2. Chapters 4 & 5: Volcanoes What you will learn
How plate tectonics leads to volcanic activity
The parts of a volcano and the products of a volcanic eruption
External or extrusive landforms (volcanic)
Internal or intrusive landforms (plutonic)
Effects of volcanoes – positive and negative using case studies
Predicting volcanoes using a case study.
Know how this topic appears on the exam paper

3. Volcano Intro Clip

4. Common Exam Questions
Explain how the study of plate tectonics has helped us to understand the occurrence of volcanoes
Discuss the positive (and negative) impacts of volcanoes
Examine the processes that have led to the formation of any two volcanic landforms

5. Mind Map Volcanoes
In groups think of everything you remember about volcanoes since Junior cert
How they occur
Effects
Examples etc
Activity: Take down the mind map from the board

6. Activity: label the diagram of a volcano

7. Parts of a volcano Keywords
Vent
Fissure
Cone shaped mountain
Magma chamber
Lava

8. The Distribution of Volcanic Activity
Volcanoes occur in three types of locations
Mid Ocean Ridges (at constructive plate boundaries)
Subduction zones (at destructive plate boundaries)
Hotspots in the middle of the plates

10. Volcanoes at Divergent Margins
As plate separate, magma rises through the crust and out through the vent or fissure in the volcano; the lava cools and solidifies to form new crust (or a new layer to the volcano)
Mid-ocean ridges are created in this way
Lava plateau form where the lava spreads out rather than forming a volcano

11. Volcanoes at Convergent Margins
Subduction occurs where the heavier plate is pulled down under the lighter plate due to gravity and is melted deep in the mantle
This produces an explosive viscous (thick) lava; eruptions are violent due to intense build up of pressure
Dome volcanoes are steeply sloping cones with convex sides; formed because the lava is so thick and barely able to flow; it cools and solidifies forming a dome; layers build up but could also be destroyed by very violent eruptions

12. Volcanoes at Hotspots
Hot spots form when a rising column of very hot magma called a thermal plume forces its way through a fault in the oceanic crust; they do not drift with the plates; they have a fixed position
Shield volcanoes form where the lava runs freely & quickly creating gentle slopes

13. Remember we have done this already in chapter 1….
Can you remember the connection between plates and volcanic activity?
Activity: Read the sample answer on volcanoes and plate boundaries. In groups summarise the answer in bullet points into your copy books

14. Active, Dormant & Extinct Volcanoes
Active – almost constantly erupting
Dormant – no eruption for more than 100 years
Extinct – no eruptions in historic times

15. Products of Volcanic Eruptions Keywords
Lava
Pyroclasts and pyroclastic flows
Poisonous gases
Ash, pumice and dust
Water Vapour

16. 1. Lava Two types of Lava – Acidic and Basic
Type of lava changes depending on the plate boundary
Contains silica – The amount of silica determines how sticky the lava is.

17. Lava
Acid lava is high in silica which prevents gases escaping; is very explosive; found at convergent (destructive) plate margins
Basic lava is low in silica; lava flows freely; found at divergent (constructive) plate margins. Gentle lava eruptions

18. Activity: In pairs fill in the following tables
Properties
Acid Lava
Basic Lava
Silica Content
Trapped Gases
Type of eruption
Typical location
Examples

19. 2. Pyroclasts
Hot ash, lava and rock fragments that are thrown out of the volcano. Sometimes called volcanic bombs.
Pyroclastic Flows are boiling clouds of ash and rock which travel at great speeds (600km/hr) down the sides of the volcano. Also called Nuée ardentes.

20. 3. Poisonous Gases
Carbon dioxide
Chlorine
Sulpher dioxide

21. 4. Ash, Pumice and Dust
Power of the eruption turns rock into a fine ash inside the vent.
The ash is thrown many kilometres into the sky and may be carried by winds across the world. Can disrupt air travel.
When lava is thrown from the volcano it becomes full of air bubbles. If it cools quickly the bubbles become trapped in the rock and it is now called pumice. Some pieces contain so much air that they float in water.

22. 5. Water Vapour
Volcanoes along subduction zones release huge amounts of water vapour
(From the sea water that’s carried into the mantle by the sinking oceanic plates)
As the water vapour rises into the air it cools quickly creating torrential rain.
This can trigger lahars

23. Lahars
Word that describes a mixture of water and rock fragments flowing down the slopes of a volcano.
Looks like a large amount of wet concrete
Lahars vary in speed and size
Volcanic eruptions can trigger one or more lahar by quickly melting snow and ice on a volcano.

