Causes of Earthquakes and Volcanoes
CONSTRUCTIVE MARGIN : where plates are pulling apart. Frequently erupting
volcanoes, frequent but gentle earthquakes as the plates are moving apart with
very little resistance.
DESTRUCTIVE MARGIN : Ocean plate collides with a Continental plate.
(oceanic plate is denser and heavier so is driven beneath the oncoming plate).
Occasional powerful Volcanoes and regular powerful earthquakes if plates have
got ‘stuck’. Plus deep ocean trench on sinking plate
COLLISION MARGIN : where 2 plates collide and are both continental plates.
Neither ‘sinks’ so produce a collision zone of rising mountain ranges. No
volcanoes but infrequent powerful earthquakes as mountains re-adjust
CONSERVATIVE MARGIN : where 2 plates slide past each other in different
directions or at different speeds. Friction causes them to ‘stick’ so pressure builds
up – and is released as frequent, possibly severe earthquakes
There are clear patterns of TECTONIC activity around the earth. Both Volcanoes and Earthquakes tend to occur in certain places – and not in
other places. Where you get Volcanic activity, you often find Earthquake activity – and both tend to take place at the edge of the world’s Tectonic
Plates. Places far from tectonic margins (where 2 plates meet) get few earthquakes and/or volcanoes.
There are 4 main parts to the earth’s structure : an
Inner Core of iron, surrounded by an Outer Core.
The majority of the earth is the MANTLE. Inside
this Convection Currents are moving. In hot areas
the convection currents rise towards the Crust.
When they get there they spread apart – dragging
the crust in separate directions to give a
‘Constructive Margin’. As the convection currents
continue they cool and begin to sink back towards
the core. As they do they drag some of the crust
down where it collides with other crust to form a
‘Destructive Margin’.
Volcanoes and Earthquakes are a feature of the
edges of the plates because this is where plates
are either pulling apart (constructive margin) or
colliding (destructive margin).
Volcanoes
Volcanoes erupt at Destructive and Constructive margins – though they are often more explosive and powerful at Destructive
margins due to them starting deep within the crust. At Constructive margins they are more surface features as plates move apart.
In both cases the built-up pressure has a number of consequences.
Sequence of Eruption Events
Warning Signs of an Eruption
Explosion of built-up steam and
gas which disintegrates solidified
vent from previous eruption
Gas and steam emissions
increase
Ash cloud of pulverised rock,
steam, and gas rises into the
air. In sufficient quantities
this can cover the
surrounding area in a layer of
hot ash which burns crops,
vegetation and possibly
people. Causes breathing
problems in very young & old
Underground water
becomes more acidic
and hotter
Surface snow and ice
may melt with rising
ground temperatures
Collapsing ash cloud can lead
to a Pyroclastic flow of
superhot steam, ash and gas
rolling forward at up to
200mph which incinerates all
in its path as it rolls downhilll.
Trees and vegetation
may die as roots are
heated
Surface earth tremors
are noticed as magma
is forced up the vent
Volcanic bombs of liquid lava
are shot out by pressure of
gases from erupting vent.
Small burrowing animals
evacuate the area as soil
temperatures rise
Streams of lava may pour out of main
vent and secondary vents (called Magma
when inside the crust & volcano)
Small animals may die from
rising carbon dioxide
emissions close to the ground
Volcano Impacts
Economic
Ash injected into upper atmosphere can be blown far
and wide, disrupting air travel and reducing light and
global temperatures for weeks and months.
Benefits
• Volcano Tourism
• Skiing industry
• Mineral mining (sulphur)
• Big yields of farm crops
Problems
• Eruptions can cause tourists to cancel
visits
• Lava flows can damage ski lifts
• Hot ash can destroy fields of crops
• scientific researchers come to monitor the
volcano
Social
Environmental
• communities have year-round jobs in tourism
with summer volcano hikers and winter skiers.
• Lava flows can stop movement if roads are
blocked
• medical use of hot spa water and mud can
improve health.
