Each individual volcano is unique in its own way, but they can be grouped into families according to shape, size, and type of volcanic material. In addition, these similarities and differences are caused by the composition of the magma and the effects of its mixing with surface water.

• composite cone/stratovolcano - These volcanoes are made of many layers of rubble, old lava, and dome rocks. They grow to be higher than 3,000 meters abve their bases. They are created from multiple eruptions that occur over many years. Composite cones can continue growing with each eruption until their slopes collapse. Examples include Mount St. Helens, Mount Rainier, Mount Fuji, and Klyuchevskoy Volcano (Russia).
• domes - Lava domes are found on the outside slopes of composite cones or within their craters. These are a little small, but still volcanoes in their own right. Their eruptions can start explosively, forming pits with pyroclastic debris. However, the explosive activity decreases as the gas content and pressure decrease. With lower gas pressure, the lava then flows out slowly, forming thick stubby flows or bulbous domes.
• calderas - (Spanish for "cauldron") These are very large craters formed when the ground surface collapses. After large amounts of ash, pumice, and rock are emitted from the original volcano, the magma chamber is partly empty, so that the ground above the chamber caves into the void. Calderas can range in size from a few to 60 kilometers in diameter. The creation of calderas are usually accompanied by large volumes of erupted material, causing hurricane-like masses of hot debris that leave ash and pumice over large areas.
• cinder cones/scoria cones - These are relatively small volcanoes made of basaltic fragments. The most common types of volcanoes on earth, they are made up of cinders (nut-sized pieces of red or black lava containing bubblelike cavities known as vesicles) and form steep-sided mounds with a little crater at the top. They are usually found in clusters, sometimes in groups of a hundred or more. They can also occur on the slopes of other volcanoes.
• maars - A maar is a small volcano with a wide crater, several hundred meters to a few kilometers in diameter. The floor of their craters are usually beneath the level of the surrounding countryside. They are formed from steam explosions that occur when rising magma mixes with groundwater or surface water.
• shield - Shield volcanoes have broad, low slopes, like an upside-down shield. They are made of solidified basaltic lava that was originally very fluid. Because this type of lava can flow long distances, they construct gentle slops and broad summits.

Forces of Nature: ThinkQuest 2000 (Team #C003603)

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