Geography Revision
Year 9 and 10
The layers of the Earth
Destructive Plate Boundary
Constructive Plate Boundary
The Kobe Earthquake – Richer part of
the world
Kobe is located in the south
east of Japan, near a
destructive plate margin. It is a
megacity and has one of the
largest container ports in the
World. Although further from
a plate margin than most of the
cities in Japan, Kobe is still
found on a fault line.
At this plate margin, the Pacific plate
is being pushed under the Eurasian
plate, stresses build up and when they
are released the Earth shakes. This is
known as an earthquake happening along
a subduction zone. The focus was only
16km below the crust and this
happened on the 17th Jan 1995 at
5.46am. 10 million people live in this
area.
The earthquake that hit
Kobe during the winter of
1995 measured a
massive 7.2 on the
Richter scale (or 6.9 on
the more current Moment
magnitude scale).
The Effects
The effects of this earthquake
were catastrophic for an
MEDC. despite some buildings
having been made earthquake proof
during recent years many of the
older buildings simply toppled over
or collapsed. A lot of the
traditional wooden buildings survived
the earthquake but burnt down in
fires caused by broken gas and
electricity lines.
More than 5000 died in the quake
300,000 were made home less
More than 102,000 buildings were destroyed
in Kobe, especially the older wooden
buildings.
Estimated cost to rebuild the basics = £100
billion.
The worst affected area was the centre.
This was because it was built on
easily moving ground which LIQUIFIED,
allowing building to collapse and sink.
The worst effected area was in the central part of Kobe including the main docks and port area. This area is built on soft and
easily moved rocks, especially the port itself which is built on reclaimed ground. Here the ground actually liquefied and acted
like thick soup, allowing buildings to topple sideways.
Emergency aid for the city needed to use damaged roads but many of them were destroyed during the earthquake.
Raised motorways collapsed during the shaking. Other roads were affected, limiting rescue attempts.
Many small roads were closed by fallen debris from buildings, or cracks and bumps caused by the ground moving.
The earthquake occurred in the morning when people were cooking breakfast, causing over 300 fires, which took over 2 days to
put out.
Haiti Earthquake – poorer part of the
world
Haiti is the poorest country in the Western
Hemisphere, its GDP is only $1,200 per person,
207th in the world, its HDI is incredibly low
at 0.404, 145th in the world, and 80 % of its
9.7 Million people live below the poverty line.
Port Au Prince, the capital, is on a fault line running off the Puerto Rico Trench, where
the North American Plate is sliding under the plate. The fault line is a strike slip
fault, the Caribbean Plate south of the fault line was sliding east and the smaller
Gonvave Platelet north of the fault was sliding west. There were many aftershocks
after the main event. The earthquake occurred on January 12th 2010, the epicentre
was centred just 10 miles southwest of the capital city, Port au Prince and the quake
was shallow—only about 10-15 kilometres below the land's surface. The event measured
7.0 on the Richter Magnitude scale.
The Effects
•316,000 people died and more than a million people were made homeless, even in
2011 people remained in make shift temporary homes. Large parts of this
impoverished nation where damage, most importantly the capital Port Au Prince,
where shanty towns and even the presidential palace crumbled to dust. 3 million
people in total were affected. Few of the Buildings in were built with earthquakes in
mind, contributing to their collapse
•The government of also estimated that 250,000 residences and 30,000 commercial
buildings had collapsed or were severely damaged. The port, other major roads and
communications link were damaged beyond repair and needed replacing. The clothing
industry, which accounts for two-thirds of 's exports, reported structural damage at
manufacturing facilities. It is estimated the 1 in 5 jobs were lost as a result of the
quake
•Rubble from collapsed buildings blocked roads and rail links.
•The port was destroyed
•Sea levels in local areas changed, with some parts of the land sinking below the sea
•The roads were littered with cracks and fault lines
Predicting and preparing for
earthquakes
Prediction involves trying to forecast when an earthquake
will happen. Japan tries to monitior earth tremors with a belief
that warning
can be given, but this did not happen at Kobe. Foreshocks do
occur, but on a timescale useful to evcuation. Experts know
where earthquakes are likely to happen, but struggle to
establish when. Even looking at the time
between earthquakesin a particular area does not seem to
work. Similarly, experts struggle to pinoint exactly where
along a plate margin they will occur. Animal behaviour has
been used in the past
Protection invloves building to an appropriate standard
and using designs to withstand movement.
Preparation involves hospitals, emergency services
and inhabitants practising for major diasters, including having
drills in public buildings and a code of practice so that people
know what to do to reduce the impact and increase their
chance of survival.
Monitoring Volcanoes
Monitoring gas emissions
As Magma rises into magma chambers gases escape for the depressurising
magma. One of the main gases is Sulphur Dioxide, and if its quantity in escaping volcanic gas increases
this can signal the start of a major eruptive sequence.
In the Mount Pinatubo Volcanic event the amount of Sulphur Dioxide increased by 10 times in 2 weeks.
Directly before eruptions the Sulphur Dioxide level can then drop rapidly and scientists think this is due to
the sealing of gas passages by hardened magma. This increases pressure in the volcano and leads to
explosive eruptions.
