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Ardnamurchan Ring Complex

Lochaber, Highlands, Scotland


'ancient volcano at Ardnamurchan. Classic geology, most westerly mainland point and great views'

From Daniel Hill @pastclimates and Heather Rawcliffe @HjRawcliffe

The west coast of Scotland contains a chain of volcanic complexes that formed in the early Tertiary – as Europe and North America separated and the Atlantic opened. All of them provide exceptional insights to the inner workings of volcanoes. But the Ardnamurchan centre is most notable for its place in developing ideas on how magma is emplaced in the upper continental crust. 

ArdnamurchanPioneering geologists in the early 20th century mapped out a pattern of ring intrusions that they interpreted as having acted to allow the surrounding rocks to move, as magma chambers filled and emptied during the life of the volcano. 

Within the Tertiary complexes of NW Britain it is the Ardnamurchan centre that has the best-developed ring intrusions. 

Of these, the gabbroic "Great Eucrite" is the finest and is commonly described as the type example of a ring dyke. 


This interpretation has been challenged by recent research that suggests that the Great Eucrite is a dish-shaped intrusion. This illustrates the continued importance of the British Tertiary Igneous Complexes in developing ideas about the internal structure of volcanoes. 

Ardnamurchan is part of the Lochaber Geopark.

Text: Professor Rob Butler

100 Great Geosites

Related Links

Further Reading

Richey, J.E., and Thomas, H.H., 1930, The geology of Ardnamurchan, northwest Mull and Coll: Memoir of the Geological Survey [Scotland], HMSO, 393 p.
  • The classic description of the Ardnamurchan ring intrusions.
Anderson, E.M., 1936, The dynamics of the formation of cone-sheets, ring-dikes, and cauldron-subsidence: Proceedings of the Royal Society of Edinburgh, v. 56, p. 128–156.
  • An account that placed Ardnamurchan at the forefront of research into sub-volcanic complexes. 
O’Driscoll, B., Troll, V., Reavy, J. & Turner, P. 2006. The Great Eucrite intrusion of Ardnamurchan, Scotland: Reevaluating the ring-dike concept. Geology v 34, 189-193.
  • Recent work that challenges the classic description of the Great Eucrite and proposes a new model for the Ardnamurchan centre. 

Images (top to bottom):

  • Ardnamuchan Ring Complex © Lochaber Geopark 
  • Sanna Bay with gabbro hills of the volcanic ring beyond © Gordon Hatton (Source Creative Commons Attribution-ShareAlike 2.0 license.
  • Synmagmatic Slumping of Layered Gabbro © Anne Burgess (Source Creative Commons Attribution-ShareAlike 2.0 license.