How to Identify Types of Volcanoes

Look at the overall shape and size of the volcano. If the volcano is roughly conical, stands less than 1,000 feet high and has a bowl-shaped crater at the summit, it is likely to be a cinder cone. These volcanoes are created when ash and lumps of lava erupt from a single vent. They are common across western North America. Examples include Wizard Island in Crater Lake, Oregon, and the Capulin Volcano National Monument in New Mexico.

Check for a steep-sided cone radiating out from a central vent or a series of vents close together, and look for evidence that the volcano is made up of a number of layers deposited on top of one another. If the volcano fulfills these criteria, it's likely to be a composite volcano, also known as a stratovolcano. These are much larger than cinder cones and can rise to heights of 8,000 feet and above. They erupt in a very explosive way, as occurred in 1980 when an eruption at Mount St. Helens destroyed 230 square miles of forest in a few minutes.

Identify whether or not a volcano is a shield volcano by looking for gently sloping sides that create a flat, shield-like profile. Shield volcanoes tend to erupt gently in comparison with other volcanoes, extruding a fluid kind of lava that builds up very slowly over time. They occur in places where two of the tectonic plates that make up the surface of the earth are being slowly pulled apart, allowing molten rocks to rise through the gap. Although they grow slowly, they can be very large. Perhaps the most famous American example is Mauna Loa in Hawaii, whose summit stands around 56,000 feet above its underwater base.

Look for a cone with craggy knobs around the summit or with a steep-sided area immediately around the cone. These are likely to be lava domes, created when lava moving up through the volcano is too thick to be erupted or cools beside or inside the volcano's vent. The Novarupta Dome in Alaska is a good example of a volcano where the lava cooled and hardened close to the vent of the volcano.