Natural Hazards

Question 1

What is a natural hazard?

Answer 1

It is a natural process which could cause death, injury or disruption to humans, or destroy property and possessions.

Question 2

What is a natural disaster?

Answer 2

A natural hazard that has in fact happened and injures 100 people or killed 10 people or causes $16 million worth of damage

Question 3

What is a natural event?

Answer 3

Occurs in remote areas that are away from people and property

Question 4

Why are some extreme events not counted as hazards?

Answer 4

Because they do not pose any threat to human activity. For example, an avalanche in Antarctica.

Question 5

What are the two main types of hazard?

Answer 5

1) Geological hazards
2) Meteorological hazards

Question 6

What is a geological hazard?

Answer 6

Hazards that are caused by land and tectonic processes. They include volcanoes and earthquakes, landslides and avalanches.

Question 7

What is a meteorological hazard?

Answer 7

Hazards caused by weather and the climate. They include tropical storms, heatwaves, cold spells, etc.

Question 8

What is a hazard risk?

Answer 8

The probability of people being affected by a hazard in a particular area.

Question 9

What are the 3 factors that can affect hazard risk?

Answer 9

1) Vulnerability
2) Capacity to cope
3) Nature of Natural hazards

Question 10

How can vulnerability affect hazard risk?

Answer 10

1) The more people that are in an area exposed to natural hazards, the greater the probability they will be affected by a natural hazard.
2) For example, an area with a high population density on a flood plain (like Bangladesh) is very vulnerable to flooding caused by extreme weather.

Question 11

How can the capacity to cope affect hazard risk?

Answer 11

1) The better a population can cope with an extreme event, the lower the risk of them being severely affected.
2) For example, higher income countries are better able to cope with flooding because they can afford to build flood defences and evacuate people.

Question 12

How can the nature of natural hazards affect hazard risk?

Answer 12

1) Type - the risk from some hazards is greater than others (e.g. tropical storms can be predicted and monitored giving people time to evacuate but earthquakes happen very suddenly so it’s much harder to protect people).
2) Frequency - natural hazards that occur more often may carry a higher risk.
3) Magnitude - more severe natural hazards tend to have the greatest effects.

Question 13

What are the primary effects of natural disasters?

Answer 13

The immediate impacts caused by the hazard itself:
1) Buildings and roads destroyed by earthquakes
2) People are injured or killed (e.g. when buildings collapse)
3) Crops and water supplies can be damaged or contaminated
4) Electricity cables, gas pipes and communication networks can be damaged cutting off supplies

Question 14

What are the secondary effects of natural disasters?

Answer 14

The result of the primary effect:
1) The initial hazard can trigger other hazards (e.g. earthquakes can trigger tsunamis)
2) Aid and emergency vehicles can’t get through because of blocked roads or bridges - this can cause more deaths
3) A shortage of clean water and a lack of proper sanitation makes it easier for disease to spread
4) Food shortages can occur if crops are damaged, livestock are killed or supply lines are blocked.
5) The country’s economy can be weakened - damage to businesses can cause unemployment, and the reconstruction can be very expensive

Question 15

What are immediate responses to a natural disaster?

Answer 15

1) Evacuate people (before the hazard occurs if possible)
2) Treat the injured and rescue anyone cut off damage to roads or bridges
3) Recover dead bodies to prevent disease spreading
4) Provide temporary supplies of electricity and gas if regular supplies of have been damaged
5) Provide food, drink and shelter to people without homes.
6) Foreign governments or charities may send aid workers, supplies or financial donations.

Question 16

What are long-term responses to a natural disaster?

Answer 16

1) Repair homes or rehouse people who have lost their homes
2) Repair or rebuild buildings, roads, railways and bridges
3) Reconnect broken electricity, water, gas and communication connections
4) Improve forecasting, monitoring and evacuation plans
5) Improve building regulations so that buildings can withstand similar hazards in the future
6) Boost economic recovery (e.g. by promoting tourism)

Question 17

What is the Earth’s crust divided into?

Answer 17

Slabs called tectonic plates

Question 18

What are crusts the 2 crusts? What are the differences?

Answer 18

1) Continental crust is thicker (30-50km) and less dense (and usually older)
2) Oceanic crust is thinner (5-10km) and more dense (and younger because it is constantly destroyed)

Question 19

Why do the tectonic plates move?

Answer 19

Because of convection currents in the mantle.

Question 20

What are the places where the plates meet called?

Answer 20

Plate margins or plate boundaries.

Question 21

What are the 3 types of plate margin?

Answer 21

1) Destructive
2) Constructive
3) Conservative

Question 22

What happens at the destructive margins?

Answer 22

Where two plates move towards each other
1) Where an oceanic and continental plate meet - the denser oceanic plate subducts underneath the continental plate into the mantle where it is destroyed creating gas-rich magma
2) Where two of the same plates meet - the ground is folded upwards (as they both have the same density) creating fold mountains
Example: along the west coast of South America, the oceanic plate Nazca plate is being subducted beneath the continental South American plate, creating the Atacama Trench

Question 23

What happens at the constructive margins?

Answer 23

Constructive margins are where two plates move away from each other. Magma rises from the mantle to fill the gap and cools creating new crust.
Example: the movement of the Eurasian plate and the North American plate away from one another is forming the mid-Atlantic ridge.

