1. Classification Of Volcanoes
When studying the volcanoes in the world it is important to understand what the classification
of volcanoes is and how it works. There are several factors that go into account when attempting
to classify a volcano into a group and that includes things like recent activity, periodicity of
eruptions, size, potential impact and others. Though it is not common to hear it volcano
eruptions are actually not that rare. More often than not the classification of volcanoes refers to
the life cycle and that could define them as active, extinct or dormant. However, a volcano can
also be classified by the composition of the structure and that would mean that it can be a shield,
conical or stratovolcano. Finally they can also be classified because of its eruption which could be
quiet or explosive.
Active Volcanoes
A volcano will be classified as an active volcano if at the present time it is expected to erupt or is
erupting already. One of the best examples of this classification of volcanoes would be Kilauea
which has been erupting since 1983. There are a total of close to 1,500 of such volcanoes on the
planet. Every year somewhere between 50 and 70 volcanoes will erupt.
Dormant Volcanoes
The classification of volcanoes which is called dormant would be a volcano that is not erupting or
predicted to erupt in the near future. However, it has done so in recordable history. A dormant
volcano is also expected to have an eruption sometime in the future. Sometimes the difference
between a dormant volcano and an active volcano can be pretty small. That is because even
though a volcano can be dormant for hundreds of years it is still expected to have an eruption in
the future.
Mauna Kea is a volcano which is located on Big Island and its last eruption took place 3,500-
4,000 years ago. However scientists believe that it will erupt again. What makes that volcano
dormant is that currently there is no prediction as to when that eruption could take place. A
dormant volcano could be very dangerous because people in the surrounding areas are usually
not prepared and complacent leaving close to the mountain. Before its eruption in 1980, Mount
St. Helens was dormant.
Extinct Volcanoes
An extinct volcano is a volcano that no one expects will ever have another eruption. One such
volcano is also located on Hawaii’s Big Island and its name is Kohala. The last time that Kohala
erupted was close to 60,000 years ago. As of now scientists do not believe that volcano will ever
be active again. Keep in mind that this classification of volcanoes that are extinct is not
necessarily definitive as some have gone through what is called rejuvenation.
Type Classifications
Classification of volcanoes can also be done because of the type of composition and structure of
the volcano. A shield volcano is dome shaped and low. These volcanoes are mountains that have
been shaped by the flows and can cover larger areas. The simplest form of volcanoes would be
the cinder cone type. These volcanoes have erupted from one single vent and a bowl shaped
crater will be found in the summit. The most common type of volcano is the strato or composite.
These are tall mountains that have steep sides and which have alternated magma and layers of
rock.

2. Eruption Classification
There are two types of classification of volcanoes based on eruption and these are central or
explosive and fissure or quiet. An explosive eruption happens because of a buildup of gas under
very viscous slow flowing and thick magma. These types of eruption are very violent and rapid;
more often they will spew volcanic material, lava and ash onto a large area. A fissure or a quiet
eruption will emit a lot of lava from a fracture or fissure. Because lava would usually have a low
viscosity, the gas can easily escape.
Samples Of Volcanoes
There are several places in the world which can demonstrate the classification of volcanoes but
most active volcanoes will be found in the Pacific Ring of Fire. There are, however, volcanoes not
located in the Pacific which are active; some of them include Etna and Vesuvius, Mount Pinatubo
and Stromboli.
Classification of volcanoes that are dormant will include a lot of the volcanoes still found in the
Ring of Fire and other places nearby. One example would be Mount St. Helens previous to its
1980 eruption. Before a dormant volcano is about to erupt it is usually proceeded by small
tremors and earthquakes.
Finally when you are looking at extinct volcanoes you can look at the ones in the Eiffel district in
West Germany as well as several volcanoes in USA. There are two volcanoes in Northern Ireland
which are also extinct volcanoes and those are Skye and Mull.
The Effects Of Volcanic Eruptions:
Unlike other natural disasters such as floods, wild fires and earthquakes,
volcanoes can have some positive effects, even though they can be very
disastrous.
Let us see some negative effects of volcanoes:
Eruptions occurring close to human settlements may spill and destroy lives
and property. People often have to be evacuated.
Example: Chaparrastique volcano in El Salvador started erupting on 29 Dec,
2013. Anyone living within 2 miles of the volcano is evacuated.
Source: BBC News:www.bbc.co.uk/news/world-latin-america-25545555
Ash discharged very high into the stratosphere can have negative
consequences on the ozone layer. Read more about that here.
Landscapes and natural sceneries can be destroyed.
Ash and mud can mix with rain and melting snow, forming lahars. Lahars
are mudflows flowing at very fast pace.
Some positive effects of volcanoes include:
Different types of erupting volcanoes provide extraordinary scenery, so
beautiful and natural that they attract tourists to the area, bringing in some
economic value.
Places close to volcanic activities tend to have higher potential
forgeothermal energy, which can be an advantage to the towns and cities.

