1. Geological Natural Disasters
Geological natural disasters are caused by natural events occurring within the earth’s crust.
Some geological natural disasters include:
earthquakes
volcanoes
tsunamis
avalanches.
Let’s investigate the causes and effects of these four geological natural disasters.

2. Earthquakes
Earthquakes occur when the tectonic plates that make up the earth’s surface move apart, bump into each other or slide under each other.
When two tectonic plates suddenly move or collide, seismic waves (vibrations which carry energy) move outwards. This point is called the ‘focus’.
Since the focus is usually deep underground, the location of the earthquake is often referred to as the point on the earth’s surface directly above the focus. This point is called the ‘epicentre’.
Geologists use an instrument called a seismograph to measure the strength of the seismic waves created by an earthquake. This then enables the size of the earthquake to be measured using the Richter scale.
Scientists have not yet discovered a way of predicting exactly when and where an earthquake will occur. However, they do know that earthquakes occur along fault lines, and we know where these fault lines are.
1st link: Monkey See (shows diagram of how an earthquake forms under the earth’s surface)
2nd link: National Geographic (includes info about effect on human life)

3. What features of an earthquake can you see on the diagram?

4. Volcanoes
A volcano is a mountain with a crater or vent which allows hot lava, rock fragments, volcanic ash and gases to erupt from the earth’s crust.
Volcanoes are usually located along fault lines where tectonic plates meet.
Lava is semi-fluid rock which has been heated under the surface of the earth. Initial flows of lava can move at up to 10 km/h. Once a lava flow becomes established, it can move as fast as 60 km/h.
Along with lava and ash, volcanoes release gases. Common volcanic gases include water vapour, carbon dioxide, sulphur dioxide, hydrogen chloride and hydrogen sulphide.
Volcanic eruptions can vary in their size and level of explosiveness. Scientists use the Volcanic Explosivity Index, based on a range of characteristics, to measure the size of a volcanic eruption.
1st link: Monkey See (basic facts)
2nd link: National Geographic (includes info about effect on human life and importance to our living planet)

5. What features of a volcanic eruption can you see on the diagram?

6. Tsunamis
Tsunamis are caused by underwater earthquakes. Shockwaves cause the water level to rise above sea level, then gravity pulls the water into a giant wave.
Tsunamis can travel at speeds of 805 km/h (as fast as a jet plane).
Tsunamis are generally unnoticed out in the ocean, forming only a slight swell. As the tsunami approaches the shore and hits shallow water, it slows down but increases in height.
A typical wave period for a destructive tsunami is about 12 minutes. During this time, the wave will both peak and recede, causing wide-spread destruction on land and sweeping debris back out to sea.
The Pacific Tsunami Warning System, based in Hawaii, monitors seismic activity in the Pacific Ocean. When large underwater earthquakes are detected, tsunami warnings can be issued to affected populations.
1st link: TedEd – How tsunamis work (cartoon)
2nd link: BBC One: Bang goes the theory (Earthquake and Tsunami simulation)

7. What features of a tsunami can you see on the diagram?

8. Avalanches and landslides
Avalanches are a rapid flow of snow down a slope. They are caused by four factors: a steep slope, snow cover, a weak layer in the snow and a trigger.
Natural avalanche triggers may include increased snowfall, melting snow, wind, rain, earthquakes, rockfall and icefall. Artificial avalanche triggers may include skiers, snowmobiles and controlled explosions.
Avalanches have the ability to transport masses of snow at high speeds. As well as snow, avalanches may carry stones, boulders and trees with them.
Avalanches and landslides are most common during winter and spring. In mountainous areas, avalanches pose a very serious threat to life and property.
There are three main categories of avalanche: a dry snow avalanche, a wet snow avalanche and a slab avalanche. These avalanches vary according to their size, composition and destructive properties.
Video links to BBC Earth Unplugged: Avalanches
What are some similarities and differences between avalanches and landslides

9. What features of an avalanche can you see on the diagram?
Encourage the students to identify the key features of these natural disasters on the diagrams.

10. Tuning In: Meteorological Natural Disasters
Meteorological natural disasters are caused by extreme weather conditions in the earth’s atmosphere.
Tropical cyclones (also known as hurricanes, typhoons or tropical depressions) are one example of a meteorological natural disaster.
Let’s investigate the causes and effects of this example.

11. Cyclones, Hurricanes & Typhoons
Cyclones are intense tropical storms with powerful winds and heavy rain. They can also be referred to as hurricanes, typhoons or tropical depressions.
Cyclones usually begin over warm seas where there is low atmospheric pressure. The warm, moist air begins to spiral into a strong, circling storm.
Once crossing over onto land, cyclones typically weaken. This is because they are cut off from their primary energy source.
Cyclones have three main parts: the rainbands, the eye and the eyewall. Weather in the eye of a cyclone is usually calm. The diameter of the eye is usually around 50 km in length, but can be as large as 320 km.
Cyclone intensity is measured by the storm’s wind speed, on a scale of The strongest cyclones are known as category 5 and can move as quickly as 300 km/h. Winds this fast cause intense damage, such as ripping trees from the ground and flattening buildings.
Video links to UK Met Office video – discusses the difference between the three (they are all the same, however the only difference is where they occur)

12. What features of a tropical cyclone can you see on the diagram?

13. Hydrological Natural Disasters
Hydrological natural disasters are caused by the amount of water present on the earth’s surface.
Some hydrological natural disasters include:
flooding
drought.
Let’s investigate the causes and effects of these two hydrological natural disasters.

