restless earth booklet, revision, tgaw, geography
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The Restless Earth Revision
Name:
Plate tectonics
The Earth's crust is made up of seven principal tectonic plates and numerous other smaller
plates. The plates are sections of the crust that "float" on the mantle, which is made up of
molten rock. Where the plate's meet, huge forces mean that they can form features such as
volcanoes, fold mountains, deep-sea trenches and earthquakes.
There are two main types of tectonic plate.
Oceanic crust is often only about 5km thick, but is very dense.
Continental crust is considerably thicker, often being approximately 30km deep, but is less
dense.
The Earth's Tectonic Plates all move very slowly on the mantle, meeting along the four main
boundaries that can be found in the next section. The plates move due to convection currents
in the mantle. These are hot currents of molten rock that slowly move within the mantle and
cause the plates above them to move, usually by as little as one or two centimetres each year.
Plate Boundaries
Destructive Plate Boundaries : Also known as convergent boundaries or compressional boundaries.
•These cause violent volcanoes and earthquakes, as well as deep-ocean trenches and fold
mountains.
•An oceanic plate and continental plate move towards each other.
•The denser oceanic plate dives under the lighter continental one, creating a deep ocean trench.
•As the oceanic plate goes deeper into mantle it melts in the subduction zone, due to friction and
the increased temperature.
•The newly molten rock is lighter that that which surrounds it, so it will rise towards the surface and
cause volcanoes on the earth's surface.
•The continental crust is crumpled by the collision of the two plates creating Fold Mountains.
•If the magma rises offshore it will form an Island Arc, like the West Indies and Japan.
A good example of a
destructive plate
boundary is where the
Nazca plate dives
underneath the South
American plate. This
has caused volcanoes,
earthquakes and the
formation of the Andes
Mountain Range.
Constructive Plate Boundaries
Also known as divergent or tensional boundaries.
Although often not as violent as those on destructive plate boundaries, volcanoes and
earthquakes do occur on constructive plate boundaries. They also cause mid-ocean
ridges to form.
Two plates move away from each other.
Molten rock (magma) rises from the mantle to fill the gap between the two plates.
This forms a mid-ocean ridge.
Volcanoes can also form here, along the edges of the plate boundary, due to the rising
magma. These volcanoes are called shield volcanoes.
A good example of a
constructive plate
boundary can be found
where the
NorthAmerican plate
is moving away from
the Eurasian plate.
This has caused
theMid-Atlantic ridge
to form and has
created Iceland
through volcanic
activity.
Conservative Plate Boundaries
Also known as passive plate
boundaries.
The main effects of a
conservative plate boundary
are earthquakes, which can be
fairly violent and frequent.
Two plates slide past each
other, without creating or
destroying any land.
As they move past each other
they often get stuck, building
up great pressure until finally
they jolt past each other. This
sudden movement is what
causes earthquakes.
The best-known example of a
conservative plate boundary is the San Andreas Fault, where the North American and Pacific
plates are actually moving in the same direction, but at a different speed.
Collision Margins
Where two continental crusts
collide neither can sink.
Instead they push into each
other forcing material to be folded up
into huge mountain ranges.
Often this movement and
pressure can cause earthquakes, but
no volcanoes will occur on these
boundaries.
The best example is found where the
Indian plate collided with the
Eurasian plate to form the Himalayas.
Volcanoes Volcanoes are formed along two types of plate boundary: destructive and constructive
boundaries. The basic shape of a volcano is similar throughout the world, however there are
many factors which influence how the volcano is built.
Volcanoes occur where molten rock (magma) is allowed to escape to the surface of the
earth. This usually occurs at plate boundaries through cracks in the crust called vents.
Once it has reached the surface, the magma becomes known as lava. The composition of the
lava determines the shape of the final volcano.
Volcanoes also throw out ash, steam, dust, pumice, and gases, which can be poisonous.
However it is the lava that mainly helps to shape the volcano. There are three main volcanic
cones: acid lava cones, composite cones and basic lava cones.
Acid cone volcanoes are steep sided
due to the fact that the lava is thick
and acidic, meaning that it doesn't
flow far before solidifying, for example
Mt. Pelee.
