1.
Volcanoes
A volcano is a landform (usually a mountain) where molten rock erupts through the surface of
the planet.
In simple terms a volcano is a mountain that opens downward to a pool of molten rock (magma)
below the surface of the earth. It is a hole in the Earth from which molten rock and gas erupt.
The name "volcano" has its origin from the name of Vulcan, a god of fire in Roman mythology.
As pressure in the molten rock builds up it needs to escape somewhere. So it forces its way up
“fissures” which are narrow cracks in the earths crust. Once the magma erupts through the
earth’s surface it’s called lava.
There are around 1510 'active' volcanoes in the world. We currently know of 80 or more which
are under the oceans.
An earthquake occurs when two plates pushing past each other cause a fracture in the Earth’s
crust.
1.1. Lava and Magma
Magma is liquid rock inside a volcano.
Lava is liquid rock (magma) that flows out of a volcano. Fresh lava ranges from 1,300° to 2,200°
F (700° to 1,200° C) in temperature and glows red hot to white hot as it flows.
1.2. Three layers the Earth
1.
Crust
The crust is the outer layer of Earth. It is about 18 miles thick. It is the part we live on.
2. Mantle
The second layer is called the mantle. It is about 1,800 miles thick.
3. Core
The inner layer is called the core.
The earth is divided into three main layers – a hard outer crust, a soft middle crust, and a
center core. The outer crust is broken into massive irregular pieces called “plates”. These plates
are moving very slowly, driven by energy forces deep within the earth. Earthquakes occur when
these moving plates grind and scrape against each other.
1.3. Causes of volcano eruptions
and Earthquakes
The Earth's crust is made up of huge slabs called plates, which fit together like a jigsaw puzzle.
These plates sometimes move. These are the Seven Major Plates :
1.
2.
3.
4.
5.
6.
7.
Pacific
North American
South American
African
Eurasian
Antarctic
Indo-Australian
Between the Earth's crust and the mantle is a substance called magma which is made of rock and
gases.
When two plates collide, one section slides on top of the other, the one beneath is pushed
down. Magma is squeezed up between two plates.
When magma erupts through the earth's surface it is called lava.
Over half of the world’s volcanoes arise in a belt around the Pacific Ocean called the Ring of
Fire.
Types of Plate Boundaries
A. Divergent - Spreading Center - Constructive Margin. Characterized by ocean ridges and
sea floor spreading.
B. Convergent - Characterized by trenches and island arcs
1. Ocean - Ocean (Japanese Islands)
2. Ocean - Continental (Cascade Mountains)
3. Continent - Continent (Himalayas)
C. Transform - Plates moving past one another along strike- slip faults.
2.
Volcanic Eruptions
As well as the danger from the hot lava, an erupting volcano can trigger are life threatening
things.
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



tsunamis
flash floods
earthquakes
mud flows
rock falls.
2.1. Effect of Volcanoes
on people and the environment
Volcanoes can have a very serious effect on the lands and people around them when they erupt.
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




Buildings are destroyed and people are made homeless.
People are killed.
Clouds of ash cover plants making them inedible.
Poisonous gases kill people and animals.
Dust causes pneumonia and illnesses to the survivors.
Dark skies, severe winds and heavy rains may follow an eruption for months afterwards.
2.2. People living within Volcanoes and Earthquakes
One in 10 people in the world live within 'danger range' of an active volcano.
People can get used to living near a volcano, but it is always a little dangerous. Scientists have
estimated that at least 200,000 persons have lost their lives as a result of volcanic eruptions
during the last 500 years.
People set up homes on the slopes of volcanoes because of the rich, fertile soil produced.
Earthquakes can be a warning of volcanoes. Earthquakes can happen days or hours before a
volcanic eruption happens. They both have to do with Tectonic plates and they are both can be
very destructive. Earthquakes along with volcanoes can cause deaths and loss of homes.
3.
The different parts of a Volcano
The image below shows the different parts of a volcano.
Definitions
Magma - Molten rock beneath Earth's surface.
