In height they are typically about one twentieth their width. Shield volcanoes feature a gentle (usually 2° to 3°) slope that gradually steepens with elevation (reaching approximately 10°) before flattening near the summit, forming an overall upwardly convex shape. However, the extents of the volcano have not been confirmed. In September 2013, a team led by the University of Houston's William Sager announced the discovery of Tamu Massif, an enormous extinct submarine shield volcano of previously unknown origin which, approximately 450 by 650 km (280 by 400 mi) in area, dwarfs all previously known volcanoes on the planet. Mount Everest, by comparison, is 8,848 m (29,029 ft) in height. Accounting for this subsidence and for the height of the volcano above the sea floor, the 'true' height of Mauna Loa from the start of its eruptive history is about 17,170 m (56,000 ft). The mass of the volcano is so great that it has slumped the crust beneath it a further 8 km (5 mi). The summit of the largest subaerial volcano in the world, Mauna Loa, lies 4,169 m (13,678 ft) above sea level, and the volcano, over 60 mi (100 km) wide at its base, is estimated to contain about 80,000 km 3 (19,000 cu mi) of basalt. With the exclusion of flood basalts, mature shields are the largest volcanic features on Earth. Īctive shield volcanoes experience near-continuous eruptive activity over extremely long periods of time, resulting in the gradual build-up of edifices that can reach extremely large dimensions. These are eruptive features which occur along linear fissure vents and are distinguished from shield volcanoes by the lack of an identifiable primary eruptive center. Shield volcanoes are similar in origin to vast lava plateaus and flood basalts present in various parts of the world. Examples of pyroclastic shields include Billy Mitchell volcano in Papua New Guinea and the Purico complex in Chile an example of a felsic shield is the Ilgachuz Range in British Columbia, Canada. Although the term is generally applied to basaltic shields, it has also at times been applied to rarer scutiform volcanoes of differing magmatic composition-principally pyroclastic shields, formed by the accumulation of fragmental material from particularly powerful explosive eruptions, and rarer felsic lava shields formed by unusually fluid felsic magmas. Whereas stratovolcanoes and lava domes are the product of highly viscous flows, and cinder cones are constructed of explosively eruptive tephra, shield volcanoes are the product of gentle effusive eruptions of highly fluid lavas that produce, over time, a broad, gently sloped eponymous 'shield'. Of these four forms, shield volcanoes erupt the least viscous lavas. Shield volcanoes are distinguished from the three other major volcanic types- stratovolcanoes, lava domes, and cinder cones-by their structural form, a consequence of their particular magmatic composition. Geology Structure ĭiagram of the common structural features of a shield volcano The term 'shield volcano' is taken from the German term Schildvulkan, coined by the Austrian geologist Eduard Suess in 1888 and which had been calqued into English by 1910. Giant shield volcanoes are found on other planets of the Solar System, including Olympus Mons on Mars and Sapas Mons on Venus. They include the largest volcanoes on earth, such as Tamu Massif and Mauna Loa. However, they are most characteristic of ocean island volcanism associated with hot spots or with continental rift volcanism. Shield volcanoes are found wherever fluid low- silica lava reaches the surface of a rocky planet. Repeated eruptions result in the steady accumulation of broad sheets of lava, building up the shield volcano's distinctive form. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more viscous lava erupted from a stratovolcano.

An Ancient Greek warrior's shield-its circular shape and gently sloping surface, with a central raised area, is a shape shared by many shield volcanoes.Ī shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground.

Shield volcanoes diagrams