Volcanic plug

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Edinburgh Castle in Scotland is built upon an ancient volcanic plug

A volcanic plug, also called a volcanic neck or lava neck, is a volcanic landform created when magma hardens within a vent on an active volcano. When forming, a plug can cause an extreme build-up of pressure if volatile-charged magma is trapped beneath it, and this can sometimes lead to an explosive eruption. If a plug is preserved, erosion may remove the surrounding rock while the erosion-resistant plug remains, producing a distinctive landform.

Volcanic plug in the Ochoco National Forest of Oregon, USA
Volcanic plug near Rhumsiki, Far North Province, Cameroon

Examples of landforms created in this way in the United States include Morro Rock, California; Lizard Head, Colorado; and Shiprock, New Mexico. Devils Tower in Wyoming, as well as Little Devils Postpile located in Yosemite National Park, are also thought to be a volcanic plug by many geologists. The only example of a volcanic plug in the eastern USA is the highly eroded Stark's Knob basaltic structure located along the Hudson River near Saratoga Springs, New York.[citation needed] However, some geologists believe Stark's Knob is not a plug at all, but merely an outcrop of an ancient submarine lava flow. The Ailsa Craig, Bass Rock, North Berwick Law and Dumgoyne hill are examples of volcanic plugs located in Scotland. Borgarvirki is a volcanic plug located in north Iceland. A volcanic plug is situated in Italy, in the town of Motta Sant'Anastasia

Subsequent glacial erosion can lead to exposure of the plug on one side, while a long slope of material remains on the lee side. Such landforms are called crag and tail. Examples include the Castle Rock in Edinburgh, Scotland.

Sigiriya Rock Fortress.
Trosky Castle ("Panna" Tower), Czech Republic.

Another example is Sigiriya (Lion's rock), an ancient rock fortress and ruins of a castle situated in central Matale District of Sri Lanka. It is a popular tourist destination and also popular for the ancient paintings (frescos) very similar to the paintings in Ajanta Caves of India. It was built during the reign of King Kasyapa (477 – 495 AD) and one of the seven World Heritage Sites (Ref:202) in Sri Lanka.[1][2] Sigiriya rock is the hardened magma plug from an extinct and long-eroded volcano. It stands high above the surrounding plain, visible for miles in all directions. The rock rests on a steep mound that rises abruptly from the flat plain surrounding it. The rock itself rises 370m and is sheer on all sides, in many places overhanging the base. It is elliptical in plan and has a flat top that slopes gradually along the long axis of the ellipse.[3] The Sigiriya site has the remains of an upper palace sited on the flat top of the rock, a mid-level terrace that includes the Lion Gate and the mirror wall with its frescoes, the lower palace that clings to the slopes below the rock, and the moats, walls and gardens that extend for some hundreds of metres out from the base of the rock. The upper palace on the top of the rock includes cisterns cut into the rock that still retain water. The moats and walls that surround the lower palace are well preserved.[4]

Another building on a volcanic plug is the 14th century Trosky Castle in the Czech Republic.

[edit] References

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  1. ^ "UNESCO page - Ancient City of Sigiriya" (html). UNESCO.org. http://whc.unesco.org/en/list/202. Retrieved 2008-01-18. 
  2. ^ "Exploring Sigiriya Rock". AsiaExplorers.com. http://www.asiaexplorers.com/srilanka/sigiriya.htm. Retrieved 2008-05-05. 
  3. ^ "Encyclopædia Britannica Article about Sigiriya" (html). Encyclopædia Britannica. http://www.britannica.com/eb/article-9067705/Sigiriya. Retrieved 2008-01-18. 
  4. ^ "Sri Lanka: Slip Into Antiquity". The Epoch Times. http://en.epochtimes.com/news/5-5-4/28449.html. Retrieved 2005-05-04. 
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