Natural Hazards (Yr 10)

Question 0

How is the earth structured?

Answer 0

From inside to out, there’s the:

Inner core - solid iron and nickel
Outer core - very hot and liquid
Mantle - hot molten rock
Crust - the outer shell of the Earth.

Question 1

What is a natural hazard?

Answer 1

A naturally occurring process that has the potential to cause loss of life or property. Examples include tsunamis, earthquakes, volcanoes, droughts, tornadoes etc.

It’s important to realise that without people, those events would just be natural processes not hazards.

Question 2

How to the tectonic plates move?

Answer 2

Within the mantle, there are convection currents, meaning the molten rock within is heated, loses density and rises, moves in a certain direction, cools slightly and gains density, falling back down again before continuing the cycle.
As it moves in a certain direction, it drags the crust and tectonic plates along with it, resulting in the movement of the plates.
(It moves like a conveyor belt)

Question 3

What are tectonic plates?

Answer 3

A massive, irregularly shaped slab of solid rock, composed of both continental and oceanic crust.

Question 4

What are the 2 types of crust?

Answer 4

Oceanic - heavier (denser), it can sink and is continuously being destroyed and renewed.

Continental - lighter, cannot sink, permanent (can’t be destroyed or renewed).

Question 5

What are the 4 plate boundaries?

Answer 5

Collision
Conservative
Constructive
Destructive

Question 6

What is a collision plate boundary?

Answer 6

When 2 continental crust / plates are moving towards each other.
As continental crust can’t sink or be destroyed, the rock and land buckle and the build up in pressure forces the land to be pushed upwards, forming mountains.
Earthquakes can occur on these margins but there are no volcanic eruptions.

Question 7

What is a conservative plate boundary?

Answer 7

When 2 plates are slowly sliding past / alongside each other.
Due to the irregular shape of the plates, when two plates stick or catch, pressure builds up.
When the rock breaks or the plates give and the pressure is released (and the plate moves/jolts) it creates severe earthquakes but, as crust is neither created or destroyed, there are no volcanic eruptions.

Question 8

What is a constructive plate margin?

Answer 8

When 2 plates (oceanic crust) move away from each other.
As the plates move away, a gap appears in between where lava can easily escape either as a flow or an eruption.
When the lava cools, it forms new oceanic crust and a mid-oceanic ridge.
They also have large eruptions but they’re gentler than those of the other plate boundaries.

Question 9

What is a destructive plate boundary?

Answer 9

When an oceanic and continental crust move towards each other.
As the oceanic crust is denser/heavier that the continental crust, it is forced downwards (subduction zone).
Due to the force downwards and an increase pressure, extremely violent earthquakes can be triggered.
Also, the heat from the mantle and friction turns the descending oceanic crust into magma which tries to rise to the surface, forming volcanoes and volcanic eruptions.

Question 10

What’s a hotspot?

Answer 10

A hotspot is an area where the mantle is hotter than other areas and the crust is also quite thin but don’t take place in a plate boundary e.g. Hawaii.

Question 11

What are the primary issues of a volcanic eruption?

Answer 11

Volcanic gasses - they produce larger amounts of gasses which can be deadly.

Pyroclastic flow - an avalanche of super heated gas, ash and rock travelling up to 100km/h which destroys everything.

Nuée ardentes - destructive cloud of gas, dust and ash.

Lava flow - masses of molten rock pour from the volcano.

Ash falls - ash can fall over 100s of miles, blanketing settlements, farmland and causing buildings to collapse.

People, animals and plants suffocated by CO2

Question 12

What are the secondary issues of a volcanic eruption?

Answer 12

Tsunamis - large eruptions can cause the crater to collapse into the ocean triggering a giant sea wave.

Lahars - mudflows occurring in frozen areas. The volcano melts the snow and ice on the top of the volcano which rushes down the volcano, mixing with ash and other debris.

Landslides - they can tiprigger landslides on the volcanos slopes.

Fires starting from lava flows

People suffer psychological problems

People left homeless

Shortage of food and clean water

Roads and buildings broken and destroyed

Sulphur dioxide released causes acid rain

Question 13

Are the impacts of volcanoes more severe in LEDCs?

Answer 13

Yes because:

Their houses are poor quality so are unable to withstand the shaking and the weight of the ash.

They can’t afford better quality housing, warning and preparation facilities, defenses, and the cost to clean up and restore the buildings afterwards.

