Shield Volcano
The Internal Structure of a Typical Shield Volcano
Source: http://pubs.usgs.gov/gip/volc/fig15.gif
Shield volcanoes form the largest volcanoes on Earth. They have gentle upper slopes and somewhat steeper lower slopes (somehow resembling a warrior’s shield, thus its name). It is built up slowly by the accretion of thousands of flows of low viscosity basalitic magma (which is very fluid) that easily spreads over great distances from the summit vent, then cooling as thin gently sloped sheets. The viscosity of magma is dependent on its temperature and composition. Shield volcanoes erupt magma as hot as 1,200 °C, compared with 850 °C for most continental volcanoes, which are usually composed of acidic lava. Because of the fluidity of the lava, major explosive eruptions do not occur in shield volcanoes. Lava also erupts from the vents along fractures that develop on the flanks of the cone. This gives the shield volcanoes the circular/oval shape with nearly flat summits.
The Internal Structure of a Typical Shield VolcanoSource: http://pubs.usgs.gov/gip/volc/fig15.gif
Shield volcanoes form the largest volcanoes on Earth. They have gentle upper slopes and somewhat steeper lower slopes (somehow resembling a warrior’s shield, thus its name). It is built up slowly by the accretion of thousands of flows of low viscosity basalitic magma (which is very fluid) that easily spreads over great distances from the summit vent, then cooling as thin gently sloped sheets. The viscosity of magma is dependent on its temperature and composition. Shield volcanoes erupt magma as hot as 1,200 °C, compared with 850 °C for most continental volcanoes, which are usually composed of acidic lava. Because of the fluidity of the lava, major explosive eruptions do not occur in shield volcanoes. Lava also erupts from the vents along fractures that develop on the flanks of the cone. This gives the shield volcanoes the circular/oval shape with nearly flat summits.
The largest shield volcano, Mauna Loa volcano on the Island of Hawaii
Source: http://volcanoes.usgs.gov/Imgs/Jpg/Photoglossary/shieldvolcano1_large.jpg
Newberry Volcano, Oregon
USGS photo by Lyn Topinka
The Hawaiian Islands are composed of linear chains of the shield volcanoes. The islands are more than 15,000 feet above the ocean floor. For the Mauna Loa, the largest shield volcano, it is about 13,677 feet above sea level and its summit is 28,000 feet above the ocean floor. In Northern California and Oregon, many of the shield volcanoes have diameters of 3 or 4 miles and heights of 1,500 to 2,000 feet.
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