Transcript Tectonic Landscapes Revision

Q3: Tectonic Landscapes
15 marks
Location and characteristics of
tectonic activity
The distribution of earthquakes and volcanoes in the world
• Volcanoes and earthquakes usually occur in narrow lines along the plate
boundaries.
• An exception to this are volcanoes that occur at hotspots.
• Areas of particular note include; The Pacific Ring of Fire, the Mid-Atlantic Ridge, SE
Europe, SE Asia
Reasons why earthquakes and volcanoes both occur where they do
• The Earth’s crust is divided into plates.
• Oceanic crust found under seas & oceans is thin but dense (heavy)
• Continental crust found on land is thicker but less dense
Reasons why earthquakes and volcanoes both occur where they do
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The plates move 5-10cm every year as they are floating on the mantle.
This movement is caused by convection currents in the mantle.
The convection currents can cause the plates to collide or move apart.
The pressure or gaps created at the boundaries of the plates can result in either
earthquakes or volcanoes
Reasons why earthquakes and volcanoes both occur where they do
The movement of the land mass on the crust is known as Continental Drift.
• Most volcanoes are found at plate boundaries, however, a hotspot is another place
where volcanoes can occur
• Hotspots are fixed points in the mantle which generate heat – they usually occur
under oceans
• Intense heat causes a build-up of pressure and magma erupts through the crust
• If magma rises above the ocean surface it will form a volcano
• Hotspots usually create chains of volcanic islands as the plate moves over the
hotspot. Hawaii and the Galapagos Islands were formed in this way.
The characteristic features of plate boundaries
Conservative
Plates can move in 3 directions
Convergent plate boundary
continental and oceanic crust
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Plates move together
Heavier oceanic crust is subducted
Friction during subduction causes earthquakes
The oceanic plate melts as it sinks, turning into magma
Magma builds up in the magma chamber
Pressure increases
Pressure forces magma upwards through weak points in the continental crust
Magma erupts to surface
Repeated eruptions build a volcano, e.g. Mount St Helen’s, USA
Convergent plate boundary
oceanic and oceanic crust
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Plates move together
The heavier of the two oceanic crusts is subducted
Friction during subduction causes earthquakes
The oceanic plate melts as it sinks, turning into magma
Magma builds up in the magma chamber
Pressure increases and forces magma upwards through weak points in the crust
Magma erupts to surface
Repeated eruptions build a volcano in the ocean – these are called volcanic island
arcs e.g. Japan
Convergent plate boundary
continental and continental crust
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Plates move together
Plates fold and fault crust upwards to form fold mountains, e.g. The Himalayas
Earthquakes can also happen as rock is folded and faulted
There are no volcanoes as the crust is NOT subducted and melted.
Divergent plate boundary
oceanic and oceanic crust
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Plates move apart
Magma rises to fill the gap
Repeated eruptions of lava will build ocean floor ridges (Mid-Atlantic Ridge)
If enough lava builds to reach sea level, this will form volcanic islands (Iceland)
Conservative plate boundary
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Plates move past each other
The plates are jagged and get stuck
As they try to move pressure builds up
Eventually the pressure snaps and the plates jerk forward
This releases shockwaves, which travel through the Earth’s crust, e.g. San Andreas
Fault, California
The methods used to measure earthquake magnitude
The Richter Scale
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Measures the strength and magnitude of an earthquake
Seismographs measure the vibrations
The vibrations are printed out on a seismogram
The seismogram is translated to give a score on the Richter Scale ranging from 1-9
 Scientific
 Easier comparison
 Objective
 Remote measurement
 Requires scientific equipment
 Can be misleading
The methods used to measure earthquake magnitude
The Mercalli Scale
• Measures the intensity and amount of destruction
of an earthquake
• Measures on a scale from 1-12
• Uses information from eyewitnesses
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No expensive equipment needed
Gives a useful indication on the effects
Is a subjective score (based on opinion)
The person measuring has to be on site of the earthquake
The characteristics of the focus and epicentre of an earthquake
• The focus is the point below the surface where the pressure snaps and the
shockwaves are released from. This where the earthquake begins.