There’s poor infrastructure in LEDCs meaning it’s harder to get away from the volcano, send help to people within the towns (because of poor roads) and also, due to poor telecommunications, it’s harder to broadcast to everyone that an eruption is occurring meaning a greater loss of life.

They have poorer healthcare so are unable to attend to those who are injured or ill e.g. Due to the gasses or ash from the volcano.

Question 14

Why do people stay in volcanic areas?

Answer 14

Believe the volcano won’t erupt again - some haven’t erupted in centuries.

Geothermal (renewable) energy sources

Always lived there - there may be families or friends. They may like the area.

Poor - no other option, can’t afford to move, land is cheap, may not be payed well for their (farming) skills in other areas.

Employed in the area - other countries may not need farmers, tourism is higher, precious stones and metals can be found.

Confident in the government - people believe the government will protect and prepare them, give warnings and monitor.

Question 15

What precautions are against a volcanic eruption?

Answer 15

Developments constructed in low risk zones.

Barrier walls divert flows and stops lava flowing to the settlements.

Planning and escape routes help so people can leave and evacuate quickly.

Dykes - direct and slow the lava flow.

Question 16

What causes an earthquake?

Answer 16

An earthquake is caused by a sudden movement within the Earth due to the tectonic plates moving against each other and building pressure which is released when the rock breaks.
Although they’re common at all plate margins, they can take place in the centre of plates too.

As pressure is released along fault lines, energy is released causing shocks or seismic waves.
These waves radiate from the focus.
They then cause damage at the epicentre and decrease in strength as they spread.

Question 17

What does focus, fault, seismic waves and epicentre mean?

Answer 17

Focus: where the energy is released beneath the crust
Fault: crack in the earth
Seismic waves: vibrations generated by earthquakes.
Epicentre: the point on the earths surface directly above the focus of the earthquake.

Question 18

What’s the richter and mercalli scale?

Answer 18

Scales to measure an earthquake

Mercalli:
Descriptive scale
12 point scale
Measures intensity and level of damage

Richter:
Measures size
Logarithmic - each no’ is x10 bigger than the previous
Moderate is 5, above 6 is strong.

Question 19

What are the effects of an earthquake?

Answer 19

Ground shaking - the severity depends on the strength of an earthquake, geological conditions and distance from epicentre.

Landslides and snow avalanches - caused due to the shaking weakening the slopes.

Tsunamis - because of seismic sea waves.

Liquefaction - groundwater rising and turning soft ground to mud so homes built on clay for example sink into the mud and collapse.

Question 20

Case study:

Sichuan responses:

Answer 20

Long term:
Government located £2 million from its emergency relief fund.
Rebuilding of homes and schools
Government pledged $10 million rebuilding fund and banks passed any debts survivors owed.

Short term:
Soldiers were parachuted in to help with food, water and medicine. 
Temporary accommodation
Government asked for international aid
Helicopters sent to help

Question 20

Case study:

Sichuan secondary hazards:

Answer 20

Slope failure and landslides which blocked river valleys creating quake lakes.

Rising water levels and pressure threatened to breach the dam and cause flooding.

Bad weather made it harder for rescue operations.

Question 20

Case study:

Sichuan impacts:

Answer 20

69,000 deaths
7000 schools destroyed - weren’t built properly
Affected the centre of china - rural area - where there’s poor infrastructure
80% buildings destroyed
Severe fuel shortage as the coal mines were damaged

Question 21

Case study:

Canterbury responses:

Answer 21

Long term:
Building codes for new buildings to prevent them from collapsing
Red Cross gave grants to families with children below 5
$898 million paid towards buildings and reconstruction.
Water and sewerage were restored
Areas of land, homes and roads were cleared of silt to further prevent liquefaction.

Short term:
Calm and stayed indoors
Army and firefighters sent quickly
People helped one another
Buildings had to be assessed. 
$6-7 million international aid

Question 22

Case study:

Canterbury secondary hazards:

Answer 22

Flooding
Landslides
Liquefaction

Question 23

Case study:

Canterbury impacts:

Answer 23

Tens of thousands of people left without water and power.
Land was raised up to 4 meters.
Evacuation centres set up and schools closed.
No one died.
$4 billion worth of damage.
Historic buildings demolished.

Question 24

How can homes be prepared for an earthquake?

Answer 24

Fastening shelves and cabinets onto the wall with L-shaped brackets.
Secure brick chimneys.
In the attic, nail plywood to ceiling joists around the chimney for protection against falling bricks.
Remove heavy items from the walls and locate beds away from windows.
Bolt the house to its concrete foundation.

