Download Tectonic activity – The essentials

Tectonic activity – The
essentials
The earth’s crust is made of huge floating plates (rock).
The earth is like a broken egg shell. These plates float on the
mantle (molten material) in different directions a few
cm/year. Plates meet at plate boundaries or margins
There are 3 different types of plate margin:
1. Constructive
2. Destructive
3. Conservative
World map showing plate boundaries and their
movement
2 plates move away from one another. Magma rises
from the mantle. New crust is created. Volcanoes get
formed.
At a destructive boundary the plates are moving towards each other. This tends to
involve a continental plate (a plate carrying land) and an oceanic plate (a plate
carrying ocean).
The oceanic plate is denser than the continental plate so, as they move together, the
oceanic plate is forced underneath the continental plate. The point at which this
happens is called the subduction zone. As the oceanic plate is forced below the
continental plate it melts to form magma. The magma collects to form a magma
chamber. This magma then rises up through cracks in the continental crust. As
pressure builds up, a volcanic eruption may occur.
At a conservative boundary the plates are sliding horizontally past each other.
No land is created at a conservative boundary and none is destroyed.
Volcanoes do not occur along these boundaries but earthquakes are very
common. A very well-known example of a conservative boundary is the San
Andreas Fault, which runs through the state of California in the USA.
How are fold mountains
formed? (destructive margin)
Fold mountains e.g. Alps, Rockies, Himalayas are formed when two
plates move together (a destructive plate margin). This can be where
two continental plates move towards each other or a continental and an
oceanic plate.
The movement of the two plates forces sedimentary rocks upwards into
a series of folds. Fold mountains are usually formed from sedimentary
rocks. When plates and the continents riding on them collide, the
accumulated layers of rock crumple and fold like a tablecloth that is
pushed across a table.
Case study fold mountains: The
Andes – how do people use them?
FARMING – subsistence farming occurs on steep slopes e.g.
potatoes. Terraces (steps cut into hillsides to create areas of flat land)
retain water and limit soil erosion. Most crops are grown in the valleys
e.g. rice, cotton, soy beans. Llamas are use as pack animals (mainly
males carrying equipment) and the females are used for milk and meat
and wool is used in clothes and rugs.
MINING – Andean countries are important for tin, nickel, silver and
gold mining. Towns grow as a result of job creation. However, this brings
an increased crime rate.
HEP (Hydroelectric power). Steep slopes and narrow valleys can easily
be dammed; there is lots of precipitation and spring melt snow to
generate electricity
TOURISM – There are many natural attractions e.g. mountains,
volcanoes, glaciers and lakes. Some people follow the Inca trail (ancient
people) to see famous early settlements e.g. Machu Picchu
World map showing the distribution of volcanoes
(spread of)
A cross section of a volcano and its features
Composite Volcano
The shape of a volcano depends on the type of magma and the kind of vent out of
which the lava comes. If very runny magma erupts, the lava spreads out quickly to
form a low, gently sloping shield volcano e.g. Mauna Loa, Hawaii.
If a vent becomes blocked, smaller vents often break out around it (through
cracks/weaknesses in the rock) and form small cones on the side of the main one
(secondary). This is called a composite volcano. When thick sticky magma erupts
through a central vent, the lava forms a steeper sided cone.
Cause/effects Montserrat eruption 1995-8
Cause:
Destructive plate margin – Caribbean plate moves towards and underneath the North
American Plate (gets subducted, as it is oceanic crust i.e. is heavier)
Effects
Effects
Primary:
 2/3 of the island was covered in ash
 50% of the population were evacuated
to the north of the island to live in
makeshift shelters
 23 people died in 1997
 Plymouth - the capital was evacuated
 The airport and port were closed
 Farmland was destroyed
 Many schools and hospitals were
destroyed
Secondary:
 Floods as valleys were blocked with ash
 Forest fires caused by pyroclastic flows
 As most of the southern area was destroyed
any remaining inhabitants have had to endure
harsh living conditions in the North.
Transport remains a problem for people
travelling to the island as the port and airport
remain closed.