Parasitic Cone - A small cone-shaped volcano formed by an accumulation of volcanic debris.
Sill - A flat piece of rock formed when magma hardens in a crack in a volcano.
Vent - An opening in Earth's surface through which volcanic materials escape.
Flank - The side of a volcano.
Lava - Molten rock that erupts from a volcano that solidifies as it cools.
Crater - Mouth of a volcano - surrounds a volcanic vent.
Conduit - An underground passage magma travels through.
Summit - Highest point; apex
Throat - Entrance of a volcano. The part of the conduit that ejects lava and volcanic ash
Ash - Fragments of lava or rock smaller than 2 mm in size that are blasted into the air by
volcanic explosions.
Ash Cloud - A cloud of ash formed by volcanic explosions.
4.
Types of Volcanoes and
the Shapes of Volcanoes
4.1. Types of Volcanoes
There are 3 different types of volcanoes:
1. Active - eruptions can be anytime and often.
2. Dormant - has been a while since it has erupted, but could at anytime.
3. Extinct, meaning it hasn't erupted in a very long, long time so it probably won't ever
again.
4.2. Shapes of Volcanoes
The type of magma in the earth creates four different types volcanoes:
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

shield volcanoes
composite volcanoes
cinder cones
lava domes
4.2.1. Shield Volcano – flat
If the magma is runny, the gas can escape easily and there will not be an explosion. The magma
just comes out of the mountain and flows down the sides.
Shield volcanoes are shaped like a bowl or shield in the middle with long gentle slopes made by
the lava flows.
Examples include the volcanoes in Hawaii and Mount Etna.
4.2.2. Composite Volcano - tall and thin
If the magma is thick and sticky (like honey), the gas cannot escape, so it builds up and up until it
explodes sending out huge clouds of burning rock and gas.
Composite volcanoes are steep-sided volcanoes composed of many layers of volcanic rocks,
usually made from thick sticky lava, ash and rock debris (broken pieces).
Composite volcanoes are also known as strato-volcanoes.
Examples include Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta and Lassen in
California, Mount Hood in Oregon, Mount St. Helens and Mount Rainier in Washington and Mt.
Etna in Italy
4.3. Cinder cones
Cinder cones are circular or oval cones built from erupting lava that breaks into small pieces as it
shoots into the air. As small pieces fall back to the ground, they cool and form cinders around
the vent.
4.4. Lava domes
Lava domes are formed when erupting lava is too thick to flow and makes a steep-sided mound as
the lava piles up near the volcanic vent.
5.
Volcano Vocabulary
Active volcano: A volcano that is erupting or has erupted within
historical time and is considered likely to do so in the future.
Ash: Fine particles of rock dust blown from an explosion vent.
Ashfall: Volcanic ash that has fallen through the air from an
eruption cloud.
Vent: A vent is an opening at the Earth's surface of a volcanic
conduit.
Composite Volcano: A steep volcanic
flows and pyroclastic eruptions.
cone
built
by
both
lava
Compound Volcan: A volcano that consists of a complex of two
or more vents, or a volcano that has an associated volcanic
dome, either in its crater or on its flanks. Examples are
Vesuvius and Mont Pelee.
Conduit: A passage (pipe) followed by magma in a volcano.
Crater: A steep-sided, usually circular depression
either explosion or collapse at a volcanic vent.
formed
by
Dormant volcan: A volcano which is presently inactive but which
may erupt again.
Eruption: The process by which solid, liquid, and gaseous
materials are ejected into the earth's atmosphere and onto the
earth's surface by volcanic activity.
Fault: A crack or fracture in the earth's surface.
Fissures:
volcano.
Elongated
fractures
or
cracks
on
the
slopes
of
a
Geysers: Springs that throw boiling water high in the air. They
are caused by volcanic heat warming trapped ground water.
Hot
Spot: A volcanic center, 60 to 120 miles across and
persistent for at least a few tens of million of years, that is
thought to be the surface expression
plume of hot mantle material.
of
a
persistent
rising
Lava: Magma which has reached the surface through a volcanic
eruption. Streams of liquid rock that flow from a crater or
fissure.