Shield cone volcanoes are wide-based, with gentle
slopes. Their lava is runny and thin, which means that it
can travel a long way before cooling and solidifying.
Often these eruptions are non-violent and can last for
years, such as the one at Kilaueain Hawaii.
Composite Cone volcanoes are steep-sided,
and made of alternate layers of ash and lava.
Often the lava cools to create a plug in the
vent, meaning that a huge explosion is needed
to remove it. The best example is Mt. St.
Helens.
VOLCANO CASE STUDIES RICH WORLD- Eyjafjallajökull,
Iceland April 2010 POOR WORLD- Mt. Pinatubo, June 1991 (The Philippines)
CAUSES North American \Eurasian tectonic plates move apart on Constructive Plate Boundaries
•Mt. Pinatubo had not erupted for over 600 years. Its slopes had become fertile, well-cultivated paddy fields. People did not expect it to erupt •On 12th June the mountain erupted. Measurements and predictions by scientists had meant that over 200,000 people had been evacuated by the time that the mountain erupted.
EFFECTS/IMPACTS Primary: 1. 800 people were evacuated from their homes. 2. The eruption produced a giant ash cloud which went on to cancel all flights, leave thousands of people stuck in foreign countries and causing millions of pounds in economic losses. 3. The eruption released gases such as carbon dioxide which contribute to global warming. 4. The eruption melted a glacier which caused huge floods and damaged land, homes and disrupted many lives. Secondary 5. Flight cancellations impacted tourism in other countries meaning even more money was lost. 6. The thousands of people ‘stuck’ abroad meant that they couldn’t get to their jobs at home. Businesses lost out on a lot of money because of this. 7. The Kenya flower industry was impacted because it could export its flowers to other countries. This meant they lost out on 6-7 million Kenyan shillings per day. Kenya is a poor country (LEDC) therefore the impact of this was significant. 8. There was a rise in respiratory problems (breathing problems) because of the ash. 9. All flights were cancelled because the ash could clog up
•PRIMARY: The eruption sent a huge cloud of gas and ash up into the atmosphere. Torrential rain then caused much of the ash to be deposited back on the ground as mud. •An area of over 600km in radius had ash falls from the volcano, with nearly 50cm falling near the mountain itself. •Most terrifying of all were the lahar's that was produced. These are huge, speeding mudslides, formed by the ash and the torrential rain that swept down covering entire villages in a think layer of mud, often up to 10 feet deep. They destroyed over 200,000 homes and covered 50,000 hectares of farmland. •SECONDARY: Although a relatively small number of people were killed (350), the effects of the eruption were devastating. Diseases such as malaria and cholera spread quickly in the refugee camps set up to help the evacuee's. Over the next few years, heavy rains caused ash and dust from the eruption to create more devastating lahars.
the engines on planes and cause them to fail.
RESPONSES -Insurance companies recovered travellers losses -Scientific monitoring of volcano was improved by increasing government investment -People stuck abroad and had bank wavers to recover costs -Technological investments were made so engineers can better predict where ash paths -Engineer teams received greater support training so they could be better equipped when dealing with future hazards
There were insufficient funds to rebuild the area; over 10 years later the region is still in recovery mode Aid was given from rich world countries such as the British Red Cross to buy vital medical supplies
Earthquakes
Main Concepts
Earthquakes occur along faults, which are large cracks in the earth's crust. Most of these are
associated with the larger plate boundaries, along which the largest earthquakes usually
occur.
They are caused by the sudden jerking movements of the fault, either laterally or vertically,
and are almost impossible to predict.
Earthquakes are measured in two ways:
1•The Richter scale measures the magnitude of an earthquake using an instrument called a
seismograph. The Richter scale is logarithmic, meaning that an earthquake measuring 7 is 10 times
more powerful than one measuring 6, and 100 times more powerful than one measuring 5.
2 •The mercalli scale measures the damage caused by an earthquake. It rates each quake from I to
XII, depending on how much damage was done, and is dependent not only on the magnitude of
depth of the earthquake.
The point at which an earthquake actually begins, deep below the earth's surface is called the focus.
