Features of Volcanoes

A volcano is an opening in the surface of the Earth from which magma (molten subsurface rock ) and associated gases and ash erupt; also, the form or structure, sometimes conical, that is produced by the ejected material.  Volcanic activity may create vast plateaus where flood basalts emerge from cracks, covering the surface with massive flows of lava (molten rock above the surface) and subsequently dissected by streams.

Common to all volcanoes is a magma chamber . The magma chamber is a huge, subterranean caldron of molten rock  that is less dense than the surrounding rock and rises buoyantly, sometimes under great pressure to the surface. The main conduit through which magma moves toward the surface is the central vent.  A crater sits at the top of a volcano and is the location where much of the lava, gas, rock fragments and ash are ejected from.

Figure 16.1 Mt. St. Helens last major eruption left the huge crater seen in the center of the photograph. Courtesy USGS CVO 

Lateral vents are found on the sides of some volcanoes where lava is extruded. An extremely large crater is some times found at the summit of a volcano. These massive craters called calderas, are created when pressure builds inside the volcano until the top is literally blown off, magma drains back into the central vent and the top of the cone collapses in. Crater lake formed in the caldera of Mount Mazama.  

Figure 16.2 Watch "Crater Lake" courtesy of Britannica

Explore Crater Lake with Google Earth

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