Volcanoes

Volcanoes

Volcanoes are one of the most destructive yet fascinating geological land forms in

our natural environment. They consist of a fissure in the earth's crust above which a

cone of volcanic material has accumulated. The cone is formed by the deposition of

molten or solid matter that flows from the interior of the earth through an indented vent,

called a crater, which is found at the top of the cone. In this report I will discuss

different states of volcanic activity, different forms of volcanoes and their properties and

locations.

Some volcanoes are more active than others. Some are even in a state of constant

eruption an example of this is Izalco, located in El Salvador, it first erupted in 1770 and

has been in a state of eruption ever since. In a belt that circles the Pacific Ocean their are

many active and erupting volcanoes. For obvious reasons this area is referred to as the

Ring of Fire. The activity of the volcanoes varies , for example, Vesuvius will continue

in a state of moderate activity for long or short time periods and will then become

stagnant or in-active for months. If an eruption succeeds prolonged dormancy it will

usually be fairly violent, as was the eruption of Mount Saint Helens after 123 years of

stillness. The potential danger of an active volcano can be seriously threatening to

civilization for more reasons than just the initial eruption of molten rock, disasters, such

as mud flows, triggered by an eruption are also serious hazards.

Composite cones are formed from a combination of eruptions. First the volcano

will have an explosive eruption that ejects huge amounts of steam, gas, and ash. This is

followed by the ejection of lava. Most composite cones are built of layers of fragment

materials and flows of lava, all inclined outward away from the vent. Both Etna, in

Sicily, and Vesuvius, near Naples are examples of composite cones. The most common

type of volcanic cones are stratovolcanoes. A large stratovolcano will be built with many

layers of ash and lava. Mt. Saint Helens, Rainier, and Mt. Fuji are all examples of strata

volcanos.

Shield volcanoes are made of thousands of thin lava flows. Because the flow of

the lava is generally fast, it is able to travel far from the vent. The resulting volcanic land

form has a broad base and gentle slopes. Shield volcanoes are the largest volcanoes.