Natural Hazards (Yr 10) Flashcards
How is the earth structured?
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.
What is a natural hazard?
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.
How to the tectonic plates move?
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)
What are tectonic plates?
A massive, irregularly shaped slab of solid rock, composed of both continental and oceanic crust.
What are the 2 types of crust?
Oceanic - heavier (denser), it can sink and is continuously being destroyed and renewed.
Continental - lighter, cannot sink, permanent (can’t be destroyed or renewed).
What are the 4 plate boundaries?
Collision
Conservative
Constructive
Destructive
What is a collision plate boundary?
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.
What is a conservative plate boundary?
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.
What is a constructive plate margin?
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.
What is a destructive plate boundary?
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.
What’s a hotspot?
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.
What are the primary issues of a volcanic eruption?
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
What are the secondary issues of a volcanic eruption?
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
Are the impacts of volcanoes more severe in LEDCs?
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.
Why do people stay in volcanic areas?
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.
What precautions are against a volcanic eruption?
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.
What causes an earthquake?
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.
What does focus, fault, seismic waves and epicentre mean?
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.
What’s the richter and mercalli scale?
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.
What are the effects of an earthquake?
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.
Case study:
Sichuan responses:
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
Case study:
Sichuan secondary hazards:
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.
Case study:
Sichuan impacts:
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
Case study:
Canterbury responses:
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
Case study:
Canterbury secondary hazards:
Flooding
Landslides
Liquefaction
Case study:
Canterbury impacts:
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.
How can homes be prepared for an earthquake?
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.
What are the 3 Ps to reduce and earthquake?
Prediction
Protection
Preparation
How can an earthquake be predicted?
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.
What’s the epicentre?
The point on the Earth’s surface straight above the focus
What’s the focus?
The point IN the earth where the earthquake starts.
How are volcanoes formed?
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.
What are the primary/immediate impacts of an earthquake?
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
What are the secondary impacts of an earthquake?
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
Are the impacts of earthquakes more severe in LEDCs?
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
Why do people live in earthquake prone areas?
They’ve always lived there
They’re employed there
They’re confident in the support
Some feel severe earthquakes won’t happen again
How can the impacts of an earthquake or volcanic eruption be reduced?
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
What’s a shield volcano?
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
What’s a composite/strato volcano
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
How do people try to predict volcanic eruptions?
(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
What planning strategies reduce the impact of a volcanic eruption?
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
What building techniques reduce the impact of an eruption?
(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
