Weathering has also given rise to circular 'rock basins' formed by the accumulation of water and repeated freezing and thawing. These stacks are vulnerable to frost action and often collapse leaving trails of blocks down the slopes called clitter or clatter. Each stack may include several tiers or pillows, which may become separated: rocking pillows are called logan stones. These can be monolithic, as at Haytor and Blackingstone Rock, but are more usually subdivided into stacks, often arranged in avenues. Where joints happen to be unusually widely spaced, core blocks can survive and remain above the weathering surface, developing into tors. Tor near the summit of Knocknagun, in Wicklow, Ireland 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 are closely spaced, the large crystals in the granite readily disintegrate to form a sandy regolith known locally as growan. When the cover rocks eroded away it was exposed to chemical and physical weathering processes. įor example, the Dartmoor granite was emplaced around 280 million years ago.

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. Many hypotheses have been proposed to explain their origin and this remains a topic of discussion among geologists and geomorphologists, and physical geographers. Tors are mostly less than 5 meters (16 ft) high. Tors are landforms created by the erosion and weathering of rock most commonly granites, but also schists, dacites, dolerites, ignimbrites, coarse sandstones and others. Kit-Mikayi, a celebrated tor near Kisumu, Kenya

What is tor in geography