hazardous earth

The structure of the Earth and plate movement

The structure of the Earth

Crust: outer layer of the Earth . Oceanic crust is generally thinner and least dense part of Earth structure. Contain rocks rich in silicon, oxygen,aluminium.potassium sodium (soap)

Two types of crust: continental crust- 30-70km thick sedimentary rocks and igneous. Oceanic crust- 6-10km thick basaltic in nature

Lithosphere: upper rigid part of mantle falls into lithosphere. Between crust and asthenosphere

Asthenosphere: below lithosphere is asthenosphere. Semi molten/viscious flow slowly

Mantle: contain Silicate rocks like iron and magnesium

Outer core:semi molten contain iron and nickel

Inner core: solid iron and nickel

Convection currents and plate movement

Heat from Earth's core warms mantle material.

Hot material becomes less dense and rises.

Reach crust forced sideways as cannot pass through crust

Friction from convection currents and crust cause tectonic plate to move

Cooler material sinks to core then process repeats.

Mantle flow, ridge push and slab pull contribute to tectonic plate movement.

Slab pull: at subduction zone slab pull comes into effect. Weight of tectonic plate subducted below the overlying plate into the mantle dragging rest of the plate along behind it.

Ridge push: weight of the ridge pushes the rest of the tectonic plate away from mid oceanic ridge often towards subduction zone

Continental drift

The theory that continents have moved over geological time from their previous positions.

Pangea

The ancient supercontinent in which all the present-day continents were joined together.

Plate tectonics

The theory that Earth’s lithospheric plates move and interact with one another.

Sea floor spreading

The process in which new oceanic crust forms at mid-ocean ridges and moves outwards.

Mid oceanic ridge

An underwater mountain range where new oceanic crust forms.

Paleomagnetism

The record of Earth’s past magnetic field preserved in rocks as they cool.

Magnetic reversal

A change in Earth’s magnetic field in which magnetic north and south switch places.

Oceanic crust

The relatively thin, dense crust beneath the oceans.

Subduction

The process in which one tectonic plate sinks beneath another into the mantle.

Evidence for continental drift and plate tectonics

Continental drift theory — Alfred Wegener

In 1912, German scientist Alfred Wegener proposed the theory of continental drift.

He argued that around 300 million years ago, Earth's continents formed one supercontinent called Pangaea.

Pangaea later split into Laurasia in the north and Gondwanaland in the south.

These landmasses continued to break apart and drift to form today's continents.

Wegener used geological and biological evidence to argue that continents now separated by oceans were once joined.

Limitation: Wegener could not explain the physical mechanism that moved the continents, so his theory was initially rejected by many scientists.

2. Geological evidence for continental drift

A. The fit of South America and Africa

The coastlines of South America and Africa appear to fit together like pieces of a jigsaw.

This suggests they were once joined as part of Pangaea.

The fit is particularly convincing when continental shelves are considered rather than modern coastlines alone.

B. Evidence from ancient glaciations

Glacial deposits dating to approximately 290 million years ago have been found in South America, Antarctica and India, as well as other former Gondwanan continents.

Glacial scratches, called striations, also indicate the direction of ice movement.

These patterns make more sense when the continents are reconstructed as one landmass, rather than in their present positions.

C. Matching rock sequences

Rock sequences in northern Scotland closely match those in eastern Canada.

Their similar geological characteristics suggest they formed under similar conditions when the areas were connected.

This supports the idea that the Atlantic Ocean opened after the landmasses separated.

3. Biological evidence for continental drift

A. Mesosaurus fossils

Fossil remains of the freshwater reptile Mesosaurus are found in both South America and southern Africa.

It is unlikely that this reptile could have crossed the Atlantic Ocean.

This suggests South America and Africa were once connected.

B. Glossopteris plant fossils

Fossils of this ancient plant have been found across former Gondwanan continents, including India and Antarctica.

The distribution is difficult to explain if these continents have always been separated.

