AS/A Level GCE OCR AS/A Level Geography
Topic 2.5 – Hazardous Earth (AS)
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Introduction
Overview
Delivery guides are designed to represent a body of knowledge about teaching a particular topic and contain:
- Content: A clear outline of the content covered by the delivery guide;
- Thinking Conceptually: Expert guidance on the key concepts involved, common difficulties students may have, approaches to teaching that can help students understand these concepts and how this topic links conceptually to other areas of the subject;
- Thinking Contextually: A range of suggested teaching activities using a variety of themes so that different activities can be selected which best suit particular classes, learning styles or teaching approaches.
Curriculum Content
Overview
| 1. What is the evidence for continental drift and plate tectonics? | |
| Key Ideas
| Content |
| 1.a. There is a variety of evidence for the theories of continental drift and platetectonics. |
• the basic structure of the Earth including the lithosphere, asthenosphere and the roleof convection currents
|
| 1.b. There are distinctive features and processes at plate boundaries. |
• the global pattern of plates and plate boundaries
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| 2. What are the main hazards generated by volcanic activity? | |
| Key Ideas
| Content |
| 2.a. There is a variety of volcanic activity and resultant landforms and landscapes. |
• explosive eruptions (higher viscosity magma) located at convergent (destructive)plate boundaries
|
| 2.b. Volcanic eruptions generate distinctive hazards. |
• lava flows, pyroclastic flows, gas emissions, tephra and ash
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| 3. What are the main hazards generated by seismic activity? | |
| Key Ideas
| Content |
| 3.a. There is a variety of earthquake activity and resultant landforms and landscapes. |
• shallow-focus earthquakes
|
| 3.b. Earthquakes generate distinctive hazards. |
• ground shaking and ground displacement
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| 4. What are the implications of living in tectonically active locations? | |
| Key Ideas
| Content |
| 4.a. There are a range of impacts people experience as a result of volcanic eruptions. |
• reasons why people choose to live in tectonically active locations
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| 4.b. There are a range of impacts people experience as a result of earthquake activity. |
• reasons why people choose to live in tectonically active locations
|
| 5. What measures are available to help people cope with living in tectonically activelocations? | |
| Key Ideas
| Content |
| 5.a. There are various strategies to manage hazards from volcanic activity. | Case studies of two countries at contrasting levels of economic development to illustrate strategies used to cope with volcanic activity including:
• attempts to mitigate against the event, such as lava diversion channels
|
| 5.b. There are various strategies to manage hazards from earthquakes. |
• attempts to mitigate against the event such as land-use zoning
|
| 5.c. The exposure of people to risks and their ability to cope with tectonic hazardschanges over time. |
• changes in the frequency and impacts of tectonic hazards over time
|
Thinking Conceptually
Overview
Common misconceptions or difficulties learners may have:
There are a number of misconceptions that students may well have about this topic. Plate tectonics refers to the global tectonic thermodynamic paradigm that emerged in the late 1960s and geologists use to explain how the whole planet works as a system, continental drift is pre-1960 theory that the continental crustal blocks are not static but have moved through geological time (either independent or as part of lithospheric tectonic plates).
Mantle convection driven by the flux of geothermal energy is a key idea and this is intimately linked to the plate tectonic paradigm, indeed it is true to say that mantle convection is plate tectonics. However most textbooks and popular science media still present an old continental drift theory developed in the 1940s where the continents (islands of ‘Sial’) were carried along like battle ships ploughing through a sea of oceanic crust (‘Sima’) carried like rafts by currents in the ‘semi-molten’ mantle. In the 1980s it was shown that any current in the asthenosphere would be too weak to move the rigid lithosphere.
The current plate tectonic model holds that it is cooling at the top not heating from below that drives convection: imagine if the skin on custard continued to thicken until its density rises high enough so that the thick dense skin started to slide into the custard at the edges of the jug, tearing a crack in the middle of the surface and allowing warm custard to erupt along a mid-custard jug ridge – the cold skin sliding down into the warm custard and the gentle upwelling in the custard are a convection system driven by cooling at the surface.
In plate tectonics the sources of geothermal heat driving the system is the decay of the radioactive isotopes of U, Th and K in the mantle and crust, with some residual heat from the formation of the Earth (from the core and mantle). The lithosphere cools by losing heat at the Earth’s surface (mostly over the ocean bed). As it cools it thickens and becomes denser until it subsides into the mantle at convergent plate boundaries forming subduction zones. As the cool, dense, thick lithospheric slab descends it causes further cooling in the surrounding mantle; this process is called slab-pull and is the main mechanism causing the tectonic plates to move. Hot mantle material rises up to fill the space where plates are being pulled apart at divergent plate boundaries, lifting the seabed to form mid-ocean ridges which causes the tectonic plate under the action of gravity to slide down off the ridges (ridge-push).
