- 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 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.