It supports the theory that they were once joined.

C. Brachiopod fossils

Similar brachiopod fossils occur in limestone in India and Australia.

These similarities provide further evidence that landmasses now separated were once connected or shared similar marine environments.

Overall conclusion: Wegener's geological and biological evidence strongly suggested that continents had once been joined. However, he could not adequately explain how continental movement occurred.

4. Development of plate tectonic theory

From the 1940s onwards, new evidence helped scientists develop Wegener's theory into the modern theory of plate tectonics.

A. Discovery of mid-ocean ridges

Scientists discovered large underwater mountain chains, including the Mid-Atlantic Ridge.

Similar features were identified in the Pacific Ocean.

These ridges provided evidence that new oceanic crust could form along the ocean floor.

B. Paleomagnetism

every 400k years earths magnetic field reverses polarity south and North Pole switch

Magma rises at mid-ocean ridges and cools to form new oceanic crust.

As the magma cools, magnetic minerals align with Earth’s magnetic field and preserve its polarity in the rock.

When polarity reverses, newly formed rocks record the opposite magnetic direction.

Create series of alternating magnetic stripes along sea floor

Crust is older the further away from mid oceanic ridge

Prove sea floor spreading

C. The age of ocean-floor rocks

Oceanic crust is youngest near mid-ocean ridges.

Rocks become progressively older farther from the ridge.

This supports the idea that new crust forms at ridges and moves outwards.

1.4 Global pattern of plates and plate boundaries

Pacific Plate: much of its boundary is associated with the Pacific Ring of Fire, where earthquakes and volcanoes are common.

Nazca Plate and South American Plate: the Nazca Plate subducts beneath South America, producing the Andes and frequent earthquakes.

North American and Eurasian plates: move apart along the Mid-Atlantic Ridge, creating new oceanic crust.

Indian and Eurasian plates: collide, forming the Himalayas.

Pacific and North American plates: slide past each other along the San Andreas Fault in California.

1.5 Types of plate boundary

1. Constructive (divergent) plate boundary

Features

Mid-ocean ridges, e.g. the Mid-Atlantic Ridge.

Rift valleys can form on land, e.g. the East African Rift Valley.

Shield Volcanic activity and shallow earthquakes.

New oceanic crust.

Processes

Two plates move apart.

Mantle material rises to fill the gap.

Reduced pressure causes some mantle rock to melt, producing magma.

Magma rises, cools and solidifies to form new oceanic crust.

Repeated formation of crust causes sea-floor spreading.

2. Destructive (convergent) plate boundary

There are two main types involving oceanic crust, plus a continental collision boundary.

A. Oceanic–continental

Features

Deep ocean trench.

Fold mountains.

Volcanoes, often steep-sided composite volcanoes.

Earthquakes at different depths.

Processes

The oceanic and continental plates move towards each other.

The denser oceanic plate subducts beneath the continental plate.

Friction and pressure along the subduction zone can cause earthquakes.

Water released from the sinking plate helps cause melting in the mantle above, producing magma.

Magma rises and can erupt, forming volcanoes.

Compression can fold and uplift rocks, forming mountains.

B. Oceanic–oceanic

Features

Deep ocean trench.

Volcanic island arc, e.g. Japan.

Earthquakes at different depths.

Volcanoes.

Processes

Two oceanic plates move towards each other.

The older, denser plate usually subducts beneath the other.

Friction and pressure can cause earthquakes.

Water released by the subducting plate helps generate magma.

Magma rises and erupts, forming volcanic islands that can develop into an island arc.

C. Continental–continental collision

Features

High fold mountains, e.g. the Himalayas.

Thickened continental crust.

Powerful earthquakes.

Little or no volcanic activity from the collision itself.

Processes

Two continental plates move towards each other.

Neither plate readily subducts because continental crust is relatively buoyant.

The crust is compressed, folded and pushed upwards.

The crust thickens, forming high fold mountains.