The tourist industry is still suffering with few
visitors except for cruise ships looking at the
volcano
 Over half the population left the island and
have not returned
Immediate/long term responses Montserrat
eruption 1995-8
Immediate:
Farmers quickly collected what harvest they could as first eruptions happened
Inhabitants nearby were evacuated to a ‘safe zone’ in the north
Long term:
£41 million was given in aid by the British Government.
Money was given to individuals to help them move to other countries (7000 left).
Riots occurred as locals complained that the British were not doing enough to help
the island
The MVO (Montserrat Volcano Observatory) was set up to study the volcano and
provide warnings for the future
A Risk assessment was done to help islanders understand which areas are at risk
and reduce problems for the future.
Monitoring and predicting eruptions
How can you predict and monitor volcanic eruptions?
1. Earthquakes are a sign of an impending eruption
2. ‘Swelling’ (magma building up) on the sides of a volcano
3. Tiltmeters detect a change in slope caused by shifting
magma under the rock surface
4. Global positioning systems (GPS) use satellites to
detect movement as little as 1mm
5. Digital cameras on the edge of craters allow
volcanologists to make safe observations
6. Changing gases escaping from a vent are a sign of an
imminent eruption. Tiny robots called ‘spiders’ are now
used to collect samples.
Supervolcanoes
What is one?
A supervolcano is a mega colossal volcano that has the capacity to erupt a 1000
times more material (ash, lava) than a normal volcano.
What are its characteristics?
 Much wider and less steep than normal volcano
 Much bigger scale, emitting far more material than a normal volcano (1,000km
cubed, instead of 1km cubed)
 They have large depressions (calderas – a collapsed magma chamber) instead
of a cone shape)
What are the likely effects of an eruption?
 The effects could be global e.g. dramatically affecting climate as an ash cloud
could reduce incoming solar radiation (small ice age?)
 A huge area of land could be covered, resulting in crops failing, huge air
transport problems and thousands of people dying
World map showing the distribution of
earthquakes (spread of)
A cross section of an earthquake and
related features
Key terms - earthquakes
Epicentre – the point on the earth’s surface directly above the focus
Focus – the point in the earth’s crust where the earthquake happens
Shock waves – seismic waves generated by the earthquake, which
pass through the earth’s crust
Richter Scale – logarithmic scale (each increase in 1 means a 10 fold
increase in energy) which measures the strength of an earthquake.
There is no upper limit
Mercalli Scale – a means of measuring earthquakes by describing and
comparing damage done on a scale of 1 to 12.
Case study (MEDC):
Kobe Earthquake, Japan 1995
Cause
Kobe is near a destructive plate margin where the Pacific Plate (oceanic
crust) gets subducted (forced underneath) below the Eurasian Plate
(continental crust) as it is heavier.
Effects
Primary:
 Nearly 200,000 building s collapsed and roads are destroyed e.g.
Hanshin elevated highway
 Many bridges collapsed along 130km section of bullet train route
 120 of 150 quays in the port are destroyed
Secondary:
 Water pipes and gas mains burst. Electricity supplies disrupted
 Wall of fire up to 500m wide sweeps city (caused by broken gas pipes
and ruptured electricity mains)
 5,500 people killed; 40,000 injured; 180,000 houses destroyed
 230,000 homeless – living in temporary shelters. Shortage of blankets,
clean water and food)
 Major industries forced to close e.g. Panasonic and Mitsubishi
 10 trains derailed
 Temples destroyed in nearby Kyoto
Responses
Immediate:
 Friends and neighbours, joined by emergency services searched through rubble
 Hospitals struggled to cope, treating people in corridors
 Major retailers e.g. 7-Eleven, helped provide essentials e.g. food
 Motorola gave people telephone connections free of charge
 Railways were 80% operational within a month
Long term:
• Infrastructure e.g. water, gas, electricity and phone services were fully operational
by July 1995
• All rail services back to normal by August
• Within a year, the port was 80% operational
• Rubber blocks were put under bridges to absorb shocks
• New buildings were built further apart (to prevent domino effect) and with flexible
steel frames
Case study (LEDC):
The Sichuan Earthquake, China, 2008
Cause
The pressure resulting from the Indian Plate colliding with the Eurasian
Plate, was released on 12th May 2008, leading to an earthquake
measuring 7.9 on the Richter Scale.
