tectonic hazards mark scheme answers

why do people live in areas at risk of volcanic eruptions?

• geothermal energy can be harnessed by using steam from underground heated by magma - can produce electricity such as in ireland

• volcanic areas (hot springs) attract tourists - which creates employment and may have a multiplier effect

• mining - magma and lava may contain minerals (gold, silver, diamonds, copper and zinc) - basalt can be used in construction + to build roads

• fertile (nutrient rich) soil - produce crops and rich harvests

• people believe the chances of volcano erupting are very slim

• many people don’t have a choice as they can’t afford to live away from volcanoes as they provide jobs + their friends and families live there

• some places are well prepared so people feel safe (confident in the defences)

why do people live in earthquake zones?

• plate margins often coincide with favourable areas for settlement - such as coastal areas where there’s ports

• offer job opportunities, such as san francisco and la

• risk is outweighed by economic or social opportunities

• engineering can make people feel safe - earthquake proof buildings (people are confident in the defences)

• protection, planning and monitoring may be advances - potential risks are reduced

• fault lines associated with earthquakes can allow water supplies to reach the surface

what are general reasons that people live in areas at risk of tectonic hazards?

• they’ve always lived there - moving away would mean leaving family and friends

• employed in the area - would have to find new jobs

• people living in poverty have other priorities - money, food, security, family

• people can’t afford to move - housing may be cheaper in some hazardous zones

primary effects of earthquakes

• buildings collapse

• communication links damaged or destroyed

• loss of power / water supply

• people may be injured or killed / trapped under rubble

• people made homeless - accepted as primary

primary effects of volcanic eruptions

• houses submerged under lava flow

• properties destroyed by fire

• people injured or killed

• roads blocked by lava

• trees/crops burnt or covered by lava

• air pollution

ridge push

• magma rises as the plates move apart

• the magma cools to form new plate material

• as it cools it becomes denser and slides down away from the ridge

• this causes other plates to move away from each other

slab pull

• the denser plate sinks back into the mantle under the influence of gravity

• it pulls the rest of the plate along behind it

convection currents

• heat rising and falling inside the mantle creates convection currents generated by radioactive decay in the core

• these currents move the plates

processes causing volcanic activity at CONSTRUCTIVE MARGINS

• two plates move apart

• magma rises through the crust, and some can erupt producing volcanoes (usually gentle sided basic lava cones)

earthquakes at constructive margins as plates move apart

• faults are formed at the margin and earthquakes can occur here - they are usually of low magnitude

• some may be linked to volcanic activity

• most happen at shallow depths below the surface where the plates are moving apart

processes causing volcanic activity at destructive margins

• two plates move towards each other

• the denser plate sinks below the lighter, less dense plate and melts in the subduction zone

• hot magma rises up through the overlying mantle and crust, and some can eventually erupt out at the surface producing volcanoes

• (magma becomes increasingly viscous or sticky as it rises to the surface, producing composite volcanoes which are steep sided and have violent eruptions)

earthquakes at destructive margins

• as the two plates converge, pressure builds up

• the rocks eventually fracture causing an earthquake - most happen at shallow depths below the surface where the plates collide

• they also occur at greater depth, in the lower part of the subduction zone

earthquakes at conservative plate margins

• plates move past each other (in opposite directions) or side by side moving at different speeds

• as the plates move, friction occurs and plates become stuck

• pressure builds up

• when pressure is released, it sends out huge amounts of energy, causing an earthquake

• earthquakes can be very destructive as they occur close to the earth’s surface

• there are NO volcanoes at a conservative plate margin

why do earthquakes and volcanic eruptions occur at a DESTRUCTIVE PLATE MARGIN?

