue of its bol ...

, in Edinburgh * North Berwick Law, in

North Berwick North Berwick (; ) is a seaside resort, seaside town and former royal burgh in East Lothian, Scotland. It is situated on the south shore of the Firth of Forth, approximately east-northeast of Edinburgh. North Berwick became a fashionable holi ...

, Scotland * Three in or near

Stirling Stirling (; ; ) is a City status in the United Kingdom, city in Central Belt, central Scotland, northeast of Glasgow and north-west of Edinburgh. The market town#Scotland, market town, surrounded by rich farmland, grew up connecting the roya ...

, Scotland, including the rock on which

Stirling Castle Stirling Castle, located in Stirling, is one of the largest and most historically and architecturally important castles in Scotland. The castle sits atop an Intrusive rock, intrusive Crag and tail, crag, which forms part of the Stirling Sill ge ...

stands * "Scrabo Hill" in

Newtownards Newtownards (; ) is a town in County Down, Northern Ireland. It lies at the most northern tip of Strangford Lough, 10 miles (16 km) east of Belfast, on the Ards Peninsula. It is in the Civil parishes in Ireland, civil parish of Newtow ...

Northern Ireland Northern Ireland ( ; ) is a Countries of the United Kingdom, part of the United Kingdom in the north-east of the island of Ireland. It has been #Descriptions, variously described as a country, province or region. Northern Ireland shares Repub ...

, site of the

Scrabo Tower Scrabo Tower is a high 19th-century lookout tower or folly that stands on Scrabo Hill near Newtownards in County Down, Northern Ireland. It provides wide views and is a landmark that can be seen from afar. It was built as a memorial to Charles ...

* Ailsa Craig, famous for curling stone mining * Crag and tail features have been identified on the Amundsen Sea continental shelf off West Antarctica.

References

* Holmes, Arthur, ''Principles of Physical Geology,'' Halsted, 1978, 3rd ed., pp 421 – 422 Glaciology Glacial landforms Erosion landforms Mountains * * {{glaciology-stub

Origin

Examples

See also

References