Thursday, April 22, 2010

Shield Volcano

A shield volcano is a tall, broad volcano with gently sloping sides. Shield volcanoes are usually built up over time by flow after flow of fluid basaltic lava that comes out from vents or fissures on the surface of the volcano, resulting in their relatively flat, broad profile. In contrast, steeply sloped stratovolcanoes better match the popular stereotype of a volcano. Some of the largest volcanoes on Earth are shield volcanoes. The name derives from a translation of "SkjaldbreiĆ°ur", an Icelandic shield volcano whose name means "broad shield", from its resemblance to a warrior's shield. Shield volcanoes are characteristic of the Hawaiian chain; Manua Kea is an example, with a basal diameter of around 200?km, 4000?m beneath the sea.

Shield volcanoes can be so large that they are sometimes considered to be a mountain range, such as the Ilgachuz Range and the Rainbow Range, both of which are located in Canada. These shield volcanoes formed when the North American Plate moved over a hotspot similar to the one feeding the Hawaiian Islands, called the Anahim hotspot. Shield volcanoes can be found in many places around the world, including Australia, Ethiopia, and the Galapagos Islands. The Piton de la Fournaise, on Reunion Island, is one of the most active shield volcanoes on earth, with one eruption per year on average.

Mount Okmok, Aleutian Islands (A Shield Volcano)

A Shield Volcano Kilauea, Hawaii (Video)