Geography plate techtonics
Terms in this set (33)
What is a tectonic plate
There are two types of crust: oceanic and continental crust. The oceanic crust is found under the sea and is thinner and more dense than the continental crust.
What are convection currents
Heat from the core causes convection currents in the mantle. These currents slowly move the crust around. In some places the crust is destroyed. In other places new crust is formed.
Destructive plate boundary
A destructive plate boundary is sometimes called a convergent or tensional plate margin. This occurs when oceanic and continental plates move together. The oceanic plate is forced under the lighter continental plate. Friction causes melting of the oceanic plate and may trigger earthquakes. Magma rises up through cracks and erupts onto the surface.
collisional plate boundary
Collision zones form when two continental plates collide. Neither plate is forced under the other, and so both are forced up and form fold mountains.
constructive plays boundary
A constructive plate boundary, sometimes called a divergent plate margin, occurs when plates move apart. Volcanoes are formed as magma wells up to fill the gap, and eventually new crust is formed.
Conservative plate boundary
Conservative plate boundary
A conservative plate boundary, sometimes called a transform plate margin, occurs where plates slide past each other in opposite directions, or in the same direction but at different speeds.
Friction is eventually overcome and the plates slip past in a sudden movement. The shockwaves created produce an earthquake.
What is Continental drift
In 1915, the German geologist and meteorologist Alfred Wegener first proposed the theory of continental drift, which states that parts of the Earth's crust slowly drift atop a liquid core. The fossil record supports and gives credence to the theories of continental drift and plate tectonics.
Evidence for continental drift
The fossil record supports and gives credence to the theories of continental drift and plate tectonics.
What are earthquakes
An earthquake is a sudden shockwave caused by rocks being under stress from the movements of plates at plate boundaries. Eventually the stress in the rock builds up enough to deform and reach breaking point. At that point, the stored up energy is released in the form of shockwaves.
Large earthquakes are usually connected with plate boundaries. Earthquakes happen often but most are too small for us to notice. Seismometers record earth movements.
How to detect and measure earthquakes
The power of an earthquake is measured using a seismometer. A seismometer detects the vibrations caused by an earthquake. It plots these vibrations on a seismograph.
The strength, or magnitude, of an earthquake is measured using the Richter scale. The Richter scale is numbered 0-10.
How to prepare for earthquakes
Preparation: building to standards to withstand movement (reinforced corner joints, interlocking 'birdcage' frames, computer controlled counter-weights) can help protect, however, for poor, rapidly growing cities such as Port-au-Prince this is not possible;
Planning for Earthquakes
Planning: hospitals, emergency services + inhabitants can practise for disasters
(e.g. drills, codes of practice so people know what to do). Lacking in Haiti due to decades of civil unrest, conflict, poor governance
Effects of an earthquake
Earthquakes can destroy settlements and kill many people. Aftershocks can cause even more damage to an area. It is possible to classify the impacts of an earthquake, by taking the following factors into account:
short-term (immediate) impacts
social impacts (the impact on people)
economic impacts (the impact on the wealth of an area)
environmental impacts (the impact on the landscape)
A volcano is an opening in the Earth's crust. It allows hot magma, ash and gases to escape from below the surface. There are two types of volcanoes shield and composite
Composite volcanoes are made up of alternating layers of lava and ash
found at destructive or compressional boundaries.
The eruptions from these volcanoes may be a pyroclastic flow rather than a lava flow. A pyroclastic flow is a mixture of hot steam, ash, rock and dust.
A pyroclastic flow can roll down the sides of a volcano at very high speeds and with temperatures of over 400°C.
Shield volcanoes Shield volcanoes are usually found at constructive or tensional boundaries.
They are low, with gently sloping sides.
They are formed by eruptions of thin, runny lava.
Eruptions tend to be frequent but relatively gentle.
Effects of a volcanic eruption
Volcanic eruptions can have a devastating effect on people and the environment.
However, unlike earthquakes, volcanoes can also have a positive impact on an area. These positive impacts can help to explain why people choose to live near volcanoes.
Good effects of volcanic eruptions
They provide nutrients to the surrounding soil. Volcanic ash often contains minerals that are beneficial to plants, and if it is very fine ash it is able to break down quickly and get mixed into the soil. They also create opportunities for tourism
How to predict for volcanic eruptions
Hundreds of small earthquakes are caused as magma rises up through cracks in the Earth's crust. Seismometers are used to detect earthquakes.
Temperatures around the volcano rise as activity increases.
