Transcript Earthquakes - SLC Geog A Level Blog

Edexcel AS Geography
Unit 1 – Global Challenges
Topic 1 – World at Risk
Global Hazard Patterns
Hazard Risk in Your Local
Area
• Looking at disaster hotspots shows that
some places are at more risk than others
• California and the Philippines suffer from
multiple hazards, but you need to think
about places closer to home
• In the exam, the examiners may ask you
about real or potential hazard risk in your
local area.
Hazard Risk in Your Local
Area
• You need to be able to talk about:
• Any past events that might have happened in
the area you live, e.g. droughts that have
occurred
• Any likely future events that could happen,
e.g. Landslides caused by coastal erosion
• The impact of these events on people,
property and the environment
Hazard Risk in Your Local
Area
• Researching the history of hazard events
in your local area could be done by:
• Researching historic newspapers
• Searching online
• Interviewing older residents
• Research the 4 main hazards faced by this
area (Attiki, Greece)
Greece deaths
Disaster Date
•
•
•
•
•
•
•
•
•
Extreme temperature
Earthquake
Earthquake
Earthquake
Wildfire
Extreme temperature
Earthquake
Volcano
Storm
• Storm
•
No Killed
20/7/1987
12/8/1953
7/9/1999
1928
24/8/2007
3/7/1988
20/6/1978
July 1956
March 1987
1000
455
143
103
67
56
50
48
48
Νοvember 1961
43
Source: "EM-DAT: The OFDA/CRED International Disaster Database
www.em-dat.net - Université Catholique de Louvain - Brussels - Belgium"
Greece affected
Disaster Date
•
•
•
•
•
•
•
•
•
•
Earthquake
Earthquake
Earthquake
Earthquake
Earthquake
Earthquake
Earthquake
Earthquake
Earthquake
Earthquake
20/6/1978
7/9/1999
24/2/1981
13/9/1986
9/3/1965
may 1967
1/9/1966
13/5/1995
15/6/1995
5/2/1966
No Total Affected
600100
115139
80400
45300
30253
16583
15123
15060
13900
11050
Source: "EM-DAT: The OFDA/CRED International Disaster Database
www.em-dat.net - Université Catholique de Louvain - Brussels Belgium"
Greece monetary losses
Disaster Date
•
•
•
•
•
•
•
•
•
•
Earthquake
Wildfire
Drought
Earthquake
Earthquake
Wildfire
Flood
Earthquake
Flood
Earthquake
Damage (000 US$)
7/9/1999
24/8/2007
March 1990
24/2/1981
13/9/1986
June 1998
2/2/2003
13/5/1995
24/10/1994
15/6/1995
4200000
1750000
1000000
900000
745000
675000
600000
450000
437700
422700
Source: "EM-DAT: The OFDA/CRED International Disaster Database
www.em-dat.net - Université Catholique de Louvain - Brussels Belgium"
Attiki natural disasters
• Choose 4 disasters for Attiki and research them to produce some
fact files for our local area.
You could choose...
• Droughts
• Earthquakes
• Floods
• Wild fires
Or any others you think are interesting!
Remember to cover the impact of these events on people,
property and the environment.
Also..Which hazard event is most likely to be repeated?
How do you rate the risks of such an event?
Hazard Distribution –
Geophysical
• Geophysical hazards (especially volcanoes,
earthquakes and to some extent tsunamis) usually occur
near plate boundaries so knowledge of plate tectonics in
required.
Platetectonics
• The lithosphere (the Earth’s crust and the rigid upper
part of the mantle) is divided into 7 large and several
smaller plates.
• The plates, which are rigid, float like rafts on the
underlying semi-molten mantle (called the
asthenosphere) and are moved by convection currents.
• Convection currents are generated by hotspots within
the asthenosphere which cause magma (molten
material) to rise towards the earth’s surface.
• These currents can cause the plates above to move
together, apart or side by side.
Crust
• Plates are made of two types of crust:
• Continental crust – is composed of older,
lighter (less dense) rock of a granitic type
• Oceanic crust - is composed of much
younger, denser rock of a basaltic
composition.
Hazard Distribution –
Geophysical
• Volcanoes and earthquakes most commonly
occur at the boundaries where the plates meet.
• There are three types of plate boundary –
constructive, destructive and conservative.
