Fragile World Autumn 1 Half Term Assessment Revision Flashcards
What is Continental Drift?
Continental Drift was a theory first created by Alfred Wenger in 1912, which stated that big land masses such as continents could move across the Earth’s surface.
Evidence to show Continental Drift
- The Jigsaw Fit
- Convection Currents
- Studying Fossils
- Geological Patterns
- Paleomagnetism
What is the Jigsaw Fit?
The evidence of the Jigsaw Fit, is that some of the Continents almost look like they were connected to each other can you can fit most of them together like a jigsaw puzzle. An example would be the East Coast of South America and the West Coast of Africa.
What are Convection Currents (in the Earth’s mantle)?
Another piece of evidence to suggest the realism of Continental Drift was the convection currents in the Earth’s mantle. This would mean that the magma, nearest to the Earth core would get heated, due to the severe amounts of Radioactive Decay and rise as it is less dense. When it gets to the top, it cools and sinks. This goes in a cycle and the plate will very slowly move in the direction that the magma pushes it in. (Some parts of the have more radioactive decay, resulting in a faster current, meaning the plate on top moves quicker, or vice vera, slower).
What are the Study of Fossils?
The Study of Fossils are one of the main pieces of evidence behind Continental Drift. Some similar fossils are found on different continents, an example being the Mesosaurus. Some of it’s fossils were found in regions that were supposedly close together when the Earth was in a state of Pangea. An animal like the Mesosaurus wouldn’t have been able to travel to these supposed places that were once nearby due to today’s oceans, and an animal like this, wouldn’t have been able to swim these mind of lengths at that time.
What are the Geological Patterns?
Geological Patterns can show similar patterns of Rock Layers on various different continents, which can show that they were either very close to each other or even joined together physically. Similar groups have been found in Australia, South America, Antarctica and Africa.
An example would be the fact that coal has been found deep in the ground in Antarctica. Coal needs warm climates to form in, suggesting that Antarctica was once a lot closer to the equator, meaning it would’ve moved since.
What is Paleomagnetism?
Paleomagnetism is the process of sea floor spreading, which also suggests the creation of new sea floor, allowing the continents to move and spread out across the globe. This is done by volcanoes and lava cooling with the iron pointing towards the North Pole, but every 100 mill years the polarity switches, meaning that they then pointed south. It was this that creates the evidence of Sea-Floor Spreading. Scientist know this because of the change of Polarity from the iron in the rocks at the sides of the Mid-Ocean Ridge.
The Stages of the Earth’s Split:
- Permain
- Triassic
- Jurassic
- Cretaceous
- Present Day
The State of Permain
Around 225 million years ago, the first state that the Earth was put into. It only included a Supercontinent called Pangea.
The State of Triassic
Around 200 million years ago, the Earth has separated into two main continents, which went by the name of Laurasia (in the North) and Gondwanaland (in the South), along with the Sea of Tethys in the middle of the two.
The State of Jurassic
The World at this point, 150 million years ago has started to slowly split into 7 regimented Continents, but still didn’t look like it does today.
The State of Cretaceous
It was at this point, 65 million years ago, that the continents really started to break away from each other, separating and were beginning to refine themselves into the shapes and the continents which we all know too well today. (However, India had only just started it’s journey to the Eurasian Plate).
Why are earthquakes and volcanoes are found along plate boundaries?
The reason Volcanoes and Earthquakes are usually near plate boundaries because they are the areas that the plates can collide, diverge and subduct.
Differences Between Oceanic and Continental Crust
Continental Plate:
- 70km Thick
- 3.6 Billion Years Old
- Made Of Granite and is Less Dense
Oceanic Plate:
- 7km Thick
- 200 Million Years Old
- Made Of Basalt and is More Dense
Which Plate Subducts?
- Continental | Oceanic
- Oceanic | Oceanic
- Continental | Continental
If any Plate Converges towards another, the Denser Plate will always subduct.
If a Continental Plate collides with a Oceanic, then the Oceanic will subduct
If an Oceanic and Oceanic plates collide, then the older and/or denser will subduct to create a deep sea trench.
If a Continental and Continental plates collide, then subduction does not take place, instead the crust is squeezed together and creates fold mountains instead.
The Different Types of Tectonic Plate Bounderies
- Divergent (Constructive) Plate Boundaries
- Convergent (Destructive) Plate Boundaries
- Conservative (Transform) Plate Boundaries
What is a Divergent (Constructive) Plate Boundary?
Divergent Plate Boundaries are where the two plates are moving away from each other.
What happens at a Divergent (Constructive) Plate Boundary?
Convection currents move the plates away from each other (they diverge). A gap appears in the crust and the upper mantle moves up and starts to melt. This magma then solidifies and creates new land. This Process can create Shield Volcanoes, Mid-Ocean Ridges and Continental Rifts.
