Physical Processes &Tectonic Hazards (Edexcel A Level Geography)

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Bridgette Barrett

Written by: Bridgette Barrett

Reviewed by: Jenna Quinn

Earthquake Waves & Hazards

  • The movement felt during an earthquake is the result of seismic waves

  • These are the released energy radiating through the Earth

  • There are three types of seismic waves:

Characteristics of Seismic Waves

Wave type

Characteristics

Primary - P waves

  • Body wave

  • Fastest

  • Reach the surface first

  • Travel through liquids and solids

  • Cause backwards and forwards shaking

  • Least damaging

Secondary - S waves

  • Body wave

  • Slower than P waves

  • Only travel through solids

  • Cause a sideways motion

  • More damaging

Love - L waves

  • Surface wave

  • Slowest

  • Cause a side to side motion

  • Larger and energy is focussed on the surface

  • Most damaging

Seismic waves during an earthquake
Seismic waves

Primary and secondary hazards

  • Every earthquake is unique but they have common hazards which are either

    • Primary (a direct result of the earthquake)

    • Secondary (a result of the primary hazards)

Primary and Secondary Earthquake Hazards

Primary hazards

Secondary hazards

Ground shaking

Crustal fracturing (when the movement causes the Earth's crust to crack)

Landslides and avalanches - the movement of the Earth may trigger the collapse of material down steep slopes

Liquefaction - when the shaking causes particles in the ground to move further apart causing them to act like a liquid rather than a solid

Flooding - caused by tsunami

Volcanic Hazards

Primary and secondary hazards

  • Although they are all unique, volcanic eruptions have common hazards

    • Primary (a direct result of the eruption)

    • Secondary (a result of the primary hazards)

Primary and Secondary Volcano Hazards

Primary hazards

Secondary hazards

Pyroclastic flow - a mix of dense, hot, rock, ash and gases

Lava flow - most move slowly enough that they are not a risk to human life but can reach over 1000oC

Ash falls - can travel many km, causing injuries, damage, deaths and disruption to transport

Gas eruptions - gases trapped in the magma are released during an eruption, they may form gas clouds which are hazardous to health

Lahars - a mixture of rocks, mud and water which flow down the volcano. They are fast-flowing and destroy everything in their path

Jökulhlaups - floods caused by a sudden release of water and rocks when glacial ice is melted by the eruption

Causes of Tsunami

  • When an earthquake occurs beneath the sea bed this can lead to a tsunami

    • As the sea bed jolts water is displaced and forced upwards creating a wave

    • As the wave approaches the land they slow and the wavelength becomes compressed 

      • This leads to an increase in wave height: they frequently reach 5-10 meters, but can reach 30 meters 

    • As the wave reaches the shore a vacuum is created and the water recedes rapidly out to sea leaving the sea bed exposed

formation-of-a-tsunami
Tsunami formation as a result of an earthquake
  • Other causes of tsunami include:

    • Landslides which may be due to earthquakes and volcanic eruptions displacing the water

    • Underwater volcanic eruptions

    • Rarely they can be caused by a meteor strike 

  • Tsunami usually occur close to plate boundaries and are most common in the area surrounding the Pacific Ocean - 'Ring of Fire'

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Bridgette Barrett

Author: Bridgette Barrett

Expertise: Geography Lead

After graduating with a degree in Geography, Bridgette completed a PGCE over 25 years ago. She later gained an MA Learning, Technology and Education from the University of Nottingham focussing on online learning. At a time when the study of geography has never been more important, Bridgette is passionate about creating content which supports students in achieving their potential in geography and builds their confidence.

Jenna Quinn

Author: Jenna Quinn

Expertise: Head of New Subjects

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.