If the focus is deep then the effects of the earthquake may be less as the shockwaves have more
rock to move through. Obviously this also depends on what type of rock it is. The point directly
above the focus, on the earth's surface, is called the epicentre. The effects of the earthquake are
usually worst here, and then radiate out from this spot.
Effects of Earthquakes
The effects of an earthquake can be easily split up into two sections.
Primary effects are those that occur immediately as the earthquake happens. These include
buildings collapsing, roads and bridges being destroyed and railway lines being buckled. All occur
due to the shaking of the ground.
Secondary effects are the subsequent effects of the quake, and can be even more devastating then
the primary ones. The main secondary effects are:
•Fires: usually from ruptured gas lines. This was the main cause of death and damage after the San
Francisco earthquake in 1906.
•Tidal waves: A tidal waves caused by an earthquake is called a tsunami. They can travel very
quickly across entire oceans, before engulfing land 1000's of miles away. The 1964 Alaskan
earthquake caused considerable damage in several Californian coastal areas. Although Los Angeles
has escaped so far, its is still considered to be a tsunami hazard prone area.
•Landslides can often be triggered by earthquakes, causing huge amounts of material to be moved
very quickly. This is actually what occurred just before the volcanic eruption on Mt. St. Helens. They
are most likely to occur where the land is steep, saturated or weak.
•Diseases can spread very quickly in the unsanitary conditions often left behind by massive
earthquakes. Water becomes contaminated very quickly, and in Less Economically Developed
Countries (LEDC's) especially; access for the medical services can be badly hampered by the damage
caused by the quake. The most common diseases to be associated with earthquakes are therefore
water-borne ones like cholera and typhoid.
EARTHQUAKE CASE STUDIES
RICH WORLD- Kobe, Japan 1995 POOR WORLD- Haiti 12th January 2010.
CAUSES •The earthquake occurred at 5.46am on the 17th January 1995. It measured 7.2 on the Richter Scale and lasted 20 seconds. •Kobe lies on the Nojima fault, a destructive boundary, where the Philippine plate dives below the Eurasian plate. This plate boundary is the reason for Japan's existence but also means that there is a constant earthquake threat. •Kobe was unlucky in the sense that the focus of the earthquake was very close to the surface and the epicentre was right beside the city.
Haiti lies on a conservative plate boundary this means earthquakes are likely. Haiti lies between the Caribbean and North American tectonic plate. The earthquake measured 7.0 magnitude on a seismograph. The earthquake struck an area where lots of people live causing wide scale damage
EFFECTS/IMPACTS
•Primary effects included a death toll of approximately 5,500, with another 30,000 injured and 250,000 made homeless. Over 100,000 buildings collapsed. Infrastructure damage included a 1km stretch of elevated road, numerous railway bridges, and 120 of the city's 150 quays. •Secondary effects included the fact that electricity, gas, water and sewage systems were all hugely disrupted. Emergency services found it very difficult to get into the city due to the massive destruction of the roads. Many temporary shelters were required, as well as food and medicines. Cold weather meant that diseases spread quickly.
• Primary An estimated 300,000 people were injured in the initial aftermath The buildings in Port-Au-Prince and other areas of Haiti were in very poor condition in general and were not designed or constructed to be earthquake resistant meaning many were destroyed The dust from the rubble polluted the air. Secondary Haiti doesn’t have enough doctors to help people who have been hurt. Thousands of people were left homeless because Haiti couldn’t afford to place people in shelter. There was no where for people to be evacuated to. This meant people couldn’t get to safety. Many people had to cope with the sadness of losing family members. 30,000 commercial buildings had collapsed or were severely damaged. Haitian Government reports that between 217,000 and 230,000 people had been
identified as dead. Many animals habitats where destroyed by the earthquake. Haiti has very poor roads (infrastructure). This meant emergency services couldn’t get to the people who needed help.
RESPONSES •A week after the earthquake fires still were burning, 2 million homes still were without power and 1 million were without water. The fires destroyed over 7,000 more homes. Hundreds of aftershocks, 74 strong enough for people to feel, meant people were too afraid to return to their homes for weeks after the event. •Tough new laws, building codes and emergency plans were brought in after criticism of the Japanese Government. Work is continuing to try to predict future earthquakes, but as yet there is very little way of giving any significant warning time.
