Pyroclastic shield
In volcanology, a pyroclastic shield or 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.[1] They typically display low-angle flank slopes and often have a central caldera caused by large eruptions. Lava is commonly extruded after explosive activity has ended. 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
- Masaya, Nicaragua
- Billy Mitchell, Bougainville, Papua New Guinea
- Emi Koussi, Chad
- Gran Canaria[2]p.448, Spain. The basaltic shield building, 1,000 km3, was followed by the formation of a central caldera and further 1,000 km3 of felsic eruptions through five million years (Mogan and Fataga formations)[dubious – discuss]
- Loloru, Bougainville, Papua New Guinea
- Purico Complex, Chile
- Rabaul Volcano, New Britain, Papua New Guinea
- Sacabaya, Bolivia
- Tata Sabaya, Bolivia
- Tenerife, Spain. The "Las Cañadas Volcano" (LCV) large ash, pumice fallout and ignimbrite deposits that covered most of the central basaltic shield in the period 3.5 mya - 180,000 BP [3] pp.231-232[dubious – discuss]
- Pico Basilé, Equatorial Guinea[4]
See also
- Stratovolcano – Type of conical volcano composed of layers of lava and tephra
- Pyroclastic fall – Deposit of material ejected from a volcanic eruption
Categories:
References
- ^ "Global Volcanism Program | Educational Resources | Types and Processes Gallery | Shield Volcanoes". Volcano.si.edu. Retrieved 2012-12-24.
- ^ Schmincke, H.-U; Sumita, M (1998). "Volcanic evolution of Gran Canaria reconstructed from apron sediments: synthesis of VICAP project drilling". Proceedings of the Ocean Drilling Program, 157 Scientific Results. Proceedings of the Ocean Drilling Program. Vol. 157. CiteSeerX 10.1.1.488.3644. doi:10.2973/odp.proc.sr.157.135.1998.
- ^ Troll, Valentin R.; Carracedo, Juan Carlos (2016-05-26). The Geology of the Canary Islands. ISBN 9780128096642.
- ^ "Global Volcanism Program | Santa Isabel". volcano.si.edu. Retrieved 2018-06-13.
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External links
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