Pyroclastic shield
In volcanology, a pyroclastic shield or terrestrial ignimbrite shield is an uncommon type of shield volcano. Unlike most shield volcanoes, pyroclastic shields are formed mostly of pyroclastic and highly explosive eruptions rather than relatively fluid basaltic lava issuing from vents or fissures 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 the cessation of explosive activity commonly superposes the vent region. The paucity of associated plinian fall deposits indicates that pyroclastic shields are characterized by low plinian columns.
Pyroclastic shields are commonly known to form in the Central Andes of South America as well as in Melanesia (the island of Bougainville alone has two). There are also pyroclastic shields in Africa, such as Emi Koussi in Chad.
Examples
- Ambrym, Vanuatu
- Apoyeque, Nicaragua
- Billy Mitchell, Bougainville, Papua New Guinea
- Emi Koussi, Chad
- Loloru, Bougainville, Papua New Guinea
- Purico Complex, Chile
- Rabaul, New Britain, Papua New Guinea
- Sacabaya, Bolivia
- Tata Sabaya, Bolivia
External links
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