of Volcanic Eruption
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
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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