What is an earthquake?
An earthquake is the shaking and vibration of the Earth's crust due to movement of the Earth's plates (plate tectonics). Earthquakes can happen along any type of plate boundary.
Earthquakes occur when tension is released from inside the crust. Plates do not always move smoothly alongside each other and sometimes get stuck. When this happens pressure builds up. When this pressure is eventually released, an earthquake tends to occur.
The effects of an earthquake can be devastating - they can destroy settlements, change landscapes, and cause many deaths.
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The size of an earthquake is measured on a Richter scale 0-10 of magnitude using an instrument called a "seismograph". Seismographs are basically pens suspended over a paper-covered rotating drum. When the earth trembles the pen makes a larger squiggle on the drum, allowing the size of the shaking to be measured. Each whole number on the Richter scale represents an earthquake 30 times larger than the number below it. Earthquakes that measure less than 3.0 are not usually felt, while one of 5.0 produces the same amount of energy as the Hiroshima atomic bomb. Earthquakes measuring around 7 or 8 on the Richter scale can be devastating. The largest recorded quake happened in Chile in 1960 and measured 9.5.
A volcano is an opening in the Earth’s crust that allows magma, hot ash and gases to escape. Volcanoes can look like mountains or small hills, depending on what type they are.
Magma is molten rock - rock that is so hot it has turned into liquid. When magma reaches the surface of the Earth it is called lava and comes out of the volcano as a volcanic eruption, along with gases and ash.
Most volcanic eruptions are caused by tectonic plates moving towards each other, which usually produces violent eruptions. Other volcanoes, such as Mauna Loa in Hawaii are caused by hot spots in the Earth’s crust. These do not erupt violently and lava usually flows slowly out of them.
Eruptions from volcanoes can be very dangerous. They can produce:
Volcanoes can, however, help people living near them earn money by bringing in tourists to the area and improving the soil so that crops can be grown.
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Earthquakes can destroy settlements and kill many people. Effects of earthquakes are often classified as primary and secondary impacts. Primary effects occur as a direct result of the ground shaking, eg buildings collapsing. Secondary effects occur as a result of the primary effects, eg tsunamis or fires due to ruptured gas mains. It is also possible to classify the impacts of an earthquake by taking the following factors into account:
|Social impacts||Economic impacts||Environmental impacts|
|Short-term (immediate) impacts||People may be killed or injured. Homes may be destroyed. Transport and communication links may be disrupted. Water pipes may burst and water supplies may be contaminated.||Shops and business may be destroyed. Looting may take place. The damage to transport and communication links can make trade difficult.||The built landscape may be destroyed. Fires can spread due to gas pipe explosions. Fires can damage areas of woodland. Landslides may occur. Tsunamis may cause flooding in coastal areas.|
|Long-term impacts||Disease may spread. People may have to be re-housed, sometimes in refugee camps.||The cost of rebuilding a settlement is high. Investment in the area may be focused only on repairing the damage caused by the earthquake. Income could be lost.||Important natural and human landmarks may be lost.|