The Earth:
Layers: Crust: outer layer, solid rock, thin layer, divided into plates
Mantle: very hot layer, comprises rocks in a molten or semi-molten state
Core: centre of earth, hottest layer, comprises iron and nickel
7 Plates: Eurasian Plate, Indian Plate, African Plate, American Plate, Nazca Plate,
Pacific Plate, Australian Plate.
Plates carry the continents and the oceans, constantly moving: continental
drift
Plate Movement: Plate collision: fold mountains eg. the Rockies
Plates separate: volcanoes eg. Mount Etna
Plates rub: earthquakes eg. the San Andreas Fault
Earthquakes:
-When plates slide past each other
-The place within the crust where the earthquake occurs is the focus.
-The point on the surface above the focus is the epicentre.
-Earthquakes produce shockwaves:
-A seismograph measures shock waves
-The Richter Scale records the size of the shock waves
-Tsunami is large sea waves due to earthquake activity under the sea eg. SE
Asia, 2004
-Effects of earthquakes:
-Loss of life eg. the Afghanistan earthquake in 1998 killed over 4,000 people.
-Collapse of bridges and buildings, hindering transport and movement of
people and goods. Expensive to rebuild
-Damage to gas mains and electricity pylons can cause fires
-Earthquake prevention:
-Construct earthquake proof buildings
-Construct buildings on stable ground
-Study seismic records to attempt to predict where earthquakes are likely to
occur
Volcanoes:
-When two plates separate, the magma under the earth’s crust reaches the surface,
cools and hardens to form lava
-Sometimes the lava forces its way upwards through a vent forming a volcanic
mountain
-Mid Atlantic Ridge: Beneath the Atlantic Ocean the North American Plate is
separating from the Eurasian Plate. Magma fills the gap between the two plates. The
magma then cools and hardens forming a chain of mountains called the Mid Atlantic
Ridge. Some have risen above sea level eg. Iceland or the Azores
-The Pacific Ring of Fire: On the edge of the Pacific Ocean some of the world’s plates
separate and collide. It is here that most earthquakes and volcanoes occur.
-San Francisco and Los Angeles on the west coast of America have felt the effects of
devastating earthquakes.
-The world’s active volcanoes are found in the Pacific Ring of Fire eg. Mt St Helens,
Mt Fujiyama, Mt Pinatubo, Krakatoa, Aconcagua
-Types of Volcanoes:
-Active: frequently erupting eg. Mt Etna
-Dormant: not erupted for a long time eg. Mt St Helens
-Extinct: not erupted in recent times eg. Slemish Mt, Co. Antrim
-Advantages of volcanoes:
-Fertile soils eg slopes of Mt Vesuvius
-Precious stones and minerals eg. gold, silver, lead and copper
-Building materials eg. granite (formed beneath the surface)
-Hot springs (geysers) generate electricity eg. Iceland
-Tourism eg. Mt Vesuvius and Mt Etna
-Disadvantages of volcanoes:
-Loss of life
-Damage to property eg. eruption of Mt Vesuvius in AD 79 buried Pompeii
and Herculaneum
-The eruption of Mt Pinatubo in the Philipines in 1991 had major effects on
the environment:
1. The cloud of gas, ash and dust blocked out the sun’s rays and
resulted in a drop of several degrees in global temperatures
2. Millions of tons of sulphur dioxide were released into the
atmosphere. This will form acid rain in the future, harmful to flora and fauna
Fold Mountains:
-When two plates collide eg. The Andes, The Rockies and the Magillicuddy’s Reeks
Exam Questions:
(Past Papers)
-With the aid of a diagram, explain how Fold Mountains are formed
-Name 1 range of Folds Mountains in Ireland
-Label Epicentre, focus and colliding plates on the diagram
-Name the parts of a volcano
-‘Volcanoes result in the formation of Igneous Rocks’ – select one Igneous Rock and
explain how it is formed
-The Pacific Ring of Fire shows: the location of many earthquakes and volcanoes, an
area subject to bush fires, an area of hot springs or an area with a hot desert type
climate.
Skool.ie
Earthquakes | Volcanoes | Fold Mountains
Volcanoes, earthquakes, fold mountains
Volcanoes, earthquakes, and the formation of fold mountains are all evidence of the
continental activity that takes place beneath the earth’s crust (surface).
This crust is made up mainly of igneous rocks, in particular granite and basalt.
Beneath the crust is the mantle which is made up of hot molten rocks. This hot
flowing material is known as magma .
