Tor (rock formation)

A tor, which is also known by geomorphologists as either a castle koppie or kopje, is a large, free-standing rock outcrop that rises abruptly from the surrounding smooth and gentle slopes of a rounded hill summit or ridge crest. In the South West of England, the term is commonly also used for the hills themselves – particularly the high points of Dartmoor in Devon and Bodmin Moor in Cornwall. Although English topographical names often have a Celtic etymology, the Oxford English Dictionary lists no cognates to the Old English word in either the Breton or Cornish languages (the Scottish Gaelic tòrr is thought to derive from the Old English word). It is therefore accepted that the English word Tor derives from the Old Welsh word tẁrr or twr, meaning a cluster or heap. Tors are landforms created by the erosion and weathering of rock; most commonly granites, but also schists, dacites, dolerites, ignimbrites, coarse sandstones and others. Tors are mostly less than high. Many hypotheses have been proposed to explain their origin and this remains a topic of discussion among geologists and geomorphologists, and physical geographers. It is considered likely that tors were created by geomorphic processes that differed widely in type and duration according to regional and local differences in climate and rock types. For example, the Dartmoor granite was emplaced around 280 million years ago. When the cover rocks eroded away it was exposed to chemical and physical weathering processes. Where joints are closely spaced, the large crystals in the granite readily disintegrate to form a sandy regolith known locally as growan. This is readily stripped off by solifluction or surface wash when not protected by vegetation, notably during prolonged cold phases during the Quaternary ice ages – periglaciation. Where joints happen to be unusually widely spaced, core blocks can survive and remain above the weathering surface, developing into tors. These can be monolithic, as at Haytor and Blackingstone Rock, but are more usually subdivided into stacks, often arranged in avenues.

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Related concepts (5)

Cornubian batholith

The Cornubian batholith is a large mass of granite rock, formed about 280 million years ago, which lies beneath much of Cornwall and Devon in the south-western peninsula of Great Britain. The main exposed masses of granite are seen at Dartmoor, Bodmin Moor, St Austell, Carnmenellis, Land's End and the Isles of Scilly. The intrusion is associated with significant quantities of minerals particularly cassiterite, an ore of tin which has been mined since about 2000 BC. Other minerals include china clay and ores of copper, lead, zinc and tungsten.

Moorland

Moorland or moor is a type of habitat found in upland areas in temperate grasslands, savannas, and shrublands and montane grasslands and shrublands biomes, characterised by low-growing vegetation on acidic soils. Moorland, nowadays, generally means uncultivated hill land (such as Dartmoor in South West England), but also includes low-lying wetlands (such as Sedgemoor, also South West England). It is closely related to heath, although experts disagree on what precisely distinguishes these types of vegetation.

Dartmoor

Dartmoor is an upland area in southern Devon, England. The moorland and surrounding land has been protected by National Park status since 1951. Dartmoor National Park covers . The granite which forms the uplands dates from the Carboniferous Period of geological history. The landscape consists of moorland capped with many exposed granite hilltops known as tors, providing habitats for Dartmoor wildlife. The highest point is High Willhays, above sea level. The entire area is rich in antiquities and archaeological artefacts.