The misconception that the mantle is made of magma or ‘semi-liquid’ is misleading, the mantle is solid (otherwise it would not transmit S-waves), magma only exists locally and mostly as thin films on crystal boundaries like water in a slightly damp sponge. Students will be familiar from GCSE (9-1) Physics/Science with states of matter and relationships for atmospheric gases, plate tectonics and volcanic processes apply the same ideas to geothermal heat and rocks in the mantle and crust. Students of geography are aware that solid materials do flow such as ice in glaciers or flow in the mantle causing isostatic rebound after an ice sheets melt (silly putty® has similar viscoelastic properties unlike glass which does not flow); this happens very slowly within the crystalline structure of minerals (e.g. ice, quartz). Magma is formed by partial melting (often with very small percentages of melt) and are understandable as relationships: at mid-ocean ridges melting occurs because P drops while at hot spots P drops and T increase, while above subduction zones the water released from the sediments acts in the same way as cryolite flux in aluminium smelting (GCSE Chemistry) lowering the melting point of the rock.
In addition, students should understand that the earth’s crust and tectonic plates are dynamic and always changing, for example through the study of hotspots (e.g. Hawaii) and continental rifting (e.g. East African Rift Valley). The timescale of plate movement is immense but looking at the changes in continents over geological time should also help to develop better understanding (supercontinent cycling).
There are a large number of key terms that students need to understand in order to fully access the subject. Explicit teacher help to reinforce learning will be very valuable. Comparing the impacts of a variety of up to date case studies will help to illustrate this.
Conceptual links to other areas of the specification – useful ways to approach this topic to set learners up for topics later in the course:
Understanding the physical structure of the Earth and the changing nature of the crust and tectonic plates is a key foundation to understanding global climate change, the world’s oceans, and surface processes such as glaciation and coastal landscape systems. A peach is a good analogy for the layered structure of the Earth: cut a large peach in half and the stone will be around 50% of the diameter and the skin <0.2% which is about the same proportions as the core, mantle and crust, but remember the crust is only the top tenth of the lithosphere. The dynamic processes of plate tectonics govern the location of the world’s oceans, continents and mountain systems. These in turn influence the sequestering of carbon into the mantle at subduction zones, ocean circulation and atmospheric processes, which affect global climate on a scale from individual seasons to tens of millions of years. The Hazardous Earth topic therefore links intrinsically with both the Physical Systems component of the course, and the Geographical Debates component, in particular Climate Change and Exploring Oceans. The Oceans topic in particular helps explain how and why climate has changed in the geological past and explains the relief of ocean basins, including ocean ridges and rifts, ocean trenches and guyots.
In this topic students will gain understanding of a range of specialised concepts which are relevant across the specification including place, location, scale, change, vulnerability, causality, inequality, mitigation and adaptation, sustainability, risk and resilience. They will engage with models, theories and generalisations, and in doing so understand that new knowledge is continually being created, revised and updated and that old ideas and theories may well be discarded.
Thinking Contextually
Overview
Contextual learning should emphasise problem solving, take an enquiry approach with multiple contexts for decision making and offer students the opportunity to monitor their learning and thereby become more reflective learners. In this topic students will develop an in-depth understanding of patterns, processes and concepts related to our hazardous earth at a range of temporal and spatial scales, and will recognise and analyse the complexity of people-environment interactions.
They will;
- identify, assimilate, analyse and communicate data and develop graphicacy skills – manipulating maps, diagrams, graphs and images including using GIS
- use patterns in data sets to make predictions about the distribution and characteristics of relevant features and processes
- develop as critical and reflective learners, able to articulate opinions, suggest relevant new ideas and provide evidenced arguments.
- use the UK School Seismology Project to explore real earthquake data on the Earth and from 2019 from Mars too as part of MarsQuake.
1. What do we know and what needs to be consigning to room 101?
Our understanding of plate tectonics is developing all the time. Sometimes the changes are so dramatic that what we thought we knew needs re-thinking.
So what do we need to rethink and what do we know for sure? Try this refresher quiz to check out what you know and what you need to rethink. At the end of the topic try this quiz again, check out how many more answers you get right and see if you can clearly explain your answers this time!
2. What drives the plates?
Explores the different processes likely to be driving plate movement by use of a kinaesthetic learning pupil role play.
A group role play can be used to demonstrate convection currents, ridge-push and slab pull. An extension activity analyses a map of the Nazca plate to allow students to discover the importance of slab-pull.
3. A Card sort with a difference
The information on the cards contains both evidence and theory. Some of the theories are out of date and have been discarded. Through engaging in this activity students will clarify the difference between theory and evidence and will be challenged to decide which elements of theory can now be discarded and which are new or still relevant.
Task One
Sort the cards into two piles, (a) Theory and (b) Evidence You may find that some cards contain both. Justify which pile you wish to include these cards in by explaining which is the stronger element of the text the evidence or the theory.
Task Two
Decide which of the theory cards still stand and which need to be discarded.
4. How can you develop understanding of the Terms and Definitions?
This set of activities offers some teaching strategies to facilitate reinforcement of new terms. They encourage questioning and feedback to help form student learning.
(a) Assessing your key word understanding grid
Give out the assessing your key word understanding grid. Read out each Key word with its definition and a sentence that contains the word in an appropriate subject context. Students fill in the table accordingly.