The crust of the earth is not in one single piece. The crust is broken up into a number
of sections called plates that fit together rather like a jigsaw. These plates move
(float) on the molten rock beneath them. This movement is known as ‘Continental
Drift’ and both earthquakes and the formation of fold mountains are closely
associated with plate movements. Volcanoes tend to occur at plate boundaries or
where the crust of the earth is particularly thin.
Earthquakes
Earthquakes are sudden movements in the earth’s crust that cause a tremor or
vibration. They usually occur along the edges of the plate boundaries; these edges are
called fault lines . Where the plates collide or rub against one another is where the
earthquake actually happens.
The term focus is used to describe the spot deep within the earth’s crust where the
earthquake starts. The epicentre is the place on the earth’s surface directly above the
focus. Shock waves are sent out from the epicentre and focus and they cause the
severe damage often associated with earthquakes. The nearer the epicentre, the more
severe the damage.
The instrument used to record the shock waves is called a seismograph and the scale
used to measure the strength of an earthquake is called the Richter Scale . This scale
ranges from 1-12 and each step up on the scale means that an earthquake is 10 times
more powerful than the preceding step (e.g. a force 6 earthquake on the Richter Scale
is 10 times more powerful than one that measures 5).
Predicting when earthquakes will occur has not yet proven possible. We can predict
reasonably well where they will occur, that is on the lines where the plates meet (the
fault lines) but not when they will occur as they can occur suddenly, without warning.
They can cause great damage, especially in built-up areas. Earthquakes can also occur
at sea and may then produce giant waves called Tsunamis. One wave on the coast of
Alaska in 1958 measured over 500 metres high. If these waves reach land they can
cause huge damage.
Students preparing for a question on earthquakes should have some information on
one particular earthquake e.g. the great quake in Chile in 1960 which measured 9.5 on
the Richter scale, or the 1998 quake in Afghanistan which measured 6.1 or the 2002
quake in southern Italy which measured 5.4.
Volcanoes
Volcanoes occur when hot molten magma forces its way to the surface through a
narrow channel in the earth’s crust called a vent. These vents are usually found at
plate boundaries or where the earth’s crust is very thin. When the hot molten rock
reaches the surface it is known as lava . The process of the lava reaching the surface
is called an eruption. Repeated eruptions around a vent eventually build up a coneshaped mountain. Volcanoes are classified as being active (erupting regularly),
dormant (no eruption for a very long period) and extinct (when they have not erupted
in recorded time and are considered unlikely to erupt again). The most significant area
of active volcanoes in the world is around the Pacific Ocean. About two thirds of
volcanoes are found in this region known as the ‘Pacific Ring of Fire.’ Italy contains
some of Europe’s best-known volcanoes such as Vesuvius near Naples and Mount
Etna on the island of Sicily. Etna’s last recorded eruption was in October 2002.
Volcanoes can have both constructive and destructive effects. Students should be
aware of each. The constructive effects include:
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The soil produced by lava can be fertile and beneficial e.g. coffee growing
regions of South America.
New land can be created e.g. the island of Surtsey off the coast of Iceland.
Volcanic activity my produce hot springs or geysers which gush out hot water
from below the ground. These can be used to help generate electricity as in
New Zealand.
Volcanoes are often important tourist attractions.
The destructive effects include:
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Eruption often causes great loss of life and damage to property. This damage
can be caused by the lava flows or by poisonous gasses that are often released
during eruptions.
Fold mountains
Fold mountains are found in places where the earth’s plates collide and the crust
buckles up. The upfolds that occur become mountains (these upfolds are called
anticlines) and the down folds are called synclines. Nearly all of the major mountain
ranges of the world have been formed in this way. The three major mountain-building
periods are known as the Caledonian mountain building period, the Armorican period
and the Alpine period.
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The Caledonian mountains were formed about 400 million years ago and
include such mountains as the Scandinavian Highlands and the mountains of
Donegal.
The Amorican mountains were formed about 250 million years ago. The
mountains of north-west France and of the south of Ireland were formed at this
time.
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The Alpine mountains include not only the Alps but also the Andes, the
Rockies and the Himalayas. These are the youngest (formed about 35 million
years ago) and consequently the highest mountains in the world.
The effects of mountains include:
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They can act as barriers between people.
They can have an effect on the climate of a region by making a region colder
due to their height or cutting off rain-bearing winds thus creating drought
conditions.
They can be suitable locations for coniferous forests.
They can provide suitable sites for hydro-electric plants.
They can prove attractive to tourists.