Composite lava are highly viscous with a high melting point. They are light colored and have low density, and have a high percentage of silica. They flow slowly and seldom travel far before solidifying. The resultant cone is therefore steep sided. The rapid solidifying of lava in the vent obstruct the flow of the out-pouring lava, resulting in loud explosions.
Shield Lava: These are the hottest lavas, about 1,000°C. (1,830°F.) and are highly fluid They are dark colored like basalt, rich in iron and magnesium but poor in silica. They flow out of volcanic vent quietly and are not very explosive. Due to their high fluidity, they flow readily with a speed of 10 to 30 miles per hour. They affect extensive areas, spreading out as thin sheets over great distances before they solidify. The resultant volcano is gently sloping with a wide diameter and forms a flattened shield or dome.