• Air flights are delayed & diverted due to
ash clouds
• Geothermal energy is a renewable energy
source using steam from hot rocks near the
surface.
• air contaminated with ash and acidic fumes
causes breathing difficulties.
• Farmland is supplied with mineral nutrients as
ash is washed into the soil
•water supplies contaminated with acidic
lava and ash
• Global cooling can follow as ash spreads
through the upper atmosphere.
Earthquakes
Seismic waves of energy move in all directions from the FAULT where the
earthquake happens – the FOCUS. This may be near the surface or deep in the crust
depending on the type of plate margin. The place directly above the Focus on the
surface – which may receive the most shaking – is the EPICENTRE
Earthquakes
are
measured
using
SEISMOGRAPHS which detect movements in the
earth. The RICHTER scale is a measure of the
strength of earth movement, while the MODIFIED
MERCALLI scale measures the impact on people
& surface features such as building & trees
Earthquake Event
Ground shakes
Ground shakes
Primary Effect
Secondary Effect
Homes collapse
Homeless refugees (social)
Factories collapse
More unemployed (economic)
Shops collapse
Looting from shops (political)
Gas pipes fracture
Leaking gas starts fires (social)
Water pipes broken
Fires can’t be put out (social)
Lack of fresh water(social)
Disease such as cholera from
drinking contaminated water (social)
Ground shakes
Liquefaction of tall office
buildings
Lack of money made by business –
less tax revenue for the city
(economic)
Landslides
Roads blocked
Isolated areas are cut off and lack
essential medical supplies (social)
Ground shakes
Tunnels & bridges collapse
Factories in other areas run out of
key supplies (economic)
Tsunami
Flooding of coastal areas by
tidal wave
Riots in refugee camps with not
enough aid (political)
LEDC Earthquake Haiti 2010
The Haiti earthquake of January 13th 2010 was one of the largest casualty events of the last decade – but wasn’t the largest of
earthquakes. How far did Haiti’s poverty contribute to the death rate of almost 250,000 people?
Haiti is one of the poorest 20% of countries in the world. Whilst it hasn’t
suffered from any serious earthquakes for almost 200 years it is frequently
flooded with it lying in the main Atlantic hurricane path.
The earthquake of January 2010 registered 7.0 on the Richter scale – which
is a large event, though larger ones do take place each year around the
world. It occurred on a fault line running almost directly under the capital Portau-Prince so the epicentre was focused on the most densely populated parts
of the country. It was caused by the fracture of a Conservative margin as the
Caribbean plate slide one way, and the North American plate went the other
way.
•No significant earthquake for 200 years – so the country was not prepared, nor were buildings earthquake-ready.
•Fault-line ran right under the capital city – Port au Prince, so it got maximum ‘shake’.
•Buildings were poorly constructed – with many slum dwellings, so they collapsed easily. Also the density of buildings in the city meant there was
no escape from falling debris.
•Corruption of officials and building constructors meant government buildings were made of weaker materials than expected. The presidential
palace and UN offices collapsed.
•Disruption of airport, port and roads meant there was a delay of over a week in organising rescue of trapped people. Planes didn’t land for 48
hours – took 5 days to get the port working
•Lack of army or emergency teams to put an after-earthquake plan in place until US army came
•Hospitals destroyed – so very little blood supplies for transfusions; medicines for those with on-going health conditions (heart pills) or to stop
injuries becoming infected.
•Water supplies disrupted – people forced to drink dirty water contaminated by broken sewage systems. Disease broke out rapidly in the tropical
heat with so many dead bodies unburied.
•Looters shot & lynched by survivors who felt they were stealing food from their neighbourhood
•Main jail broken open and 4000 criminals escaped to form violent gangs taking food from others with machetes, knives and guns.
•A month after the earthquake, 14 people are killed searching for tins of food in a damaged supermarket which collapsed on them.
