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29 Cards in this Set

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Describe the nature of the different types of plates that exist beneath the Earth's crust.

The surface of the Earth, referred to as it's 'crust' is often compared to the surface of the skin of an apple, in terms of relative size.




Beneath the surface lie plate boundaries which propagate the movement which we can perceive in the form of slow moving land masses, seismic events and volcanic activity.




There exist two fundamental plate types;




Oceanic Plates:


- These are dense in nature. When colliding with continental plates, they tend to subside beneath them forming a subduction zone which may then lead onto the formation of mid-oceanic ridges, and so forth. They are made out of a broken layer of basalt rock known as sima , meaning silica and magnesium.




Continental Crust


- This is lighter and less dense than the oceanic crust, meaning that it tends to be more buoyant and does not subside when colliding with oceanic crust.


- Made out of bodies of mainly granite rocks known as sial; that is silica and aluminium rocks.




The lower layer of sial forms the upper layer of the sima, and can be thought of as a graduated transition in rock. Sial rock is thicker than the corresponding Sima, but also less dense which is why continental land masses tend not to sink beneath oceanic masses when colliding against each other.

Describe the nature of the shape of the Earth.

The Earth is a geoid which is a shape that is contorted at it's centre (the equator) due to the centrifugal force produced by the spin of the Earth, which means that the North and South poles are slightly squashed towards the centre, while the equator bulges outwards due to this centrifugal force.

Describe the structure of the Earth.

The crust and the upper part of the mantle is known as the lithosphere, ranging from 0-100km deep. It is here where tectonic plates are formed and propagate.




The mantle is the next section. Mostly made out of silica which is thick and made out of liquid due to the immense heat and pressure generated.




Just under the lithosphere lies the asthenosphere. This is a shifting layer of soft rock which lies just above the denser part of the mantle.

Describe the progression of the continental drift.

Pangea (Permian) [225 mil. years ago] > Laurasia & Gondwanaland (Triassic) [200 mil. years] > Jurassic [135 mil. years] > Present day.

How did the initial ideas of continental drift come about?

As early as 1620, English Philosopher Francis Bacon was aware of the fact that either side of the Atlantic Ocean appeared to fit together much like a jigsaw puzzle.




Over the course of the next few centuries, geologist Alfred Waegner in 1912 was able to collect this evidence and ideas, and publish his theory called 'continental drift', which stated that all current continents were once joined in a supercontinent known as Pangea, and over time split up into the individual continents we know today.

What evidence did Waegner use to present his ideas on continental drift?

> Continental Fit


- The idea that the South-American eastern seaboard and the Western South-African seaboard appear to fit perfectly like a jigsaw.


> Geological Evidence


- Rocks of the same age, type, and formation have been found on separate ends of the Earth, like matching pairs in Southern-Brazil and South-America for example.


> Climatogical Evidence


- It has been found that coal deposits in areas like the UK must have initially been formed in tropical conditions, which suggests that the land mass must have been closer to the equator at the time of formation, as current climatic conditions would not support the formation of coal.


> Biological Evidence


- Like the rocks, often similar fossils of the same type and age are found on separate coasts on either ends of the Atlantic.




- Continental Fit


- Geological Evidence


- Climatological Evidence


- Biological Evidence


- Paleomagnetism

What is Paleomagnetism?

Paleomagnetism was the process by which was able to be used to prove the idea of continental drift initially proposed by Alfred Waegner.




The theory describes the mechanism by which plates move through a phenomenon known as sea-floor-spreading.




During vast surveys of the ocean floor in 1948 and following in the 50's, scientists were able to map out the sear floor and discovered ridges spanning thousands of kms along the sea floor. Magnetic surveys revealed that the ridges were composed of strips of iron-rich material that were arranged in strips of oscillating polarisation. Because the earth reverses its magnetic polarity every ~400k years, the fragments in the iron are able to capture the magnetic polarisation of the earth at the time of formation as tiny magnetised fragments within the material align with the polarity of the earth, and remain that way after cooling and condensing.




What was found was that the magnetic polarisation was mirrored on either end of the ridge at the centre, and perpendicular to it. This revealed that the material must have been emanating from the centre of the ridge itself. After examining the age of the rocks it was found that rocks closer to the ridge, such as in the case of Ireland (1million years old) are much newer than the rocks further away, spanning up to 200 million years old. This brought the crucial evidence that the sea floor was spreading, and gave the first hints at the process which governed the movement of tectonic plates.