• The type of movement and the degree of activity
at the plate margins almost totally controls the
distribution, frequency and magnitude of
earthquakes and volcanic eruptions.
Hazard Distribution –
Earthquakes
Earthquakes
• The main earthquake zones are clustered
along plate boundaries.
• The most powerful earthquakes are
associated with destructive or
conservative plate boundaries
Destructive Plate Boundaries
Destructive Plate Boundaries –
plate converge
1. An oceanic plate and a continental plate move towards each other
•
•
•
•
•
•
•
•
•
•
•
Eg Alongside South America is the Nazca Plate (oceanic ) and the American Plate
(continental)
Also the Philippines
The oceanic plate is forced downwards as it is denser than the continental plate
This results in a subduction zone
An ocean trench forms too – (where the sea water is deeper here)
Friction occurs and the force of the compression as the plates meet causes
stresses in the crust and pressure occurs as the oceanic plate subducts
When the pressure is released the point at which it is released is called the focus
The ground surface immediately above shakes
The point on the surface where the maximum damage occurs is the epicentre
The oceanic plate breaks off and melts over a long time period
Newly formed magma rises at the continental plate and forms volcanoes and fold
mountains eg Andes
Destructive Plate Boundaries
• 2. The same process occurs where two plates of oceanic crust are
moving towards each other
• The denser of the two will be subducted
• e.g. This has formed the volcanic islands of Indonesia.
• As one plate moves under the other they can get stuck. This causes
pressure to build up.
• When the pressure becomes too much the plates jerk past each other,
causing an earthquake.
• Sometimes the magma rises offshore to form an island arc of volcanic
islands eg Caribbean islands and Japan
Ocean-ocean convergence
Continental-continental
convergence
Destructive Plate Boundaries
3. Collision - Two continental plates move towards each
other
• They are of equal density so there is no subduction
• The rocks are forced upwards to form fold mountains
• Eg The Indian and Eurasian plates are moving together
forming the Himalayas and Mount Everest is slowly
growing
• Earthquakes occur in these locations
• eg Large areas of countries can be affected by these
shallow highly damaging earthquakes eg India and Iran
• There is no volcanic activity in these locations
• The Kashmir earthquake of 2005 occurred in this way.
Constructive Plate Boundary
Constructive Plate Boundaries
•
•
•
•
•
•
•
•
•
•
Both volcanoes and earthquakes occur at constructive plate boundaries
Two plates move away from each other (diverge) due to convection currents in the
asthenosphere
Molten magma rises to fill the gap and forms new oceanic crust through volcanic
activity
Eg North American plate is moving away from Eurasian plate so Atlantic ocean is
getting 3cm larger – USA and Europe are moving apart
Mid oceanic ridges are formed eg The Mid Atlantic Ridge
Islands may be visible above the water’s surface as islands eg Iceland
Earthquakes occur here due to friction and pressure release.
There are many earthquakes here. These earthquakes tend to be shallow and
low magnitude as lava rises.
Most (not Iceland!) tend to be under the sea so pose little hazard to humans.
The plates do not move apart in a uniform way – some parts move faster than
others. This causes pressure to build up. When the pressure becomes too
much, the plate cracks, making a fault line and causing an earthquake. Further
earthquakes may also occur along the fault line once it has been created.
Constructive/Divergent
Conservative/Transform Plate
Boundary
Conservative Plate Boundaries
• Earthquakes also occur at Conservative boundaries
• A conservative boundary occurs where two plates are moving
past each other laterally
• The two plates get locked together in places and pressure builds
up. As with destructive boundaries, this causes the plates to jerk
past each other (or to crack forming fault lines) releasing the
energy as an earthquake
• For example, the Pacific plate is moving past the North American
plate.
• Many earthquakes occur along this boundary and its fault lines, e.g.
The San Andreas Fault runs through California.
• These earthquakes are often shallow and some are very high
magnitude.
Other earthquakes
• A small minority of earthquakes occur within
plates, usually involving the reactivation of
ancient faultlines eg Shropshire, UK
• Also earthquakes can occasionally occur due to
human activity such as dam and reservoir
building, which increase the weight and
therefore stress on the land. Earthquakes then
can happen where there is no record of
earthquakes.
• Eg Killari, India (1993)10,000 killed by an
earthquakes caused by dam construction.
