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.