• 9 months after, following heavy tropical storms, cholera breaks out in the refugee camps still with 1 million people in – 500 die due to poor
sanitation conditions, overflowing sewage ditches, poor hygiene and lack of clean water. 1 million refugees in tent cities have to be evacuated in
November 2010 as Hurricane Tomas tracks across Haiti bringing dangerously high winds and rainfall.
During
Hours Later
Before
Poor Building Construction :
many people live in self-built
homes, and low quality building
materials & lack of Building
Codes meant many buildings
collapsed at the first shaking.
Months Later
Location : the epicentre of the
earthquake was in the most
densely populated part of Haiti
so the capital city got most
‘shake’ from a ‘surface’ quake
Why was the Haiti
earthquake so
devastating?
Transport Disruption
- the main runway in
Haiti was put out of
action by the
earthquake for days
so little medical aid
could be flown in.
Days Later
Refugee Camps : the slow arrival of food,
clean water and medical care meant some
survivors died from injuries. Months later the
poverty of Haiti meant many were still living in
camps with no proper toilets or clean water
leading to cholera deaths & hurricane danger.
Public Disorder : lack of police meant
gangs took over the streets leading to
violence, looting and lynching of looters.
MEDC Earthquake: Kobe, Japan 1995
Where / When / Why : On January 17th 1995 a 7.2 magnitude earthquake hit the port city of Kobe on the south
coast of Japan – the largest earthquake in Japan for 47 years. Caused by the Philippine plate sliding under the
Eurasian plate it lasted 20 seconds where there was solid rock – but over 2 minutes on less solid reclaimed land
in Tokyo Bay.
Primary Effects :
• Over 6000 died. Many more injured
• 200,000 buildings destroyed including offices, factories, houses, and port facilities.
• Elevated roads collapsed and 130km of railway track put out of use.
• Gas and water pipes fractured and 300 fires broke out
Secondary Effects :
• It was the middle of winter so survivors had to be given refuge fast to avoid hypothermia
• There were over 700 after-shocks so many people left Kobe – not all returned.
• Some companies were forced to close as their factories were so badly damaged eg Mitsubishi
• The port was put out of action for 3 months – reducing the imports & export trade for the area
One of the positive aspects of earthquakes is if lessons are learnt which can reduce the impact of future earthquakes. As a result of the Kobe
earthquake in 1995 – these earthquake precautions were put in place in the following months and years. However they need either good
planning, and/or cost money – so are often out of the reach of LEDCs
Building zones : restricting the type of
buildings allowed on reclaimed land. New
housing has to be built on solid ground &
use fire-resistant materials.
Rubber Shock Absorbers bridge
supports now have to have rubber pads to
absorb the shock waves are prevent bridge
& road collapse
Building Spacing Office blocks
have to be a certain distance apart
to stop a ‘domino effect’ if one
collapses
Retro-engineering : putting a stronger support
framework around existing buildings – such as the
red girders around Kobe port tower
Before the
Earthquake
MEDC : Japan
Earthquake of January 1995
Kobe – port city
6,436 deaths
LEDC : Haiti
Earthquake of January 2010
Port-au-Prince – capital city
250,000 deaths
 Building codes mean buildings have to
be designed to withstand a certain
amount of earth tremor.
 No building codes. Many poorer people build
slum housing out of materials they can find.
 Strong building materials used – steel,
reinforced concrete, strengthened glass
etc.
 Fire crews trained so they know what
to do in an earthquake. Residents
trained to hide under door frames.
 Cheap building materials used to cut costs.
Weak cement and poor concrete fracture
easily.
 No training of police, army or emergency
services of what to do in an earthquake
emergency
During the
Earthquake
 Few buildings collapse.
Thousands of buildings collapse
 Most tunnels, bridges and elevated
roads absorb the earth movements
 Many buildings are very close together so
people are crushed in narrow alleyways
between buildings and on streets by falling
debris
After the
Earthquake
Thermal image equipment used to
locate trapped bodies. Powerful
equipment lifts debris off survivors.
 Gangs of looters cause violence on the
streets
 Effective medical services treat the
injured rapidly
Follow up.
