There are four different types of volcanoes. A volcano is categorized both by formation and appearance. Different types of volcanoes also indicate the types of expected eruptions. The different types of volcanoes are: composite (or stratovolcanoes), shield, cinder cones and spatter cones. Throughout the world, one can see pictures of the four types of volcanoes, each type indicative of the active underground world we often view as static.
Layers, or strata, of rock and lava form the composite or stratovolcanoes. These volcanoes come in a number of shapes. A composite volcano like Mt. Rainier resembles a helmet. The sides of this type of volcano are usually steep, some reaching a pointy peek at the top. Mt. St. Helens, also in Washington, and Mt. Shasta in Northern California are both composites. As well, the recognizable Mt. Fuji in Japan is one of the largest composites in the world.
The composite volcano, when dormant, is generally a beautiful and impressive mountain. However, eruptions are particularly intense. As magma rises to the eruption point, it tends to get clogged due to high viscosity. The pressure needed to force the magma out of the volcano is huge, and the result is an explosion of both rock and lava. It is quite dangerous to witness such an eruption up close.
Shield volcanoes are also enormous. However, they differ from the stratovolcanoes since they are made of numerous layers of flowing lava. Hot spots may occur far from the central vent of the volcano.
Shields erupt frequently, but tend not to be highly explosive. These are some of the best volcano eruptions to witness at a relatively close, but still safe, range, since lava spray is uncommon. Both Mauna Loa and Kilauea in Hawaii are examples of the shield volcano. Shields also form on the ocean floor, gradually building height through a steady stream of magma.
Cinder cones are likewise relatively gentle in eruption. They tend to occur in mountain ranges with other types of volcanoes. A central vent forms a volcano made up of lava fragments. Cinders grow quickly but tend not to exceed about 800 feet (243.84m) in height. Occasionally, cinders form on ground with no known history of volcanic activity. In 1934, Paricutín erupted out of a Mexican cornfield and in approximately five days, grew to 300 feet (91.44m) tall.
Puʻu ʻŌʻō, pronounced poo-oo, is a Hawaiian spatter cone that has produced a continuous flow of lava since 1983. Occasional eruptions have been as high as 1500 feet (457.2m). The lava flow tends to be low in viscosity, and readily moves down the cone to cover the surrounding area. The Hawaiian volcano has caused the loss of a great deal of usable land and roads due to the constant flow. The lava tends to come down from the initial eruption in spattered formations, making it dangerous to come too close. While restricting access to some of the highways, Puʻu ʻŌʻō has added 544 acres of land to Hawaii’s main island.
One further classification of volcanoes is when geologists refer to a volcano as complex. A complex volcano can be combinations of any of the above volcanoes, but are primarily classified by the fact that they have at least two vents, often erupting in quite different ways.