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