A volcano is a vent in the earth's crust through which magma (molten rock) and .
The magma, once it reaches the surface, is called lava. The lava forms a .
hill around the vent or opening. The lava can flow out as a viscous liquid, or it may .
explode from the vent as solid or liquid particles.
Types of Volcanoes.
There are three different types of volcanoes that can be formed around a vent. The .
ways to identify each type are what it is composed of and what into what shape it is .
formed. The shield volcano, which takes its name form its resemblance to the shields of .
early Germanic warriors, is a quietly erupting flow that forms gently slopping mountains. .
The dome that is formed over a period of time involving multiple one to ten meter thick .
lava flows. This type of volcano is found mostly in Hawaii and Iceland.
The second type of volcano dome formation is the cinder-cone. This volcano has .
high gas content and high viscosity (the thickness of the lava), therefore producing a .
much more explosive eruption than that of the shield volcano. These volcanoes blew .
volcanic bombs and cinders into the air which land beside the vent to form a step-sided .
cone. Since these volcanoes consist of loose materials they do not grow as large as other .
volcanoes. Most cinder-cone volcanoes are formed by a single eruption.
The third type of volcano is the composite volcano. It is the tallest of all the .
different types. It is a combination of shield and cinder-cone volcanoes. It goes through .
a cycle of quiet eruptions followed by an explosive eruption of extremely viscous lava. .
The fluid lava forms an erosion resistant shell over the existing debris forming a strong, .
deep-sided volcanic cone.
A volcano can also be classified by how active it is or has been in the past. .
Geologist use the terms: active, dormant, and extinct to classify how active it is. If a .
volcano has erupted within the past fifty years it is referred to as active.