Question 25

What are the 3 Ps to reduce and earthquake?

Answer 25

Prediction
Protection
Preparation

Question 26

How can an earthquake be predicted?

Answer 26

Satellite surveying

Strain meter recording the stress and compression of the earth

Water table level - water levels rise as the ground stresses before an earthquake.

GPS - records changes in the form of the volcano.

Seismicity - sends shock-wave info from vibrations and tremors because of magma chambers.

Gas measuring - analysing gasses and the amount released provides I of about the magmas nature.

Geophysical measurements - physical changes e,g. Temperature.

Ground deformation - record movements in the ground due to the magma rising towards the vents.

Question 27

What’s the epicentre?

Answer 27

The point on the Earth’s surface straight above the focus

Question 28

What’s the focus?

Answer 28

The point IN the earth where the earthquake starts.

Question 29

How are volcanoes formed?

Answer 29

Destructive margins - the oceanic plate is denser than the continental crust so it moves down into the mantle which melts to form a pool of magma that then rises through cracks in the crust called vents. This magma erupts onto the surface forming a volcano.

Constructive margins - magma rises up into the gap created by the plates moving apart forming a volcano.

Question 30

What are the primary/immediate impacts of an earthquake?

Answer 30

Buildings and bridges collapsing

People injured and killed

Electricity cables damaged

Gas pipes broken and leaks

Telephone poles destroyed

Underground water and sewerage pipes broken

Question 31

What are the secondary impacts of an earthquake?

Answer 31

Landslides and tsunamis triggered

Gas leaks ignited starting fires

People left homeless

People suffer psychological problems if they know people who’ve died or lost homes

Shortage of clean water and little sanitation

Roads blocked or destroyed

Businesses damaged causing unemployment

Question 32

Are the impacts of earthquakes more severe in LEDCs?

Answer 32

Yes -
There’s more poor quality housing which is less stable so is destroyed more easily

Infrastructure is poorer - poor quality roads make it harder to reach injured people

They don’t have enough money to protect themselves e.g. By making buildings earthquake proof or resources to react straight away

Healthcare is worse

Question 33

Why do people live in earthquake prone areas?

Answer 33

They’ve always lived there

They’re employed there

They’re confident in the support

Some feel severe earthquakes won’t happen again

Question 34

How can the impacts of an earthquake or volcanic eruption be reduced?

Answer 34

Prediction - can help evacuation

Building techniques - earthquake proof or able to withstand pyro clastic flows and ash

Planning - future developments planned to avoid areas with earthquakes, firebreaks reduced fires, emergency services, evacuation routes planned

Education - governments educate people, make survival kits

Aid - international aid

Question 35

What’s a shield volcano?

Answer 35

Shield volcanoes are usually found at constructive or tensional boundaries.
They are low, with gently sloping sides.
They are formed by eruptions of thin, runny lava.
Eruptions tend to be frequent but relatively gentle.

Gentle slopes and a wide base
Frequent eruptions of basic lava
Lava flows at high speeds and for long distances before cooling
Usually non-violent eruptions

Question 36

What’s a composite/strato volcano

Answer 36

Composite volcanoes are made up of alternating layers of lava and ash (other volcanoes just consist of lava).
They are usually found at destructive or compressional boundaries.
The eruptions from these volcanoes may be a pyroclastic flow rather than a lava flow. A pyroclastic flow is a mixture of hot steam, ash, rock and dust.
A pyroclastic flow can roll down the sides of a volcano at very high speeds and with temperatures of over 400°C.

Steep sided with a distinctive cone shape
High with a narrow base
Explosive eruptions of lava & ash
Layers of alternating ash & lava
Secondary or parasitic cones formed when the main vent gets blocked

Question 37

How do people try to predict volcanic eruptions?

Answer 37

(Unlike earthquakes, it’s possible to predict an eruption)

Look for tiny earthquakes

Look for any escaping gas, especially sulphur

Look for changes in the shape of the volcano e.g. Bulges when magma has built up

Due to increased pressure and heat, there may be an increase in water levels or water vapour

Question 38

What planning strategies reduce the impact of a volcanic eruption?

Answer 38

Future developments can be built in areas of less risk

Firebreaks reduce the spread of fires

Trained emergency services

Evacuation routes established

Diversions to divert the flow of lava

Question 39

What building techniques reduce the impact of an eruption?

Answer 39

(Can’t withstand lava or pyro clastic flows)

Can be strengthened to not collapse under the weight of falling ash

Barriers can divert the flow of lava away from houses