24. Activity
Work in pairs to discuss the positive and negative effects of volcanoes.

25. Good Effects of Volcanoes
Energy – geothermal energy (hot water) is piped to many homes and businesses in Iceland
Food production is abundant in volcanic regions; lava cools to form basalt which weathers to a mineral-rich soil
Tourism – volcanoes & geysers attract tourists in the millions e.g. Mt Vesuvius, Italy & Old Faithful, Yellowstone National Park, USA
New land is created Iceland and Hawaii are two examples
Minerals

26. Bad Effects of Volcanoes
Toxic gases (carbon dioxide, hydrogen, carbon monoxide & sulphur) are released
Pyroclasts (fiery volcanic bombs) rain down on surrounding areas
Nuée Ardente are clouds of hot gases & pyroclasts running down the side of a volcano at high speed
Lahar is a fast moving volcanic mudflow
Jokulhlaups are glaciers which are melted by an eruption beneath them
Climate change may occur if eruptions are particularly devastating
Can disrupt air travel

27. Volcanic Landforms
Intrusive (plutonic): occur beneath the surface but are visible because of weathering and erosion.
Extrusive (volcanic): Features found on the earth’s surface.

28. Intrusive (plutonic) Landforms
Batholiths
Sills
Dykes
Laccoliths
Lopoliths

29. Extrusive (volcanic) Landforms
Volcanic cones - shield volcanoes and volcanic domes.
Lava Plateaux

30. Intrusive Landforms
Batholith
Sill
Dyke
Laccoliths
Lopoliths

31. Intrusive Landforms
Batholith – a large mass of igneous rock (granite) that formed as magma from the mantle pushed into the crust and slowly cooled down and became solid.
Activity:
Read the notes in your book about
Batholiths. Summarise the main points and
draw the diagram in your copy.

32. Sills: Magma forces its way between layers of rock and becomes solid as large flat areas of igneous rock.
Dykes: Magma slices across rock layers and becomes solid and forms a wall of basalt or granite. It runs perpendicular to the rock layers.
Laccoliths: Magma seeps between rock layers pushing them up to form dome like structures.
Lopoliths: Form the same way but the weight of the magma causes the rock to sag downwards.

33. In pairs name the following intrusive features

34. Extrusive (volcanic) Landforms
Volcanic cones
Shield volcanoes
Volcanic domes
Lava plateau

35. Extrusive Landforms
Volcanic Cones: magma rises from the crust. Gas bubbles expand and help the magma to force its way through the cracks. Once the magma reaches the surface an eruption occurs which gradually forms a volcanic cone. There are two types
1) shield volcanoes 2) volcanic domes

36. Shield Volcanoes Broad, gentle, concave slopes e.g. Mauna Loa, Hawaii.
Associated with hotspots – highly fluid basic lava.
Basic lava flows easily over the ground for many kms before it becomes solid.
Mount Loa is 4,160m above sea level but from its base it is 10,000m high. 2km taller than Mount Everest.

37. Volcanic Domes
Mounds that form when acidic lava is erupted slowly and piles up covering the vent rather than flowing away.
Common at subduction zones.
Steep sided convex slopes that are very unstable and may callopse causing massive landslides.
Mount St. Helen USA.

38. Lava Plateau
Steep sided flat topped uplands of basalt that cover large areas
Formed by large but less explosive eruptions of highly fluid basic lava that pours from long narrow openings or fissures in the crust.
E.g. Antrim Plateau in County Antrim.
Have the same characteristics
Cover large areas of land
Have a layered structure
Each lava eruption makes the plateau higher.

39. Name the features

40. Exam Question
Discuss the formation of any two volcanic landforms.

41. Investigative Learning
In groups investigate how volcanic eruptions can be predicted.
Use your book to help. Find at least 4 methods.
Discuss the results with the class.

42. Homework Write into your copies how volcanoes can be predicted.
Finished chapter today so traffic light the keywords and the chapter.

43. End of chapter
Look back at the chapter objectives you wrote at the start of the chapter.
Have you achieved these or are you still working on them??
Traffic light your progress