An exposure of bedrock rising above its surroundings and formed by (1) subaerial weathering causing spheroidal modification to the form of outcrops; (2) differential weathering and removal of weathered debris by mass wasting and stripping; (3) slope retreat of larger inselbergs or (4) frost weathering in periglacial conditions followed by solifluction. joints usually control the detailed form of a tor. Tors are associated with both tropical and periglacial environments, are often used as an example of equifinality (i.e. similar forms being produced by different processes) and may be polygenetic in origin. One view of British examples, especially used in relation to tors on Dartmoor, is that they formed in two stages by deep subsurface weathering during tertiary tropical conditions, followed by removal of weathering products during the pleistocene by periglacial processes. Alternatively, they are regarded as essentially relict periglacial forms. The koppies or kopjes of Africa are similar in form and are usually interpreted in terms of the third theory.
[See also clitter, corestone, gruss/grussification]
- The geomorphic impact of glaciers as indicated by tors in north Sweden (Aurivaara, 68° N). Geomorphology 57: 403-421. (2004)
- A general model of autochthonous blockfield evolution. Permafrost and Periglacial Processes 21: 289-300. (2010)
- The granite tors of Dartmoor, Southwest England: Rapid and recent emergence revealed by Late Pleistocene cosmogenic apparent exposure ages. Quaternary Science Reviews 61: 62-76. ; ; et al. (2013)
- The problem of tors. Geographical Journal 121: 470-487. (1955)
- The origin of granite tors, Dartmoor, Devonshire. Proceedings of the Yorkshire Geological Society 33: 315-340. ; (1962)
- Cosmogenic 10Be and 26Al exposure ages of tors and erratics, Cairngorm Mountains, Scotland: Timescales for the development of a classic landscape of selective linear erosion. Geomorphology 73: 222-245. ; ; et al. (2006)