What you will need to know in unit 4.2...
4.2.1 The processes experienced at each type of plate boundary which cause earthquakes and volcanic
eruptions.
4.2.2 The main characteristics of earthquakes: focus, epicentre, seismic waves.
4.2.3 Types of volcano: strato-volcano (composite cone), shield, cinder cone.
4.2.4 The classification of volcanoes as active, dormant, or extinct.
4.2.5 The main features of volcanoes: crater, vent, magma, magma chamber, secondary cone.
4.2.6 Volcanic hazards: lava flows, ash falls, lahars, pyroclastic flows, tephra, volcanic rocks, toxic gases; the significance of speed, size, frequency, and spread.
4.2.1 The processes experienced at each type of plate boundary which cause earthquakes and volcanic
eruptions.
4.2.2 The main characteristics of earthquakes: focus, epicentre, seismic waves.
4.2.3 Types of volcano: strato-volcano (composite cone), shield, cinder cone.
4.2.4 The classification of volcanoes as active, dormant, or extinct.
4.2.5 The main features of volcanoes: crater, vent, magma, magma chamber, secondary cone.
4.2.6 Volcanic hazards: lava flows, ash falls, lahars, pyroclastic flows, tephra, volcanic rocks, toxic gases; the significance of speed, size, frequency, and spread.
4.2.1 The processes experienced at each type of plate boundary
which cause earthquakes and volcanic eruptions.
which cause earthquakes and volcanic eruptions.
In 4.1, as part of our work on the mechanisms of earthquakes and volcanoes, we sketched and labelled diagrams of destructive and conservative plate boundaries to show how these hazards occur. We also completed two 4-mark questions: one explaining how a destructive plate boundary can lead to the formation of volcanoes, and another outlining how a conservative boundary can generate earthquake events. This content does not need to be revisited for the current unit.
Here is a brief reminder:
How volcanoes form at destructive plate boundaries:
How earthquakes occur at conservative plate boundaries
Here is a brief reminder:
How volcanoes form at destructive plate boundaries:
- Oceanic and continental plates converge, and the denser oceanic plate is subducted beneath the continental plate.
- As it sinks, the oceanic plate melts due to heat and pressure, forming magma in the mantle.
- The magma, being less dense than the surrounding rock, rises through cracks and weaknesses in the continental crust.
- The magma erupts at the surface, building a volcano, often forming a chain of volcanic mountains along the boundary.
How earthquakes occur at conservative plate boundaries
- Two plates slide past each other in opposite directions or at different speeds.
- The plates become stuck due to friction, even though they continue trying to move.
- Stress and pressure build up as the plates remain locked.
- When the pressure is released suddenly, the plates jerk past each other, producing an earthquake.
4.2.2 The main characteristics of earthquakes...
Earthquakes are sudden releases of energy within the Earth's crust that produce vibrations called seismic waves. These waves spread outward from the focus, which is the point underground where the rocks first break. The epicentre is the point on the Earth's surface directly above the focus, and it is usually where the shaking is felt most strongly. Understanding these key features helps explain why the effects of an earthquake vary across different locations.
Task 1 - Watch the video below from 3: 34 to the end.
Source: https://commons.wikimedia.org/wiki/File:Epicenter_Animation.gif
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The types of waves
1. P-waves (Primary waves)
P-waves are the fastest seismic waves, so they arrive first. They move by compressing and stretching the ground in the same direction they are travelling, a bit like a slinky being pushed and pulled. They can travel through solids and liquids.
2. S-waves (Secondary waves)
S-waves arrive after P-waves because they are slower. They move the ground up and down or side to side, at right angles to their direction of travel. Unlike P-waves, S-waves can only travel through solids, not liquids.
3. Surface waves
These waves travel along the Earth's surface, rather than deep underground. They are usually the slowest, but they cause the most damage, making the ground roll or shake strongly. There are two types: Love waves (side-to-side motion) and Rayleigh waves (rolling, wave-like motion).
Task 2 - Now, please create your own mega labelled diagram by hand on A4 paper (to be scanned and digitised at the end) that shows the main characteristics of earthquakes including focus, epicentre and seismic waves.
4.2.3 Types of volcano...
Volcanoes come in different shapes and sizes depending on how they erupt and the type of lava they produce.
The three main types are strato-volcanoes (composite cones), shield volcanoes, and cinder cones.
The three main types are strato-volcanoes (composite cones), shield volcanoes, and cinder cones.
- Strato-volcanoes are steep-sided and built from many layers of ash and lava, often producing explosive eruptions
- Shield volcanoes have gentle, wide slopes formed by runny lava that spreads over large distances, leading to quieter eruptions.
- Cinder cones are small, steep volcanoes made from fragments of rock and ash that are thrown out during short, explosive eruptions. Understanding these types helps explain why volcanic hazards vary from place to place.
Background Understanding.
There are broadly speaking, three different types of volcano that exist around the world (see text above the video). All volcanoes can be explosive but not all of them kill people. Additionally, many millions of people live close to or on volcanoes. What is the attraction?