The question was also posed - How come the Earth does not grow? And this was answered by the discovery of a mechanism which allows for the perpetual equilibrium of surface mass. This was known as subduction, the process by which oceanic plates subdue beneath continental plates as they distance themselves from the point of creation at such ocean-ridges. Because this material is constantly being renewed and destroyed, growth or shrinkage is not possible.




By the same token, continental land mass, known for being much more geologically complex, do not share the same characteristic as oceanic masses whereby they are constantly being renewed and destroyed, but simply remain above the aesthenosophere due to their lower density and subsequent higher buoyancy, which is also why the denser oceanic crust subdues beneath it.

Describe Oceanic & Continental plate divergence.

In the case of oceanic crust, you get sea floor spreading like in the case of the Mid-Atlantic Ridge.




In the case of continental crust you get rift valleys.




Oceanic divergence forms chains of submarine mountains that stretch on for thousands of km. Regular breaks occur called transform faults which closely resembles the discs that separate each segment of our own spines.




Over time, these faults can contract and widen, causing frictional stress with each other and can result in shallow-focus earthquakes. (>70km). Such ridges can form mountains up to 4km in height. New crust is being formed via magma rising from the asthenosphere.




In the case of continental crust which is undergoing divergence, the separation force of the convection current caused by the rising and separating magma causes the land to bulge and fracture, causing fault lines such as the ones seen in the Great African Rift Valley and the San Andreas fault. As the plates continue to move apart, the land that is left in-between two faults sinks downward as the material which previously supported beneath it is know being moved away. Volcanos may also be found here.

Describe Oceanic-Continental Plate convergence.

This is the process by which oceanic plates converge in a destructive manner with continental plates.




- Oceanic plates are much denser and newer than continental plates (200mil vs 1500mil), and as a result upon convergence, the oceanic plate is forced under the continental plate, forming what is known as a deep ocean trench.


- The oceanic crust is forced to depths upwards of 100km, being totally destroyed by 700km. During this process, the material is heated up dramatically due to the increasing temperature as the core is approached, causing it to melt in what is called the Benioff zone. The increasing friction between the two plates also provides significant friction to aid in the heating process, and this build up in tension by suddenly relive itself in the form of deep-focus earthquakes.


- As the two plates move together, the continental plate is forced upwards due to compression, buckling and uplift, forming young fold mountains such as that of the Andes.


- The oceanic crust is caused to melt in what was previously mentioned as the Benioff Zone, and this newly formed magma has a much lower density than the surrounding asthenosphere, and as a result this causes it to rise toward the surface where the continental plate lies. Through the cracks and fissures in the buckled continental plate the magma may find its way to the surface and form a volcano proceeding an eruption.




- Oceanic beneath continental; subduction; deep ocean trench.


- Fold mountains


- Melt in Benioff zone > Magma plume > cracks and fissures > volcano.


- Friction build up, tension release, deep focus earthquakes.

Describe oceanic-oceanic plate convergence.

Oceanic plate which is denser / faster subducts beneath the other corresponding plate. This forms a deep ocean trench like the Marianas Trench. The material then melts in the Benioff zone due to friction & heating as the mantle is approached. This forms magma plumes as the melted material (magma) is less dense than the surrounding asthenosphere. Magma plumes then rise to form a series of submarine volcanic islands such as those seen in the Marianas Island Arc, which form with subsequent plate movement.

Describe continental-continental plate convergence.

The two continental plates are not dense enough to cause subduction much like oceanic plate convergence. As such, with the convergence the plates tend to compress, buckle and cause uplift, forming high fold mountains such as that of the Himalayas.




Because there is no opportunity for material to be destroyed, melted, to form magma, magma plume formation does not occur and hence why volcanoes do not form on such margins. Due to the constant convergence and friction however, shallow-focus earthquakes may occur.

Describe conservative plate movement.

When two plates slide past each other, conservative margins form. There is no opportunity for subduction here, as the plates do not converge; hence why volcanos do not form here, as rock does not get melted and destroyed into magma.




They are responsible for powerful shallow-focus earthquakes, however, as seen in the case of L.A. (1994) as well as San Francisco (1986 & 1904), due to the San Andreas Fault system which runs down California, extremely tectonically active.




These powerful shallow-focus earthquakes typically occur to the 'sticking' that takes place due to the increasing stress and tension that is placed on the plates through the friction of its movement, propagated by convection currents taking place in the asthenosphere. This tremendous force can cause the stress to build up to a point at which it can no longer be sustained, at which point it is released suddenly, which tremendous amounts of energy, in a violent earthquake.

