Scher1
Volcanoes
In this paper I will be discussing volcanoes. I will first be focusing on the different stages
that are involved in a volcanic eruption. Then I will discuss the two basic elements of volcanic
eruptions and note the major eruptions that have occurred throughout the world. To conclude the
paper I will move on to talk about the different types of volcanoes.
There are two specific stages to an eruption, which starts deep within the Earth. The first
stage of the eruption revolves around the temperature deep within the volcano. It is so hot that
some rocks slowly melt and become a thick flowing substance called magma. The second stage
has to do with the mass of the rock surrounding the magma in the volcano. Magma is lighter than
the solid rock that surrounds it, and it is this factor that causes the magma to rise and collect in
magma chambers. The magma can remain in these chambers for years until eventually some of
the magma pushes through vents and cracks in the Earth's surface. Sometimes the pressure of
colliding plates causes magma to rise. This colliding of plates is known as subduction, which
usually occurs when the oceanic plate goes under the continental crust (Lopes, 20).
Some volcanic eruptions are more explosive than others. How explosive an eruption is
depends on how runny or sticky the magma is. The flow of the magma depends on two factors:
the temperature and the silica content (Lopes, 23). Magma with low silica content is thin and
runny, which allow gases to escape easily from the volcano. When magma with low silica
content erupts, it flows faster and more easily out of the volcano due to its high temperature. An
example of this type of magma is called basaltic magma. Lava flows rarely kill people because
they move slowly enough for people to get out of their way. Lava flows, however, can cause
considerable destruction to buildings in their path. Magma that is thick and sticky is said to have
high silica content, which means that gases cannot escape easily due to the magma’s cool
Scher2
temperature. This type of magma causes pressure to build up within the volcano until the gases
escape and explode. In this type of eruption, the magma blasts into the air and breaks apart into
pieces, which can range from tiny particles of ash to large boulders. An example of this type of
magma is called granitic magma.
The temperature also affects what color the lava will be when it erupts from the volcano.
“By observing the color with which a body glows one can make an accurate estimate of the
temperature”(Bullard, 53). When the color of the lava comes out as red, it is a sign that the
temperature is cooler than when the lava erupts having a whitish color. The contrasting colors of
the lava are tested with a tool called the “optical pyrometer”(Bullard, 53). Using this tool a
volcanologist is able to measure the temperature of the lava by “matching the color of the lava
with the same color that appears on the electrically activated cell of the instrument”(Bullard, 53).
Another instrument called the “thermoelectric pyrometer” is also very useful when it comes to
dealing with lava at close range (Bullard, 54). Both of these instruments help scientists to
determine the temperature of the lava of different volcanoes, which leads them to discover when
an eruption might occur.
The two elements of a volcanic eruption are those that are explosive and those that are
non-explosive (Lopes, 28). One of the famous volcanoes that have explosive eruptions is Mount
St. Helens. The most active volcano in the world, Kilauea volcano, on the island of Hawaii, is a
non-explosive volcano. These non-explosive eruptions are the least dangerous type of volcanic
eruptions since they rarely kill people. Explosive eruptions produce fragments of rocks from
erupting lava and the surrounding rock, and some eruptions produce very fine volcanic ash.
Explosive volcanoes are also what cause avalanches and landslides when they erupt.
Throughout history there have been many significant volcanic eruptions occurring
Scher3
throughout the world. Mount Vesuvius in Naples, Italy, remains one of the most dangerous
volcanoes in the world. The deadly power of Vesuvius was demonstrated in AD 79, when an
eruption wiped out the Roman cities of Herculaneum and Pompeii. Another significant eruption
occurred on Mount Etna, in Sicily, Italy. This volcano is known for being one of the world's
most active volcanoes. Since 1500 BC, more than 150 incidents of lava eruptions have been
recorded. The largest and most destructive eruption of Mount Etna came in the spring of 1669.
The 1902 eruption of Mount Pelée on the Caribbean island of Martinique has been called
the worst volcanic disaster of the twentieth century. More than 30,000 people are thought to have
died in this eruption. While most of these eruptions have occurred outside of the U.S., one major
eruption that occurred in the U.S. was the 1980 volcanic eruption of Mount St. Helens. Most
recently, in the year 2010, two major volcanic eruptions occurred, one in Iceland and the other in
Indonesia.
There are four main kinds of volcanoes: cinder cones, composite volcanoes, shield
volcanoes and lava domes. Cinder cones are the simplest type of volcano. Most of these
volcanoes are shaped like a crater, have very smooth steep slopes, and are formed by the piling
up of ash, cinders, and rocks that have erupted from the cone. An example of a Cinder cone
volcano is the Sunset Crater located in Arizona. Composite volcanoes are volcanoes that are
build on various layers consisting of lava, ash, and mud. “The essential feature of a composite
volcano is a conduit system through which magma from a reservoir deep in the earth’s crust rises
to the surface” (Watson). These volcanoes are very steep and are considered the world’s most
common type of volcano because they look the most like the way a typical volcano is shown in a
picture. Some examples of composite volcanoes include, Mount St. Helens in Washington, Mt.
Fuji in Japan, and Mount Shasta in California.
Scher4
The third type of volcano is called the shield volcano. This volcano consists of broad and
gentle slopes that are built almost entirely of fluid lava flows. “ They are built up slowly by the
accretion of thousands of highly fluid lava flows called basalt lava that spread widely over great
distances, and then cool as thin, gently dipping sheets” (Watson). An example of the shield
volcano is Mauna Loa on the island of Hawaii. This is considered to be the largest shield volcano
as well as the word’s largest active volcano. The last type of volcano is called a lava dome. Lava
domes are formed by small masses of lava and grows by expanding from the inside. “ As it
grows its outer surface cools and hardens, then shatters, spilling loose fragments down its
sides…volcanic domes commonly occur within the craters or on the flanks of large composite
volcanoes” (Watson). Some examples of lava domes include Mont. Pelée in Martinique and
Lassen Peak in California.
While volcanoes are still considered to be very unpredictable in terms of when they will
erupt, these natural landforms are very interesting to view and continually draw people from all
around the world to study them. It is because of this unpredictability and uncertainty that this
natural landform is so interesting to contemplate and learn more about.
Scher5
Work Citied
Bullard, Fred M. "Temperature Observations." Volcanoes in History, in Theory, in Eruption.
[Austin]: University of Texas, 1962. 53-54. Print.
Lopes, Rosaly. "Chapters 2 and 3." The Volcano Adventure Guide. Cambridge [u.a.: Cambridge
Univ., 2005. 18-27-38-40. Print.
"Natures Deadliest Killers." A History of Volcanoes in 10 Great Eruptions. Web. 03 Mar. 2012.
<http://www.randomhistory.com/history-of-volcanoes.html>.
Watson, John. "Volcanoes: Principal Types of Volcanoes." Web. 03 Mar. 2012.
<http://pubs.usgs.gov/gip/volc/types.html>.