Lava Flow: An outpouring of lava onto the land surface from a
vent or fissure.
Magma: Molten rock beneath the surface of the earth.
Magma chamber (Magna reservoir): The subterranean cavity
containing the gas-rich liquid magma which feeds a volcano.
Mantle:
core.
The
zone
of
the
earth
below
the
crust
and
above
the
Ring of Fire: The regions of mountain-building earthquakes and
volcanoes which surround the Pacific Ocean.
Stratovolcano: A volcano
pyroclastic material.
composed
of
both
lava
flows
and
Vent: The opening at the earth's surface through which volcanic
materials issue forth.
Volcanic
volcano.
eruption:
When
hot
rocks
and
lava
burst
from
a
Volcano: A vent in the surface of the Earth through which
magma and associated gases and ash erupt; also, the form or
structure, usually conical, that is produced by the ejected
material.
Vulcan: Roman god of fire and the forge, after whom volcanoes
are named.
6.
Earthquakes
6.1. Elastic Rebound Theory
Elastic Rebound Theory Explains how energy is stored in rocks
1. Rocks bend until the strength of the rock is exceeded
2. Rupture occurs and the rocks quickly rebound to an
undeformed shape
3. Energy is released in waves that radiate outward from the
fault.
6.2. The Focus and Epicenter of an Earthquake
The point within
hypocenter.
The point
epicenter.
Earth
directly
where
above
the
faulting
focus
begins
on
the
is
the
focus,
surface
is
or
the
Seismographs record earthquake events.
6.3. Where Do Earthquakes Occur and How Often?
80% of all earthquakes occur in the circum-Pacific belt
–
–
–
most of these result from convergent margin activity
~15% occur in the Mediterranean-Asiatic belt
remaining 5% occur in the interiors of plates and on
spreading ridge centers
–
more than 150,000 quakes
are recorded each year
strong
7. Activities
7. 1. Answer these questions:
 What is a Volcano?
 What is the name of a god of fire in Roman mythology?
enough
to
be
felt
 What are “fissures”?
 What is the difference between lava and Magma?
 How many volcanoes are there in the world?
 What are the three layers the Earth is made of?
 What causes volcanoes to erupt?
 When magma erupts, what is it called?
 What is the Ring of Fire?
 What are the different types of volcanoes?
 How many different shapes of volcano are there?
 What is an earthquake?
 What is the cause of earthquakes?
 How likely is it that your area will experience an earthquake?
 What is the e p i c e n t e r ? A n d t h e h y p o c e n t e r ?
 Is there any relationship between earthquakes and volcanoes?
6.2. Check the answer that best matches the question:
1. A volcano is………
a. A mountain or hill formed around a crack in the earth's
crust.
b. A mountain with a jagged peak.
c. A mountain or hill with a flat top.
2. The hot rock under the earth's surface is called………
a. Lava
b. Magma
c. Dormant
3. The hot rock that flows down the sides of the volcano
is………
a. Lava
b. Magma
c. Dormant
4. The opening in the top of a volcano is a………
a. Dormant
b. Magma
c. Crater
5. All volcanos erupt all of the time………
a. True
b. False
6. Volcanoes erupt because of……
a. The pressure in the earth forcing the hot rock through a
crack.
b. An earthquake happening nearby
c. The earth getting overheated.
7. What USUALLY causes an earthquake to happen?
a.
b.
c.
d.
The plate breaks
People shake the ground
A fault slips
A giant stomps around causing the ground to shake
8. W h a t d o e s a n e a r t h q u a k e u s u a l l y c r e a t e ?
a.
b.
c.
d.
Hurricanes
Freaky noises
Volcanoes
None of the above
9. Which is an earthquake measuring device?
a. Pendulum
b. Seismograph
c . None of the above
6.3. Write the different parts:
6.4.
Unscramble
these
corresponding definition:
1.tuicnod:
2.agma:
3.oniptpure:
4.olcnvao:
5.hsa:
6.ltafu:
words.
After
that,
give
the