1. What are volcanoes like?
Lesson 5
Wednesday, 21 November 2018
What are volcanoes like?
To be able to explain the differences between the three main types of volcano. (B grade)
To be able to explain how the three main types of volcanoes were formed using key terminology. (A-A* grade)
To be able to describe a volcano by referring to its main parts.
(C-D grade)
Learning objectives;
To develop a greater understanding of the structure of a volcano.
To develop a greater knowledge of the different types of volcano.

2. Starter Figure 1 Easy Name the plate boundary in figure 1. (1 marks)
Medium
Name one other boundary which can create a volcanic eruption. (1 marks)
Hard
Explain how a volcano is formed at this boundary . (4 marks)

3. What is a volcano?
A volcano is an opening or vent in the earth’s surface through which molten material erupts and solidifies as lava.
Active volcano – liable to erupt e.g. Mt Etna
Vent
Dormant (sleeping) volcano – a volcano which has not erupted for many years. For example, Mt Pinatubo erupted in 1991 after 500 years of dormancy.
Extinct volcano – a volcano which has not erupted for many thousands or millions of years e.g. Edinburgh.
Write down your own definitions of active, dormant and extinct.
Why might a volcano become extinct?

4. What are the parts of a volcano?

5. Main vent- This is where the magma rises up through.
Structure of a volcano
Main vent- This is where the magma rises up through.
Layers of ash.
Rock plug- Created by cooled ash at the top of the vent.
Lahar- A mud slide made of melted snow and volcanic ash.
Side vent- if the main vent becomes blocked a side vent and secondary cone is created.
Magma chamber- The viscous magma here traps hot gases, the pressure builds up and they are released in eruptions.
Lava- Acidic lava escapes from main and side vents and moves slowly and cools quickly to create steep slopes.
Pyroclastic flow- A destructive torrent of hot ash, rocks, gases and steam moving at 200 mph.
Crater- The ‘dip’ at the top of the volcano created by explosions.
Ash cloud- contains steam, ash and volcanic bombs

6. What are the different types? Diagram and formation description
Volcano type
Margin type
Diagram and formation description
Products produced
Description of magma
Volcano example
Shield Volcano
Composite Volcano
Hot Spots

7. Shield volcanoes
These volcanoes are created at constructive margins. This is where two plates are moving apart from each other and magma moves to the surface through the gap.
A good example is the North America and Eurasian Plate creating Surtsey, Iceland.
The emerging lava is more fluid and therefore the shape of the volcano is low and wide. This is why it is called a ‘shield’ volcano.
The eruptions from these volcanoes are generally more gentle and can last for several months.

8. Composite or strato volcanoes
These are formed at destructive margins where one plate slides underneath the other.
An example is Montserrat formed by the Caribbean and South American plate.
A slab of ocean floor slides down and is melted due to friction. This is called the subduction zone. This melted magma warms up slowly and mixes with water and carbon dioxide released from the rock.
The hot magma is more sticky rises in violent eruptions to form steep sided volcanoes.
Layers of ash and lava build around the main vent to form a strato volcano.
The eruption is explosive and rock molten and solid flies from the volcano. This is followed by gas and steam which forms huge clouds called nees ardentes.

9. An example is Mauna Loa Hawii.
Hot spot volcanoes
In places where the plate is particularly thin, magma may be able to escape to the surface.
An example is Mauna Loa Hawii.
As the plate continues to move the volcano dies out and a new volcano is formed on another area of the plate.
Hot spots can create chains of shield volcanoes. They therefore have gentle oozing lava.

10. Exam practise
Outline the characteristics of a shield volcano (2 marks)
Explain the formation of a composite volcano (4 marks)