(b) What Am I? Game
This develops understanding of the terms and definitions introduced in this topic.
(c) Pair the term to the definition
Card sort activity. Cut out the terms and definitions separately from the table. Put the students into small groups and ask them to pair the terms to the definitions.
(d) Word of the week
Students commit to using a selected term from the list of terms as often as possible during the week and report back the following week. These are posted on the wall.
(e) Students vocabulary list
Students write their own list of terms and definitions which they continually add to during the unit.
5. Tectonic Processes shaping the Earth’s surface
Students place key terms in the appropriate place on the diagram showing Lithosphere/plate processes and interaction with the mantle.
Place the key terms below in the appropriate place on the diagram.
Key terms
(a) Mid Ocean Ridge
(b) Subcontinental collision, subduction
(c) Ridge Push
(d) Slab Pull
(e) Ocean Subduction
(f) Hot Spot Volcanoes and Ocean Plateaus
Further Activities
(a) Use the further references and include the terms from the diagram to explain the features and processes operating at;
(i) Divergent plate boundaries
(ii) Convergent plate boundaries
(iii) Conservative plate boundaries
(b) This activity to reinforce learning is a map from memory using the diagram showing Lithosphere/plate processes and interaction with the mantle. The activity helps to support thinking skills strategy, designed to develop knowledge, visual literacy and complex inter-relationships.
6. Why was there an earthquake in Nepal?
This activity is designed to help students understand why earthquakes might occur at mountain belts. The earthquakes are the result of a range of processes such as thrust faulting and not folding.
What do your students imagine an earthquake is? Ask them to see if they can come up with any explanation for why earthquakes might occur when folding takes place. They may well infer that there are other processes operating.
Watch the video and explanation for the formation of the Himalayan mountain range and Tibetan plateau. This is the result of the collision between the Indian Plate and Eurasian Plate which began 50 million years ago and continues today. Note the term ‘Accretionary wedge’ which is in the glossary. This is an opportunity to reinforce the term. Complete the diagram on Learner Resource 5 using the Geological Society website.
7. It’s all about patterns and processes
This resource sets students a number of tasks to help them interrogate patterns and distributions, to understand how data may be spread out over an area (in this case earthquake location) and to consider explanations for why or how the patterns of earthquakes are distributed.
Give out a copy of the resource Fig. 1 (LR6) Put the students into pairs or small groups and pose the following questions;
Look at the pattern shown on the diagram. How might you describe the pattern? What does it represent? Why are different colours used?
Thinking geographically, what else do you need to know? What would help you describe the pattern more effectively? Are there any spatial associations between other distributions?
Conclude that the pattern shown is of earthquakes. The colours represent strength and depth.
8. Why are shallow and deep earthquakes found in different places?
9. Where do volcanoes occur? Why are some volcanoes explosive and others not?
The main factors that determine how a volcano will erupt are gas content and viscosity. This is different at different margins. Volcanoes at subduction zones contain more gas and are more explosive. Students will understand the different locations and nature of volcanic eruptions at each margin.
Ask your students to use this link to review the three main types of plate boundaries on Learner Resource 8.
Ask your students to identify globally where the vast majority of volcanic eruptions occur. Do most volcanoes occur on land or sea?
Ask them to note the different types of volcanoes which can occur at the following:
- at convergent (destructive) plate boundaries
- at divergent (constructive) plate boundaries
- eruptions not at plate boundaries (hot spots) such as the Hawaiian chain and the East African Rift Valley
Ask your students to describe the different types of volcanoes and to investigate their causes and features. Draw out the differences between volcanoes at convergent (destructive) plate boundaries, divergent (constructive) plate boundaries and so called hot spots such as the Hawaiian chain. Explain why some volcanoes are explosive and others not.
10. The puzzle of hotspots
11. Examining the different types of volcanic eruptions and the various hazards they generate
12. Why do people live in earthquake prone areas?
13. Why do people continue to live in the shadow of an active volcano?
14. Manage hazards from a volcanic activity
Students will explore the various strategies to manage hazards from volcanic activity including attempts to mitigate against:
- the event itself, such as lava diversion channels
- vulnerability such as community preparedness
- losses, such as rescue and emergency relief. This information will support students understanding in preparation for their case studies.
15. Managing hazards from earthquakes
Students will review the hazards arising from earthquakes which include: ground shaking; liquefaction; mass movements such as landslides and tsunamis.
They will then examine the various strategies to manage hazards from earthquakes. These include:
- attempts to mitigate against the event such as land-use zoning
- attempts to mitigate against vulnerability such as building design
- attempts to mitigate against losses such as insurance.
16. Risk and resilience
Students will explore the exposure of people to risks and their ability to cope with tectonic hazards changes over time.
They will investigate how and why the risks from tectonic hazards have changed over time including:
- changes in the frequency and impacts of tectonic hazards over time
- the degree of risk posed by a hazard and the probability of the hazard event occurring (the disaster risk equation)
Acknowledgements
Overview
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