14. Flooding
Flooding occurs when a piece of land (that is usually dry land) is submerged under water. Some floods happen suddenly and recede quickly, while others take days or months to build and regress.
Flooding can be caused by thawing snow and ice, heavy rain or storm surges. This can lead to overflowing drainage systems, rivers breaking their banks, dam failure and elevated sea levels.
Flash floods are fast-moving flood waters effecting low-lying areas, such as canyons and valleys. These can happen after heavy rain from a slow moving thunderstorm. Flash floods are particularly dangerous, as they strike quickly with little warning.
Like other natural disasters, floods can be categorised according to their level of severity. However, even minor floods are dangerous. Flood waters should be avoided at all times.
Video links to Disaster Management WVI – Floods explained

15. What features of flooding can you see on the diagram?

16. Drought
Droughts occur when there is a period of below-average rainfall in a particular area. This can cause top soil to dry out, groundwater to sink and streams and rivers to dry up.
A drought can last for weeks, months or even years. In severe cases, droughts may be declared after as few as 15 days.
Living organisms need water to survive. Because of this, droughts are one of the worst natural disasters that can occur. Prolonged drought can cause plants and animals to die and crops to fail. This can lead to famine for the human population.
In areas where there aren’t many trees, droughts can cause erosion. Hot winds blow away the dry topsoil, which creates terrible dust storms.
There are three main categories of drought: meteorological (a reduction in rain), agricultural (a reduction in crop irrigation) and hydrological (a reduction in lake and reservoir levels).
Video links to Droughts 101 by Nat Geo

17. What features of a drought can you see on the diagram?

18. Other Natural Disasters
Some natural disasters are difficult to classify into one category. This is because they are often caused by a combination of natural events (such as climate or extreme weather) and human actions (such as irresponsibility or careless land use).
A bushfire is one example of a natural disaster which has both natural and human causes.
Let’s investigate the causes and effects of this example.

19. Bushfires
Bushfires are uncontrollable blazes that usually start in areas of bushland or wilderness. They can be caused by lightning, agricultural clearing, campfires and dropped cigarettes. Some bushfires are deliberately lit.
Bushfires are very destructive and extremely dangerous. They are large, fast- moving and difficult to bring under control. Bushfires can even jump over gaps that are in their path, such as rivers and roads.
Bushfires are more frequent during the hottest and driest months of the year. While every continent (except Antarctica) experiences bushfires, they occur most commonly in Australia.
Even though bushfires cause extensive damage, they play an important role in nature. Bushfires burn plants and trees which may be old and diseased, making way for new plants and trees to grow in their place.
There are two main categories of bushfire: mountainous (fires on hilly areas) and grassland (fires on flat areas).
BBC Earth Unplugged: What causes wildfires (different name as this is what it is called in North America)

20. What features of a bushfire can you see on the diagram?

21. Effects of Natural Disasters
Displaced populations – due to the widespread destruction of buildings and property, many natural disasters leave people without a home. This can cause a massive movement of survivors from one area to another, placing a huge amount of pressure on services such as health care and education.
Health risks – survivors of natural disasters are often in danger of becoming seriously ill, even after the immediate risk of the disaster event has passed. Health complications resulting from infection and disease can lead to rising death tolls if medical assistance is not readily available to survivors.
Food shortages – due to the destruction of crops and agricultural supplies, food can become scarce following a natural disaster. Aid organisations play a vital role in ensuring that survivors are provided with the nutritional support they need, including fresh, clean drinking water.
Emotional trauma – survivors of natural disasters are often at risk of conditions such as PTSD (post-traumatic stress disorder). Children in particular require special treatment to recover from these experiences.

22. Management of Natural Disasters
Natural disasters cannot be prevented. However, the risk to lives and property can often be lessened through the implementation of a sensible natural disaster management plan.
The management of a natural disaster event falls into four main categories:
1) Reducing the risks through town planning and building design
2) Being prepared by having an evacuation plan
3) Providing immediate relief to disaster-affected communities
4) Supporting the long-term recovery of disaster-affected communities

23. Introducing Disaster Risk Reduction and Resilience
As you watch the Introducing Disaster Risk Reduction and Resilience video, record your notes about the strategies they use.
For example:
Risk assessments
Early warning systems
Contingency plans
Which strategies have you experienced in your life?
1st link: Introducing Disaster Risk Reduction and Resilience video on the UNISDR website.
2nd link: BBC Earth Unplugged – Can natural disasters be good for nature?