Volcanoes Essay Research Paper VolcanoesA volcano is

Volcanoes Essay, Research Paper

Volcanoes

A volcano is a vent in the earth s crust through which magma (molten rock) and

gas are released. The magma, once it reaches the surface, is called lava. The lava forms a

hill around the vent or opening. The lava can flow out as a viscous liquid, or it may

explode from the vent as solid or liquid particles.

Types of Volcanoes

There are three different types of volcanoes that can be formed around a vent. The

ways to identify each type are what it is composed of and what into what shape it is

formed. The shield volcano, which takes its name form its resemblance to the shields of

early Germanic warriors, is a quietly erupting flow that forms gently slopping mountains.

The dome that is formed over a period of time involving multiple one to ten meter thick

lava flows. This type of volcano is found mostly in Hawaii and Iceland.

The second type of volcano dome formation is the cinder-cone. This volcano has

high gas content and high viscosity (the thickness of the lava), therefore producing a

much more explosive eruption than that of the shield volcano. These volcanoes blew

volcanic bombs and cinders into the air which land beside the vent to form a step-sided

cone. Since these volcanoes consist of loose materials they do not grow as large as other

volcanoes. Most cinder-cone volcanoes are formed by a single eruption.

The third type of volcano is the composite volcano. It is the tallest of all the

different types. It is a combination of shield and cinder-cone volcanoes. It goes through

a cycle of quiet eruptions followed by an explosive eruption of extremely viscous lava.

The fluid lava forms an erosion resistant shell over the existing debris forming a strong,

deep-sided volcanic cone.

A volcano can also be classified by how active it is or has been in the past.

Geologist use the terms: active, dormant, and extinct to classify how active it is. If a

volcano has erupted within the past fifty years it is referred to as active. A volcano that

erupted many years ago but now has no sign of life is called dormant. If scientist feel that

a particular volcano will not ever erupt again they term it extinct.

Volcanic Structure

There are four main parts of a volcano. The vent is the channel that gas, ash and

Rock is ejected. Secondly, the magma chamber that hold the magma. Thirdly, the cone is

simply the mountain that is formed around the vent. Finally, the crater is a bowl shaped

depression surrounding the vent.

There are many unseen forces beneath a volcano that alter rock below the crust to

cause a volcano, and completely change the landscape of the earth. A volcano effects the

earth in many different ways. Of course, the most obvious is the mountain formed on the

surface.

One of the most dramatic changes to the geological features of the earth is a

caldera. A caldera is a huge bowl-shaped crater in the ground at least 2 miles in diameter.

Scientists assume that these massive craters are formed at the end of a volcanoes life once

the magma chamber is emptied. This causes the volcano to collapse under its own

weight. The second deepest lake in the United States, Crater Lake, was formed in a

caldera. It is approximately six miles across and two thousand feet at the deepest point.

An interesting formation underneath a volcano is a lava tunnel. Lava tunnels start

out as horizontal lava channels which form when the surface of a large lava flow hardens

but the lava beneath remains molten and continues to flow. At the end of the eruption the

lava channel is empty and then referred to as a lava tunnel. The tunnels can be anywhere

from a few inches to several yards in diameter. The Kasamura tunnel is the largest

known lava tunnel. It is near the Kilauea volcano in Hawaii, and it twists for more than

six miles beneath the surface.

An igneous intrusion is formed when the intense pressure of the rocks above a

magma chamber force some of the magma through cracks and weak places in the earth.

The magma then solidifies producing masses of igneous rock. One type of igneous

intrusion is a dike. A dike is hardened magma in a vertical crack or fissure forming a

sheetlike mass of igneous rock. A sill is exactly like a dike except it hardens to form a

horizontal sheet of igneous rock. The sill may be hundreds of feet thick and extent for

many miles. A third type of igneous intrusion is the laccolith. A laccolith results from

unusually stiff intruding magma that may not flow easily enough to spread between layers

of rock to for a sill. Instead the magma pushes upward on rocks causing domelike bulges

on the earth s surface. The final type of igneous intrusion is the batholith. The bathollith

is nothing more than a larger laccolith.

Types of Eruptions

There are five types of eruptions a volcano can go through. A volcano can also

consist of any combination of erupti

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