3. Some ash and lava breakdown become soils that are rich in nutrients, and
become good areas for crop planting activities.
Why do volcanoes erupt?
Let us start with what the earth is made of:
The earth is made up of three layer parts. The outer crust is the layer on which we
live. It is estimated to be about 1800 miles deep. Then there is the mantle; and then
the core (inner and outer core)
The mantle is made up of molten material and gases. Molten materials are solids
(like rock) that have turned into liquid because of extreme heat. The name for molten
rock and other gases in the earth’s mantle is Magma. Magma is liquid made up of many
crystals, fragments and gases including oxygen, silicon, iron, aluminium, magnesium
and manganese. When they cool off on the earth’s surface, they turn into magmatic or
igneous rocks.
Whenever extreme pressure builds in the mantle, along fault lines (openings or
cracks in weak spots in the earth’s crust) an eruption is likely to happen next. During
an eruption, molten materials (soon to become lava) gush out through spaces in the
crust to the surface.
NOTE: Molten rock is called magma when it is inside the crust but once it gets to the
surface of the earth it is called lava.
Eruptions can be in the form of lava fragments shooting into the atmosphere and
forming thick clouds of lava. Some also flow slowly (non-violent) from the vent,
flooding the area around it. Very fine particles of ash may also be discharged high into
the stratosphere and further carried away by wind action.
Fresh lava is believed to be about 2,200°F. It can be red hot as it shoots from the vent
and turn into gray or black as it cools. Lava rich in silicon is like honey, and flows a lot
more slowly from the vent. In other types, lava also comes in thick, pasty form.

4. Common types of volcanoes
Shield Volcanoes
This is very fluid lava, usually from multiple vents or fractures, spreading over very
large areas. The fluid-like nature (viscous – say veez-kos) of the lava, it does not allow
it to pile up like a cone. The result is usually an elevation with a shape like a warrior’s
shield. Mount Kilauea and Maunaloa in Hawaii are good examples of shield volcanoes.
They are usually found at constructive or tensional boundaries.
Lava Domes
They are produced from eruptions with less viscous lava. Because it is less viscous,
they do not spread far and cool off (hardens) sooner. This means they pile around the
vent and the dome grows only because of the expansion of the vent area within. Lava
domes tend to have steep walls and rock types such as andesites, dacites or rhyolites
(say rai-o-lites)
Cinder Cones
These are the most common in the study of volcanoes. When lava is ejected into the air
above, the fragments and fine particles fall as cinders (ash) around the vent, forming a
cone. The height of cinder cones usually depend on how long the eruption takes and
how much lava comes out. The cone has a depression (crater) in the middle where the
vent is. Cinder cones can rise as high as 1200ft. A good example of a cinder cone is the
Paricutin Volcano in Mexico.
Composite Volcanoes
These are usually awesome in nature, rising up to about 8000ft. They are also known
as stratovolcanoes and they include Mount Cotopaxi in Ecuador and Mount Fuji in
Japan. They are seen as massive mountains. They are formed by alternating layers of
ash, rock, dust and lava, (pyroclastic) and hence the name ‘composite’. They have
steep slopes with a peak.