Earthquakes, Volcanoes and Fold Mountains – JC Geography Notes

Earthquakes, Volcanoes and Fold Mountains – JC Geography Notes


  •  An earthquake is a series of seismic waves or tremors in the earth’s crust.
  •  They usually occur along the edge of plate boundaries in areas called fault lines.
  •  They are caused when pressure builds up at the edge of the plates as they collide or slide past one another.
  • When this pressure is released a huge amount of energy is released causing the plates to shake. This shaking movement is the earthquake.
  • The Earthquake occurs in the place where the plates collide.


  • Tremors are the waves of seismic energy which spread out from the Focus.
  •  Aftershocks are the smaller tremors which may occur hours or days after the original earthquakes. They can also be extremely dangerous because they may cause already damaged buildings to collapse.
  •  The Focus is the place deep in the earth’s crust where the earthquake begins.
  • The Epicentre is the place on the surface of the earth, directly above the Focus. The tremors are strongest at this point.


  •  The strength or force of an earthquake is measured on a Seismograph.
  • The scale used to describe this force is called the Richter Scale. This scale ranges from 1- 12.
  •  People are still unable to predict when earthquakes will occur, but we can predict where the plates meet and could cause an earthquake.
  • Earthquakes can also occur at sea and produce giant waves called tsunamis e.g. Asian tsunami, 26th December 2004.



  • Volcanoes occur when hot molten lava forces its way to the surface through a narrow channel in the earth’s crust called a vent.
  • These vents are usually found at plate boundaries.
  • When the hot molten rock reaches the surface it is known as lava.
  •  The process of the lava reaching the surface is called an eruption.
  •  Volcanoes can be classified as being either active, dormant or extinct
  • Active: The volcano erupts regularly.
  • Dormant: The volcano has not erupted for a long period.
  • Extinct: The volcano has not erupted in a long time and is unlikely that it will ever erupt again.

Pacific Ring of Fire: An area around the Pacific ocean where around two thirds of the world’s volcanoes are located.

Constructive Effects of Volcanoes:

  • The soil produced by lava can be fertile and can help the growth of crops.
  • The heat from volcanoes can be used to create energy e.g. In Iceland
  • New land can be created e.g. Surtsey off the coast of Iceland
  • Are often tourist attractions which are beneficial to the local economy.

Destructive effects of Volcanoes:

  • Loss of life.
  • Damage to property and infrastructure.
  • Poisonous gasses which are often released during eruption.

Fold Mountains

  • Fold Mountains are formed when the plates of the earth’s crust collide and the crust buckles up.
  • The upfolds form the mountain and are called anticlines and the downfolds are called synclines.
  • Nearly all major mountain ranges have been formed this way.
  •  Mountain building periods:
    • The Caledonian mountains were formed about 400 million Years ago e.g. Mountains of Donegal.
    •  Armorican mountains were formed about 250 million years ago e.g. Macgillycuddy reeks in South of Ireland.
    • The Alpine Mountains were formed about 35 million years ago and are the highest in the world. Eg Alps, Himalayas.

Effects of mountains:

  •  They act as barriers between people.
  • They can affect the climate of a region by making a region colder due to their height or by cutting off rain-bearing winds.
  • They can be suitable locations for coniferous forests.
  • They can be used as land to graze animals such as sheep
  • They can provide suitable sites for hydro-electric plants.
  • Become areas visited by hill walkers and tourists.


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