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Volcanoes and how they work
A volcano usually resembles a mountain in the shape of a cone. It is an opening of the surface of the Earth downward to a pool of extremely hot, molten rock (magma).

Volcanoes are locations where new Earth is born. They represent a superlative of geological processes. On the one hand, processes can be very slow, and on the other, very fast and dramatic, in the form of eruptions and earthquakes.

When pressure builds up, eruptions occur. Eruption products consist of lava (magma that reaches the surface of the Earth) and gases that come up and spill over the sides of the volcano or fill the air with volcanic material. As a result of a volcanic eruption, one can find lava flows, mudflows, falling ash and much more.  
How many volcanoes are active and dangerous?

  • 1500 volcanoes are potentially active on Earth
  • 70 volcanoes are currently in eruption
  • 10% of the human population is directly exposed to volcanic risk

Several large cities are located close to an active or dormant volcano.
Volcanic damage from 1900 to 2006
 Number of eventsPeople killedHomelessTotal AffectedDamage (Million$)
Africa152213180 710500 3539
Americas6967 84135 6801 123 5872808
Asia8021 45697 9002 668 287697
Europe1178314 00026 22444
Oceania20366546 000248 422400
Are all volcanoes the same? What are their characteristics?
There are several types of volcanoes. They basically differ in shape, composition, and type of eruption. Volcanic scenery may look like any of the following:

Different classifications of volcanoes can be found in the various sources below:

The volcano types we will be studying in the exercises are:

  • Strato volcano (Composite volcano): explosive eruptions, pyrocalstics, symmetrical, steep slopes;
  • Shield volcano: non-explosive eruptions, fluid basaltic lava, gentle broad slopes

    The eruptive behaviour of a volcano depends on the magma’s viscosity (a quantity that is related to a fluid's resistance to flow). High viscosity (high resistance to flow) causes an explosive activity, and low viscosity an effusive activity.


    More on volcanoes
    Volcanoes on EarthVolcanic hazardsVolcano monitoring
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