Ground deformation
The movement of magma within the lithosphere can deform the ground above, this has been witnessed at
Yellowstone beneath Yellowstone Lake. This swelling of the volcano signals that magma has collected near
the surface. Scientists monitoring an active volcano will often measure the tilt of the slope and track
changes in the rate of
swelling. Mount St Helens showed this prior to its eruption in 1980.
Thermal monitoring
Both magma movement, changes in gas release and hydrothermal activity can lead to thermal emissivity
changes at the volcano's surface. We can use satellite imagery, activity of minor extrusive features such as
geysers and hot springs and mapping to monitor this.
Satellite Images and Remote Sensing
Remote sensing is the use of satellites to detect things about the Earth’s surface. This is useful
for monitoring any changes in volcanoes at the surface.
Using satellites we can monitor the thermal activity of the volcano to check for upwelling magma, we can
check for escaping Sulphur dioxide using gas sensing and we can look to see if the ground is deforming by
checking before and after images of the ground. The satellite can also judge if the ground is being uplifted
by measuring the distance between the satellite and the ground.
Some other useful signs
Some other useful warning signs:
·
Earthquakes are a frequent sign of an impending eruption and their frequency
and strength can be recorded
·
Bulging on one side of the volcano - the swelling is obvious and a clear sign of
magma moving
·
Tiltmeters can identify small, subtle changes in the landscape
·
Global Positioning Systems (GPS) use satellites to detect movement of as
little as 1mm
·
Satellites can detect changes in surface temperature
·
Digital cameras can be used to check for changes in volcanic activity
·
Gases being emitted from the vent change before an eruption
·
Robots called 'spiders' are often deployed to look inside the rim of the volcano
·
The past frequency of eruption is often investigated: the gap between
eruptions and the pattern of lava flows, ash movement and lahars can tell people
about how the volcano is likely to behave
Tropical Storms
How do Tropical Storms form?
Hurricanes need a lot of heat to form and a sea surface temperature of at least 26°C, which is why they
usually occur over tropical seas. They also need to be between 5 and 20° north or south of the equator.
It works like this:
1. When this warm and wet air rises, it condenses to form towering clouds, heavy rainfall. It also
creates a low pressure zone near the surface of the water.
2. Rising warm air causes the pressure to decrease at higher altitudes. Warm air is under a higher
pressure than cold air, so moves towards the ‘space’ occupied by the colder, lower pressure, air. So
the low pressure ‘sucks in’ air from the warm surroundings, which then also rises. A continuous
upflow of warm and wet air continues to create clouds and rain.
3. Air that surrounds the low pressure zone at the centre flows in a spiral at very high speeds - anticlockwise in the northern hemisphere - at speeds of around 120 km/h (75 mph).
4. Air is ejected at the top of the storm – which can be 15km high – and falls to the outside of the
storm, out and over the top, away from the eye of the storm. As this happens, it reduces the mass
of air over the ‘eye of the storm’ - causing the wind speed to increase further. Some ejected air also
cools and dries, and sinks through the eye of the storm, adding to the low pressure at the centre.
5. The faster the winds blow, the lower the air pressure in the centre, and so the cycle continues. The
hurricane grows stronger and stronger.
6. Seen from above, hurricanes are huge circular bodies of thick cloud around 450 km (300 miles)
wide. The cloud brings heavy rain, thunder and lightning.
7. In the centre is the eye of the hurricane, about 45 km across (30 miles) across. Often there will
be no clouds in the eye. Seen from below it will seem calmer, with a circle of blue sky above. The
eye is formed because this is the only part of the hurricane where cold air is descending.
8. In the northern hemisphere, the prevailing easterly tropical winds tend to steer hurricanes toward
land - although their course is unpredictable. As hurricanes move inshore, their power gradually
reduces because their energy comes from sucking up moist sea air.
Tropical Storms and Climate Change
• Global warming by the end of the 21st century will likely cause tropical cyclones
globally to be more intense on average (by 2 to 11%).
• This change would imply an even larger percentage increase in the destructive
potential per storm, assuming no reduction in storm size.
• Anthropogenic warming by the end of the 21st century will likely cause tropical
cyclones to have substantially higher rainfall rates than present-day ones, with a
model-projected increase of about 10-15% for rainfall rates averaged within about
100 km of the storm center.
Hurricane Katrina
•Katrina was a category 4 storm.
•Storm surges reached over 6 metres in height.
•New Orleans was one of the worst affected areas because it lies below sea
level and is protected by levees. These protect it from the Mississippi River
and Lake Ponchartrain. The levee defences were unable to cope with the
strength of Katrina, and water flooded into the city.
•Despite an evacuation order, many of the poorest people remained in the
city.
•People sought refuge in the Superdome stadium. Conditions were
unhygienic, and there was a shortage of food and water. Looting was
commonplace throughout the city. Tension was high and many felt
vulnerable and unsafe.
•1 million people were made homeless and about 1,200 people drowned in
the floods.
•Oil facilities were damaged and as a result petrol prices rose in the UK and
USA.
There was much criticism of the authorities for their handling of the
disaster. Although many people were evacuated, it was a slow process
and the poorest and most vulnerable were left behind.
$50 billion in aid was given by the government.
The UK government sent food aid during the early stages of the recovery
process.
The National Guard was mobilised to restore and maintain law and order
in what became a hostile and unsafe living environment.