Chapters 4 & 5: VolcanoesWhat you will learn

1.How plate tectonics leads to volcanic activity2.The parts of a volcano and the products of a volcanic eruption3.External or extrusive landforms (volcanic)4.Internal or intrusive landforms (plutonic)5.Effects of volcanoes – positive and negative using case studies6.Predicting volcanoes using a case study. 7.Know how this topic appears on the exam paper

Volcano Intro Clip

• http://www.youtube.com/watch?v=uZp1dNybgfc

Common Exam Questions

1. Explain how the study of plate tectonics has helped us to understand the occurrence of volcanoes

2. Discuss the positive (and negative) impacts of volcanoes

3. Examine the processes that have led to the formation of any two volcanic landforms

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

Activity: label the diagram of a volcano

Parts of a volcano Keywords

• Vent• Fissure• Cone shaped mountain• Magma chamber• Lava

The Distribution of Volcanic Activity

Volcanoes occur in three types of locations

1. Mid Ocean Ridges (at constructive plate boundaries)

2. Subduction zones (at destructive plate boundaries)

3. Hotspots in the middle of the plates

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

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

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

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

Active, Dormant & Extinct Volcanoes

• Active – almost constantly erupting

• Dormant – no eruption for more than 100 years

• Extinct – no eruptions in historic times

Products of Volcanic Eruptions Keywords

1. Lava

2. Pyroclasts and pyroclastic flows

3. Poisonous gases

4. Ash, pumice and dust

5. Water Vapour

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.

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

Activity: In pairs fill in the following tables

Properties Acid Lava Basic Lava

Silica Content

Trapped Gases

Type of eruption

Typical location

Examples

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.

3. Poisonous Gases

• Carbon dioxide

• Chlorine

• Sulpher dioxide

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.

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

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.

Activity

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

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

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

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.

Intrusive (plutonic) Landforms

1. Batholiths2. Sills3. Dykes4. Laccoliths5. Lopoliths

Extrusive (volcanic) Landforms

1. Volcanic cones - shield volcanoes and volcanic domes.

2. Lava Plateaux

Intrusive Landforms

1. Batholith2. Sill3. Dyke4. Laccoliths5. Lopoliths

Intrusive Landforms

1. 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 anddraw the diagram in your copy.

• 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.

In pairs name the following intrusive features

Extrusive (volcanic) Landforms

1. Volcanic cones2. Shield volcanoes3. Volcanic domes4. Lava plateau

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

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.

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.

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 characteristics1. Cover large areas of land2. Have a layered structure 3. Each lava eruption makes the plateau higher.

Name the features

Exam Question

• Discuss the formation of any two volcanic landforms.

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.

Homework

• Write into your copies how volcanoes can be predicted.

• Finished chapter today so traffic light the keywords and the chapter.

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