Geography -- Restless Earth

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Plate Margins

Subduction

  • when two plates meet and one goes under the other.
  • the oceanic crust goes under the Continental.
  • eg.Nazca (O) subducting under South America (C)

Collision

  • When two continental plates crash into each other
  • eg.Indo-Australia plate froming the Himalayas as it crashes into the Eurasion plate

Constructive

  • When two plates move away from each other.
  • the magma rises, cools and creates land between the plates.
  • eg.Mid-Atlantic ridge between the Americas and Europe/Africa

Conservative

  • When two plates move right past each other
  • eg.San Andres fault wer Pacific plate (O) and N. America plate (C) move in the same direction
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Plate Names

  • North America Plate
  • South America
  • Juan de Fuca Plate
  • Caribbean Plate
  • Cocos Plate
  • Nazca Plate
  • Pacific Plate
  • Scotia Plate
  • African Plate
  • Arabian Plate
  • Eurasian Plate
  • Philippine Plate
  • Pacific Plate Indo-Australian Plate
  • Antartica Plate
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Subduction

Convection currents in the mantle cause the plates to move together. If one plate is made from oceanic crust and the other from continental crust, the denser oceanic crust sinks under the lighter oceanic crust. This is known as subduction. A lot of pressure is put upon the oceanic crust and it it destroyed as it melts to form magma.

An island arc is formed when an oceanic plate subducts under another oceanic plate. E.g Islands of the CAribbean and Indonesia.

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Constructive

When plates move apart, a constructive plate boundry is made. this usually happens under the ocean. As the plates pull apart, crack and fractures are formed between the plates where there is no solid crust. Magma forces its way into the cracks and makes its way to the surface to form volcanoes.

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Collision

If two continental plates meet each other, they collide to create mountain ranges.

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Conservative

At conservatice plate margins, the plates move right past each other. they move in a similar direction at slightly different angles and speeds. 

As one plate is moving faster and in a different direction than the other, they get stuck. Eventually, the build up of pressure causes an earthquake. At a conservatice plate margin, crust is being neither destroyed or made. 

E.g San Andreas Fault, California

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Fold Mountains and Trenches

Trenches

  • Mariana Tench
  • Chile Tench
  • Java Trench

Fold Mountains

  • Rocky Mountains
  • Andes
  • Pyrenees
  • Alps
  • Himalaya
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Andes and Uses

  • Range of young fold mountains
  • Formed 65 million years ago
  • Longest range of fold mountains

Uses

  • Farming. People grow vegetables, soybeans, rice and cotton.
  • Llamas. Male llamas can carry more than 25% of their body. used for transtport of items. Female llamas used for meat, silk and their wool to make clothes and rugs.
  • Minerals. Tin, nickel, silver and gold can be found. Biggest gold mine in the world called the Yanacocha
  • Hydroelectric Power. Steep slopes and narrow valleys are an advantage for HEP.
  • Torism. Attraction such as mountain peaks, volcanoes, glaciers and lakes.
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Volcanoes

Composite Volcanoes

  • Steep slpoes
  • NArrow base
  • Eruptions are not frequent but violent
  • Secondary cones; layers of think ash and lava

Shield Volcanoes

  • Wide base
  • Gentle slopes
  • Low, rounded peak
  • Layers of runny lava with little ash
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Mt. St. Helens

  • May 18, 1980
  • In Cascade Mountain Range, Washington state, US
  • Caused a landslide (biggest ever) 
  • Wiped out all living things up to 27km north of the crater
  • 50 killes 
  • Trees unrooted and tossed around
  • Ash clogged up in the air-conditioning systems, shortage of masks
  • US president Carter promised to send 2$ million extra
  • Helicopters were sent for search and rescue
  • Priority to save the survivors and tend to the injured
  • Buildings, roads and bridges that were damage needed re-building. 
  • Drainage around the area had to be checked for a flood because of debris
  • Forest area had to re-planted
  • 10 years later, it is a tourist place: more popular than before, greenery and wildlife appearing
  • Made a national monument in 1982 : $4 million spent on it.
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Nyiragongo Eruption

  • 17 January 2002
  • In Democratic Republic of Congo
  • 147 killed and 120,000 homless
  • 15% of Goma destroyed
  • 4,500 builidng collapsed
  • Earthquakes felt through Goma and Gisyeni for 3 months after eruption
  • City of Gome was well equipped: had food, first aid etc
  • Charity organizations could not give what Goma needed most: money
  • Many buildings needed repairing
  • Still an active volvano
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Earthquakes

Marketrasen, Lincolnshire on 27 Feb 2008

focus was 18.6km from the surface.

FOCUS is where earthquakes begin, deep inside the earth's crust

deep focus earthquakes cause less damage than shallow focus ones.

EPICENTRE is where the earthquake is most strongly felt. 

SHOCK WAVES rediate out from the epicentre

PRIMARY WAVES are the initial, weak waves. They cause the surface to move forward and backwards

SECONDARY WAVES are the stronger waves that move at right angles to the outward movement of the main wave.

LONGITUDINAL WAVES are the most powerful and cause an up-and-down movement

TRANSVERSE WAVES are also the most powerful and cause a side-to-side movement

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Northridge Earthquake

  • January 17, 1994
  • Struck in San FErnando Valley near Nothridge
  • Affected 3 counties; Los Angeles, Venture and Orange
  • Lasted for 10-20 seconds
  • 14,000 aftershocks reported
  • 57 killed and over 87,000 injured
  • 12,000 builidings damaged
  • Major highways, the postal service, radio/television shows and hospitals were affected.
  • 20$ Billion to fix all damages
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Mercalli Scale

1. Barely felt

3. Slightly felt indoors as though a large truck were passing

5. Felt by almost everyone; sleeping people are awakened; dishes and windows break

8. Slight damage to well-built structures; poorly built structures are heavily damaged; walls, chimneys and monuments fal

10. Few structures survive; most foundations destroyed; water moved out of banks of rivers and lakes; avalanches and rockslides; railroads are bent

12. Total destruction; objects thrown into the air; land appears to be liquid and is visibly rolling like waves

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Prediction, Protection and Preparation

We can PREDICT earthquakes but it is challenging. It is possible to monitor tremors althouh they don't always lead to major quakes

PROTECTION can involve builidngs earthquake proof structures. The ones that sway without collapsing are expensive but should survive.

PREPARATION includes having earthquake drills with evacuation procedures and rescue plans. 

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Tsunamis

Tsunamis are ocean waves triggered by earthquakes. They are secondary effects of the quake.

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Tsunamis

Tsunamis are ocean waves triggered by earthquakes. They are secondary effects of the quake.

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