Download Geography

By: (9b)
Maria.A.S
William.P.I
 Plate tectonics: set of ideas that describes and explains
the global distribution of earthquakes, volcanoes, fold
mountains and rift valley.
 The cause of earth movement is huge convection currents
in the earth’s interior, which rise towards the earth’s
surface, drag continents apart and cause them to collide
 These cause the earth’s surface, drag continents apart and
cause them to collide
 7 large plates : Pacific, Indo-Australian, Antarctic, North
America, South American, African and Eurasian
 4 small plates : Caribbean, Iranian, Arabian, Juan de Fuca




a.
b.
Inner core: solid, 5 times more
dense than surface rocks
Outer core: semi-molten
Mantle: semi-molten and
about 2900 km thick
Crust: solid, 2 main types
(depth between 10-70 km);
Continental : mostly formed
of granite, less dense than
oceanic crust
Oceanic: plunges beneath the
continental one when they
come together
 Distribution of the world’s volcanoes and
earthquakes is very uneven, mostly along plate
boundaries which are regions of crustal instability
and tectonic activity
 There are over 1300 active volcanoes in the world,
many of them under the ocean (3/4 active
volcanoes & located in the pacific of ring)

Example active volcanoes (pacific ring of fire):
a.
Taal volcanoes & Mt. Pinatubo (Philiphines)
Ulawun (Papua New Guinea)
Krakatoa, Merapi, Tambora, Kelut (Indonesia)
Popcatapetl & Colima (Mexico)
Mt. Fuji (Japan)
Etc.
b.
c.
d.
e.
f.

A destructive plate boundary is sometimes called
a convergent or tensional plate margin. This occurs when oceanic
and continental plates move together. The oceanic plate is forced
under the lighter continental plate ( A section of the crust that
makes up the Earth’s landmasses) . Friction causes melting of the
oceanic plate and may trigger earthquakes. Magma rises up through
cracks and erupts onto the surface.

a.
b.
E.g:
Mt St. Helens,USA and Soufriere, Montserrat(Carribean)
Nazca plate is forced under the South American Plate.


a.
b.
A constructive plate boundary, sometimes called
a divergent plate margin, occurs when plates move apart.
Volcanoes are formed as magma wells up to fill the gap,
and eventually new crust is formed.
Example:
the mid-Atlantic Ridge.
Eldfell volcano, Heimaey (Iceland)
 Mauna Loa, Kilauea (Hawaii) and Teidi (Tenerife) are
located over hot spots.
 Hot spots=> isolated plumes of rising magma that
have burned through the crust to create active
volcanoes.
 => Result of a sudden release of energy in the Earth's crust
that creates seismic waves
 About 500,000 earthquakes are detected each year by
sensitive instruments
 Most of them occur in linear chains ( such as along the
west coast of South America)
 Some earthquakes appear from plate boundaries (mid-west
of USA), plate movement.
Some earthquakes are the result of human activity.

Examples:
a.
Build large dams and deep reservoirs (increases pressure
underground)
b.
Mining removes underground rocks and minerals
c.
Testing of nuclear weapons underground
=> trigger earthquakes (the very long reach of very large
earthquakes)