Earthquake hazards
• Primary hazards – result from ground
movement and shaking. The surface
waves can cause buildings and
infrastructure (like pipelines and roads)to
collapse.
• Secondary hazards – soil liquefaction,
landslides, avalanches, tsunamis and
exposure to adverse weather. These
increase the death toll.
Read p 9-10 Pearson
Volcanoes
• Most of the world’s active volcanoes are at
constructive and destructive plate margins
as well as hotspots.
• However, hazard risk can also come from
dormant volcanoes that have not erupted
in living memory eg Mt St Helens
Constructive boundaries
• Constructive plate boundaries – most of the
magma that reaches the earths surface wells up
as volcanoes at ocean ridges, such as the mid
Atlantic ridge.
• These volcanoes are mostly on the sea floor and
do not represent major hazards except on
islands like Iceland.
• Rift valleys are also present where continental
crust is being stretched eg East African Rift
valley has 14 active volcanoes which can
produce big explosions.
East African Rift Valley
• The East African Rift is a geological zone
where continental plates in Eastern Africa
have developed a tectonic plate boundary.
A rift is a fracture in Earth's surface that
widens over time.
• This is a part of the larger Great Rift
Valley, where the African Plate is in the
process of dividing into two new tectonic
plates called the Somali Plate and the
Nubian Plate.
Destructive boundaries
• Destructive plate boundaries – some 80% of the
worlds most active volcanoes occur along
destructive boundaries.
• Soufriere Hills in Montserrat formed when 2
oceanic plates converged.
• When oceanic plates are sub ducted beneath
continental plates, explosive volcanoes, such as
Mt St Helens, are formed.
• The ‘Ring of Fire’ around the pacific has many
such volcanoes, including those in the
Philippines
Hotspots
• Volcanoes can occur far away from any plate
boundaries, e.g. in Hawaii
• These volcanoes are thought to be caused by in
localised areas of the lithosphere where there is
a high heat flow and where magma is rising
from a large chamber beneath the crust as a
plume.
• As a lithospheric plate moves over the hotspot a
chain of volcanoes forms.
• Areas like Hawaii are called volcanic hotspots
Hawaii hotspot
Volcanic hazards
• Volcanic Hazards – Apart from the local
impacts of lava flows the most
catastrophic impacts of volcanoes are
pyroclastic flows, ash falls, tsunamis and
mudflows/lahars.
• Read p 10-11 Pearson
Hazards: Distribution – Slides
Slides include a variety of rapid mass movements – eg
rock slides, debris flows, snow avalanches, rainfall
and earthquake induced landslides.
Land Slides
• Landslides are the 7th biggest killer with over 1,400
deaths per year, ranking above both volcanoes and
droughts.
• Most places that are vulnerable to landslides are
mountainous areas, often after abnormally heavy rain
and/or seismic activity.
• Human factors also play a part. Deforestation of hill
sides, eg SE Asia, and building upon hill slopes, eg
Hong Kong, are problematic if there are heavy rains.
Landslides
Snow avalanches
• Snow avalanches are concentrated in high
mountainous areas such as Rockies of N
America, S. Alps of N Zealand.
• Avalanches tend to occur on slopes that are
more than 35 degrees.
• On average 40 deaths occur in Europe and 100
in North America from avalanches.
• Recent research has reported that global
warming may be increasing avalanche activity.
• However trends in deaths have slowed due to
better management.
Read p 11 Pearson
Hydro meteorological Hazards:
• These extreme weather hazards tend to
be more widespread in their distribution .
• They are growing in frequency.
• They are increasingly unpredictable in
their locations.
Drought
• Droughts have a dispersed pattern.
• Over one third of the earth’s land surface has
some level of drought exposure.
• This includes 70% of the worlds people and
agricultural value.
• This means drought has a vast impact on the
worlds food security.
Causes of droughts
• 1. Variations in the movement of the inter
tropical convergence zone (ITCZ). As it
moves N or S through Africa it brings a
band of seasonal rain. In some years high
pressure bands expand which block the
rain bearing winds. This can lead to
famines in Ethiopia where farmers depend
on the rains.
• 2. E Nino can bring major changes to
rainfall patterns. It brings drought
conditions to Australia and Indonesia
• 3. Changes in mid latitude depressions. In
temperate regions like the UK depressions
bring rainfall. However if anticyclones (high
pressure) form and block the depressions
and persist (so they are forced northwards)
then very dry conditions may result.