• The epicentre is the point directly above the focus on the surface of the Earth. The
shockwaves are felt strongest at the epicentre.
• The most damage and destruction will occur at the populated area nearest to the
epicentre.
Management of the effects of tectonic
activity
The reasons why people continue to live in areas of volcanic activity
Fertile soil for crops
Ash makes the soil fertile,
for example coffee grown
on slopes of volcanoes in
Columbia.
Perception
People think that scientists
who monitor the volcano
can give enough warning
for an evacuation if an
eruption happens.
Friends & Family
People who have lived in a volcanic area for
years and/or have many friends & family
nearby will not want to move. Poverty may
also prevent people from leaving the area.
Geothermal energy
Properties in Reykjavik, Iceland
benefit from cheap electricity
produced by geothermal power.
Tourism
The areas around volcanoes are scenic & many
people want to visit features like craters,
geysers & hot springs, e.g. Iceland. Many
people have jobs in the tourism industry.
The reasons why people continue to live in areas of earthquakes
Jobs
Earthquake areas are usually rich in
minerals. Many people have jobs in the
mining industry here.
Environment
Many earthquake areas have been
developed for the wealthy. People want to
live there for the fantastic environment,
e.g. Malibu in California
Perception
People think that earthquake proof
buildings will keep them safe in the
event of a tremor, e.g. Japan
Tourism
Many earthquake prone areas have amazing
scenery and people have jobs in the tourism
industry, e.g. San Francisco & New Zealand
Prediction and prevention of the effects of earthquakes
Prediction
Prediction is not possible,
but seismometers can
measure movement. An
increase in tremors can
suggest a large
earthquake is increasingly
likely, so people can begin
to prepare.
Building Design
Education & Planning
Earthquake-proof buildings
Schools & businesses in
have automatic shutters on
Japan practice
windows to stop glass
earthquake drills such as
shattering onto streets,
ducking under tables. In
interlocking frameworks,
the USA the government
counter-weights and rubber
shock absorbers. San Francisco has info packs about how
airport has columns standing to prepare an earthquake
emergency survival kit.
on 1.5m ball bearings.
Prediction and prevention of the effects of volcanic eruptions
Monitoring
Tiltmeters and GPS can
be used to detect
changes in the shape of
the volcano and crater as
the magma rises. Gases
can be monitored as CO2
and Sulphur Dioxide
increase just before an
eruption.
Defence
Lava flows can be cooled with
water to make them move
more slowly and stop.
Diversion channels can be
built to guide lava flows away
from villages. In Iceland in
1973 lava was directed out to
sea and away from a town.
Education
People who live close to
volcanoes are taught to
look out for signs the
volcano is going to erupt.
Locals who live on Sicily
know how to look for
changes in the
consistency of the lava.
Cause and effects of a named earthquake: Turkey 1999
Causes:
Destructive plate boundary; Eurasian, African & Arabian plates caused the north
Anatolian fault to move 3m. The epicentre was at the town of Izmit, which lies on top
of soft rock; clay & sand.
Effects on People:
18,000 dead, 300,000 homeless, motorway destroyed - hard for emergency services to
access the scene, people suffered emotional trauma, $10 billion rebuild costs.
Effects on Environment:
A fire at the Tupras oil refinery meant 700,000 tones of oil was burnt causing air
pollution, Pekim sewage works damaged causing rivers to be polluted, Yaolva chlorine
factory leak, land raised out of the sea at the coast near the Sea of Marmara.
Cause and effects of a named volcanic eruption: Montserrat 1997
Causes:
Destructive plate boundary; North American plate is subducting below the Caribbean
plate. Chances Peak erupted ash, which covered the southern half of the island. There
was also several pyroclastic flows of hot rock and ash.
Effects on People:
19 dead, 150 homes destroyed, Farm Village and Trant Village totally buried under ash,
Bramble Airport was closed, roads were covered with ash and rocks, 8,000 people had
to leave the island and never returned – emotional trauma.
Effects on Environment:
Ash and rock covered 4km2 of the island, pyroclastic flows caused the River Belham to
flood, pyroclastic flows removed all the vegetation in the south of the island including
the ridges surrounding Farrell’s Yard.