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A volcanic plug, also called a volcanic neck or lava neck, is a volcanic object created when magma hardens within a vent on an active volcano. When present, a plug can cause an extreme build-up of pressure if rising volatile-charged magma is trapped beneath it, and this can sometimes lead to an explosive eruption. Glacial erosion can lead to exposure of the plug on one side, while a long slope of material remains on the opposite side. Such landforms are called crag and tail. If a plug is preserved, erosion may remove the surrounding rock while the erosion-resistant plug remains, producing a distinctive upstanding landform.
Examples of volcanic plugs
Near the village of Rhumsiki in the Far North Province of Cameroon, Kapsiki Peak is an example of a volcanic plug and is one of the most photographed parts of the Mandara Mountains. Spectacular volcanic plugs are present in the center of La Gomera island in the Canary Islands archipelago, within the Garajonay National Park.
Borgarvirki is a volcanic plug located in north Iceland.
A volcanic plug is situated in the town of Motta Sant'Anastasia in Italy.
Saint Michel d'Aiguilhe chapel, whose construction started in 969, near Le Puy-en-Velay in France. The volcanic plug rises about 85 metres (279 ft) above the surroundings. Another building on a volcanic plug is the 14th century Trosky Castle in the Czech Republic.
In the United Kingdom, two examples of a building on a volcanic plug are the Castle Rock in Edinburgh, Scotland, and Deganwy Castle, Wales. The Law, Dundee, Ailsa Craig, Bass Rock, North Berwick Law and Dumgoyne hill are other examples of volcanic plugs located in Scotland. There are over 30 volcanic plugs in Northern Ireland, including Slemish in Ballymena, Tievebulliagh, Scawt Hill, Carrickarede, Scrabo and Slieve Gallion.
North America and the Caribbean
There are several volcanic plugs in the United States, including Morro Rock in California, Thumb Butte in the Sierra Prieta of Arizona, and Shiprock in New Mexico. Devils Tower in Wyoming and Little Devils Postpile in Yosemite National Park, California, are also believed to be volcanic plugs by many geologists.
In Canada, the Northern Cordilleran Volcanic Province gives rise to several confirmed and suspected plugs. Chief among these is Castle Rock, located in British Columbia, which last erupted during the Pleistocene.
The southern coast of Saint Lucia is dominated by the iconic Pitons, a UNESCO World Heritage site. The twin peaks, Gros Piton and Petit Piton, steeply rise more than 770 metres (2,530 ft) above the Caribbean.
- the Pinnacles in the Coromandel Peninsula
- Bream Head in Northland
- Paritutu and the adjacent Sugar Loaf Islands in Taranaki
- St. Paul's Rock at Whangaroa Harbour
- Piha's Lion Rock, which hosted a fortified Maori pa.
In New Zealand's South Island, Ōnawe Peninsula on Banks Peninsula is a prominent volcanic plug, and erosion of Saddle Hill near Dunedin has also revealed a plug. Dunedin's Mount Cargill displays two plugs: its main summit and the subsidiary summit of Buttar's Peak.
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Taung Kalat, Burma.
Dent de la Rancune, a challenging climbing site in the Chaîne des Puys, France.
Trosky Castle ("Panna" Tower), Czech Republic.
Devils Tower, Wyoming, USA.
Shiprock, New Mexico, USA.
St. Paul's Rock, above Whangaroa Harbour, Northland, New Zealand.
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- Wilson, H E et al (1986) Geological Survey of Northern Ireland, HMSO
- "The Nut, Stanley". Discover Tasmania. Government of Tasmania. 2011. Retrieved 30 June 2013.
- "Wollumbin/Mt Warning Shield Volcano". Geological sites of NSW. Cartoscope Pty Limited. Retrieved 30 June 2013.