Nature of Indonesian Boxing Day Tsunami 2004.

- Caused by a magnitude 9.1 Earthquake on December 26th.


-


- Australia Plate subducting beneath Burma plate slipped.


- The epicentre was close to land, about 150km away. This meant that the tsunami arrived a mere few minutes after the initial shakes were felt.


- Waves were 20m here, and reached up to a kilometre inland.


- Places in Africa were also affected by high tides, but most of the wave energy had been dissipated by then.

Social Impacts of the Indonesian Boxing Day Tsunami 2004.

- Most affected regions were Indonesia, Sri Lanka and India.


- Because of the lack of a warning system it meant that no one was prepared for the oncoming Tsunami; it took many by surprise.


- Tourists near coastlines were unaware of the symptoms of an oncoming tsunami; such as the receding shoreline and approached beaches to see what was happening, and put themselves in danger from the Tsunami. Many died this way.


- Over 250,000 people died.


- One third of those who died were children, and up to 4x as many women died on coastal areas as they waited for returning fishermen or to protect children.

Economic impacts of Indonesian Boxing Day Tsunami 2004.

- $15 Billion dollars in immediate damages.


- Great impact to local fishing communities as 60% of the fleet and industrial infrastructure in coastal regions in Sri Lanka destroyed.


- Fishing and agriculture is a major source of economic activity in South-East Asia which is why the damage to fishing fleet and coastal habitats significantly hit the economy.


- Tourism badly hit as many feared the possibility of a recurrence, and despite assurances that most tourist infrastructure was not affected, income fell drastically, and this also had a major economic effect on the region as they heavily rely on tourism for income.



Environmental impacts of Indonesian Boxing Day Tsunami 2004.

- Drinking water and farm fields contaminated by salt water which affected agriculture and wildlife particularly in coastal regions.


- Significant damage to coastal habitats, coral reefs, forests and other ecosystems.

Management of Indonesian Boxing Day Tsunami 2004: Short-Term Responses.

- No Tsunami warning system as in place for the Indian Ocean, which reflects the economic wellbeing of neighbouring nations in the area. Despite this however, the rapid succession of the tsunami begs the question if it would have made much of a difference.


- Main response focused on dealing with the aftermath. There were significant issues due to the broken transport and communication links which mean that cooperation between national borders was required.


- NGOs and humanitarian aid agencies mostly focused on providing sanitation facilities to contain the spread of waterborne diseases like Cholera and Typhoid. They implemented drastic policies like rapid burial and in some instances burning of dead bodies to prevent further spread of disease, and it is believed that this helped to keep the incidence count relatively low.


- $7 Billion raised Worldwide mostly by rich countries like the US, and neighbouring nations like Australia which were closely connected to the region.


- Massive public fundraising response likely due to the nature of the time period around christmas.


- Most of the aid was not actually delivered however, due to problems. It is suspected possible Government corruption.

Management of Indonesian Boxing Day Tsunami 2004: Long-Term Responses.

- Set up the Indian Ocean Tsunami Warning system in response, with international cooperation to ensure that the next time round they will receive an adequate response.


- The programme was set to lead an international effort to provide early tsunami warnings across the globe.


- The system was scheduled to go online in late 2006. Tragically another smaller tsunami hit around this time, but the warning system was not in place to by this time.

Nature of Japanese 2011 Earthquake and Tsunami.

- 9.0 Magnitude Earthquake on the Richter scale.


- Slippage of the subducting Pacific plate beneath the Eurasian plate caused the earthquake, and the tsunami. (Destructive).


-

Social Impacts of the Japanese 2011 Earthquake and Tsunami.

- Immediate power outages in Tokyo reportedly affected some 4 million homes.


- Over 15,000 deaths.


- Partial Nuclear Reactor meltdown at Fukushima lead to widespread radiation exposure, health effects from the incident still being studied today and are unsure whether or not will lead to widespread onset cancer development.


- 20km wide exclusion zone set up around Fukushima due to the radiation exposure.


- Japan was largely prepared for the Earthquake; they have annual earthquake simulation days and are very well informed about what to do in the event. It was the onset tsunami that caused the real damage, and that most were not prepared for.


- During the initial earthquake phone lines were quickly overloaded as workers in Tokyo rushed out into open areas on the streets, wearing hard-hats and other protective clothing, many trying to communicate with family.

Economic Impacts of the Japanese 2011 Earthquake and Tsunami.

- Cost of over $200 Billion, the most expensive natural disaster in history.


