UNIDAD AICLE: Volcanoes and Earthquakes. Natural risks

5. VOLCANOES AND EARTHQUAKES. NATURAL RISKS

Volcanoes and earthquakes are phenomena related with the plates boundaries, and both are great natural disasters which cause hundreds of victims around the world.

 Volcanoes

Volcanoes are openings in the Earth’s crust through which magma flows from inside the planet to the surface.

Magma is a mixture of molten minerals, gases and pieces of solid rock.

Listen, repeat and label the structure of a volcano:

http://www.educaplay.com/es/recursoseducativos/1682751/volcano.htm

Materials expelled by volcanoes:

• ·         Liquid materials: it is called lava.
• ·         Gas materials: are released from magma when it reaches the surface. The main gases are water vapour, hydrogen sulphide and carbon dioxide. Gases are the cause of explosive eruption.
• ·         Solid materials or pyroclasts:

o   Ash consists of particles less than 2 mm in diameter.

o   Lapilli are particles between 2 and 64 mm.

o   Volcanic bombs are rocks larger than 64 mm.

Build your own volcano. In groups of three students, build your own volcano following the instruction of this video: http://www.wikihow.com/Make-a-Soda-Bottle-Volcano

Earthquakes

Earthquakes are sudden movements of the surface layers of the Earth produced by the fracture of rocks.

An earthquake has the following elements:

• ·         Hypocentre: it is the point in the Earth’s crust where the earthquake starts.
• ·         Epicentre: it is the point on the Earth’s surface that is directly above the hyponcentre.
• ·         Seismic waves: they are vibrations that extend in all directions from the hyponcentre.

The magnitude of an earthquake pointing out how much energy is released during a tremor. It is measured by the Richter scale.

The intensity of an earthquake is determined by studying how much destruction it causes. It is measured by the 12-degree scale of Mercalli.

Natural disasters made by volcanoes and earthquakes

Volcanoes and earthquakes can cause very serious catastrophes, which we can minimize using prediction and prevention measures.

·         Prediction measures: it consists in finding out when, where and how a catastrophic event can occur. There are many signs that can help us to predict a volcanic eruption just before it occurs, but it is very difficult to predict an earthquake. We just only can know the probability that an earthquake occur in an area.

·         Prevention measures: we can avoid catastrophes if we take the correct prevention measures. The most important measures to prevent disasters are:

o   Produce risk maps that indicate areas of high risk.

o   Inform the people who live in the area about the risks is high.

o   Establish civil protection programmes for catastrophic situations.

o   Build dykes to slow down or change the course of the rivers of lava, or build earthquake-resistant buildings that can absorb any vibrations.

Talking about seismic disasters in Andalusia:

In groups of four students, search for information about historical earthquakes in Andalusia and make a poster about the most important. Make a presentation of the work done.