Types of Volcanoes
Most people have never seen a real volcano but have learned about them through movies or books. So when most people think of a volcano, they usually conjure up the Hollywood version: a huge, menacing conical mountain that explodes and spews out masses of lava which falls on rampaging dinosaurs, screaming cave people, or fleeing mobs of betogaed Romans--depending on their favorite volcano disaster movie. While those types of volcanoes do indeed exist, they represent only one "species" in a veritable zoo of volcano shapes and sizes.
Some types of volcanoes are easily recognizable and some are not. The "Hollywood" types are easily recognized. Many are located in populated areas and have well-known names: Vesuvius, Krakatoa, Fujiyama, and Mount St. Helens. These volcanoes are typically tens of miles across and ten thousand or more feet in height. As illustrated in the figure above, they have moderately steep sides and sometimes have small craters in their summits. Volcanologists call these "strato-" or composite volcanoes because they consist of layers of solid lava flows mixed with layers of sand- or gravel-like volcanic rock called cinders or volcanic ash.
Another easily recognized type of volcano (seen at right) is the "cinder cone." As you might expect from the name, these volcanoes consist almost entirely of loose, grainy cinders and almost no lava. They are small volcanoes, usually only about a mile across and up to about a thousand feet high. They have very steep sides and usually have a small crater on top.
A third easily recognized volcano may be familiar to you from news reports from Hawaii: the "shield" volcano. This type of volcano can be hundreds of miles across and many tens of thousands of feet high. The individual islands of the state of Hawaii are simply large shield volcanoes. Mauna Loa, a shield volcano on the "big" island of Hawaii, is the largest single mountain in the world, rising over 30,000 feet above the ocean floor and reaching almost 100 miles across at its base. Shield volcanoes have low slopes and consist almost entirely of frozen lavas. They almost always have large craters at their summits.
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