Task 3 - To understand why some volcanoes are more dangerous than others, we must find out a little more about the mechanisms behind each.
Using this website, complete the fact finding task about cinder cone, composite and shield volcanoes on the first page of the worksheet. You will need to conduct your own Google research on cinder cone volcanoes. Use the worksheet below to record your findings.
There are broadly speaking, three different types of volcano that exist around the world (see text above the video). All volcanoes can be explosive but not all of them kill people. Additionally, many millions of people live close to or on volcanoes. What is the attraction?
Task 3 - To understand why some volcanoes are more dangerous than others, we must find out a little more about the mechanisms behind each.
Using this website, complete the fact finding task about cinder cone, composite and shield volcanoes on the first page of the worksheet. You will need to conduct your own Google research on cinder cone volcanoes. Use the worksheet below to record your findings.
4.2.4 The classification of volcanoes...
Volcanoes can be classified according to their level of activity.
An active volcano is one that is currently erupting or has shown signs of erupting recently.
A dormant volcano is not erupting at the moment but could erupt again in the future, as it still contains magma beneath the surface.
An extinct volcano is one that is not expected to erupt again because there is no longer any magma supply feeding it. This classification helps scientists assess volcanic hazards and understand the potential risks in different areas.
Task 4 - Create your own brief factsheet about the three different volcano classifications above. You should include:
1. The title
2. A definition
3. Your closest example to your school
4. A photo of that volcano.
For your extinct volcano information, you should find out why a once active volcano is now well and truly extinct. What are the processes at work that cause this to happen? Try to find a good quality diagram to back up your findings.
Complete this work as a table on word / three PowerPoint slides.
4.2.5 The main features of volcanoes...
Volcanoes are made up of several key features that help explain how they erupt and behave.
Beneath the surface lies a magma chamber, where molten rock is stored, and from this chamber magma rises through a vent until it reaches the surface. When an eruption occurs, the material escapes through a crater, and sometimes through additional side passages that form secondary cones.
Although many of these features are hidden underground, scientists know they exist through evidence such as patterns of earthquake activity, ground deformation, gas emissions, and seismic imaging, which allows us to build a picture of what is happening beneath the Earth’s surface.
These methods help us monitor volcanoes and understand the processes that shape them.
Beneath the surface lies a magma chamber, where molten rock is stored, and from this chamber magma rises through a vent until it reaches the surface. When an eruption occurs, the material escapes through a crater, and sometimes through additional side passages that form secondary cones.
Although many of these features are hidden underground, scientists know they exist through evidence such as patterns of earthquake activity, ground deformation, gas emissions, and seismic imaging, which allows us to build a picture of what is happening beneath the Earth’s surface.
These methods help us monitor volcanoes and understand the processes that shape them.
Source: https://www.nps.gov/subjects/volcanoes/anatomy-of-a-volcano.htm
Crater - The crater is the bowl-shaped opening at the top of a volcano where lava, ash, and gases are released during an eruption.
Vent - The vent is the main channel through which magma travels from the magma chamber to the surface.
Magma - Magma is molten rock stored beneath the Earth’s surface. When it erupts onto the surface, it is called lava.
Magma Chamber - The magma chamber is a large underground store of magma found beneath a volcano. It supplies the molten rock that erupts.
Secondary Cone - A secondary cone is a smaller cone-shaped volcano that forms on the sides of a main volcano when magma escapes through secondary vents.
Task 5 - Complete the labeling of a cross section activity below.
4.2.6 Volcanic hazards...
Volcanic hazards are dangerous events caused by volcanic activity that can threaten people, property, and the environment. During an eruption, a volcano may produce lava flows, ash falls, pyroclastic flows, lahars, toxic gases, and volcanic rocks. Some hazards move slowly, while others travel at very high speeds and can cause severe loss of life. The impact of a volcanic eruption depends on the size of the eruption, how often it occurs, how fast the hazards move, and how widely they spread.
Understanding these factors helps explain why some eruptions are far more destructive than others.
Task 6 - You will be answering a 25 mark sample IGCSE Paper 1 (Physical Geography) based just on volcanic hazards and the factors that affect them. Generally, the paper is structured as follows. 1 mark, 2 marks, 3 marks, 4 marks, 3 marks, 5 marks, 7 marks. (Pin code: 1234357)
You will need to access both the information documents below (adding additional notes, or using a highlighter to extract key information) and read the information carefully before attempting the questions below.
(a) Define the term volcanic hazard. [1]
(b) Name two volcanic hazards produced during a volcanic eruption. [2]
(c) Describe the characteristics of pyroclastic flows. [3]
(d) Explain how ash fall can cause problems for people and the environment. [4]
(e) Describe the ways in which lahars can affect settlements near a volcano. [3]
(f) Explain why the impact of volcanic hazards varies depending on their speed and size. [5]
(g) Assess the extent to which the spread and frequency of volcanic hazards influence the level of risk to people. [7]
[Total: 25 marks]
For a printable copy of this exam, click on the tab below.
Contact M Podbury at the email address stated at the bottom of this page for a mark scheme to go with this question.
