FREE ESSAY ON VOLCANOES

VOLCANOES

Volcanoes
JACK KNOFF
WR 327
Technical Report
Spring '99
Introduction
In this report I plan to discuss the geological event of volcanic eruptions and the
disasters they cause. To me, this is a fascinating topic and timely seeing how the 19th
anniversary of the eruption of Mt. St. Helens is upon us. I hope to inform people of the
mass destruction that is caused by the eruption of a volcano. The scope of my report will
be limited to: 1) describing what comes out of a volcano, 2) explaining the seven
different types of volcanoes, 3) explaining the five types of volcanic eruptions, and 4)
explaining the disasters they can cause people. The procedure for completing this report
first started by watching educational television programs that featured volcanoes and the
upcoming anniversary of the eruption of Mt. St. Helens. From there, I decided that the
topic of volcanoes would be a good subject for my analytical report. Then I began my
research, first looking online for websites that contained information and pictures of
volcanoes. After this, I looked for publications about volcanoes in the library, finding
many books that pertained to my topic. Having an abundance of data, I began to sort
through all of it and found what I thought to be the most informative. I then prepared an
outline of the subjects I wanted to write about and arranged the data and visuals to fit
my outline. And of course from there, I began to write this report using the technical
writing methods taught during lecture and described in the book.
Collected Data
If we look through volcanoes we can view the interior of the earth. More than just lava
flows are spewed out of volcanoes when they erupt. The three main components that erupt
out of a volcano are: lava, ash, and bombs. When all three of these components lump
together, the solid fragments are called pyroclastics. Pyroclastic rocks can be erupted
in two different ways: they can be airfall deposits or pyroclastic flows.
There are seven different types of volcanoes: Submarine volcanoes; Ridges and vents;
Shield volcanoes; Lava plateaus and Flood basalts; Lave domes; Composite volcanoes;
Cinder and Scoria cones; and Calderas. Each of these volcanoes is found in different
geographical locations and have different eruptions. Along with different types of
volcanoes, there are also different types of eruptions. The five eruption types are:
Pelean, Vulcanian, Strombolian, Hawaiian, and Icelandic. These volcanoes have different
levels of explosiveness, and their eruptions occur due to their geographic location.
A volcanic hazard is destructive natural process that has a probability of reoccurring.
Losses from volcanoes include: people's lives, property, livestock, and the productive
capacity of the area. The factors of predicting volcanic activity are: the longer a
volcano is inactive, the greater the chances are for it to become active; eruptive
behavior may change with time; and some hazards are indirectly related to an eruption,
making it difficult to forecast. Being informed of volcanoes in your area and knowing
cautionary steps can save your life.
What Comes out of Volcanoes?
Volcanoes are dark windows to the interior of the Earth (Decker 104). Volcanic products
are our only direct samples of the Earth's composition from deeper levels. Most people
think that lava flows are the only products spewed from volcanoes, but actually volcanic
ash and larger solid fragments, called cinders and blocks, form the major products of
observed volcanic eruptions (Decker 104). The three components that erupt from a volcano
are: lava ash, and bombs. The volcanic debris that lumps together all the sizes of solid
fragments is called pyroclastics (See Figure 1). Pyroclastics come from three sources:
magma that is cooled and broken into fragments by expanding gases at the moment of
eruption; fragments of old crater walls which are ripped loose in explosive eruptions;
and clots of liquid lava thrown into the air which cool during their flight. Pyroclastic
rocks are set apart by the general size of fragments. Volcanic dust is fine; volcanic ash
is gritty, with particles up to the size of rice; cinders include pieces as big as
Ping-Pong balls; and blocks cover all other fragments up to the size of a house. Volcanic
bombs are block-sized clots of liquid lava thrown from erupting vents. Pyroclastic rocks
can be erupted in two different ways: they can be airfall deposits or pyroclastic flows.
The contrast in explosive debris tells something of the nature of its previous eruptions
and thus helps to predict the nature of possible future eruptions (Decker 105).
The Seven Different Types of Volcanoes
The seven different types of volcanoes are: Submarine volcanoes; Ridges and vents; Shield
volcanoes; Lava plateaus and Flood basalts; Lava domes; Composite volcanoes; Cinder and
scoria cones; and Calderas.
Submarine volcanoes and volcanic vents are found on certain zones of the ocean floor.
Some are active at the present time and, in shallow water, disclose their presence by
blasting steam and rock-debris high above the surface of the sea (e.g. USGS/Cascades
Volcano Observatory, Vancover, Washington). Many others lie so deep within the ocean
floor that the tremendous weight of the water results in such confining pressure, that it
prevents the formation and explosive release of steam and gases.
