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Phases of Volcanic Eruption

When a volcano is about to erupt, such as Mount Saint Helens threatened to do in late 2004, excitement and interest in volcanos rises. However, many people may not know the different phases of volcanic eruption. Below is an explanation of the different stages a volcano experiences through eruption to inactivity.

A Volcanic Eruption
When a volcano erupts the lava is highly charged with steam and gases like carbon dioxide, hydrogen, carbon monoxide, and sulfur dioxide, which escape from the lava’s surface explosively, developing into a thick cloud. The cloud itself frequently discharges showers of rain and lightning, especially if the cloud is heavily charged with dust particles.

Along with the cloud of gases, large and small bits of the lava are shot upward, forming a fiery fountain of particles. These fiery fragments are classified as bombs, cinders, or ash, depending on their size and shape. These objects can either fall out onto the external slopes of the volcano or back into the crater to be ejected again and again.

When the lava rises to the top it flows over the rim of the crater and can often ooze through fissures in the side of the volcano cone. This is often referred to as the crucial point of the eruption. At the end of an eruption there is a final ejection of fragmental material before the volcano calms down and begins the cooling stage.

The Cooling Stage of a Volcano
For a long time after a volcano has ceased to erupt, it continues to emit acid gases and vapor. This period is referred to as the fumarolic stage of a volcano.

After the fumarolic stage, hot spring may rise from the volcano such as the geysers of Yellowstone National Park. If the last traces of volcanic heat disappear, springs of cold water, often filled with minerals, may issue from the volcano and from the ground around the volcano. At this point the volcano is inactive.

The Inactive Period of a Volcano
After a volcano becomes inactive, it progressively reduces size due to erosion from water streams, glaciers, wind, or waves. If enough erosion occurs the volcano may become completely obliterated, with only the volcanic pipe left. The volcanic pipe is a “pipe” filled with lava and other volcanic material that extends from the earth’s surface to the former lava reservoir. Good examples of volcanic pipes are the diamond mines of South Africa.

Of course, some volcanoes are much more active than others, and some have been said to be in a state of permanent eruption, at least for the present time. Some constantly active volcanoes are found in a belt called the Ring of Fire that encircles the Pacific Ocean and a similar belt in Central and South America.


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