Tor rock formation

A tor is a prominent freestanding rock outcrop that rises abruptly from the smoother surrounding slopes of a hilltop or ridge. These striking landforms occur in many regions of the world but are especially characteristic of granitic landscapes. In parts of South West England, particularly on Dartmoor in Devon and Bodmin Moor in Cornwall, the term is also used for the hills on which these rock masses stand, reflecting the cultural and geographical importance of these features.

Etymology

Although many English place names have Celtic origins, the English word tor does not appear to have cognates in either Breton or Cornish. Linguistic research suggests that the term derives from the Old Welsh word meaning a “cluster” or “heap”, eventually adopted into Old English with a similar sense of a rocky mass. Scottish Gaelic usage is also thought to derive from this older root. The consistent association of the word with conspicuous piles of rock highlights its descriptive origins.

Formation and Geological Processes

Tors form through prolonged weathering and erosion of bedrock, most commonly granite but also other resistant lithologies such as schist, dacite, dolerite, ignimbrite, and coarse sandstone. They are typically less than a few tens of metres in height but can appear much larger in open landscapes. Their development is complex and reflects an interplay of geological structure, climate, and geomorphological history.
Granite batholiths such as the Cornubian massif in South West England were emplaced hundreds of millions of years ago. As overlying rocks eroded, the granite became exposed to both chemical and physical weathering. The spacing of joints within the rock plays a critical role: closely spaced joints allow the granite to disintegrate into a sandy regolith—locally termed “growan”—which can be removed by slope processes such as solifluction or surface wash, particularly during cold periglacial phases of the Quaternary.
Where joints are widely spaced, large core blocks can resist disintegration and protrude above the weathering surface. These blocks evolve into tors, often appearing as stacked or tiered formations. Individual stacks may be arranged in lines or “avenues”, with their upper blocks forming rocking features known as logan stones. Frost action destabilises these towers and contributes to their collapse, producing surrounding accumulations of angular boulders called clitter or clatter.
Weathering also creates rock basins—shallow circular depressions formed by repeated cycles of freezing and thawing in pooled water. These features are well developed at locations such as Kes Tor on Dartmoor.

Chronology and Exposure Ages

Recent cosmogenic nuclide dating has provided new insights into the age of British tors. Studies of Dartmoor tors indicate that most have surface exposure ages of less than 100,000 years, with none older than 200,000 years. This suggests that the present-day tors emerged relatively recently, likely at the onset of the Devensian glaciation. In contrast, tors of the Scottish Cairngorms exhibit much older exposure ages, ranging between approximately 200,000 and 675,000 years, with even glacially modified examples dating between 100,000 and 150,000 years. These differences highlight the influence of regional climates and geomorphological histories on tor evolution.

Global Distribution and Examples

Tors occur worldwide in a variety of climatic and geological settings. Well-known examples include Haytor and Blackingstone Rock in Devon, distinctive tors in the Cairngorms of Scotland, and isolated tor-like formations in the granitic highlands of southern Siberia. Beyond Europe, significant tors occur in Africa, such as the celebrated rock formation near Kisumu in Kenya, where dramatic spheroidal weathering has sculpted prominent rounded blocks.

Landform Significance

Tors serve as indicators of long-term weathering and landscape stability, providing insights into past climatic regimes and geomorphological processes. Their distinctive forms make them important features for geological study as well as for cultural and recreational appreciation. In regions such as Dartmoor, tors have shaped local lore, navigation traditions, and historical land use, becoming icons of the surrounding landscape.