INTRODUCTION: HOW DO VOLCANOES ERUPT? 1.) Heated material from deep (asthenosphere/mantle)
The cause of it all… What causes volcanoes to erupt???What causes volcanoes to erupt??? The shift...
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![Page 1: The cause of it all… What causes volcanoes to erupt???What causes volcanoes to erupt??? The shift in the Earth’s plates are what causes volcanoes to form.The.](https://reader030.fdocuments.in/reader030/viewer/2022013108/56649db15503460f94a9feae/html5/thumbnails/1.jpg)
The cause of it all…
• What causes volcanoes to erupt???
• The shift in the Earth’s plates are what causes volcanoes to form.
• As the plates join or separate some of the molten rock is exposed.
• viscosity, resistance of a fluid to flow.
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Where do volcanoes erupt???
• Convergent plate boundaries – where two of Earth’s plates join together
• Divergent plate boundaries – where two of Earth’s plates move apart RING OF FIRE!!
• Hot spots – active areas below the earths crust
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Structure of a Volcano
• Magma – the molten, or liquid-like, rock within the Earth
• Lava – magma that reaches Earth’s surface
• Vent – an opening through which molten (liquid-like) rock flows onto Earth’s surface
• Volcanoes always have one central vent, but can also have several smaller side vents.
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Structure of a Volcano
magma
central vent
side vent
lava
old layers of lava
ash cloud
Earth’s crust
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Types of volcanoes
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There are three types
• Shield Volcano
• Cinder Cone
• Composite Volcano
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Shield Volcano
• Shaped like a long, flat dome
• Built up by many eruptions of lava• Sides are layers of lava
• Lava flows out gently and for great distances
• Hawaii is made up of this type of volcano.• One of Earth’s most active volcanoes
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Shield Volcanoes• The magma inside a shield volcano is rich in iron
and magnesium and is very fluid.
• Since the magma is very fluid, the lava coming out of the volcano tends to flow great distances.
• When shield volcanoes erupt, the flowing lava gives the volcano the shape of a gently sloping mountain.
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Shield Volcanoes• Eruptions of shield volcanoes are mild and can
occur several times.
• Mauna Loa in Hawaii is an example of a shield volcano.
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Shield Volcanoes
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Cinder Cone
• Steep sides
• Cone-shaped hill
• Formed from eruption of cinders and other rock fragments
• Very explosive eruptions
• Magma is thick and resists flowing
• Eruptions have a lot of cinder and ash.
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Cinder Cone Volcanoes
• The magma inside a cinder cone volcano has large amounts of gas trapped in it.
• Eruptions from cinder cone volcanoes are violent and explosive because of all the gas trapped in the magma.
• The large amounts of hot ash and lava thrown out of the vent fall to the ground forming the cone shape that these volcanoes have.
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Cinder Cone Volcanoes
• Cinder cone volcanoes are usually only active for a short time and then become dormant (inactive).
• Paricutin in Mexico is an example of a cinder cone volcano.
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Cinder Cone Volcanoes
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Composite Volcano
• Cone-shaped
• Steep near top, flatter towards bottom
• Built of layers of lava and rock fragments
• Produce a lot of lava and ash
• These produce very explosive eruptions because gas is trapped inside the volcanoes. This is due to lava from previous eruptions plugging the holes in a volcano’s side.
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Composite Volcanoes• The magma inside a composite volcano is rich in
silica and much thicker than magma from a shield volcano.
• Gases get trapped inside this thicker magma.
• Eruptions from composite volcanoes can be flowing lava or explosions. The explosive eruptions come from the trapped gases and produce cinders and ash.
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Composite Volcanoes• These different types of eruptions are what give
composite volcanoes their alternating layers of lava and cinders.
• Composite volcanoes have much steeper slopes than shield volcanoes.
• Mount Fuji in Japan and Mount St. Helens in the USA are examples of composite volcanoes.
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Composite Volcanoes