 World’s main fold mountains are related to the main
collision zones (destructive plate margins and collision
margins)
 In contrast, older fold mountains are related to folding
between 250 and 450 million years ago, when the
location of plate boundaries was different from that of
today.
Constructive
Margins
caused when two plates move away from each other
(diverge). When they move apart from each other a ‘gap’
is created. The gap is filled with hot, molten lava that
solidifies when it reaches the surface (meeting either the
sea or air). Land is therefore formed. Earthquakes and
volcanoes are associated with constructive plate
margins.
Destructive
Margins
the heavier oceanic crust slides under the lighter,
less dense continental crust.
This results in both volcanoes and earthquakes,
due to land being lost (destroyed).
Collision
Plate Margins
occur where two continental crust plates meet. As
they are the same density neither is able to slide
under the other one. Therefore, fold mountains
are created. Earthquakes are common at collision
plate boundaries.
Conservative
Margins
They are caused by the friction as the plates rub
next to each other.
 The plates move at different speeds and in different
directions. This is because of the convection currents
that operate underneath the earth.
 Volcano is opening the earth’s crust trough which
hot molten magma (lava), molten rock and ash are
erupted onto the land.
 They are formed when molten (Molten is melted,
liquid), sticky rock called magma (Magma is
melted rock inside the Earth), forces its way
through a crack in the Earth’s crrust (Crust is the
top layer of the Earth).
There are 2 type of volcano:
 Shield volcanoes
A shield volcano is a type of volcano usually built almost
entirely of fluid lava flows.
 Cone-shaped volcanoes
A cone-shaped volcanoes is the cone-shaped hill formed
as material from volcanic eruptions piles up around
the opening.
In type of volcano there are divided into:
 Active volcanoes
Active volcano are volcanoes that have erupted in recent
times and could erupt again
 Dormant volcanoes
Dormant volcanoes are volcanoes that haven’t erupted for
many years or centuries and could errupt again
 Extinct volcanoes
An extinct volcano is one that are believed will never erupt again
because there is no lava or magma supply to it.
Vent – a crack on the
side of a volcano
where magma can
escape
Crater – a deep hollow
at the top of a volcano
Throat- that allows
maga pass through
before it reaches to
to the surface.
 Volcanic Strength
The strength of a volcano is measured by the volcanic explosive index.
This is based by the amount of material ejected by the volcano.
 Predicting Volcanoes
The main methods of predicting volcanoes:
 Chemical sensors to measure increased sulphur levels
 Seismometers to record swarms of tiny earthquakes that accur as the
magma rises
 Laser to detect the physical swelling of the volcno
 Living with a volcano
 Some countries, such as Iceland and Philippines, were created
byvolcano activities
 Volcanic soil are rich, deep and fertile,and allow intensive agriculture to
take place
 Volcanics areas are important for tourism
Case Study
Montserrat is a small island in the Caribbean. There is a
volcano on the south of the island called Chances Peak.
The volcano had been dormant for over 300 years. In 1995
the volcano began to give warning signs, than the volcano
active for 5 years, the most intense eruption is in 1997.
Before the eruption the island(11 000 people) had been
evacuated, 19 people were killed by the eruption the people
choose to stay behind to watch over the crops. Volcanic
eruptions and lahars have destroyed large areas of
Montserrat. he capital, Plymouth, has been covered in
layers of ash and mud. Many homes and buildings have
been destroyed, including the only hospital, the airport
and many roads.
 Short-term responses and results
 Evacuation.
 Abandonment of the capital city.
 The British government gave money for compensation and
redevelopment.
 Unemployment rose due to the collapse of the tourist industry.
 Long-term responses and results
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An exclusion zone was set up in the volcanic region.
A volcanic observatory was built to monitor the volcano.
New roads and a new airport were built.
Services in the north of the island were expanded.
The presence of the volcano resulted in a growth in tourism.
 Earthquakes are a sudden and violent shaking of
surface of the earth
Focus - refers to the place beneath the
ground where the earthquake takes place
Epicenter – is the point on the ground
surface immediatly above the focus
Deep focus earthquake – associated
with aubduction zones.
Fault - a planar fracture or discontinuity in a
volume of rock, across which there has been
significant displacement along the fractures as
a result of earth movement
Shallow focus earthquake – generally
located along constructive boundaries and
conservative boundaries
Earthquake damage
 Strength of earthquake and number of aftershock – the
stronger the earthquake the more damage it can
 Population density – an earthquake that hits high population
density could inflict more damage
 The type of building – MEDCs generally have better quality pf
building rather than LEDCs
 The time of day – an earthquake during busy time may cause
more death than quite time
 The distance from the centre (epicentre)- the closer to
epicentre the greater damage that is done
 The type of rock and sediment- some material may act like
liquid when shaken
 Secondary hazards – such as mudslides and tsunami
 Several of way dealing with earthquake:
 Leave the area
 Do nothing and accept the hazzard
 The main ways of dealing with earthquake:
 Better forecasting and warning
 Building design and building in good location
 Several ways predicting and monitoring earthquake:
 Recording changes in electrical conductivity
 Nothing strange and unusual animal behaviour
 Checking history evidence
 Measuring crustal movement
Building design
Building design in the enviorment must responds
quickly to eathwuak force like building a single storey
building. A high building responds slowl to
earthquake. Places of the building also must be
affective, like not building the house beside steep soil
because it can cause mudslides
Case Study
 Kashmir, Pakistan, 2005 (LEDC)
On 8 October 2005, an earthquake measuring 7.6 on the
Richter scale hit the Kashmir region of Pakistan. The
earthquake was the result of collision between the
Indian and Eurasian plates.
Effects
 Primary effects
 Buildings collapsed.
 79,000 people were
killed.
 Landslides, and large
cracks appeared in the
ground.
 Secondary
effects
 Broken sewerage pipes
contaminated water
supplies and spread
disease.
 People died of cold
during the harsh winter.
Responses
 Short term
 Long term
 The army and emergency
 Schools and hospitals were
services arrived to join the
rescue effort.
 Tents were given out by
charities.
 Aid workers arrived from
abroad to find survivors
and treat the injured.
rebuilt.
 Building regulations were
improved to reduce
damage and the death rate
in future earthquakes.