Volcanic plug
Encyclopedia
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
landform created when magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
hardens within a vent on an active volcano. When forming, a plug can cause an extreme build-up of pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
if volatile
Volatiles
In planetary science, volatiles are that group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O...
-charged magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
is trapped beneath it, and this can sometimes lead to an explosive eruption. If a plug is preserved, erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
may remove the surrounding rock while the erosion-resistant plug remains, producing a distinctive upstanding landform. Examples include Shiprock
Shiprock
Shiprock is a rock formation rising nearly above the high-desert plain on the Navajo Nation in San Juan County, New Mexico, USA. It has a peak elevation of above the sea level. It lies about southwest of the town of Shiprock, which is named for the peak...
, New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
; The Nut
Stanley, Tasmania
Stanley is a town on the north-west coast of Tasmania, Australia. Travelling west, Stanley is the second-last major township on the north-west coast of Tasmania, Smithton being the larger township in the Circular Head municipality...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
; and the Pitons
Pitons
The Pitons are two volcanic plugs in a World Heritage Site in Saint Lucia. The Gros Piton is 771 m, and the Petit Piton is 743 m high; they are linked by the Piton Mitan ridge.- Geography :...
of Saint Lucia
Saint Lucia
Saint Lucia is an island country in the eastern Caribbean Sea on the boundary with the Atlantic Ocean. Part of the Lesser Antilles, it is located north/northeast of the island of Saint Vincent, northwest of Barbados and south of Martinique. It covers a land area of 620 km2 and has an...
.
Crag and tail
A crag is a rocky hill or mountain, generally isolated from other high ground. Crags are formed when a glacier or ice sheet passes over an area that contains a particularly resistant rock formation...
. An example is the Castle Rock
Edinburgh Castle
Edinburgh Castle is a fortress which dominates the skyline of the city of Edinburgh, Scotland, from its position atop the volcanic Castle Rock. Human habitation of the site is dated back as far as the 9th century BC, although the nature of early settlement is unclear...
in Edinburgh
Edinburgh
Edinburgh is the capital city of Scotland, the second largest city in Scotland, and the eighth most populous in the United Kingdom. The City of Edinburgh Council governs one of Scotland's 32 local government council areas. The council area includes urban Edinburgh and a rural area...
, Scotland.
Further examples of volcanic plugs in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
include Morro Rock
Morro Rock
Morro Rock is a volcanic plug located just offshore from Morro Bay, California, at the entrance to Morro Bay Harbor. A causeway connects it with the shore, effectively making it a tied island. The area surrounding the base of Morro Rock can be visited. The rock is protected as the Morro Rock State...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
; Lizard Head
Lizard Head
Lizard Head is a mountain in Colorado, one of the 637 peaks above 13,000 feet in elevation in the state...
, Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
; and Laurel Hill
Snake Hill
Snake Hill is an igneous rock intrusion jutting some 150 feet up from the floor of the Meadowlands in Secaucus, New Jersey, USA. It was largely obliterated by quarrying in the 1960s that reduced its height by one-quarter and its base area by four fifths...
, New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
. Devils Tower
Devils Tower National Monument
Devils Tower is an igneous intrusion or laccolith located in the Black Hills near Hulett and Sundance in Crook County, northeastern Wyoming, above the Belle Fourche River...
in Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
, as well as Little Devils Postpile
Little Devils Postpile
Little Devils Postpile, in Yosemite National Park in California, United States, is a set of columnar joints in a basalt plug resembling the Devils Postpile formation. It is located along the Tuolumne River a few miles west of Tuolumne Meadows.-See also:...
located in Yosemite National Park, are also thought to be a volcanic plug by many geologist
Geologist
A geologist is a scientist who studies the solid and liquid matter that constitutes the Earth as well as the processes and history that has shaped it. Geologists usually engage in studying geology. Geologists, studying more of an applied science than a theoretical one, must approach Geology using...
s. Another example of a volcanic plug in the eastern USA is the highly eroded Stark's Knob
Stark's Knob
Stark's Knob is a basaltic pillow lava formation near Schuylerville, New York, United States. It formed about 460 to 440 million years ago in relatively shallow sea water...
basaltic structure located along the Hudson River
Hudson River
The Hudson is a river that flows from north to south through eastern New York. The highest official source is at Lake Tear of the Clouds, on the slopes of Mount Marcy in the Adirondack Mountains. The river itself officially begins in Henderson Lake in Newcomb, New York...
near Saratoga Springs, New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
. However, some geologists believe Stark's Knob is not a plug at all, but merely an outcrop of an ancient submarine lava flow.
