The Restless Earth Year 11 revision. Key terms Key termDefinition AsthenosphereThe upper part of the Earth’s mantle, where the rocks are more fluid. Collision.

The Restless Earth

Year 11 revision

Key terms

Key term Definition

Asthenosphere

The upper part of the Earth’s mantle, where the rocks are more fluid.

Collision plate boundary

A tectonic margin at which two continental plates come together (collide).

Conservative plate boundary

Where two tectonic plates slide past each other.

Constructive plate boundary

Tectonic plate margin where rising magma adds new material to the diverging plates.

Destructive plate boundary

Tectonic plate margins where oceanic plate is subducted.

Convection currents

Circulating movements of magma in the mantle caused by heat from the core.

Key termsKey term Definition

Core The central part of the Earth, consisting of a solid inner core and a more fluid outer core, and mostly composed of iron and nickel.

Evacuation The removal of people from an area, generally in an attempt to avoid a threatened disaster (or escape from one that has happened).

Long-term planning

Planning that takes into consideration the long term (i.e. over 5 years).

Oceanic crust

The part of the crust dominated by denser basaltic rocks. (Under oceans)

Continental crust

The part of the crust dominated by less dense granitic rocks. (Under continents)

Key terms

Key term Definition

Tectonic hazards

Threats posed by earthquakes, volcanoes and other events triggered by crustal processes.

Plate margin

The boundary between two tectonic plates.

Prediction Forecasting future changes.

Primary impacts

Impacts caused directly by the volcano/earthquake.

Secondary impacts

Impacts caused indirectly by the volcano/earthquake, for example ‘a knock on effect’ e.g. Fires caused by broken gas pipes.

Response The way and which people react to a situation.

Short-term emergency relief

Help and aid provided to an area to prevent immediate loss of life because of shortages of basics, such as water, food and shelter.

Key terms

Key term Definition

Focus The point inside the earth where an earthquake starts.

Epicenter The point on the lands’ surface, directly above the focus.

Seismic waves

Waves of energy that radiate out from an earthquake.

Magnitude The size of an earthquake, measured by the Richter Scale.

Key facts: Structure of the Earth

Key facts: The crust

Oceanic Crust

• Underneath oceans/seas

• Thinner (8-12km)

• HEAVY Basaltic rock

• (rich in Si, Mg)

Continental Crust

• On land

• Thicker(30-65km)

• LIGHT Granitic rock

• (rich in Si, Al)

Mantle

Key facts: Tectonic plates

Key facts: Constructive plate boundary

Plates are pulled apart by the convection currents in the mantle below

Magma rises between the plates, forming volcanoes

North American plate Eurasian Plate

e.g. The mid-Atlantic Ridge (Eurasian and North American plates moving apart)

Key facts: Destructive plate boundary

Lower mantle

Heavier oceanic crust gets pushed under the continental plate

The rock jolts and grinds, causing earthquakes

The movement heats up the rock and melts it. The molten rock forces its way up through the crust to form a volcano.

The area where the oceanic plate sinks below the continental plate is called the SUBDUCTION ZONE

e.g. Nazca is subducting under South American plate.

Key facts: Conservative plate boundary

Plates slide past each other. Parts of the plates get stuck and then lurch free causing earthquakes.

No rock is pushed down or melted and no gaps occur between the plates therefore there are no volcanoes.

e.g. San Andreaas Fault in California, USA. (North American and Pacific plates sliding past each other)

Key facts: Collision plate boundary

Two continental crustsmove towards each other

The plates neither sink or are destroyed – so they buckleupwards forming mountains

The rock jolts and grinds, causing earthquakes

e.g. The Himalayas (Nepal). Formed as the Indian and Eurasian continental plates push into each other

Africa

North America

South America

Europe

Australasia

Asia

Key facts: Hazards at plate margins

Key:Volcano Earthquake

Key facts: Convection currents

Circulating movements of magma in the mantle (convection currents) caused by heat from the core

Case studies!

Volcano Case Study 1:

Type: Composite volcanoName: Mt St. Helens, USA

Volcano Case Study 1:

Type Composite volcano

Name Mt St. Helens

Location Washington State, USA. On the plate boundary between the Juan de Fuca plate and North American plate.

Formation Layers of lava and ash are deposited by eruptions. The lava is....

Lava type ...mostly andesitic, which typically cools and hardens before spreading far due to high viscosity (thick like honey!), leading to...

Shape ...a steep-sided volcano.

Explosivity/ pyroclastic flows

Highly explosive with lots of boulders and debris. Nuée ardente (hot ash and gas), Lahars (mudflows of ash and water).

