Transcript Living in an Active Zone - Penyrheol Comprehensive School Moodle

Living in an Active Zone
Use this PowerPoint to complete the brainstorm on the topic of
‘Living in an active zone’
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
Video http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/tectonic_pl
ates_video.shtml
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
Plate definitions
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.
Video http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/volcanoes_
video.shtml
Do all volcanoes erupt?
Active volcano – liable to erupt e.g. Mt Etna.
Dormant (sleeping) volcano – a volcano which
has not erupted for many years. For example, Mt
Pinatubo erupted in 1991 after 500 years of
dormancy.
Extinct volcano – a volcano which has not
erupted for many thousands or millions of years
e.g. Edinburgh.
However, it is often very difficult to tell whether a volcano will erupt
again…El Chichon, Mexico erupted in 1982 after being dormant for
approximately 1200 years!
Volcanic hazards
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Lava flow
Ash
Lahars
Lava bombs
Pyroclastic flow
Volcanic Hazards
Volcanic emissions
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
Video http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/earthquakes_
video.shtml
Why do earthquakes happen?
How can we measure earthquakes?
The Richter Scale
This measures the magnitude of a tremor (how powerful it is)
using an instrument called a seismograph.
On the Richter Scale, magnitude is expressed in whole numbers
and decimal fractions. Although the Richter Scale has no upper
limit, the largest earthquake ever recorded was in 1960 in Chile. It
measured 9.5 on the Richter Scale.
Earthquakes - Factors
• Strength of the earthquake (magnitude) – more shaking means more
damage will be caused
• Distance from epicentre – closer to the epicentre the more damage will
be caused.
• Depth of the focus – the shallower an earthquake the more damage will
caused
• Number of people living in an area (population density)- the epicentre is
close to a city then more people will be affected.
• Type of rock – softer rocks are likely to shake more and fro longer causing
more damage
• Time of day – if more people are in building more people are likely to die.
• The extent of preparation – some countries are well prepared for
earthquakes and therefore have little impact (see later on how to prepare
for an earthquake
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
How can we limit earthquake damage?
predict
plan
water levels can rise in wells and
lakes because of cracks in the
rock
protect
a tiltmeter can check any movement
within the rocks
Predict
foreshocks before the main quake
can be detected by a seismometer
animals can act strangely before
the earthquake
How can we limit earthquake damage?
Plan and protect
Building in earthquake zones
This is San Francisco in the USA.
San Francisco is near the San Andreas Fault and therefore the city experiences
earthquakes.
This skyscraper has been built to be
‘earthquake-proof’.
Its wide base lowers the centre of gravity of
the building and makes it more stable.
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
Predicting eruptions
The problem of prediction
Volcanologists (people who study volcanoes) are skilled at
predicting the likelihood of an eruption.
However, it's very difficult to pinpoint exactly when an
eruption will happen. Often, moving magma doesn't result
in an eruption, but instead cools below the surface.
Monitoring potential eruptions is expensive. With many
volcanoes erupting only every few hundred years, it's not
possible to monitor every site.
Video http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/managing_haz
ards_video.shtml
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