- It's estimated that the damages were worth 6% of Japan's total economic output in 2010.


- The Yen fell in value sharply after the initial event, but quickly recuperated most of its value throughout the night as the extent of the damage became known.


- Stocks in Tokyo fell.


- Tokyo's major airports were all closed initially, and the public railway service was also halted. They reopened gradually several days later.

Environmental impacts of Japanese 2011 Earthquake and Tsunami.

- Nuclear reactor meltdown in Fukushima.


- The rushing water disabled the emergency backup diesel generators designed to shutdown the nuclear reaction in such an event, causing the reaction to continue.


- Large radiation leaks propagated by the primary explosions which took place. The extent of the radiation contamination is unknown. Fears spread that it may have contaminated the air, water and food supplies.

Management of Japanese 2011 Earthquake and Tsunami: Short-Term Responses.

- Tsunami warnings issued 3 minutes after the earthquake struck.


- Media was urging people not to return fearing the possibility of a possible tsunami, and urged everyone to remain on 'high alert'.


- Japanese Govt. and the Japanese Meteorological agency constantly monitored the progression of the tsunami, and provided regular updates, likely saving many lives.


- Military jets called in to assess the damage.


- Japanese troops sent in to help with clear up and rescue efforts.


- The Japanese Govt. is among the best prepared in the world against natural disasters, and only had to ask international communities for specific requests like Search and Rescue teams.


- People were able to receive regular updates through social media like Facebook and Twitter much before traditional media.



Management of Japanese 2011 Earthquake and Tsunami: Long-Term Responses.

- Japan was already extremely well prepared to cope with natural disasters, so they did not do much in the way of improving contingency plans for possible future events.


- Mostly focused on recovery and rebuilding. Investors and businesses went a long way in ensuring confidence particularly to international investors as to prevent them from pulling out and making economic recovery more difficult.


- Repairing critical infrastructure took a lot of time, especially transport which had over 30 bridges destroyed and 500+ unusable roads.


- Japan went through it's second stage of recovery 6 months following the incident, where WorldVision headed efforts to return children to stable environments and aid their mental recovery by offering structured activities and support.


- Helping the local fishing communities recover by revitalising the industry.


- Helping Children to recovery emotionally through Child-Friendly spaces.


- Providing relief supplies and child-friendly support to prefectures that had to be evacuated from Fukushima.


- Community-building within temporary shelter settlements.


- Japan often praised for it's 'exceptional' disaster management and response, among the absolute finest in international standards.

Nature of Iceland 2010 Eyjafjnallajokull eruption.

- Main eruptions took place between March-April in 2010.


- Despite being an Icelandic classified volcano, this particular eruption was violent because pressure had been building up under Icelandic ice sheets, which caused an explosive violent eruption once it gave way.


- A lot of the lava had rapidly cooled in contact with the ice sheets, causing it to solidify into glass-like sharp fragments which were propelled into the upper levels of the Troposphere.

Local impacts of the Iceland 2010 Eyjafjnallajokull eruption.

- Flooding due to the melting of the Icelandic ice caps, resulting in 800 people being evacuated.


- Farming > Livestock displaced and crops destroyed but farmland benefitted from longer-term soil fertility due to the nutrients in the ash.


- Local airport closure due to the ash plume.


- Drastic decline in air quality due to the heavy ash clouds.

International impacts of the Iceland 2010 Eyjafjnallajokull eruption.

- European air space had to close as experts weren't sure about how the ash could affect aircraft and did it as a precautionary measure.


- Productivity loss > 7 million passengers left stranded with an estimated total loss of £1.2 Billion in the air travel industry.


- The lack of air transport meant that African markets suffered, particularly those selling perishable goods in Kenya which had to be thrown away and lost lots of potential revenue.


- As a positive, less flights meant less carbon emissions and up to 2 Million barrels of fuel weren't used as a result.


- Tourist destinations benefitted from stranded tourists that had to prolong their stay.

Management of the Iceland 2010 Eyjafjnallajokull eruption: Short-Term Responses.

- Close monitoring from Iceland and other European Meteorological Offices.


- The deformation of topography of the volcano was mapped out with satellites.


- The first eruption to be monitored with web cameras.


- Surrounding areas were evacuated due to the uncertainty of an impending eruption, in the days leading up to the event.


- Local authorities were well prepared, and tracked the ash well through satellite observation. They enacted an effective response plan.

Management of the Iceland 2010 Eyjafjnallajokull eruption: Long-Term Responses.

-