• destructive plate margins occur when two tectonic plates move towards each other and one is subducted under the other

• (or collision boundaries - if two continental plates collide, the pressure and strain may cause an earthquake)

• if an oceanic and continental plate collide, the denser oceanic plate is subducted and sinks below the continental plate and into the earth’s mantle

• this causes part of the mantle to melt and hot magma may rise up through the overlying mantle and lithosphere

• this may eventually erupt out of the earth’s surface causing a volcano

• (slab pull and gravitational movement of plates: the denser plate sinks into the mantle under the influence of gravity, which pulls the rest of the plate along behind it)

• an earthquake may occur because as the plates converge, pressure builds up, the rock may fracture and the pressure is released as an earthquake

disadvantages of living in areas at risk of volcanic eruptions

• volcanic eruptions can kill people and damage property

• economic activity can suffer as it is hard for businesses to operate after an eruption

• habitats and landscapes are damaged by lava flows

• ash disperses in the air, and together with volcanic gases can affect breathing - it may cover the land, including fields, houses, roads, and industrial plants

• pyroclastic flows can destroy houses and trees

• eruptions may trigger tsunamis, which lead to destructive flooding of the coastline

disadvantages of living in areas at risk of earthquakes?

• in seismic areas ground shaking causes bridges and buildings to collapse, windows to shatter, power lines to collapse, water/gas mains and sewers to fracture

• immediate deaths and injuries result from crushing, falling glass, fire and transport accidents

• people become homeless

• slope failures set off avalanches

• there may be panic, fear and hunger

• longer term disadvantages include diseases spread from polluted water, civil disorder, looting, power cuts, reduced emergency services, unemployment, disability, loss of farmland and food production

how can planning reduce the effects of an earthquake / volcanic eruption?

• prepare emergency aid and distribution

• practise earthquake/volcano drills

• plan evacuation routes

• stockpile blankets, clean water and food

• educate people so they know what to do if an earthquake or volcano happens

• prepare hazard maps to show areas most at risk of damage

how can the risks of a tectonic hazard be reduced?

• monitoring – recording physical changes, such as earthquake tremors around a volcano, to help forecast when and where a natural hazard might strike

• prediction – attempts to forecast when and where a hazard will strike, this can be done to some extent for volcanic eruptions, but less reliably for earthquakes

• planning – actions taken to enable communities to respond to, and recover from, natural disasters, through emergency evacuation plans and warning systems

• protection - actions taken before a hazard strikes to reduce its impact, such as educating people or improving building design

how can monitoring and prediction reduce the risks of an earthquake?

using seismometers to monitor earth tremors, but specific times and locations are not possible to predict

how can protection reduce the risks of an earthquake?

constructing buildings so that they are safe to live in and will not collapse

• rubber shock absorbers in the foundations to absorb the earth tremors

• steel frames that can sway during earth movements

• open areas outside of the buildings where people can assemble during an evacuation

how can planning reduce the risks of earthquakes?

• hospitals, emergency services and residents may practise for an earthquake

• they have drills in all public buildings so that people know what to do in the event of an earthquake - this helps to reduce the impact and increases their chance of survival

• planning may also involve emergency evacuation plans

how can monitoring and prediction reduce the risks of volcanic eruptions?

• measuring gas concentrations, using tiltmeters to monitor changes in the volcano’s surface

• using seismometers to measure small earthquakes and tremors

• thermal heat sensors to detect changes in the temperature of the volcano’s surface

how can protection reduce the risks of volcanic eruptions?

protection is difficult but it may be possible to use earth embankments or explosives to divert lava flows away from property

how can planning reduce the risks of volcanic eruptions?

• hazard maps have been produced for many of the world’s most dangerous volcanoes, showing the likely areas to be affected

• they can be used in planning to restrict certain land uses or to identify which areas need to be evacuated when an eruption is about to happen

immediate responses of a tectonic hazard? (first/emergency actions taken by people after an event)

• providing water supplies, medicine, first aid + supplies essential to survival

• the need to search for and rescue people, getting them to safety or to hospital

• possibly moving inland or to higher ground if a tsunami

• a need to try to provide medical help

• ensure there is clean water (and food)

• a need to bury the dead, often in mass graves to stop the spread of disease

• all of this may require international aid with teams of sniffer dogs, heavy equipment, medical staff, provisions of water purifying tablets, blankets, setting up shelters, tents etc.

long-term responses (occur over weeks/months/years)

• involve the need to rebuild houses, ideally using different materials and designs, to make them less easy to destroy

• rebuild public buildings and infrastructure

• may be a requirement to rebuild roads and railways

• ensure jobs are being created - such as for local builders, electricians and carpenters

• help people to come to terms with a traumatic event and loss of parents and children

• to predict and prepare for future events and introduce measures to reduce the effects of future hazards