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What Is a Volcano?
Volcanoes are essentially mountains that vent the interior of the earth, allowing molten rock to rise to the surface and escape. The liquid rock solidifies and forms a crust which perpetuates the volcano's exterior growth. Volcanoes are considered to be active, dormant or extinct. When active, the volcano can erupt, releasing contents. When dormant, the volcano has the possibility of eruption. Volcanoes are considered extinct after 10,000 years of inactivity. The Smithsonian Institution reports that there are thousands of volcanoes on the earth, including many beneath the ocean floor. Activity reports vary but the Smithsonian's Global Volcanism Program states that over a typical decade there may be 160 recorded eruptions, with 20 or so occurring at any given time. Some are infrequent but some, like Italy's Stromboli, are continuously active.
Magma and Lava
The lifeblood of a volcano is the molten rock beneath the earth's core. When it is still underground it is called magma. When it comes to the surface of the earth and is forced out of the volcano it is called lava, which is the hardened substance that forms the outer crust of the volcano, building up with each eruption. According to the United States Search and Rescue Task Force, there are three main kinds, or shapes, of volcanoes based on the type of materials they emit. Stratovolcanoes build from eruptions of lava and tephra (fragments of rock) that pile up in layers called strata. These volcanoes develop symmetrical cones with steep sides. Cinder cones are small cone shaped volcanoes that build up from erupting lava that breaks into small pieces as the lava is expelled upward. As the lava pieces fall to the ground, the lava cools and hardens into cinders that pile up around the volcano's vent. Shield volcanoes, so called because the shape resembles a warrior's shield, are formed by flowing lava that spreads and builds up broad, sloping sides.
Tectonic Plates
Volcano formation is a simple process: Most occur when two adjacent tectonic plates (massive rock formations) deep under the earth's surface separate, producing a gap. Magma then begins to bubble up in the resultant space, forcing its way to the surface. When this happens on land, the volcano is a mountain; when it happens underneath the sea, an island can be formed.
Other Methods of Formation
A less common method of volcanic formation is when two tectonic plates collide and one is forced underneath the other. Friction causes rock to melt into magma which then works its way violently to the surface to erupt. Around the volcanic vent all vegetation is endangered as the cooling lava forms a crust over it. This in turn affects wildlife with destruction of native habitats and feeding grounds. Air quality is affected with the ash flow.