 Government emergency funds help
rebuild roads, power supplies and
buildings
 Home insurance means people can pay
to rebuild their homes
 Many survivors die trapped in ruins.
 Lack of trained medical aid means people die
of injuries and disease
 Government has very little in funds.
 Up to a million people are still living in tents
in refugee camps a year after the earthquake,
many dying from cholera in the hurricane
season 10 months after.
While earthquakes cannot be prevented from happening, it is possible to make preparation in advance. Residents can be given
advice on what to do during an earthquake, and the authorities can make sure injuries and damage are dealt with rapidly after an
earthquake.
Before an
earthquake
During an
earthquake
After an
earthquake
Building design : In Wellington, New Zealand, houses are built of wood so they ‘flex’ in an
earthquake and have light wooden roofs.
Retro-engineering / Retro-fitting : in China elevated roads and railways have been given extra
girders to prevent collapse.
Warning Advice : in New Zealand there are warning leaflets and adverts on TV to tell people what
to do in an earthquake : DROP, COVER & HOLD, and not run outside
Training Days : in Tokyo on the anniversary of the Great Earthquake of 1923 schools, workplaces
and communities spend the day practicing what they would do in an earthquake. The same was done
in California in October 2010 with 7m people.
Emergency Kits : in Wellington, New Zealand, the emergency services have kits with the main pieces
of after-care equipment they need to rescue people and stop earthquake injuries becoming fatal. They
practice using these in regular mock emergency training where police, fire and ambulance all cooperate together.
Earthquake Prediction
After the Boxing Day Tsunami disaster of December 2004 when over a quarter of a million people died a lot of effort has gone into
trying to give earthquake warnings so people can prepare. This is especially important for people in coastal areas where an early
warning of an approaching tsunami following an undersea earthquake could save many lives.
At the moment there is no
accurate way of predicting
when an earthquake might
strike. Work is being done to
see if there are patterns to
earth tremors which could
indicate a ‘big one’ is likley in
the near future.
Elephants: a lowtech early
warning system
for earthquakes?
To give Tsunami Warnings a series of seismographs have been placed on the Indian
Ocean sea bed. When they sense an earthquake a signal is sent to a transmitter
floating on the sea surface. This sends a signal to a satellite – which then informs
Warning Centres on land. They can then send out a warning to coastal residents telling
them to evacuate the coast and head inland and for higher land.
In China people are told to watch for strange behaviour in animals – cats, dogs and cattle
seem to be able to sense a build up of stress in rocks and show strange behaviour.
Before the 2004 Tsunami working elephants in Thailand broke from their chains and ran
into the forests away from their keepers hours before the earthquake which caused the
tsunami.
Living in an Earthquake Zone
If you asked someone why they lived in an earthquake zone, they might say they were born and brought up there. It takes a lot
to give up your job, college, work, friends and community to move somewhere else because you think there ‘might’ be an
earthquake ‘one day’. But these are some answer people might give :
“The risk of death or injury is really low –
I stand more chance of dying in a traffic
accident”
The figures show the number of deaths in
Japan for Earthquake deaths.
“The buildings in this city are built to be really safe. They will keep me
protected”
In San Francisco in California certain shaped buildings are not allowed because they
are more likely to collapse in an earthquake (4 diagrams), however buildings like the
TransAmerica Building in the centre of the city was designed in the 1970s to
withstand large earthquakes with :
• a pendulum in the top which sways into the hollow shoulders if the building
starts to ‘tilt’ to pull it back upright
• a pyramid shape – which is the most stable shape
• windows that fall in – not out onto the street
• deep foundations on rubber & spring shock absorbers
Earthquake
Date
Number
Killed
February 2010
1
August 2009
1
June 2008
12
July 2007
11
March 2007
1
March 2005
1
October 2004
40
January 1995
6,434
June 1948
3,769
December 1946
1,362
“I’ve been told what to do – like hide
under a table or a door frame. I’m sure I
would be OK”
Many cities have earthquake practice days,
warning leaflets and websites that tell you
how to be safe