Transcript The Restless Earth Revision - Geography

The Restless Earth
Volcanoes, Earthquakes and Fold
Mountains
Distribution of plates
Oceanic crust: newer – less
than 200 million years old;
denser; can sink; can be
renewed or destroyed.
Continental crust: older –
most over 1500 million
years old; less dense;
cannot sink; cannot be
destroyed or renewed.
Plates – Pacific
Plate covers
most of Pacific
Ocean – ‘Ring
of Fire’.
Plate
margins
Destructive plate margins:
plates move together. A
subduction zone forms
where the denser oceanic
crust sinks under the lighter
continental crust. Great
pressure is exerted and the
oceanic crust is destroyed
as it melts to form magma.
If two continental plates
meet, they collide rather
than one sinking beneath
the other. This collision
boundary is a different type
of destructive margin.
Constructive plate margins:
When plates move apart –
usually under oceans. As the
plates pull apart, cracks form
and magma wells up these
cracks, forming volcanoes.
Conservative plate
margins: the plates slide
past each other. They often
get stuck and this builds up
pressure, resulting in
earthquakes.
Landforms
Fold mountains: large
mountain ranges
where rock layers
have been crumpled
as they have been
forced together.
Ocean trenches:
deep sections of the
ocean, usually
where an oceanic
plate is sinking
below a continental
plate.
Composite
volcano: a steep
sided volcano that
is made up of a
variety of
materials, such as
lava and ash.
Shield volcano: a broad
volcano that is made up of
lava.
Case Study of Fold Mountains: The
Alps
The melt waters from
the melting snow is
used to generate
hydro-electric power
(HEP).
Farming: The fold
mountains of the Alps are
used for pastoral farming
– sheep, goats, cattle.
They practice
transhumance – the
movement of the animals
up the slopes to the
summer pastures.
Tourism is a key industry in the
Alps. In the winter, many
people come for the skiing and
other winter sports.
Countries –
Austria, Italy,
France,
Switzerland.
Life in the mountains can be
difficult due to inaccessibility, the
threat of avalanches, steep
slopes and poor soils. Tunnels
have been built through the
mountains to make travelling
easier.
Volcanoes
Shield volcanoes: so named for their
broad, shield-like profiles, are formed by
the eruption of low-viscosity lavas that can
flow a great distance from a vent, but not
generally explode catastrophically. The
Hawaiian volcanic chain is a series of
shield cones, and they are common in
Iceland, as well.
Composite volcanoes are tall
conical mountains composed of
lava flows and other ejecta in
alternate layers, the strata that give
rise to the name. Composite
volcanoes are aso known as
stratovolcanoes. Strato/composite
volcanoes are made of cinders,
ash and lava. The volcanoes are
made by another volcano. Cinders
and ash pile on top of each other,
then lava flows on top and dries
and then the process begins again.
Classic examples include Mt. Fuji
in Japan, Mount Mayon in the
Philippines, and Mount Vesuvius
and Stromboli in Italy.
Case Study: Volcanic eruption –
Montserrat, Caribbean
Primary effects: Plymouth the
capital was buried in 40m of mud.
The port & airport were destroyed.
Many homes were destroyed. Half
the population had to flee. Death &
destruction.
Cause: On a destructive Secondary effects: Small
plate margin. 1995
eruptions continued.
Soufriere Hills volcano
Infrequent ventings of
erupted.
ash into the uninhabited
areas. People still haven’t
Immediate responses:
been able to go home.
British navy sent to
Long term responses:
evacuate island;
Better monitoring of
emergency services
volcano; restricted
rescued people. People
access. Rebuilding of
moved from homes.
roads and bridges.
Helicopters. Ash cleared.
Trees replanted.
Monitoring and predicting
volcanoes: observation of
‘bulges’; use tiltmeters to
identify changes in the
landscape. Use GPS
(Global Positioning
Systems) and satellite
imaging – detect
temperature changes. Use
robots to collect gases being
emitted. Warn people &
evacuate.
Supervolcanoes
Characteristics - Much
bigger than other
volcanoes. Only a few.
An eruption would have
global consequences.
The explosion will be
heard around the
world. The sky will
darken, black rain will
fall, and the Earth will
be plunged into the
equivalent of a nuclear
winter.
Yellowstone National Park - Is
one of the largest
supervolcanoes in the world.
Scientists have revealed that it
has been on a regular eruption
cycle of 600,000 years.
The last eruption was 640,000
years ago... so the next is
overdue.
Location and causes of
earthquakes
Location : along plate
boundaries.
Causes: when pressure and tension
built up along a fault line or plate
margin is suddenly released.
Features of earthquakes
Epicentre the point at the earth’s
surface directly above the focus.
Focus – the point in the earth’s crust
where the earthquake originates.
Shock waves – seismic waves
generated by an earthquake that
pass through the earth’s crust.
Measuring earthquakes
Richter Scale - a logarithmic scale
used for measuring earthquakes,
based on scientific recordings of the
amount of movement
Mercalli Scale – a means of
measuring earthquakes by describing
and comparing he damge done on a
scale of I to XII.
Case Study of earthquakes –Haiti
2010 – poorer area of the world
Primary effects: 100,000
deaths; widespread
damage to buildings and
infrastructure.
Secondary effects: UN
had to enforce law and
order; outbreak of
disease (cholera);
homelessness;
emergency health care.
Location, features and size: The epicentre of
the magnitude 7.0 quake was near the densely
populated Haitian capital, Port-au-Prince.
Strong aftershocks rocked Haiti.
Causes: The earthquake was caused by
pressure and tension along the boundary of
the Caribbean Plate and the North American
Plate being suddenly released.
Immediate responses: International
rescue teams and emergency doctors
and aid (tents). Charities and
governments.
Long term responses:
The International Community will be working in
Haiti for many years to come trying to rebuild
what was already a very poor country. This
catastrophe will set the country back a whole
generation.
Case Study of earthquakes Kobe,
Japan, 1995 – richer area of world
Causes: the Philippine
Plate shifted beneath the
Eurasian Plate along the
Nojima fault that runs
under Kobe.
Primary effects: death (6,434
died); serious injuries (40,000);
homelessness (300,000);
gases mains erupted; water
pipes leaked; roads and
bridges collapsed) railway lines
buckled; homes without water
and electricity; fire.
Immediate responses:
rescue of trapped people;
emergency operations;
telecommunications restored;
rebuilding of roads, bridges
and the port.
Long term responses: new building have to
be earthquake proof; all citizens have to be
prepared for earthquakes; earthquake drills;
emergency services prepared; media used
to warn people.
Tsunami Case Study – Indian
Ocean 2004
A tsunami is a special type of wave where the entire depth
of the sea or ocean is set in motion by an event, often an
earthquake, which displaces the water above it and creates
a huge wave.
Cause: the IndoEffects: Waves of 25m first hit Sumatra in Banda Aceh
Australian Plate
and then Sri Lanka and Thailand. 220,000 died.
subducted
650,000 were seriously injured. 2 million were made
beneath the
homeless. Many buildings were destroyed. 1,500
Eurasian Plate.
villages were wiped out. Many people were missing
The Earthquake
feared dead.
measured 9.1 on
Responses: rescue services & emergency teams
the Richter scale.
were overwhelmed with the scale of the disaster.
The international community responded with fresh
water, food, sheeting and tents. Charities and
governments raised millions. The UK Disasters
Emergency Committee co-ordinated the British
response. The affected areas were rebuilt and a
tsunami early warning system set up.