Transcript Living in an Active Zone

Living in an Active Zone
Revision
Cross section of the Earth
Structure of the earth
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Earth is made up of four distinct layers
Crust (oceanic/ Continental)
Mantle
Outer core
Inner core
Structure of the earth
• Crust is broken up piece called tectonic
plates
• 7 large plates and 12 small plates
• These plates move because of Convection
Currents in the magma
• Where two plates meet is a plate margin
Why do the plates move?
Constructive Plate Margins
• Two oceanic plates move away from each
other shield volcanoes form creating mid
ocean ridges e.g. mid Atlantic ridge.
• When two continental plate move apart a
rift valleys are formed. Shield volcanoes
found here e.g. Iceland
Constructive plate boundary
Constructive Plate Margins
Destructive Plate Margins
Oceanic and continental Crust
• Where it involves oceanic and continental crust, the
oceanic crust is always subducted below the continental
because it is denser.
• The subduction of the oceanic crust creates a deep sea
trench and earthquakes are formed at the subduction
zone.
• Fold mountains are created on the continental crust .
• The subducted oceanic crust melts in the mantle rising
up into the fold mountain to create composite volcanoes
• E.g. Mount St Helens
Destructive plate boundary
Destructive Plate Margins
Oceanic crust only
• Destructive plate margins also can involve two oceanic
plates
• Here island arcs are formed in the oceanic crust
• E.g. Montserrat, Caribbean
Destructive Plate Margins
Types of Volcanoes
• Shield Volcanoes found on constructive
plate margins. Lava is hot and runny. Not
as explosive. Not very high. Very wide
base
• Composite volcanoes found on destructive
plate margins. Thick stick lava. Erupt
explosively. Very tall cone shaped.
Volcanic hazards
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Lava flow
Ash
Lahars
Lava bombs
Pyroclastic flow
Volcanic Hazards
Earthquakes – Causes
• Earthquakes are cause by shock waves
travelling through the earth crust
• The source of the earthquake is called the
focus, the epicentre is the point
immediately above it on the surface
• Size of an earthquake can be measured
by a seismometer along the Richter scale
• Tsunamis are a secondary hazard of an
earthquake
Epicentre
Focus
Seismic waves
Earthquakes - Factors
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Strength of the earthquake
Distance from epicentre
Depth of the focus
Number of people living in an area
Type of rock
Time of day
The extent of preparation
Why do people live there?
500 million people live in active zones
• Dramatic scenery created attracts tourists, bringing income to an
area e.g. Mount Vesuvius, Italy
• Lava and ash provide nutrients to the soil, making the land near
volcanoes very fertile and good for agriculture. E.g. Mount Etna, Italy
• Opportunities to generate electricity using the heat from the earth
(geothermal energy) E.g. Iceland
• Volcanic rock is a good building stone
• Many people cannot afford to Move (LEDCs) E.g. Mount Pinatubo,
Philippines
• Tectonic hazards are rare and often to affect an area in a persons
lifetime E.g. Montserrat volcano had not erupted for 300yrs until
recently
• Prediction and earthquake resistant building are improving. E.g.
Kobe Japan has many earthquake proof buildings
• DON’T FORGET YOU NEED TO GIVE EXAMPLES
Predicting and preparing Earthquakes
Predicting
• Laser beams used to detect plate movements
• Seismometer used to pick up vibrations
• Radon gas – escape from the cracks in the crust
before an earthquake – this can be monitored
Preparing
• Educating people via TV or in schools what to do
• Earthquake drills to prepare
• Earthquake proof buildings, designed to absorb
the energy of an earthquake and withstand
movement
Predicting and preparing Volcanoes
Predicting
• Remote sensing – satellites monitor temperature and
gas emissions
• Seismometers – measures earthquakes activity that
occurs before an eruption
• Tiltmeters – monitor changes in the shape of a volcano
as it fills with magma
• Gas emissions – indicate an increased risk
• Ultra sound – to detect movements of magma
Preparing
• Exclusion zones created around volcanoes
• Authorities must be ready to evacuate
• Emergency supplies of basic provisions must be
gathered
• Good communication systems in place
This is an
alternative
casestudy Miss Kingdom’s
class had two
different
casestudies
(New Zealand
and Pakistan).
It is up to you
which one you
lean