Thermal imaging techniques and satellite cameras can be used to detect heat around a volcano.
When a volcano is close to erupting it starts to release gases.
The higher the sulfur content of these gases, the closer the volcano is to erupting. Gas samples may be taken and chemical sensors used to measure sulfur levels.
Preparing for volcanic eruptions
a detailed plan is needed for dealing with a possible eruption. Everyone who could be affected needs to know the plan and what they should do if it needs to be put into action. Planning for a volcanic eruption includes:
creating an exclusion zone around the volcano
being ready and able to evacuate residents
having an emergency supply of basic provisions, such as food
funds need to be available to deal with the emergency and a good communication system needs to be in place
Eyafjallajokull Iceland 2010
Eursian and N American plate are diverging at a constructive plate boundary. Usually shield volcanoes form at those boundaries but eyafjallajokull is a composite volcano
Extra facts about the eruption
It erupted twice in 2010 the first eruption was a 1 on the Volcanic Explosively Index as a lava eruption; the second eruption was 10-20 times more powerful and was 4 on the VEI, with a large ash cloud.
• Cold water from melted ice chilled the lava causing it to fragment into highly abrasive glass particles that were carried into the eruption plume.
Primary effects of the eruption on people and the environment in march 2010
Disruption to air traffic across Europe; highest level since WW2;
- Over 95,000 flights cancelled all across Europe during six-day travel
ban. 20 countries closed airspace and over 100,000 travellers affected
- Sectors that depend on air-freighted imports and exports were affected, e.g. imported flowers, fruits and electronic hardware.
- The state funeral of the President of Poland was affected as national leaders were unable to attend
Flooding resulting from the meltwater from under the ice. Sections of embankment supporting the main highway were deliberately breached by the government to allow the water to pass out to sea - the prevented expensive bridges from being destroyed 'Volcano tourism' quickly sprang up,
- The layer of ash fallen on Icelandic farms and Raufarfell became wet and compact, making it difficult to farm, harvesting or grazing livestock
- the International Air Transport Association total loss for the airline industry was around US$1.7 billion
• 800 people close to the volcano were evacuated.
•The family on the farm at the summit of the volcano were forced to flee and leave their farm
• Rescuers wore face masks to prevent them choking on the ash cloud
• Airports were closed and flights were cancelled or re-routed as far away as Canada, Turkey and the Ukraine.
long term responses for the eruptions
A volcanic centre 'Iceland Erupts' was opened to attract tourists to the area to diversify income.
• Kenya destroyed 400 tonnes of flowers it was unable to airship into the UK meaning their economic development suffered.
• The eruption meant that aircraft manufacturers were forced to define specific limits on how much ash is considered acceptable for a jet engine to ingest without damage. Over 2,000 micrograms of ash per cubic metre is considered unsafe.
Haiti earthquake setting
Haiti lies right on the boundary of the Caribbean and North American plates. There was slippage along a conservative plate boundary that runs through Haiti.
On 12 January 2010, a magnitude 7 earthquake hit Haiti at 16:53 local time. The earthquake's epicentre was 25 km west of Port-au-Prince, the capital. Most people, businesses and services were located in the capital.
Haiti earthquake Primary effects
Approximately 230,000 people died and 300,000 injured
• 1.5 million people left homeless; 180,000 homes destroyed by the ground shaking
• Industry and services destroyed; roads, port and airport damaged
• ~19 million cubic metres of rubble created
• UN building collapsed and UN personnel killed
• Total cost of repair: $US 11.5 billion over 5-10years
Haiti earthquake secondary effects
•There was a severe shortage of doctors and many people died of injuries such as broken limbs
• Diseases also spread from decomposing bodies
• A year after the earthquake, many people are still living in camps out of town. •Criminals from the prison destroyed in the quake operate in these.
Haiti earthquake immediate responses
local people used their bare hands to dig people out of the rubble
• The damage to the airport and port made aid difficult to deliver
• Rescue teams from around the world arrived within 48 hours and aid (food, water, medical supplies and temporary shelter) was brought into the country from the USA and neighbouring Dominican Republic
• The UN and USA provided security to maintain law and order and ensure a fair distribution of aid
Haiti earthquake long term responses
• Some 200,000 people received cash or food for public work such as clearing rubble
• The lack of stable government has ended in a slow recovery, poor organisation and indecision
• A lack of doctors, hospitals and medical supplies many people died of their injuries or from disease
• One year on from the earthquake only 15 percent of basic, temporary houses had been built and most people remained in relief camps, where crime is high