The outermost layer of the Earth is the CRUST, which is divided into many "slabs" known as TECTONIC PLATES.
There are two types of crust:
- CONTINENTAL crust:- this is thicker and much less dense
- OCEANIC crust:- this is thinner and much more dense
Where the plates meet, it is known as either a BOUNDARY or a PLATE MARGIN.
There are three types of plate margin:
What is a DESTRUCTIVE margin?
- When an oceanic plate meets a continental plate, the oceanic plate (the more denser plate) is forced down into the mantle (below the crust) and is destroyed. This process often creates VOLCANOES and OCEAN TRENCHES. A destructive margin can also be where two continental plates meet however this has a different effect.
What is a CONSTRUCTIVE margin?
- When two plates (either oceanic, continental, or both) are moving apart from each other. EXAMPLE- MID ATLANTIC RIDGE Magma (molten rock) rises between the gap that has been created, and as it then cools, new crust is formed.
What is a CONSEVATIVE margin?
- When two plates slide past each other, or are moving in the same direction at different speeds. EXAMPLE- WEST COAST OF USA Here, crust is neither created nor destroyed.
Fold mountains are only formed at destructive margins.
They are created as the plates continuously collide, each time they collide, the sedimentary rocks that have been built up between them, are then folded and forced upwards, therefore forming mountains.
This means they are only then found at places where either there used to be a destructive margin or the currently is a destructive margin.
You can find fold mountains where an oceanic plate collides with a continental plate. EXAMPLE- THE ANDES IN SOUTH AMERICA. Also, you can find them where a continental plate collides with a second continental plate. EXAMPLE- THE HIMALAYAS IN ASIA.
Fold mountain areas will have many high mountains which are extremely rocky and will have steep slopes. They often have snow, glaciers and lakes.
What do humans use fold mountains for?
- FARMING:- higher slopes are not too good for growing crops so they are used for grazing animals such as mountain goats. lower slopes are then used for growing crops. steep slopes are sometimes terraced in order to make growing crops much easier.
- MINING:-fold mountains are a major source of metal ores. the steep slopes make the accessibility of mines rather difficult which is why "zigzag roads" have been carved into the sides of the mountains.
- HYDRO-ELECTRIC POWER:-the steep sided mountains and the high up lakes make fold mountains ideal for generating hydro electric power.
- FORESTRY:- fold mountain ranges are ideal for certain types of tree EXAMPLE- CONIFERS They're grown on the steep slopes and are used for things such as fuel, building material, paper and furniture.
- TOURISM:- the scenery of fold mountains can be extremely attractive for tourists. tunnels have been drilled through some mountains in order to make straight, fast roads. this improves communications for tourists and makes getting to other places much easier for people who live in the areas.
Earthquakes occur at all three types of plate margin. They are caused by the tension that builds up at the boundaries.
DESTRUCTIVE: tension builds up when one plate gets stuck as its moving down past the other and into the mantle.
CONSTRUCTIVE: the tension builds up along cracks within the plates as they move away from each other
CONSERVATIVE: tension builds up when plates that are grinding past each other get stuck.
The FOCUS is the point at which the shock waves spread out from; it is the starting point of the earthquake. Nearer to the focus, the waves are much stronger and will cause much more damage.
The EPICENTRE is the point on the earth's surface and is found directly above the focus.
Weaker earthquakes can occur quite frequently however stronger earthquakes are relatively rare.
Earthquakes can be measured by using two different methods:
RICHTER SCALE:- this measures the AMOUNT OF ENERGY RELEASED by an earthquake (the magnitude). Magnitude is measured by using a seismometer. The Richter scale does not have an upper limit and is logarithmic (meaning that an earthquake with a magnitude of 5 is ten times more powerful than an earthquake with a magnitude of 4) Most people cannot feel earthquakes with a magnitude of 1 or 2. Major earthquakes have a magnitude of above 5.
MERCALLI SCALE:- this measures the EFFECTS of an earthquake. The effects are measured by asking eye witnesses for observations of what happened. Observations can be in the form of photographs or words. The scale is between 1 and 12.
Earthquakes - Impacts
Earthquakes have PRIMARY and SECONDARY impacts.
Primary impacts are the immediate effects of the ground shaking. Whereas secondary impacts are the effects that happen later on.
PRIMARY IMPACT EXAMPLES:
Buildings and bridges collapse; people are injured or killed by buildings collapsing; roads, railways, airports and ports are damaged; electricity cables are damaged, cutting off supplies; gas pipes are broken, causing leaks and cutting off supplies; telephone poles and cables are destroyed; underground water and sewage pipes are broken, causing leaks and cutting off supplies.
SECONDARY IMPACT EXAMPLES:
Earthquakes can trigger landslides and tsunamis- these destroy more buildings and cause more injuries and deaths; leaking gasd can be ignited and start fires; people are left homeless; people may suffer psychological problems if they knew people who died or if they lose their own home etc; there's a shortage of clean water supplies and a lack of proper sanitation making it easier for diseases to spread; roads are blocked so aid and emergency vehicles cannot get through; businesses are damages or destroyed causing unemployment.
Earthquakes - Impacts
The impacts of earthquakes are far more severe for poorer countries.
- There's more low quality housing in poorer countries which are less stable and are therefore destroyed more easily.
- The infrastructure is often worse. poor quality roads make it difficult for emergency services for reach the injured people, leading to more deaths.
- Poorer countries have less money to help protect from earthquakes by making buildings earthquake proof etc. they do not have enough money or resources to react straight away to earthquakes, therefore more people are affected by secondary impacts.
- Health care is often worse. many hospitals do not have enough supplies to deal with lots of patients after an earthquake, meaning more people die from treatable injuries.
Earthquakes - Reducing Impacts
BUILDINGS:-Buildings can be designed in order to withstand earthquakes. Large computer controlled concrete couterweight moves in opposite way to earthquake cross-bracing allows more flexibilty and prevents cracking, and rubber shock absorbers in foundations are all good techniques.
PLANNING:- Future development can be planned in order to avoid high risk areas, reducing the number of buildings destroyed in earthquakes. Firebreaks can be made to prevent fires from spreading. Emergency services can train and prepare for such disasters, which reduces the number of people likely to die. Governments can plan evacuation routes for getting people out of dangerous areas quickly and safely after an earthquake, this reduces the number of people killed or injured by things like fires.
EDUCATION:- Governments and other organisations can educate people about what to do if there is an earthquake and how to evacuate. People can be taught how to make sufficient survival kits containing food, water, a torch, a radio and batteries, reducing the chances of people dying if they are stuck in an area.
AID:- Poorer countries already affected can receive aid from governments and organisations. The aid helps reduce the impacts (for example money aid is used to rebuild homes and reduce homelessness)
1) What is meant by the term 'focus'?
2) Where is the 'epicentre' found?
3) What are the three types of plate margins?
4) What two methods are there for measuring Earthquakes?
5) List the four ways to help reduce the impacts of an Earthquake?
6) Give two examples of primary and secondary impacts.
7) What do people use fold mountains for?
8) Where are fold mountains found?
9) What is the difference between coninental and oceanic crust?
10) Why are poorer countries more severely affected by earthquakes?