Effects
Immediate:
 55,000 reported dead within 11 days and 18,000 missing
 374,000 injured
 5 million homeless
 In rural areas, 80% of buildings collapsed
 5 million buildings collapsed, including a number of schools (one had 900
pupils which were killed).
 Communications (land and mobile phones) were cut and roads were
blocked by landslides
Long term:
 2 months later, 69,000 are confirmed dead
 Landslides blocked rivers, leading to fears of flooding
Responses
Immediate:
• 20 helicopters are sent to help by Chinese Government
• Troops parachute in to assess situation and 1000s of army troops help on
the ground
• Rescue workers search for trapped survivors
• Land flattened to put up tents to shelter people from spring rains
• Teams from Japan, South Korea and Russia help rescue effort
• Donations to Red Cross exceed £100 million, much being spent on food,
medicine, doctors, volunteers, tents, mattresses and blankets
Long term:
• 1 million temporary small homes are built for homeless
• Chinese Government pledges $10 million rebuilding fund
• Banks write off debts owed by survivors without insurance
Prediction, protection and preparation
The 3 Ps are the key to reducing the impact of earthquakes:
PREDICTION – This involves trying to forecast when an earthquake
will happen by: monitoring foreshocks (although their usefulness is
limited if you want to evacuate an area); animal behaviour has been
used but is sceptically viewed by many.
PROTECTION – Building to an appropriate standard and using
designs to withstand movement is the main form of protecting people.
Buildings can have: an interlocking steel frame which can swing during
earth movements; an automatic window shutting system to prevent
falling glass; rubber shock absorbers at base (built into foundations);
fire resistant building materials.
PREPARATION – Involves hospitals, emergency services and people
practising for disasters e.g. drills/code of practice, so people know
what to do to increase their chance of surviving.
Case Study of a tsunami:
SE Asia, Boxing Day 2004
Cause
On 26th December 2004, an earthquake (10km below the sea bed, 150
miles off the coast of the island of Sumatra, Indonesia) measuring 9.1 on
the Richter Scale happened at 7.59am local time (12.59am GMT).
The earthquake was caused by the Indo-Australian Plate subducting
(being forced underneath) beneath the Eurasian Plate.
Effects
Estimates suggested more than 220,000 died, 650,000 were injured and 2
million made homeless as a result of tsunami waves, up to 25 metres high
coming ashore in different countries. Public buildings e.g. hospitals and
schools were wiped out in some areas. Up to 1,500 settlements were
completely destroyed in the province of Banda Aceh, Indonesia.
Map showing
countries
affected
Responses
 Rescue services and emergency teams were swamped by the scale of
the disaster.
 Bodies littered the streets before being buried in mass graves.
 International Aid poured in e.g. fresh water, water purification tablets,
food, sheets and tents. Medical teams and forensic scientists arrived.
 UK government promised £75 million and public donated £372 million.
 There were organisational issues following the collection of large sums
of money but it has been spent on rebuilding projects in Sri Lanka and
Indonesia.
 A tsunami warning system was set up in 2006 around the Indian Ocean
to ensure that people know how to respond and that local authorities have
plans in place in case a tsunami happens again.
Useful websites - animations
http://www.bbc.co.uk/schools/gcsebitesize/geography/platetectonics/plateboundary
rev3.shtml (destructive/compressional plate boundaries)
http://www.bbc.co.uk/schools/gcsebitesize/geography/platetectonics/plateboundary
rev2.shtml (constructive/tensional plate boundaries)
http://www.bbc.co.uk/schools/gcsebitesize/geography/platetectonics/plateboundary
rev4.shtml (conservative/lateral plate boundaries)
Geography at the movies http://www.geographyatthemovies.co.uk/ (Tectonics)