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are characterized by steep slopes on both sides of the edifice, which lead up to a very wide summit crater. This edifice is composed of ashy tephra, usually spewed out by Strombolian eruptions. Unlike stratovolcanoes, many Scoria cone volcanoes have only one eruption event. oFelsic/Rhyolitic Shield volcanoes: These wide, relatively short volcanoes occur when low-viscosity lava flows out with minimal explosiveness, such as in Hawaiian eruptions. The lava disperses out over a wide surface area -- sometimes hundreds of kilometers -- building up a shield-shaped dome. Near the summit, the edifice gets a little steeper, giving the volcano a slightly raised center. Many shield volcanoes erupt with great frequency (every few years or so). oMafic/Basaltic The Hawaiian Island chainWhilst most volcanic activity happens at plate margins, there are cases of volcanoes erupting in the middle of plates. The Hawaiian Islands are formed by volcanic activity, despite the nearest plate margin being 3,200 km away.Some geologists have suggested that a ‘hot spot’ in the mantle, which remains stationary as the Pacific Plate moves over it, explains the existence of the island chain.The hot spot may represent the top of a mantle plume which originated deep down at the outer core—lower mantle boundary. The plate moves in a north westerly direction due to sea floor spreading along the East Pacific Rise. As oceanic lithosphere moves away from the hot spot, volcanic activity ceases and it cools, becomes denser, and slowly subsides. As new oceanic lithosphere is positioned over the hot spot, a new island will begin to form above.The islands extend for around 2,400 km, forming a chain that is progressively older from the south end to the north west end. The volcanoes are ofen very wide, with gently sloping sides comprising many thin (1 to 5 metres thick) basaltic lava flows. These are ofen referred to as ‘shield volcanoes’. Kilauea and Mauna Loa on Big Island are currently active examples.