Lava domes are formed by small masses of lava that are too thick to move a great distance. The lava cools and becomes hard, allowing lava from the next eruption to cover it and subsequently cool. The process continues until a large dome of layered lava forms. Examples of lava dome volcanoes are Mount Pelee in Martinique and Lassen Peak in California.
Shield volcanoes are built almost entirely of lava flow. Lava pours out from a central vent, flowing in all directions until it cools. The cooled lava forms in sheets that can stretch great distances. Many shield volcanoes can grow up to 1,500 feet and have diameters as large as 2 miles. The Hawaiian Islands are composed mainly of shield volcanoes. Mauna Loa, the largest volcano in the world, is a shield volcano rising 13,677 feet above sea level.
Composite volcanoes are typically steep-sided, cylindrical structures resembling mountains. The volcano is formed of cooled lava and volcanic ash, in addition to rocks and cinders. The summit of the volcano usually contains a central vent or a series of vents that allow lava to flow from all directions down the sides of the volcano. A reservoir of magma is present beneath the volcano. When the magma is emptied by eruptions, the volcano becomes dormant. Mount Shishaldin in Alaska is an example of a composite volcano.
Cinder cones are found in great numbers in volcanic areas around the world, especially in western North America. The cinder cone is formed by a simple vent that spews lava and ash; these continually cool and form layers as more lava and ash pour from the vent. A crater is formed at the summit of the volcano, which rarely grows more than 1,000 feet above sea level. Paracutin Volcano in Mexico is an example of a cinder cone volcano.