Volcano Case Study 1:

Mount Saint HelensDate: 18th May 1980

Type: Composite volcano

Primary effects: Secondary effects

• 57 fatalities, 200 houses, 27 bridges, 15 miles of railway and 185 miles of roads were destroyed

• Ash cloud reached 80,000ft in 15 minutes, circled the earth in 15 days

• The eruption removed 13% of the volcano’s rock, making it 390m shorter

• Thousands of Elk, Deer and Salmon were killed and crops were destroyed

• Major problems with sewerage disposal and water systems

• Roads closed due to low visibility from the ash

• Some airports closed for two weeks

• Fine ash getting into electrical systems caused blackouts

• 5 further eruptions between May and October 1980

Volcano Case Study 2:

Type: Composite/Fissure volcanoName: Mt Nyiragongo.

Volcano Case Study 2:

Type Composite/Fissure volcano

Name Mt Nyiragongo

Location Democratic Republic of Congo (Africa)

Formation Layers of lava have erupted from the crater and fissures. The lava...

Lava type ...has an extremely low silica content (the lava is mafic) and so flows very fast (can reach 100km/h), meaning...

Shape ...the volcano has very steep sides as the lava flows away so quickly

Explosivity/ pyroclastic flows

Low explosivity but fast-moving lava poses great danger. CO2 gas released. Ash clouds occur.

Volcano Case Study 2:

Mt Nyiragongo, Democratic Republic of Congo

Date: 17th January 2002Type: Composite / Fissure volcano

Primary effects: Secondary effects

• Homes were destroyed by ash and lava

• 100 people died• Lava filled roads making it

difficult for emergency services to move around

• Lava covered 15% of Goma city, and destroyed 30% of the city

• 400,000 people evacuated• Cholera spread because of

poor sanitation• One month after the

eruption, 350,000 people were dependant on aid

• People lost their businesses and jobs

• After the eruption, a large number of earthquakes were felt around Goma and Gisenyi

Volcano Case Study 3:

Type: Shield volcanoName: Mauna Loa, Hawaii.

Volcano Case Study 3:

Type Shield volcanoName Mauna Loa

Location Hawaii (on the ‘Hawaii Hotspot’)

Formation Mauna Loa was created as the Pacific tectonic plate moved over the Hawaiian hotspot in the mantle. Fluid lava flows out slowly from the volcano because...

Lava type ...the lava is mostly basaltic, silica-poor, and very fluid. This creates...

Shape ...a low and flat shape

Explosivity/ pyroclastic flows

Low, non-explosive.

Volcano Case Study 3:

Mauna Loa, HawaiiDate: 24th March, 1984Type: Shield volcano

Primary effects: Secondary effects

• Potential impact to the city of Hilo, though lava from the 1984 eruption did not impact the city

• In the 1950 eruption, lava reached the sea within 4 hours of the eruption and destroyed a village

• There has only been one recorded fatality from eruptions of Mauna Loa

Earthquakes

Earthquake Case Study 1: San Francisco

San Andreas Fault

Name: San Francisco, USA (MEDC)

Date: 17th October, 1989Why: • California sits near the

San Andreas fault• The Pacific and North

American plates slide past each other

• The fault slipped several metres

Earthquake Case Study 1: San Francisco

Facts 63 dead

Clay soils liquefied, causing houses to sink, gas pipes to burst fires broke

outNearly 4,000

injured

Hit during rush hour

Death toll would have been larger, but 2 big baseball teams playing so many people where at the stadium or already at home, not commuting.

12,000 homeless

Property cost $10

billion

Earthquake Case Study 1:

San Francisco, USASize: 6.9 on Richter Scale

Primary effects: Secondary effects

• 63 fatalities, 3,757 injuries and 12,000 homeless

• Upper deck of Freeway collapsed onto lower deck, causing 42 fatalities

• 1.4 million people without power following the earthquake, restored to most the same day

• Burst gas mains leading to multiple fires

• Soil liquefaction causing major property damage

• Landslides and ground ruptures

• 1.4 million people without power following the earthquake

Earthquake Case Study 2:

Name: El Salvador, Central America (LEDC) Date: 13th January and 13th February, 2001Facts: • Smallest country in

Central America with less people than London.

• Very seismically active area, at the junction of three tectonic plates

What happened?: Two major earthquakes within 1 month, plus thousands of aftershocks

Earthquake Case Study 2:

Facts

Emergency services, such as hospitals and the fire service, are not well-prepared to

deal with a large-scale disaster.

Roads and other infrastructure poor

(as LEDC)

El Salvador is a very poor LEDC

Less equipment/ training for emergency services (LEDC) so response effectiveness

reduced.

185,338 houses damagedOver 8,000

injuries

Buildings and roads are not usually designed to withstand

earthquakes here

>1.5million people

affected

Even where fire-engines are available there is no water supply for them to use or good roads to

reach the areas in need.

