Volcanoes Essay, Research Paper
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.
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
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 eruption, and it can change the way it is erupting at any
time. The least violent eruption is termed a Hawaiian eruption. This volcano is
characterized by extensive fluid lava flows from central vents and occasionally is
accompanied by lava fountains. The next classification is the Strombolian eruption. This
eruption will have moderately fluid lava flows and have frequent, violent lava fountains.
It ejects an abundance of volcanic bombs and cinders. A Volcanian Eruption has very
viscous magma therefore it has short thick flows of lava around the vent. It also is known
to have an abundance of ejecta. The Palean eruption has more viscous magma than the
Volcanian eruption. This volcano is classified by huge domes that form over the vents.
Dangerous ash flows called Nuee adrdente are common during this eruption. The final
type of eruption is the Plinian eruption. These are the most violent eruptions and also
have very violent ejecta. Normally they collapse in on themselves forming rather large
Types of Ejecta
Not only is the extremely hot lava of a volcano deadly but just is deadly is the
ejecta that a volcano blows out. This ejecta could be anywhere from a speck of dust to
several feet across. These solid ejecta are generally termed pyroclasts. Tiny droplets of
lava that are light enough to be carried long distances by the wind are called volcanic ash.
More specifically the type in this classification are no more than four milli-meters in
diameter. Volcanic cinders are slightly larger than the ash. They measure five to thirty-
two millimeters in diameter.
Larger pyroclasts are know as volcanic bombs or volcanin blocks, depending on
the way in which they are ejected from the volcano. Volcanic blocks are huge oddly
shaped lumps of hardened lava, often boulderlike in its appearance. In rare cases these
blocks can weigh many tons. Volcanic bombs harden inside the volcano and are ejected
as solid material. On the other hand, volcanic bombs are formed when lava is thrown into
the air in liquid state and hardens into rock before it lands on the ground.
Cause of a Volcano
Though there is no scientific proof of the plate tectonics theory, its is the most
widely excepted explanation for this violent phenomenon. The plate tectonics theory
proposes that the earth s crust, instead of being one large land mass, is actually several
which rest on a lake of molten lava.
It is suggested that when these plates move even the slightest amount they overlap
each other and due to the colossal size of the plates the force is very cataclysmic. Lava is
forced up through the gaps created in the rocks and shoots up through the earth s crust.
For my demonstration I decided to show a volcanic eruption. The first thing I did
was go to the craft store and buy some clay. I then molded a volcano shape out of the clay.
To cause the eruption itself I mixed: dish washing detergent, red food die, warm water,
vinegar, and baking soda. This combination causes the lava to flow out of the top of the