There are three classifications of volcanoes. Extinct volcanoes are those which scientists believe will not erupt again. Dormant volcanoes aren't active but volcanologists believe they are still capable of erupting in the future. Active volcanoes are volcanoes that are actively erupting or are in the process of erupting.
The Earth's plates shift on an ongoing basis. These shifts above volcanic hotspots can cause an active volcano to become dormant. They become dormant when the volcano is shut off from the magma chamber beneath the volcano. After the magma locates another source to the surface, it creates a new volcano. The older volcano then becomes dormant. Volcanoes can also become dormant when the angle of subduction changes and magma rises in a different location.
Magma should not be confused with lava. The difference between lava and magma is that magma is the melted rock inside the Earth's mantle. Lava is the melted rock when it reaches the Earth's surface.
Volcanoes are considered extinct when they haven't erupted in tens of thousands of years and scientists believe they will not erupt again. When they become extinct, hotspots move to a new location further to the east. When volcanoes become extinct, only the heavily eroded plug remains. The ancient city of Pompeii was developed under the fatally mistaken belief that Mount Vesuvius was an extinct volcano. The volcano erupted in 79 AD, destroying the town.
A dormant volcano can erupt when magma, hot water and gases approach the surface of the ground from below. When the rock reaches or approaches the surface, an eruption can occur. One of the best known volcanoes is Mauna Kea, which is located in Hawaii. It is one of the five volcanoes that compose Hawaii. In 2011, it is considered to be in the "post-shield" stage of volcanic evolution. The post-shield stage is one of the five stages of evolution of a volcano characterized by the volcano moving off a hotspot leading to greatly reduced lava production.
Scientists believe that although the Yellowstone Caldera in Yellowstone National Park hasn't erupted in over 640,000 years, it may still eventually erupt. This is because lava flowed from the volcano within the past 10,000 years and because there are still earthquakes in the region.
