Geography AQA A physical geography,

  • Created by: luci
  • Created on: 13-06-12 17:47

Unit 1 Geography: Notes 

The Restless Earth 

Plate Tectonics

Earth is made up of: Crust, Mantle, and Core 

2 types of crust: Oceanic (thin and dense) and Continental (think and less dense) 

3 different plate margins:

- Destructive Margins: Oceanic meets Continental  Oceanic is forced down and destroyed. 

Landforms include: Volcanoes, Fold Mountains, Ocean Trenches, and Earthquakes 

- Constructive Margins: Oceanic moves away from Oceanic  the space created allows magma to rise  magma cools and creates new crust

Landforms include: Volcanoes, Mountains and Earthquakes 

- Conservative Margins: 2 continental plates move past each other at different speeds and/or different directions  

Landforms include: Earthquakes 

Fold Mountains are formed when plates collide (destructive plate margins)

1. Sediment builds up under the sea in a geosyncline/ 

2. The sediment is compressed (as the two plates move towards each other) and folds to form a fold Mountain 

Anticline: a slope folding downwards on both sides

Syncline: a slop folding upwards on both sides 

Recumbent: Over fold

Ocean Trenches are formed in a subduction zone at destructive plate margins 

- They are inaccessible to humans 

- There are opportunities for fishing and drilling for oil and gas 

- Deepest ocean trench: Marianas Trench 



Destructive (composite cone volcanoes): 

1. When the oceanic plate is destroyed a pool of magma forms 

2. Magma rises through the vents 

3. The magma erupts onto the surface where it is called lava, forming a volcano

Constructive (shield volcanoes): 

1. Magma rises into the gap created by the plate moving apart 

2. Magma rises through the vents 

3. The magma erupts onto the surface where it is called lava, forming a volcano

Shield volcano

- Wide base 

- Gentle slopes 

- Frequent eruptions

- Non-violent eruptions with Basic Lava 

- Made of Lava only 

- E.g. Mauna Loa, Hawaii 

Composite Cone Volcano 

- Tall cone

- Narrow base 

- Steep sides 

- Long dormant periods

- Violent explosions with Acid Lava 

- Made of alternate layers of Ash and Lava 

- E.g. Vesuvius, Italy

Effects of a volcano:

- Ash and volcanic bombs are thrown out 

- Pyroclastic flows (hot gases, ash and steam) causes damage 

- When a volcano is dormant for a long period of time a plug forms when this plug is blown out it leaves a large crater called a caldera 

- Mud flows called lahars formed when hot ash melts ice. 

Predicting Volcanic Eruptions:

Signs include

- Tiny earthquakes

- Escaping gas

- Bulges

- Changing shape

Supervolcanoes e.g. Yellowstone

Yellowstone lies on top of a hotspot where magma rises towards and collects in a store beneath the surface

An explosion of a supervolcano would be devastating:

- It would affect farming as crops and animals would die 

- Communication would be damaged 

- Great loss of life 

- Global cooling would occur 

- 1000km3 of ash produced (mount St Helens: 1km3)

- Ash produced would cause a volcanic winter


Earthquakes occur at any plate boundary:

- Destructive margins…




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