restless earth booklet, revision, tgaw, geography
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The Restless Earth Revision
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
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.
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
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
boundary is where the
Nazca plate dives
underneath the South
American plate. This
has caused volcanoes,
earthquakes and the
formation of the Andes
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
boundary can be found
is moving away from
the Eurasian plate.
This has caused
to form and has
Conservative Plate Boundaries
Also known as passive plate
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
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.
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
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
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.
VOLCANO CASE STUDIES RICH WORLD- Eyjafjallajkull,
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 couldnt 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 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
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:
1The Richter scale measures the magnitude of an earthquake using an instrument called a
seismograph. The Richter scale is logarithmic, meaning that an earthquak