Question 24

What happens at the conservative margins?

Answer 24

Where two plates move sideways past each other, either in the same direction at different speeds or in opposite directions.
Example: at the San Andreas Fault, the Pacific plate is moving in the same direction as the North American plate but faster.

Question 25

What occurs where plates meet?

Answer 25

Volcanoes and earthquakes.

Question 26

What margins do volcanoes occur at? Explain how?

Answer 26

1) At destructive margins - denser oceanic plate moves down into the mantle where it melts, a pool of magma forms which then rises through cracks in the crust called vents, the magma (called lava when it reaches the surface) erupts forming a volcano.
2) At constructive margins - the magma rises up into the gap created by the plates moving apart forming a volcano

Question 27

When do volcanoes not occur at margins?

Answer 27

Some volcanoes form over parts of the mantle that are really hot called hotspots (e.g. Hawaii)

Question 28

What happens when a volcano erupts?

Answer 28

It emits lava and gases. Some volcanoes emits lots of ash which can cover land and block out the sun and form pyroclastic flows (super-heated currents of gas, ash and rock).

Question 29

What margins do earthquakes occur at? Explain how?

Answer 29

1) Destructive margins - tension builds when one plate gets stuck as it moves past the other
2) Constructive margins - tension builds along cracks in the plates as they move away from each other
3) Conservative margins - tension builds up when plates that are grinding past each other get stuck

Then the plates eventually jerk past each other, sending out shock waves - these vibrations are the earthquake. The shock waves spread out from the focus (the point in the Earth where the earthquake starts). The waves are stronger near the focus and cause more damage. The epicentre is the point on the Earth’s surface straight above the focus.

Question 30

How are earthquakes measured?

Answer 30

Using the moment magnitude scale:
1) The moment magnitude scale measures the amount of energy released by an earthquake (called the magnitude)
2) It is a logarithmic scale - this means a magnitude of 7 would cause ten times as much ground shaking than a magnitude 6 earthquake.
3) Earthquakes of magnitude 6 an below normally only cause slight damage to buildings, although they can be worse in very built up areas
4) Earthquakes of magnitude 7 an above can cause major damage and deaths

Question 31

What factors make disasters more likely?

Answer 31

1) Population - megacities with over 10 million inhabitants
2) Location - when countries are closer to plate margins, making them more susceptible (likely) to (experience) earthquakes
3) Poverty - exposure as they tend to live in vulnerable areas as it’s cheaper

Question 32

Describe the Earth’s layers?

Answer 32

THE CRUST: 65km deep - split into two types of crust (oceanic and continental)
THE MANTLE: 2870km thick (makes up half of the Earth’s structure) - made of dense, molten rock which is around 1000-4000°C
THE OUTER CORE: 2400 km deep - made of liquid iron and nickel and reaches 4000-5000°C
THE INNER CORE: 1200 km deep - made from solid nickel and iron and reaches a temperature up to 5,500°C - there is radioactive decay from materials uranium and thorium

Question 33

What is a convection current?

Answer 33

The movement of a fluid caused by a difference in temperature or density

Question 34

What are the 4 ways of preparing for a natural hazard?

Answer 34

1) Monitoring - detecting and recording physical changes and warning signs of a hazard
2) Planning - having systems in place such as evacuation routes so that if a hazardous event occurs the population is prepared in advanced
3) Prediction - using monitoring as well as historical trends and computer-based modelling to predict when a hazardous event might occur
4) Protection - increasing the resistance of a population to natural hazards by physically designing things that will withstand natural hazards

Question 35

Why do people live close to volcanoes?

Answer 35

1) Cannot afford to move
2) They’ve always lived there and moving can mean leaving their job or family
3) In richer countries, effective monitoring and evacuation plans to minimise risk

Question 36

How do people monitor earthquakes?

Answer 36

By seismometers and lasers monitor earth movements and can be used in early warning systems to give a small but vital amount of warning before a large earthquake occurs

Question 37

How do people monitor volcanic eruptions?

Answer 37

Scientists can monitor the tell-tale signs that come before an eruption, such as tiny earthquakes, escaping gas, and changes in the shape of a volcano

Question 38

How do people predict earthquakes?

Answer 38

Cannot be reliably predicted, but scientists cab forecast where they may occur by monitoring the mivement of tectonic plates

Question 39

How do people predict volcanic eruptions?

Answer 39

Can be predicted if scientists monitor volcanoes closely

Question 40

How do people protect themselves from earthquakes?

Answer 40

New buildings can use reinforced concrete that absorb an earthquake’s energy. Existing buildings and bridges can be strengthened with steel frames so they’re less likely to collapse. Automatic shut-off switches can turn off has and electricity supplies to prevent fires.

Question 41

How do people protect themselves from volcanic eruptions?

Answer 41

Buildings can be strengthened so that they’re less likely to collapse under the weight of ash. Trenches and barriers have been used to try to divert lava away from settlements.

Question 42

How do people plan for earthquakes and volcanic eruptions?

Answer 42

1) Future developments can avoid high-risk areas
2) Emergency services can prepare (e.g. by practising rescuing people from collapsed buildings)
3) People can be educated so that hey know what to do in the event of a hazard
4) Governments can plan evacuation routes to get people away quickly and safely
5) Emergency supplies like blankets, clean water and food can be stockpiled