People who live in Haiti could move away from the plate boundary and live somewhere safer. Emergency services could have better training in coping with earthquake disasters. The Haiti government had to pay millions of dollars to try to recover from the disaster. Firemen from the USA took aid for the Haitian victims. In future more aid could be given from rich countries. Doctors from other countries could go and work in Haiti to improve the health care. Pop stars made a charity single to help support the victims of the Haiti earthquake. Haiti could rebuild buildings that are earthquake proof so they won’t fall down. Disease increased because the streets were unsafe, unclean and there was no access to clean water. There was not enough food to go around from aid agencies. Money was lost because people couldn’t get to work. Resident sleep in the streets of Port- au-Prince. Rich countries donate millions to help in recovery operation.
The Formation of Fold Mountains
Form along both destructive and collision plate boundaries, in other words where two plates are
pushing towards each other.
The best examples are the Himalayas, the Rockies, the Andes and the Alps, all of which are huge
fold mountain ranges caused by the collision of two plates.
The general theory is that as two plates, with land masses on them, move towards each other they
push layers of accumulated sediment in the sea between them up into folds. Thus most fold
mountains will continue to grow, as the plates constantly move towards each other.
The Formation of Fold Mountains at Destructive Plate Boundaries: •As already seen, at a destructive plate boundary the oceanic plate is subducted beneath the
continental one. The molten material then rises to the surface to form volcanoes, either in an island
arc (e.g. the West Indies) or on the continental land mass (e.g. the volcanoes of the Andes). In both
cases Fold Mountains can be formed.
•When the Nazca plate dives under the South American one, their motion forward also has been
pushing sediment together. This, over millions of years, has been pushed up into huge fold
mountains: The Andes. Within them there are also volcanoes as the mountains are above the
subduction zone.
•If an island arc has been formed, the same idea occurs. Over millions of years the movement of the
two plates together will push the island arc nearer to the continent. As this occurs the sediments on
the seabed are folded up to become huge mountains.
The Formation of Fold Mountains at Collision Margins: •These occur less frequently, but two excellent examples are the Himalayas, where the Indian plate
is moving North and East towards the
stationary European plate, and the Alps,
formed by the collision between the
African and Eurasian plates.
•In these examples both plates are
Continental ones, and so can neither sink
nor be destroyed. The material between
them is therefore forced upwards to form
the mountains.
•For the Himalayas the material that now
forms the mountains was originally on the
bottom of the non-existent Tethy's Sea. As the Indian plate pushed towards the Eurasian one, the
sediments were folded up to form the Himalayas, leaving the only trace of the sea to be the
fossilised shells that you can find high up in the mountains.
Human uses of Fold Mountains
Humans use Fold Mountains for a wide variety of purposes:
Farming is a primary activity in all of the fold mountain ranges around the world. Mainly, due to
the height and steepness of many of the slopes, this is restricted to cattle and sheep farming.
However in the foothills of the Himalayas the Nepalese people use terraces in the mountainside to
help them grow crops, and some southern facing Alpine slopes are used for vines and fruits.
In the Alps a system called transhumance was used. This basically is the seasonal movement of
grazing animals between the high ground in the warmer summer months and the valley floors in the
colder autumn months. Nowadays transhumance is a little outdated as modern technology has
meant that farmers can stay in one place all year.
Tourism is another major use of the Fold Mountains of the world. Because they are in more
economically developed countries, the Alps and the Rockies are perhaps the best examples of the
impact of tourism. However, it is an increasing industry in both the Andes and the Himalayas, as
people look for less crowded places to go to.
•The main tourist attraction in the Rockies and the Alps is skiing. Hundreds of thousands of people
ski each year and this has brought great changes and problems to the main areas.
•The increase in tourism has meant much-improved infrastructure, a huge increase in hotels and
restaurants and the development of entire resorts. It has brought a large amount of much needed
money into these areas and allowed local people to diversify from farming into many other jobs.
•Fold Mountains have a lot of other things to attract visitors. These include hill walking, the
attractive scenery, river rafting, and climbing. All these have contributed to areas in the Alps and
the Rockies becoming all year round holiday resorts.