What is a Convergent (Destructive) Plate Boundary?
A Convergent Plate Boundary is where 2 plates, one Continental, one Oceanic are moving towards each other and eventually collide.
What happens at a Convergent (Destructive) Plate Boundary?
Convection Currents moves the plates closer to each other. Upon impact, the denser, but thinner Oceanic plate subducts. The Continental Crust does not subduct, but because of the impact from the two plates hitting each other, the edge of it would have crumpled and folded a little to create Fold Mountains. This process can result in Earthquakes and Volcanic Eruptions.
What is a Transform (Conservative) Plate Boundary?
A Conservative Plate Boundary is where 2 plates are sliding either past each other or in the same direction. One plate moves either the opposite way, or a slightly different way and at different speeds.
What happens at a Transform (Conservative) Plate Boundary?
When the two plates get jammed/stuck together, they cannot move, but the same amount of force is still exerted on each of them. This results in pressure/stress building up and eventually the pressure overcomes all other forces and the plates are released. This process can result in an Earthquake.
How do Earthquakes Occur at Divergent Boundaries?
After the magma Solidifies, small but frequent earthquakes occur when the magma’s path get blocked off or when pressure builds.
How do Earthquakes Occur at Convergent Plate Boundaries?
When the Oceanic Plate subducts immense amounts of pressure is created with the friction, which melts to plate. It is because of these amounts of pressure that it is all released through an Earthquake.
How do Volcanic Eruptions Occur at Divergent Plate Boundaries?
After the Shield Volcano forms the magma from the Mantle is pushed up by the convection currents and passes through the path created for it. The eruptions are frequent and not violent as the magma has low silica levels, as the water surrounding it, turns it runny.
How do Volcanic Eruptions Occur at Convergent Plate Boundaries?
The fact that the Oceanic plate is melting, actually ends up making the magma even more viscus. As this magma is less dense than the rest, it rises, but as it rises it cools, therefore blocking up the magma chambers as it solidifies. As more and more magma rises, it will all be blocked off in the magma chamber. Again, when the pressure overcomes all other forces, the magma will be forced up through a Composite Volcano. This will be a big eruption and powerful eruption and sometimes a Pyroclastic Flow will be formed under the rock too.
How are Earthquakes measured?
Earthquakes can be measured with two ways:
The Richter Scale or the Mercalli Scale
The Richter Scale…
- Measures The
- Scale From
- Measures Using
- What Scale
- Measures the strength of the Earthquake
- The scale goes from from 1 to greater than 8
- Measured using a seismograph
-Uses a Logarithmic scale as it increases 10 times at each stage
(2 is 10 times greater than 1, and 3 is 100 times greater than 1)
The Mercalli Scale…
- Measures The
- Scale From
- Measures Using
- What Scale
-Measures the impact or damage of the Earthquake
-The scale goes from I to XII
(People do not feel any Earth Movement to Total Destruction)
- Measured using descriptive phrases and people’s observations
- Uses a ‘Normal’ scale with Roman Numerals instead of standard numbers
What is the Epicentre?
The Epicentre is the point on the Earth’s surface directly (vertically) above the focus of an earthquake.
What is the Focus
The Focus is the point in the Earth’s Crust where the Earthquake actually happens.
What is the Fault Line?
The Fault Line is a line made on the Earth’s Crust where the Earthquake will split the ground all the way under the surface. This traces a geological fault between the plates.
What is the Surface Rupture?
The Surface Rupture is the Fault line visible on the surface of the Earth.
What are Shockwaves?
Shockwaves are powerful and are released from the focus. Primary Waves travel forwards and backwards quickly, whilst Secondary Waves move forwards backwards and Sideways slowly.
What is the Stress and Release?
Stress and Release is when pressure builds between two plates, whilst stress is placed on the fault line. When the stress builds up too much, it is released into and Earthquake.
Haiti Earthquake: The Physical Factors
Firstly, the island was situated on the edge of a tectonic plate boundary, which was a transform plate boundary
The Strength of the Earthquake was a Magnitude 7.
The depth of the focus was only 8-10km deep, meaning the shockwaves wouldn’t have been absorbed as well (as there was less crust to do so).
It’s Location was only 15km Southwest of the Haitian Capital, Port-au-Prince.
Haiti Earthquake: The Human Factors
The density of Port-au-Prince was 808.7 people per km (very dense)
Haiti had a lack of development (Human Development Index - 156th).
Haiti is the 160th worst country in terms of corruption (affected building quality, government and planning)
Before the Earthquake, 50% of the population lived in absolute Poverty
Building Codes were broken, meaning that the buildings were unsafe in the event of an earthquake, leading to many collapsing
Haiti are in $4.5 billion dollars of debt, whilst 70% of the Population remained unemployed, or underemployed.
