Geography: Physical Geography AQA

Restless Earth

• Crust: outer layer of the earth
• Plate: a section of the earth's crust
• Plate Margin: the boundary where two plates meet 
• Mantle: dense mostly solid layer between outer core and crust 
• Convection Currents: the circular currents of heat in the mantle

Oceanic Crust:

• Newer- most less than 200 million years old
• Denser
• Can sink
• Can be renewed and destroyed

Continental Crust:

• Older- most over 1500 million years old
• Less dense
• Cannot sink
• Cannot be renewed or destroyed

Destructive plate margins: 

• Convection currents in mantle cause plates move together
• Denser oceanic crust sinks under continental crust (subduction)
• Great pressure exerted and oceanic crust is destroyed to form magma
• Two continental plates meet each other, collide rather than sinking beneath each other. The collision boundary is a different type of destructive margin. 
• Severe earthquakes and violent volcanic eruptions

Constructive plate margins:

• When plates move apart constructive plate boundary results 
• Occurs under oceans; as plates move apart cracks form between plates and magma forces way into cracks and makes its way to surface form volcanoes
• Magma forces its way into the cracks and makes way to surface to form volcanoes
• New land is formed in this way too

Conservative plate margins:

• The plates sliding past each other in similar direction different angles speed
• One plate gets stuck build-up pressure causes release sudden release causes earthquake
• Crust is neither destroyed or made. 

Fold mountains and ocean trenches result from plates moving together. Found in association with subduction. 

Composite and shield volcanoes:

• Composite: destructive plate margin, steep slopes, narrow base, secondary cones, layers of thick lava ash, eruptions infrequent but violent
• Shield: constructive plate margin, wide base, gentle slopes, low rounded peak, crater, layers of runny lava with little ash, vent, eruptions frequent non-violent. 

The Andes and its people: 

• Despite high altitudes it is used for farming. In Bolivia, many subsistence (farming to provide food for farmer's own family) farmers variety of crops on steep slopes. 
• Terraces are used to create areas of flat land on slopes 
• Terracing offers advantages trying to farm in harsh environment
• Flat areas retain water in area receiving little and  limit downward movement of soil in areas where soils are thin most crops grown lower in valleys 
• Llamas synonymous Andes pack animals carrying material irrigation and buildings. 
• Machu Picchu relied on these transport materials to remote location. Females used for meat and milk
• Mining- Yanacocha fold mine largest in world joint venture Peruvian us based mining company open pit gold bearing rock loosened daily dynamite blasts and sprayed cyanide and gold extracted from resulting solution lead to contamination of water supplies.
• The nearby town Cajamarca growth of inhabitants with alternative source of jobs
• Disadvantages of growth also bring many problems and lack of services increased crime rate. 
• Hydroelectric power steep slopes narrow valleys are advantage
• More easily dammed encouraging rapid flow water generation electricity
• Yuncan project dams Paucartambo and Huachon rivers north-east Peru El Platinal project due to begin construction in Peru
• Andes Tourism  many natural attractions…