Geography Paper 1 Section A

• 1 FAN
• 1 of
• Volcanoes and Earthquakes
• Where plates meet, volcanoes and earthquakes occur.
• Volcanoes Occur at Destructive and Constructive Plate Margins
• 1) At destructive margins, the denser oceanic plate moves down into the mantle, where it
• melts. A pool of magma forms, which then rises through cracks in the crust called vents.
• The magma (called lava when it reaches the surface) erupts, forming a volcano.
• 2) At constructive margins, the magma rises up into the gap created by the plates moving apart, forming a volcano.
• Some volcanoes also form over parts of the
• mantle that are really hot (called hotspots), e.g. in Hawaii.
• When a volcano erupts, it emits lava and gases. Some volcanoes emit lots of ash, which can cover land, block out the sun and form pyroclastic flows (super-heated currents of gas, ash and rock).
• Destructive plate margin
• Constructive plate margin
• Earthquakes Occur at All Three Types of Plate Margin
• Earthquakes are caused by the tension that builds up at all three types of plate margin:
• Destructive margins — tension builds when one plate gets stuck as it moves past the other.
• :: Earthquakes
• Plate margin
• Most earthquakes
• happen at plate margins, but a few occur in the middle of plates.
• Constructive margins - tension builds along cracks in the plates as they move away from each other.
• Conservative margins — tension builds up when plates that are grinding past each other get stuck.
• The plates eventually jerk past each other, sending out shock waves. These vibrations are the earthquake.
• 3) The shock waves spread out from the focus — the point
• Shock waves
• in the Earth where the earthquake starts. The waves are stronger near the focus and cause more damage.
• 4) The epicentre is the point on the Earth's surface straight above the focus.
• 5) Earthquakes are measured using the moment magnitude scale:
• • The moment magnitude scale measures the amount of energy released by an earthquake (called the magnitude).
• • It is a logarithmic scale - so a magnitude 7 earthquake would cause ten times as much ground shaking as a magnitude 6 earthquake.
• • Earthquakes of magnitude 6 and below normally only cause slight damage to buildings, although they can be worse in very built up areas.
• • Earthquakes of magnitude 7 and above can cause major damage and deaths.
• Damage after a 7.8 magnitude earthquake in Nepal in 2015
• Learn how and where volcanoes and earthquakes form
• You'll never have to draw a map like those above, but you should have some idea of where tectonic hazards occur.