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Subject: Junior Cert Geography Teacher: Mr Lenehan Week: Week 2 Lesson: Our Restless Earth: Volcanoes

2.0 Learning Intentions

• Where volcanic activity takes places.

• The causes of volcanic activity.

• The features formed when a volcano erupts.

• The different types of volcano

• The positive and negative impacts of volcanoes.

• How people respond to volcanic eruptions.

1.1 Describe the formation and global distribution of volcanoes, earthquakes, and fold mountains in the

context of plate tectonics and structure of the Earth.

2.1 Describe the economic and social impacts of how we interact with the occurrence of volcanoes,

earthquakes, and fold mountains.

2.1 Specification

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2.3 Volcanoes

Where do volcanoes take

place?

Volcanoes occur at constructive plate

boundaries where plates separate.

As plates separate, magma rises to the earth’s

surface. It cools and hardens to form new

land.

Hence the name constructive plate boundary.

How do volcanoes form?

1. A volcanic mountain, or volcano, forms

when magma moves up to the surface

through a small opening called a vent.

2. The magma is stored underground in a large

chamber called a magma chamber.

3. As the gases build up in the magma

chamber. The pressure eventually causes the

magma to erupt out of the vent through an

opening called a crater.

4. The magma reaches the earth’s surface, it is

now called lava. It then cools and hardens

and begins to form a cone shaped mountain.

5. As well as lava, materials such as ash and

gas are also erupted from the volcano.

6. Over time after repeated eruptions, layers of

ash and lava repeatedly cool and harden

around the vent to form a cone-shaped

mountain.

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Using the notes to help you,

label the volcano.

2.4 Volcano labelling activity

Types of volcano

1. Active: Volcanoes that erupt regularly.

Example: Mount St Helens, USA

2. Dormant: Volcanoes that have not

erupted for a long time but may erupt

again.

Example: Mount Vesuvius, Italy

3. Extinct: Volcanoes that will not erupt

again.

Example: Croghan Hill, Co. Offaly.

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A volcanic feature: a mid-ocean ridge

A mid-ocean ridge is an underwater mountain

range that forms as a result of volcanic activity.

As magma rises to the ocean floor, it cools and

hardens, this happens very rapidly when lava

meets the cold sea water.

As underwater eruptions continue, the ocean floor

builds up to form a ridge of volcanic mountains.

The Mid-Atlantic ridge

The Mid-Atlantic Ridge formed when the

North American and Eurasian plates pulled

apart.

It is so high in places that it reaches the surface

of the ocean, forming volcanic islands such as

Iceland.

Video link to a video on volcanic activity around

the Pacific Ring of fire:

https://www.youtube.com/watch?v=DrwYtGf40h

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Iceland: A volcanic island

Iceland is 20 million years old and one of the

youngest nations on earth.

Underwater volcanic mountains eventually rose

above the surface of the ocean.

Iceland has active some of the earth’s most active

volcanoes such as Hekla and Krafla. Krafla has

been erupting continuously for 30 years.

2.5 Volcano revision activity

Q 1. What name is given to an underwater volcanic mountain range?

Q 2. What 2 plates slowly separated to form the Mid-Atlantic ridge?

Q 3. Explain what is meant by active, dormant and extinct volcanoes, give an example of each volcano.

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The Pacific Ring of fire

What is it?

An area of high volcanic and earthquake

activity.

Where is it?

Around the edge of the Pacific Ocean where the

Pacific plate meets many other plates.

What can be found here?

Volcanoes, volcanic islands and mid-ocean

ridges.

The Socio-economic effects of volcanoes

S o c i o - e c o n o m i c r e f e r s t o

h o w s o m e t h i n g i n f l u e n c e s a

g r o u p o f p e o p l e f i n a n c i a l l y

a n d s o c i a l l y .

Positive: Fertile soils: Lava produces fertile soils which are very

suitable for agriculture. For example, the Campana region in Italy is a fertile

farming region due to Mount Vesuvius.

Positive: Tourism: Tourists visit the sites of volcanoes, bringing

business to the local economy. In Iceland, hot springs called geysers also attract

tourism.

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Positive: Geothermal Energy: Volcanic activity can heat up

water which can be used to generate electricity.

Around 90% of Iceland’s energy is geothermal energy.

Negative: Toxic Gases: As well as lava,

gases such as sulphur dioxide are emitted from volcanoes causing acid rain.

This damages agriculture, fishing and forestry.

Negative: Loss of life: A lava flow can be

highly destructive and burn everything in its path.

This can result in a loss of human and animal life.

Negative: Lahars: When lava, ash and mud

mix with melted snow and ice, a deadly mudslide called a lahar can be created. Lahars can wipe out entire towns such as Nevado del Ruiz in Columbia in 1985.

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Mount St Helens: A Case study

What is it?

Mt St Helens is a volcanic mountain in Washington, USA.

When did it erupt?

It erupted in May 1980.

What were the effects of the eruption?

7000 large animals and hundreds of thousands of small animals were killed.

Surrounding forests were flattened, a lahar destroyed 200

homes, 400 metres was blown off the top of the mountain.

Mount St Helens: Short term

responses

Evacuation: Local authorities had been

monitoring the volcano, so they knew an eruption

was coming.

They were able to evacuate the area as a result. The

death toll of 61 would have been much higher had

they not evacuated.

Clean up: 1 million tons of ash had to be cleaned

up. This cost millions of dollars to do.

It took 10 weeks and provided 200,000 jobs for people.

Video link to footage of the Mount St Helens

eruption:

https://www.youtube.com/watch?v=AYla6q3is6

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2.6 Homework Correction

2.7 Homework Task

Mount St Helens: Long term

responses

Trees: Millions of trees have been replanted

as so many were destroyed during the eruption.

These will be fully grown by 2050.

Compensation: Compensation was paid to farmers,

business owners and people to rebuild their homes and livelihoods.

Tourism: The government has invested in tourist

accommodation to attract people to visit the area.

A 1. When magma is heated it rises up, as it nears the crust it

cools and moves sideways causing friction which pulls the

plates. The magma then cools and sinks back down into the

mantle. This process is constantly repeated.

A 2. African plate, South American plate, Eurasian plate, Nazca

plate.

A 3. At destructive plate boundaries, plates collide.

A 4. Fold mountains form when 2 plates collide. When they

collide, the heavier plate sinks down into the mantle, this is

called subduction. The lighter plate then buckles upwards,

getting crumbled and damaged in the process, causing a fold

mountain to form. The Alpine folding period.

A 5. Positive: Tourism (Skiing, hill walking)

Negative: Difficult to farm on.

Q 1. Explain why people might want to live in an area

that is prone to volcanic activity.

Q 2. Explain why so much volcanic activity takes

place around the Pacific Ring of fire.

Q 3. Explain one short term and one long term

response to the Mount St Helens eruption.

Q 4. Draw a labelled diagram of a volcano.