Pyroclastic shield
Encyclopedia
Volcanology
Volcanology is the study of volcanoes, lava, magma, and related geological, geophysical and geochemical phenomena. The term volcanology is derived from the Latin word vulcan. Vulcan was the ancient Roman god of fire....
, a pyroclastic shield or terrestrial ignimbrite shield is an uncommon type of shield volcano
Shield volcano
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...
. Unlike most shield volcanoes, pyroclastic shields are formed mostly of pyroclastic and highly explosive eruption
Explosive eruption
An explosive eruption is a volcanic term to describe a violent, explosive type of eruption. Mount St. Helens in 1980 was an example. Such an eruption is driven by gas accumulating under great pressure. Driven by hot rising magma, it interacts with ground water until the pressure increases to the...
s rather than relatively fluid basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
issuing from vents or fissure
Fissure vent
A fissure vent, also known as a volcanic fissure or simply fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is usually a few meters wide and may be many kilometers long. Fissure vents can cause large flood basalts and lava channels...
s on the surface of the volcano. They typically display low-angle flank slopes and have little or no central collapse, although a shallow sag in the shield is commonly observed. Lava is commonly extruded after explosive activity has ended. The paucity of associated Plinian
Plinian eruption
Plinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 ....
fall deposits indicates that pyroclastic shields are characterized by low Plinian columns.
Pyroclastic shields are commonly known to form in the Central Andes
Andes
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...
of South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, as well as in Melanesia
Melanesia
Melanesia is a subregion of Oceania extending from the western end of the Pacific Ocean to the Arafura Sea, and eastward to Fiji. The region comprises most of the islands immediately north and northeast of Australia...
(the island of Bougainville
Bougainville Island
Bougainville Island is the main island of the Autonomous Region of Bougainville of Papua New Guinea. This region is also known as Bougainville Province or the North Solomons. The population of the province is 175,160 , which includes the adjacent island of Buka and assorted outlying islands...
alone has two). There are also pyroclastic shields in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, such as Emi Koussi
Emi Koussi
Emi Koussi is a high pyroclastic shield volcano that lies at the south end of the Tibesti Mountains in the central Sahara of northern Chad. It is the highest mountain in Chad, and the highest in the Sahara. The volcano is one of several in the Tibesti massif, and reaches 3445 m in altitude,...
in Chad
Chad
Chad , officially known as the Republic of Chad, is a landlocked country in Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west...
.
Examples
- AmbrymAmbrymAmbrym is a volcanic island in the archipelago of Vanuatu . It is well known for its highly active volcanic activity that includes lava lake formation.-Etymology:...
, VanuatuVanuatuVanuatu , officially the Republic of Vanuatu , is an island nation located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is some east of northern Australia, northeast of New Caledonia, west of Fiji, and southeast of the Solomon Islands, near New Guinea.Vanuatu was... - ApoyequeApoyequeApoyeque is a pyroclastic shield, located in the Chiltepe Peninsula Natural Reserve in Nicaragua. It has a 2.8-km wide, 400-m-deep, lake-filled caldera.-Geography:Apoyeque is a volcanic complex that formed and occuplies the Chiltepe Peninsula...
, NicaraguaNicaraguaNicaragua is the largest country in the Central American American isthmus, bordered by Honduras to the north and Costa Rica to the south. The country is situated between 11 and 14 degrees north of the Equator in the Northern Hemisphere, which places it entirely within the tropics. The Pacific Ocean... - Billy MitchellBilly Mitchell (volcano)Billy Mitchell is a volcano located in the central part of the island of Bougainville, just northeast of the Bagana Volcano, in Papua New Guinea. It is a small, pyroclastic shield truncated by a 2 km wide caldera filled by a crater lake....
, BougainvilleBougainville IslandBougainville Island is the main island of the Autonomous Region of Bougainville of Papua New Guinea. This region is also known as Bougainville Province or the North Solomons. The population of the province is 175,160 , which includes the adjacent island of Buka and assorted outlying islands...
, Papua New GuineaPapua New GuineaPapua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands... - Emi KoussiEmi KoussiEmi Koussi is a high pyroclastic shield volcano that lies at the south end of the Tibesti Mountains in the central Sahara of northern Chad. It is the highest mountain in Chad, and the highest in the Sahara. The volcano is one of several in the Tibesti massif, and reaches 3445 m in altitude,...
, ChadChadChad , officially known as the Republic of Chad, is a landlocked country in Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west... - LoloruLoloruLoloru is a pyroclastic shield volcano located in the southern part of the island of Bougainville, Papua New Guinea. The summit consists of two nested calderas, with an andesitic lava dome and a crescent-shaped crater lake.- References :*...
, Bougainville, Papua New Guinea - Purico ComplexPurico ComplexThe Purico Complex is a pyroclastic shield located in the eastern part of the Atacama desert in Chile's II Region , approximately south of the Bolivia - Chile border...
, ChileChileChile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far... - RabaulRabaul calderaRabaul caldera is a large volcano situated in East New Britain, Papua New Guinea. It derives its name from the town of Rabaul situated inside the caldera. The highest of its multiple peaks is ....
, New BritainNew BritainNew Britain, or Niu Briten, is the largest island in the Bismarck Archipelago of Papua New Guinea. It is separated from the island of New Guinea by the Dampier and Vitiaz Straits and from New Ireland by St. George's Channel...
, Papua New Guinea - SacabayaSacabayaSacabaya is a pyroclastic shield in Bolivia. It is located on the Altiplano near to the Rio Lauca. The volcano is composed of ignimbrite, which has formed a shield. The shield is capped by an area of vents which has many overlapping craters, and is elongated in shape. At the southern end lies the...
, BoliviaBoliviaBolivia officially known as Plurinational State of Bolivia , is a landlocked country in central South America. It is the poorest country in South America... - Tata SabayaTata SabayaTata Sabaya is a stratovolcano in Bolivia. It is located at the northern end of the Salar de Coipasa, which lies in the Altiplano. It also lies at eastern end of a line of volcanoes starting with Isluga in the west, and continuing with Cabaray. Its last eruption date is unknown, but it is assigned...
, Bolivia