Volcanoes are openings in the Earth's crust that connect to the molten, 2nd layer of the Earth, the mantle. The openings in the volcanoes through which molten magma pours are called vents. Vents are connected to a series of passageways through the structure of the volcano called conduits. The conduit acts as a transport system, conducting the magma to the surface of the Earth.
Volcanoes may be classified into three types, based largely on the type of eruption and magma content. There is the ever-popular cinder cone volcano, which is conelike in structure and has a high silica content in it's magma. Cinder cones have violent, explosive eruptions. Second is the shield volcano, which has quiet, runny eruptions. The magma in a shield volcano has a low silica content, which lowers it's viscosity. The third type of volcano is called a composite volcano, meaning it has both quiet and explosive eruptions.