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.