Earthquake Case Study 2:

El Salvador, Central AmericaSize: 7.6 / 6.6 on Richter Scale

Primary effects: Secondary effects

13th January earthquake:• 844 fatalities, 4,723 injured,

108,226 houses destroyed• Many of the fatalities and much

of the damage was caused by landslides

13th February earthquake:• 315 fatalities, 3,399 injured,

41,302 houses destroyed

• More than 2,500 aftershocks, causing additional damage

• More than 500 landslides• Clean water and sanitation

became major issues• Major disruption to electricity

supplies• Damage to the telephone

system and the control tower at the airport delayed incoming relief from abroad

What factors influence the effects / impacts of a hazard?

The type of hazard

The place’s vulnerability to

hazards

The ability or ‘capacity’ to cope and recover from

an event

Impacts of earthquakes

Factor Why this affects the impact of an earthquake?

Distance from the epicentre

The effects of an earthquake are more severe at its centre.

Size of quake The higher on the Richter scale, the more severe the earthquake is.

Level of development (MEDC or LEDC)

MEDCs are more likely to have the resources and technology for monitoring, prediction and response.

Population density (rural or urban area)

The more densely populated an area, the more likely there are to be deaths and casualties.

Communication Accessibility for rescue teams.

Time of day Influences whether people are in their homes, at work or travelling. A severe earthquake at rush hour in a densely populated urban area could have devastating effects.

The time of year and climate

Influences survival rates and the rate at which disease can spread.

Preparing for earthquakes and volcanoes

1. Monitoring seismic waves2. Earthquake proof buildings3. ‘Grab bags’ containing essential items

e.g. Tinned food, bottled water, blanket4. Training emergency services5. Evacuation plans6. Early warning systems

Aims: a)Minimise loss of life

b)Minimise disruption of critical services

c)Minimise damage

Preparing for earthquakes and volcanoes

MEDC building design:

Bolting buildings to foundations and providing support walls (‘shear walls’). These are made from concrete and have steel rods embedded inside to help strengthen.

Walls reinforced and supported by adding diagonal steel beams (‘cross bracing’)

‘Base isolators’ act like shock absorbers between building and foundations. Help absorb some of sideways motion.

Deep foundations for skyscrapers

Gas and water lines specially reinforced with flexible joints to prevent breaking

Preparing for earthquakes and volcanoes

LEDC building design:Strengthening new buildings by:

- Removal of mud overlay on roof- Add diagonal bracing to frame (often timber as steel too expensive)- install ‘through-stones’. Needs training of local artisans (new skills) - strengthening of wall corners, using wire mesh and cement overlay (although mesh not often available in rural areas)- install ring beam (band of concrete) at roof level- Pointing of exterior walls with cement mortar

LEDC building design:

Strengthening old buildings by:

- Use cement/sand mortar and shaped stones in construction. - Limit thickness of mud overlay to 200mm- Install ‘knee-braces’ to reinforce the vertical/horizontal connections- Use straw roofs

Long and short-term responses to tectonic hazards

Short-term response

Long-term response

Emergency care Damage proof buildings

Foreign/national aid Education/training

Prepare emergency kits for future quakes/eruptions

Permanent relocation

Evacuation procedures in place

Evacuation plans and websites to inform citizens

Goals of disaster

management

Reduce, or avoid, losses from hazards.

Achieve rapid and effective

recovery.

Assure prompt assistance to

victims.

Video revision:

1. Continental drift2. So why do the plates move?3. Structure of the Earth 1 4. Structure of the Earth 2 5. Why do volcanoes & earthquakes hap

pen?6. Volcano formation 7. Subduction8. Shield volcano9. Mt St Helens 10.Nyiragongo film

1. Describe one way a region affected by earthquakes can prepare for this hazard. (2 marks)

2. Using an example(s), describe the effects of earthquakes on people and property. (4 marks)

3. Suggest one reason why the number of deaths varies between earthquakes. (2 marks)

4. Give two reasons why developing countries are very vulnerable to earthquake damage (2 marks)

5. Give two reasons why some earthquakes are more powerful than others (2 marks)

6. For either an earthquake or a volcanic eruption you have studied, describe the immediate responses (straight after the earthquake) in managing its impact. (4 marks)

Past GCSE questions: A

Past GCSE questions: B

7. Describe how hazard resistant design can help reduce the impact of earthquakes (4 marks)

8. Explain how building design can help reduce the impact of earthquakes (4 marks)

9. Explain how earthquakes happen on destructive plate margins (4 marks)

10. Explain how volcanoes are formed on either constructive or destructive plate boundaries. (4 marks).

11. For a named volcanic event, compare the primary and secondary impacts (6 marks)

Past GCSE questions: C

12. Describe two hazards volcanic eruptions can create for people (4 marks)

13. Explain how shield volcanoes are formed. (4 marks)

14. Describe the features of a shield volcano (2 marks)

15. Examine why the characteristics of volcanoes vary (6 marks)

16. Outline one difference between oceanic and continental crust (2 marks)

17. Describe two differences between oceanic and continental crusts (4 marks)

18. Draw an accurate labelled diagram of a destructive plate margin (4 marks)

Good luck!