What are Primary Effects?
Something that happens/is effected by the result of (e.g) an Earthquake in the short term/immediately.
What are Secondary Effects?
Something that happens/is effected by the result of (e.g) an Earthquake in the long term.
What are Social Effects?
Things that effect people’s quality of life, such as transport, health, homes and education.
What are Economic Effects?
Things that effect wealth, such as jobs, income, tax and business.
What are Political Effects?
Things that effect either affect the Government themselves or the decisions that they make.
What are Environmental Effects?
Things that effect the natural world and the things around it, such as water, land, soil and the trees e.c.t.
Where is Montserrat?
Montserrat is a Caribbean Island, north of the South American Coast. It is situated along the Plate Boundary separating the Atlantic (Oceanic) and Caribbean (Mostly Oceanic) Plate.
Where is the Montserrat Volcano Situated?
The Soufrière Hills Volcano is on the South East(ish) part of the island, nearly directly East from Plymouth. It sits at approximately 915 meters in the air.
When did the Montserrat Volcano Eruption Occur?
The Montserrat Eruption took place on the 25th June, 1997.
Which Plates Boarder the island of Montserrat?
The Caribbean Plate (moves East) and the Atlantic Plate (moves West).
Positive Outcomes of the Montserrat Eruption
The Volcanic Ash has improved soil fertility in the long term and yields are now increased.
Volcanic Ash was quarried and sold abroad, meaning Montserrat now earns income from Geothermal heat and quarrying mines
Tourism has now increased again with, people visiting the volcano as a tourist attraction, meaning new jobs are also created. National Geographic rated it ‘Top New Trip Of 2010’.
Negative Outcomes of the Montserrat Eruption
The population declined from 12,000 to 3,000.
Large areas including Plymouth were covered with 12m of ash and mud.
Over 20 villages were destroyed.
Lava set fire to Government Buildings and Police HQ’s
19 died, 7 were injured.
Health still suffers. Volcanic Ash included Quartz, which caused silicosis (respiratory disease)
Airport and Port were both Destroyed, along with many Schools ans Hospitals.
The GDP of the island is worth 15% less than it was before the Eruption.
What are Lava Flows?
Lava Flows are flows of Lava which destroy everything in their path, but move slowly enough to get out of the way of.
What are Lava Explosions?
Lava Explosions are found in Destructive Volcanoes (found on Destructive Plate Boundaries) due to the the high silica levels. When the magma pushes up through the volcano very slowly, they can solidify in the fragments, which cause huge lava domes. In an eruption, these Lava Domes crack and fall down as pyroclastic flows.
What are Pyroclastic Flows?
Pyroclastic Flows are very fast-moving currents of hot gas and rock (some from the Lava Dome). They usually hug the ground and travel downhill due to gravity. Pyroclastic Flows can reach speeds of up to 350mph.
What is Volcanic Ash?
Volcanic Ash is created by the blast out of the lava dome when the lava fragments are hoisted high into the atmosphere, these fragments then turn into ash, as they are heated, to create Volcanic Ash.
What is a Volcanic Bomb?
A Volcanic Bomb is a chunk of molten rock (bigger than 64mm in diameter) hurtled into the air when a volcano ejects viscous fragments of lava. These Volcanic Bombs can blow up at any time.
What are Lahars?
Lahars are composed of a wet slurry of mud and water (along with pyroclastic material and rocky debris). The water can come from anywhere for the Lahar to work. Lahars travel at least 30mph and can destroy cities by flooding them with this thick concrete-like slurry and then set after some time to leave the city buried as if it were never there.
Why was an Exclusion Zone Created?
There were many factors involved with coming to the conclusion of creating an Exclusion Zone in Montserrat, coving over half of the island (the South). People’s Health and Welfare had to be looked after and this Zone was created to make sure that if there was another Eruption, nobody would be effected badly. Hazards, such as Volcanic Ash, Pyroclastic Flows, areas affected by Lahars and the lingering health issues involved with Quartz contamination and more, made it simply impossible to live in this Zone healthily any more. There was also evidence to suggest another Eruption in the near future, as the Lava Dome has started to grow again too, meaning further precautions had to be made. The Exclusion Zone will also help the land recover from what it’s been through naturally and hopefully one day, the full island will be in use again.
What is a Collision Plate Boundary?
A Collision Plate Boundary is when two Continental Plates Collide. Here, there is no Subduction, as both plates come together to create Fold Mountains.
How many 7 or greater magnitude earthquakes occur each year?
Approximately 15 Seven or greater magnitude Earthquakes Occur each year.