Forestry is another big business in these mountainous regions. Examples of cultivated coniferous
forests can be seen in the Alps, where the trees have been deliberately planted as crops. However in
the foothills of the Himalayas large-scale deforestation is also taking place, with logging companies
cutting down vast tracts of the deciduous rainforest there.
Many of the Fold Mountain regions of the world are prime spots for the generation of hydroelectric
power (HEP). They have a plentiful supply of water; deep, narrow valleys with quick flowing rivers,
and they are sparsely populated, meaning that few people are displaced when a reservoir is created.
The HEP is then used either for electricity in cities some distance away, or as a power source for
local industries, such as saw and paper mills.
CASE STUDY- France, Alps
The Problems of Living in Fold Mountain Areas:
•Mountainous regions are particularly difficult to build in due to the steep sided valleys and cold
climate. Roads and other communications links have to snake their way up wherever they can, and
often these roads are not big enough to adequately service a large community.
•The climate is very cold and wet, meaning that most industrial and agricultural activity is
difficult. For farmers they have a very short growing season, and it is difficult to use machinery on
the steep slopes.
•Avalanches are a constant threat, as was seen to devastating effect in Ranrahirca, Peru, in 1962.
Huge amounts of money are spent each year to try and combat the avalanche threat, especially with
the large amount of tourists using the mountains.
The Impact of Natural Hazards
Rich world vs Poor world (responses)
Natural hazards will affect More Economically Developed Countries (MEDC's)in a differing way to
those that occur in Less Economically Developed Countries(LEDC's).
•Health Care: MEDC's have the medical resources and money to quickly get appropriate aid to
areas after a natural disaster. LEDC's often have to rely on aid from overseas as their health system,
which is inadequate. This overseas aid takes time to arrive, which could mean far more casualties.
•Emergency Services: In MEDC's who have a volcanic or earthquake risk, such as Japan and
New Zealand,there are well thought out emergency procedures. Practices in schools and places of
work mean that people know what to do it the event of a natural disaster. The Government's and
military have special emergency plans to help with the situation.
Often LEDC's do not have these emergency plans, and so (as seen in Haiti)far more damage can be
done before the emergency services reach the stricken area.
•Building Technology: Countries such as Japan and the United States have been at the
fore front of developing buildings that have more chance of resisting an earthquake. Most houses in
San Francisco are made of wood, to make them more flexible and allow them to move with the
quake. Larger skyscrapers are built with flexible foundations, which literally allow them to sway
during a quake, rather than being rigid and falling down. Many countries in areas prone to natural
hazards have building codes to say where they can and cannot build, and how high the buildings can
be. New Zealand is a good example of where this occurs. LEDC's don't tend to have the technology
available or money to pay for it, and soften their buildings are very susceptible to earthquakes. One
example was the Armenian earthquake in 1988, which was 0.1 less on the Richter scale than Kobe,
but killed 20,000 more people. Most of the Armenian houses were built of stone and so collapsed
instantly.
•Scientific Prediction: Scientists work throughout the world, trying to predict earthquakes
and volcanoes. So far they have found it very difficult to predict earthquakes, although scientists
monitoring the San Andreas Fault in California have planted a huge number of seismographs in the
ground to try to detect even the faintest of tremors. Volcanoes generally are easier to predict,
although the specific time of the eruption is not so easy to do. Scientists can measure changes within
the mountain that helps them to predict that the volcano is going to erupt. This usually allows the
Local Authorities sufficient time to evacuate people from the danger area (as seen at both Mt. St.
Helens and Mt. Pinatubo). However they still find it very difficult to accurately predict the size of the
eruption.MEDC's do tend to have more investment for this type of research and development than
LEDC's.
•Recovery: MEDC's tend to be able to recover quickly from a natural disaster, due to having the
investment and technology needed to return the area to as good as new as soon as possible.
Because LEDC's often have to rely on aid from overseas, this quick recovery is often impossible for
them
Buzz words!
Can you write a definition for each?
Human
Physical
Long term
Short term
Primary impact
Secondary impact
Social
Economic
Environmental
Sustainability
Cause
Impact
Response
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