Shield volcanoes are built almost entirely of fluid lava flows (e.g. USGS/Cascades
Volcano Observatory, Vancouver, Washington). They are formed when flow after flow pours
out from a central summit or vent, or group of vents which builds a broad, or gently
sloping cone of a flat domical shape (See figure 2). The Hawaiian Islands are composed of
linear chains of these volcanoes including Kilauea and Mauna Loa on the island of Hawaii,
two of the world's most active volcanoes (e.g. USGS/Cascades Volcano Observatory,
Vancouver, Washington).
Flood basalts and plateau basalts occur at vast composite accumulations of horizontal or
sub-horizontal flows and which, erupted in rapid succession over great areas, have at
times flooded sectors of the earth's surface on a regional scale (e.g. USGS/Cascades
Volcano Observatory, Vancouver, Washington). The Columbia Plateau of the northwestern
United States and the Deccan Plateau of southeastern India are classic examples of
plateau basalt provinces.
Lava domes are masses of solid rock that are formed when viscous lava is erupted slowly
from a vent (e.g. USGS/Cascades Volcano Observatory, Vancouver, Washington). If lava is
viscous enough, it will pile up above the vent to form a dome rather than move away as a
lava flow. Most domes are composed of silica-rich lavas that have a lower gas content
than do the lavas erupted earlier in the same eruptive sequence; nevertheless, some lava
domes still contain enough gas to cause explosions (see figure 3).
Composite volcanoes and stratovolcanoes are typically steep sided, symmetrical cones of
large dimensions built of alternating layers of lava flows, volcanic ash, cinders,
blocks, and bombs which may rise as much as 8,000 feet above their bases (e.g.
USGS/Cascades Volcano Observatory, Vancouver, Washington). Some of the most conspicuous
and beautiful mountains in the world are composite volcanoes, including Mt. Fiji in
Japan, Mt. Shasta in California, Mt. Hood in Oregon, and Mt. St. Helens and Mt. Rainier
in Washington (e.g. USGS/Cascades Volcano Observatory, Vancouver, Washington) (see figure
4).
Cinder and scoria cones are the simplest type of volcanoes. They are built from particles
and blobs of congealed lava ejected from a single vent. When gas-charged lava is blown
violently in the air, it breaks into small fragments that solidify and fall as cinders
around the vent to form a circular or oval cone. Cinder cones are numerous in western
North America as well as throughout other volcanic terrains of the world.
Calderas are among the most spectacular and active volcanic features on Earth. When a
large volume of magma is removed from beneath a volcano, the ground subsides or collapses
into the emptied space, to form a huge depression called a caldera (see figure 5). Most
calderas very active, but this does not always lead to an eruption. The possibility of
violent explosive eruptions forces detailed scientific study and monitoring of some
active calderas.
The Five Types of Volcanic Eruptions
The five types of volcanic eruptions are Pelean, Vulcanian, Strombolian, Hawaiian, and
Icelandic. The Pelean type of eruption, which is the most explosive, is represented by
many volcanoes in Central America and the West Indies. A Pelean eruption has violent and
destructive activity that takes place during the opening stages when glowing avalanches
of magma are produced. Airfall material is much less widespread than those of most
Vulcanian eruptions. The eruptive cycle generally lasts only a few years, but there are
exceptional cases such as in Santiaguito, Guatemala, where the cycle lasts more than 50
years (McBirney 240). 
The second type of volcanic eruption is referred to as the Vulcanian type. In a Vulcanian
volcano the crater crusts over solidly between eruptions. When gases accumulate beneath
the crust, the upper part of the magma column becomes thoroughly gas-saturated. Strong
eruptions sometimes disrupt the cone, followed by a cauliflower-shaped cloud, dark in
color because of high ash content, as the obstruction is blown out. As the pressure is
suddenly reduced, the gas-charged magma is disrupted by the explosively expanding gases
into pumice and ash (Bullard 185). Lava flows may flow from the crater or from fissures
on the sides of the cone. Vulcano, in the Lipari Islands off the coast of Sicily, was the
example used by Mercalli (1891), Lacroix (1908), and other scientists for the Vulcanian
type of eruption. However, many others consider Vesuvius to be an even better example
(Bullard 185).
The prime characteristics of a Strombolian eruption are the throwing out of incandescent
fragments of lava accompanied by a white eruption cloud (Bullard 242). The Strombolian
eruption is named after a volcano named Stromboli. Stromboli is one of the few volcanoes
in the world, which is in a state of permanent moderate activity. In contrast with the
Vulcanian eruption cloud, which is heavily charged with ash, the Strombolian cloud
contains little ash. The lava column crusts over lightly, and at frequent intervals mild
explosions break the crust, hurling the pasty, incandescent fragments into the air
(Bullard 242).
The Mauna Loa and Kilauea volcanoes are examples of Hawaiian type eruptions, in which
basaltic lava issues more or less quietly from a fissure that may extend for a number of
miles. Earthquakes usually proceed these eruptions, as the fissure opens to allow the
magma to reach the surface. The lava is quite fluid, and the gases escape readily without
the disruption of the lava into ash or cinders which occurs in the Pelean type of
eruption (Bullard 263). Less than 0.5 percent of the portion of the Hawaiian Islands
exposed above sea level consists of fragmental material, thus attesting to the great
predominance of the outpourings of lava at these vents (Bullard 263). 
