<P> Shield volcanoes are distinguished from the three other major volcanic archetypes--stratovolcanoes, lava domes, and cinder cones--by their structural form, a consequence of their unique magmatic composition . Of these four forms shield volcanoes erupt the least viscous lavas: where stratovolcanoes and especially lava domes are the product of highly immotile flows and cinder cones are constructed by 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". Although the term is generally ascribed to basaltic shields it has also at times been appended 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 . 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 Big Obsidian Flow in Oregon . Shield volcanoes are also related in origination to vast lava plateaus and flood basalts present in various parts of the world, generalized eruptive features which occur along linear fissure vents and are distinguished from shield volcanoes proper by the lack of an identifiable primary eruptive center . </P> <P> Active 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 . With the exclusion of flood basalts mature shields are the largest volcanic features on Earth: 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 (19,000 cu mi) of basalt . The mass of the volcano is so great that it has slumped the crust beneath it a further 8 km (5 mi); 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). Mount Everest, by comparison, is 8,848 m (29,029 ft) in height . In September 2013 a team led by the University of Houston's William Sager announced the singular origination 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 . The research has not yet been confirmed . </P> <P> Shield volcanoes feature a gentle (usually 2 ° to 3 °) slope that gradually steepens with elevation (reaching approximately 10 °) before eventually flattening near the summit, forming an overall upwardly convex shape . In height they are typically about one twentieth their width . Although the general form of a "typical" shield volcano varies little worldwide regional differences exist in their size and morphological characteristics . Typical shield volcanoes present in California and Oregon measure 3 to 4 mi (5 to 6 km) in diameter and 1,500 to 2,000 ft (500 to 600 m) in height; shield volcanoes in the central Mexican Michoacán--Guanajuato volcanic field, by comparison, average 340 m (1,100 ft) in height and 4,100 m (13,500 ft) in width, with an average slope angle of 9.4 ° and an average volume of 1.7 km (0.4 cu mi). </P> <P> Rift zones are a prevalent feature on shield volcanoes that is rare on other volcanic types . The large, decentralized shape of Hawaiian volcanoes as compared to their smaller, symmetrical Icelandic cousins can be attributed to rift eruptions . Fissure venting is common in Hawai ʻi; most Hawaiian eruptions begin with a so - called "wall of fire" along a major fissure line before centralizing to a small number of points . This accounts for their asymmetrical shape, whereas Icelandic volcanoes follow a pattern of central eruptions dominated by summit calderas, causing the lava to be more evenly distributed or symmetrical . </P>

Where can classic examples of shield volcanoes be found