Ailsa Craig
Ailsa Craig
Ailsa Craig is an island of 219.69 acres in the outer Firth of Clyde, Scotland where blue hone granite was quarried to make curling stones. "Ailsa" is pronounced "ale-sa", with the first syllable stressed...
, Bass Rock
Bass Rock
The Bass Rock, or simply The Bass, , is an island in the outer part of the Firth of Forth in the east of Scotland. It is approximately offshore, and north-east of North Berwick. It is a steep-sided volcanic rock, at its highest point, and is home to a large colony of gannets...
, North Berwick Law
North Berwick Law
North Berwick Law is a conical hill which rises incongruously from the surrounding landscape . It overlooks the East Lothian town of North Berwick and stands at 613 ft above sea level.Geologically, the law is a volcanic plug of hard phonolitic trachyte rock of Carboniferous age...
and Dumgoyne
Dumgoyne
Dumgoyne is a hill prominent on the edge of the Campsie Fells and is a well known landmark visible from Glasgow. It is a volcanic plug and is 427 m high...
hill are examples of volcanic plugs located in Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
. Borgarvirki
Borgarvirki
Borgarvirki lies between Vesturhóp and Víðidalur in the north of Iceland, and at 177m above sea level it dominates the surrounding region. Made out of basalt strata, it has been used as a fortress for centuries. Borgarvirki is a natural phenomenon, altered by humans in earlier centuries...
is a volcanic plug located in north Iceland. A volcanic plug is situated in the town of Motta Sant'Anastasia
Motta Sant'Anastasia
Motta Sant'Anastasia is a comune in the Province of Catania in the Italian region Sicily, located about 160 km southeast of Palermo and about 9 km west of Catania...
in Italy.
There are several volcanic plugs in New Zealand, including the Pinnacles in the Coromandel Peninsula
Coromandel Peninsula
The Coromandel Peninsula lies in the North Island of New Zealand. It is part of the Waikato Region and Thames-Coromandel District and extends 85 kilometres north from the western end of the Bay of Plenty, forming a natural barrier to protect the Hauraki Gulf and the Firth of Thames in the west...
, Bream Head
Bream Head
Bream Head is a promontory on the east coast of Northland in the North Island of New Zealand. Located at the end of a 30 kilometre-long peninsula, the head juts into the Pacific Ocean to the southeast of Whangarei...
, Paritutu and adjacent Sugar Loaf Islands
Sugar Loaf Islands
The Sugar Loaf Islands are a collection of five small uninhabited islands and several sea stacks near Port Taranaki, Taranaki, New Zealand. The largest island, Moturoa Island, covers approximately...
, and Piha
Piha
Piha is a northern New Zealand coastal settlement with a population of about 600. It is one of the most popular beaches in the area and a major day-trip destination for Aucklanders throughout the year, although especially so in summer.-Location:...
's Lion Rock, which hosted a fortified Maori pa
Pa (Maori)
The word pā can refer to any Māori village or settlement, but in traditional use it referred to hillforts fortified with palisades and defensive terraces and also to fortified villages. They first came into being about 1450. They are located mainly in the North Island north of lake Taupo...
. Australia's Mount Warning
Mount Warning
Mount Warning is a mountain west-south-west of Murwillumbah, near the border with Queensland in the Northern Rivers region of New South Wales, Australia...
is a volcanic plug.
Sigiriya
Sigiriya is a large stone and ancient rock fortress and palace ruin in the central Matale District of Sri Lanka, surrounded by the remains of an extensive network of gardens, reservoirs, and other structures...
(Lion's rock), the hardened magma plug from an extinct and long-eroded volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
. The rock rises 370 m (1,213.9 ft) and is sheer on all sides, in many places overhanging the base. It hosts an ancient rock fortress and ruins of a castle, one of the eight World Heritage Sites of Sri Lanka
World Heritage Sites of Sri Lanka
Eight sites of Sri Lanka have been inscribed in the UNESCO World Heritage, namely, the ancient city of Polonnaruwa , the ancient city of Sigiriya , the Golden Temple of Dambulla , the old town of Galle and its fortifications , the sacred city of Anuradhapura , the sacred city of Kandy , Sinharaja...
(Ref:202).
Trosky Castle
Trosky Castle is a castle ruin located some 10 km south of Semily, Liberec Region, Czech Republic. It is one of the most famous Czech castles and is situated on the summits of two basalt volcanic plugs. On the lower peak is the two-storey structure called Baba , and on the higher outcrop is the...
in the Czech Republic.