The Icelandic type of eruption has many features in common with the Hawaiian type. The
lava in both cases is primarily basalt, and the eruptions are quite similar (Bullard 99).
During Hawaiian type eruptions the lava piles up in dome-shaped masses, while in the
Icelandic type the lava forms plateaus with flat-laying layers. The volume of lava
involved in individual plateau building and in dome making is similar.
Volcanoes Are Disasters
A volcanic hazard is a destructive natural process that has occurred previously at a
particular volcano; therefore, there is the probability that it could occur again during
a future eruption (Fisher, Heiken, and Hulen 268). Risk is the potential loss from a
hazard; losses include people's lives, property, livestock, and the productive capacity
of the area. The magnitude of the risk increases as population increases near a volcano.
The number of human fatalities due to volcanic eruptions between 1900 and 1986 was a
total of 76,000. That's an average of 880 people per year (Fisher, Heiken, and Hulen
269).
There are many factors that affect the prediction of future volcanic activity. Some of
the factors are: the longer a volcano is inactive the chances increase for it to become
active, eruptive behavior may change with time, and some hazards are indirectly related
to an eruption making it difficult to forecast. As you can see, volcanoes can cause
horrible disasters. To prevent some of these disasters, here is a list of caution steps
and facts provided by the USGS / Cascade Volcano Observatory.
? Stay indoors.
? If you are outside, seek shelter such as a car or a building.
? If you cannot find shelter, breathe through a cloth, such as a handkerchief, preferably
a damp cloth to filter out the ash.
? When the air is full of ash, keep your eyes closed as much as possible.
? Heavy falls of ash seldom last more than a few hours-only rarely do they last a day or
more.
? Heavy fall of ash may cause darkness during daylight hours and may temporarily
interfere with telephone, radio, and television communications.
? Do not try to drive a car during a heavy fall of ash-the chance of an accident will be
increased by poor visibility.
? The thick accumulation of ash could increase the load on roofs, and saturation of ash
by rain would be an additional load. Ash should be removed from flat or low-pitched roofs
to prevent thick accumulation.
? During an eruption move away from a volcano-NOT TOWARD IT!
? Most important-DON'T PANIC-KEEP CALM.
Conclusion
In conclusion I would like to remind you that there are three main components that erupt
out of a volcano: lava, ash, and bombs. The seven different types of volcanoes are:
Submarine volcanoes; Ridges and Vents; Shield Volcanoes; Lava Plateaus and Flood Basalts;
Lava Domes; Composite Volcanoes; Cinder and Scoria Cones; and Calderas. The five volcanic
eruptions are Pelean, Vulcanian, Strombolian, Hawaiian, and Icelandic. Volcanoes are
disasters that cause losses such as: people's lives, property, livestock, and the
productive capacity of an area. The factors that affect the prediction of future
eruptions are: the longer a volcano is inactive the chances increase for it to become
active, eruptive behavior may change with time, and some hazards are indirectly related
to an eruption making it difficult to forecast. Volcanoes are disasters that cause
devastation, so please take caution if you live near a volcano.
Works Cited
Bullard, Fred M. Volcanoes of the Earth. 
USA. Library of Congress Cataloging-in-Publication Data, 1976.
Decker, Barbara, and Robert W. Decker. Volcanoes. 
San Francisco: W.H. Freeman and Company, 1981.
Fish, Richard V., Grant Heiken and Jeffery B. Hullen. Volcanoes, Crucibles of Change.
New Jersey: Princeton, 1997.
Ritchie, David. The Encyclopedia of Earthquakes and Volcanoes. 
New York: Facts on File, 1994.
USGS. Descriptions. 18 May 1999. Online posting. 
http://vulcan.wr.gov/Glossary/description-html
USGS. Photo Archives. 23 May 1999. Online posting. 
http://vulcan.wr.usgs.gov/Photo/framework-html
Bibliography
Bullard, Fred M. Volcanoes of the Earth. 
USA. Library of Congress Cataloging-in-Publication Data, 1976.
Decker, Barbara, and Robert W. Decker. Volcanoes. 
San Francisco: W.H. Freeman and Company, 1981.
Fish, Richard V., Grant Heiken and Jeffery B. Hullen. Volcanoes, Crucibles of Change.
New Jersey: Princeton, 1997.
Ritchie, David. The Encyclopedia of Earthquakes and Volcanoes. 
New York: Facts on File, 1994.
USGS. Descriptions. 18 May 1999. Online posting. 
http://vulcan.wr.gov/Glossary/description-html
USGS. Photo Archives. 23 May 1999. Online posting. 
http://vulcan.wr.usgs.gov/Photo/framework-html