This has occurred in the UK and France
(1976, 1989-92, 1995, 2003, 2006) and in
the USA midwest in the 1930s (forming the
dustbowl in the depression)
Drought hazards
Droughts can bring about:
• Failure of crops
• Loss of livestock
• Wildfires
• Duststorms
• Famine
• Population migration – refugees etc
• Economic impacts (especially in LEDCS)
Read p 7-8 Pearson
Flooding
• Flooding is a frequent hazard and it is
evident to some 33% of the world’s area,
which is inhabited by some 80% of the
world’s population.
• Regionally, high magnitude events are
frequent in India, Bangladesh and China.
Causes of flooding
• 1. The most common cause is excessive
rainfall relating to atmospheric processes,
like monsoon rainfall and tropical
cyclones. In temperate climates (like
Britain) a series of depressions can bring
excessive rainfall if heavy and prolonged.
• 2. Intense rainfall sometimes associated
with thunderstorms can result in flash
floods which can have a devastating
effect.
• 3. El Nino Southern Oscillation can bring
devastating floods – such as in
Mozambique in 1997 and 2006.
• 4. Rapid snowmelt can add water to rivers
which already have high discharges.
Flood hazards
•
•
•
•
•
Deaths through drowning and disease
Destruction of food crops
Loss of homes
Loss of infrastructure
Damages livelihoods and businesses
(MEDCS mainly)
• High insurance costs (MEDCS)
Read p 8-9 Pearson
Storms
• Includes tropical cyclones, mid latitude
storms and tornadoes.
Tropical Cyclones
• Tropical cyclones are huge storms with strong winds and torrential
rain.
• They are between 200-700 km in diameter
• They develop above sea water that is 26°C or higher. As warm,
moist air rises and condenses, it releases energy which increases
wind speed.
• Tropical cyclones lose strength when they move over land because
the energy supply from the warm water is cut off
• Most cyclones occur between 5° and 20° north and south of the
equator – more than 30° away from the equator the water isn’t warm
enough for cyclones to occur
• They tend to move westwards due to the east-west winds in the
tropics. For example, the trade winds move tropical cyclones
westwards across the Atlantic Ocean towards the Caribbean Sea
• Cyclones spin because of the Coriolis effect (the force that deflects
the path of winds due to the Earth’s rotation)
Tropical Cyclones
• Cyclones do not occur 0-5° either side of the equator because the
Coriolis effect is not strong enough to make them spin.
• The Coriolis effect is also why they move away from the equator
• Tropical cyclones are also known as hurricanes (when the occur in
the Atlantic Ocean or Caribbean Sea) and typhoons (when they
occur in the Pacific Ocean).
• Read P 7 Pearson
Hurricane Isabel
Tracking Isabel
Aftermath of Isabel
Tropical storm hazards
• Heavy rain causes damage as it leads to
floods and mudslides.
• High wind velocity can destroy structures
• And low central pressure can lead to storm
surges and coastal flooding.
• Devastation can occur eg Hurricane
Katrina
Could global warming lead
to an increase in the
strength of tropical
cyclones because of
increasing sea
temperatures?
Read p 7 Pearson
and p18 Philip Allan
Exam practice
• P 25 Pearson
Answer both Q a and b
Longer Exam Question
Describe and explain the global distribution of volcanoes (10 marks)
HINTS
• Make sure you have a clear structure – write an introduction, then describe
where they occur, followed by a section explaining why volcanoes occur
there
• In the introduction, define ‘Volcano’, e.g. ‘A volcano is a point where magma
has risen from below the Earth’s surface and been ejected above ground’.
• Next describe the global distribution of volcanoes, e.g. ‘Volcanoes can be
found all along the mid-Atlantic Ridge. They are also found around the edges
of the Pacific Ocean (Ring of fire), particularly around Japan and Indonesia,
and along the west coast of America (San Andreas Fault). They are also
found in the centre of the Pacific Ocean in Hawaii’.
• Now explain why volcanoes happen at each of the locations you have
described. Make sure you use appropriate language, e.g. ‘The mid-Atlantic
Ridge is a constructive boundary. Here the mantle is under pressure from
the overlying plates, and when they move apart pressure is released and the
mantle melts, forming magma. This is less dense than the plates so it rises
and can erupt to form a volcano.