Grade 10 Geography: Volcanoes

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Grade 10 Geography: Volcanoes

By Nadia Kajee

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What are Volcanoes?

An opening in the Earth’s crust that allows magma, ash, and gasses to erupt from below the surface. It is made up of a magma chamber, a vent, a crater, and a cone-shaped mountain made up of layers of ash and lava.

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Let’s break this down:

Volcanoes form when molten material – known as magma – from below the Earth’s surface rises through cracks or pipes and forms a magma reservoir/chamber. A magma chamber is a collection of magma from the Earth’s mantle which collects in a large underground pool.

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The magma within this chamber is under great pressure and trying to force its way upward to the surface. It forces its way up to the surface through the vent. Think of the vent as a chimney for the volcano. A volcano has a main vent but also secondary vents which may not reach the surface.

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At the top of the volcano, we find the crater – the bowl-shaped feature from which the magma from the vent erupts. Once magma has reached the Earth’s surface it is now called lava. Magma = below the earth’s surface Lava = above the earth’s surface

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Magma vs Lava

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Finally, most volcanoes are cone-shaped mountains which are formed by alternating layers of lava and ash from previous eruptions. When a volcano erupts, lava forms as well as pyroclastic flow – an intense, hot cloud of steam, poisonous gases, and volcanic ash. When this ash cloud cools and settles on top of the lava, the layers of the volcano form. This process is repeated every time the volcano erupts.

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volcanoes nave LAYERS

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Classification of Volcanoes: There are three classifications of volcanoes, which are based on the different stages of a volcano’s life.

1. Active – A volcano which erupts regularly. Example: Mount Merapi in Indonesia – erupted December 31st, 2020 (What an eruptive end to 2020!) 2. Dormant – Has not erupted recently; but because it has in recorded history it is possible to erupt in future. Example: Mount Kilimanjaro, Tanzania and Mount Fuji, Japan. 3. Extinct – Has not erupted in recorded history and will most likely not do so. Example: Mount Kenya, Kenya.

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The Four Types of Volcanoes:

Shield Volcano Cinder Cone Volcano Composite Volcano Plug Dome Volcano (Also called Volcanic Dome or Lava Dome)

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Shield Volcano

Form when lava flows out of a central vent. An accumulation of many fluid, basaltic lava flows. Experience minor, but frequent, gentle eruptions of ash and cinders. Eruptions are not explosive. Gently sloping, dome-shaped volcanoes.

As a result of its gentle slopes, it has an enormous breath where the bases are dozens of kilometres wide. Example: Mauna Loa, Hawaii

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Cinder Cone Volcano

From when eruptions shoot great quantities of ash and particles of glassy lava into the air. The particles solidify in the air and rain down the vent. Eruptions are explosive and gas-charged and are made up of ash and solid material. Lava is limited. The smallest types of volcanoes, where the cone is made up of layered ash and cinders.

The conical peaks are the steepest. Example: Monte Nuovo, Italy.

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Cra Sich 1. Cinder Cone Volcano

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Composite Volcano

Form when alternating layers of ash, lava and rocks are created by multiple, and often explosive, eruptions. Eruptions are a mix of lava flows (layers of molten rock that flow over the land surface) and pyroclastic flows. Characterised by a steep-sided conical peak.

Also known as stratovolcanoes Example: Mount Vesuvius, Italy and Mount Fujiyama, Japan

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Crater Side Vent 2.Composite Volcano

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Plug Dome Volcano

Formed when highly viscous lavas flow onto the Earth’s surface, forming thick, bulbous masses. Volcanoes with summits (plugs) of solid lava. Experience violent, explosive eruptions. Calderas are created as a result. [A caldera is a large crater formed after an eruption which has caused a summit (peak of a volcano or mountain) to collapse]

Small, steep sloping sides; jagged blocks Example: Lassen Peak, California

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Crater 8 . Lava Dome

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The Impact of Volcanoes

Volcanoes impact the environment around them, both positively and negatively.

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Positive Impact

Volcanoes result in the formation of other natural features, such as caldera, hot springs and geysers, which are tourist attractions. Volcanic ash and some volcanic material benefit the fertility of the soil surrounding the volcano, which results in better soil quality for agriculture – benefits the livelihood of farmers.

Volcanic activity is responsible for the creation of intrusive landforms (magma cooling within the crust) to create landforms – this is gone into detail in grade 11) Diamonds can be found in some old volcanic pipes but it’s very rare.

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Negative Impact

Eruptions cause serious devastation and destruction. Volcanoes can emit dangerous fumes and particles into the atmosphere, such as carbon dioxide, sulphur dioxide, hydrogen sulphide, and hydrogen halides. Mudflows, a mixture of volcanic ash and water (from melted snow or ice), can cover settlements, leaving the habitants without homes.

Volcanic ash can pollute not only water supplies but also the atmosphere, which can reduce visibility and interfere with aircrafts. Example: In 2010, the Eyjafjallajökull volcano in Iceland erupted, and the volcanic ash ejected into the atmosphere resulted in many European countries implementing the largest air-traffic shut-down since World War II.

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Example: Let’s look at an example of the impact of a volcanic eruption.

In 2002, Mount Nyiragongo , DRC erupted resulting in: 245 deaths, caused by asphyxiation by carbon dioxide. Buildings collapsing due to the lava and earthquakes. Lava covering 13% of Goma, which left 120,000 homeless.

However, with this destruction and devastation does come soil fertility but this benefit is not sowed until the devastation has been met with aid.

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In Summary,

Volcanoes are intrusive landforms, caused by magma forcing its way to the Earth’s surface through vents. They have a magma chamber, a vent, a crater, and a cone-shaped mountain. A volcano is either active, dormant, or extinct depending on the volcano’s stage of life.

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Summary (continued)

There are four main types of volcanoes: Shield Volcano Cinder Cone Volcano Composite Volcano Plug Dome Volcano Which all have different formations and eruptions which influence how the volcano will look. There are both positive and negative impacts of volcanoes, however, the devastation caused by an active volcano will outweigh the positives during the period immediately following an eruption.

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