Pressure and friction along faults cause earthquakes.

3. Conservative plate boundary

Features

Fault lines, e.g. the San Andreas Fault.

Earthquakes, sometimes powerful.

No new crust created or old crust destroyed.

No volcanoes caused by the boundary itself.

Processes

Two plates slide horizontally past each other.

Friction can cause the plates to become temporarily locked.

Stress builds up as the plates continue trying to move.

The plates suddenly slip when the stress overcomes friction.

Energy is released as seismic waves, causing an earthquake.

Viscosity

Viscosity means resistance to flow.

Low-viscosity magma: runny, flows easily and allows gas to escape more readily. It tends to produce effusive eruptions.

High-viscosity magma: thick and sticky, traps gas and can build pressure. This increases the likelihood of explosive eruptions.

2.1 Types of volcanoes and volcanic activityh

1.Explosive eruptions — convergent (destructive) plate boundaries

Causes

Usually occur at destructive plate boundaries, where plates move towards each other.

The denser oceanic plate subducts beneath another plate.

Water released from the subducting plate helps melting occur in the mantle, producing magma.

The magma often has a high silica content, making it high viscosity (thick and sticky).

Gas becomes trapped in the viscous magma, pressure builds up, and it can erupt explosively.

Features

High-viscosity magma: thick and resistant to flow.

Explosive eruptions: rapid release of gas and ash.

Composite volcanoes (stratovolcanoes): tall, steep-sided cones built from alternating layers of lava and ash.

Hazards: tephra ash clouds, pyroclastic flows, volcanic bombs and Lahars.

Examples: Mount St Helens (USA) and Mount Fuji (Japan).

2. Effusive eruptions — divergent (constructive) plate boundaries

Causes

Usually occur at constructive plate boundaries, where two plates move apart.

Magma rises to fill the gap between the separating plates.

The magma is often basaltic, with a relatively low silica content, making it low viscosity (runny).

Gas escapes more easily from runny magma, so eruptions are usually less explosive.

Lava spreads over large areas and cools to form new crust.

Features

Low-viscosity magma: runny and flows easily.

Effusive eruptions: lava flows out relatively gently rather than exploding violently.

Shield volcanoes: broad volcanoes with gentle slopes, formed by repeated flows of runny lava.

Fissure eruptions: lava can emerge through long cracks in the ground.

Landforms: mid-ocean ridges, volcanic plateaus and broad shield volcanoes.

Hazards:Lava flows and gas emissions

Examples: Iceland and the Mid-Atlantic Ridge.

Note: volcanoes at constructive boundaries are often effusive, but not every eruption is identical.

3. Volcanoes at hot spots — away from plate boundaries

Causes

A hot spot is an area where unusually hot mantle material rises and causes melting beneath a tectonic plate.

Magma rises through the crust and erupts, even though the location may be far from a plate boundary.

As the plate moves over a relatively stationary hot spot, a chain of volcanoes can form.

Hot-spot eruptions often produce low-viscosity basaltic magma and effusive lava flows, although eruption styles can vary.

Features

Shield volcanoes: broad, gently sloping volcanoes formed by repeated lava flows.

Volcanic chains: volcanoes become progressively older with distance from the active hot spot.

Example — Hawaii: the Pacific Plate moves over a hot spot, forming the Hawaiian island chain.

Example — East African Rift Valley: volcanic activity occurs as the African Plate is stretching and beginning to split. This is associated with a divergent plate setting, so it is not a classic intraplate hot spot example.

4. Size and shape of volcanoes, including supervolcanoes

A. Composite volcano (stratovolcano)

Causes

Usually forms at destructive plate boundaries.

High-viscosity magma does not flow far, so lava and ash build up around the vent.

Repeated explosive eruptions create layers of ash and lava.

Features

Tall, steep-sided, cone-shaped volcano.

Alternating layers of lava and ash.

Often has a central crater and side vents.

Eruptions can be explosive.

B. Shield volcano

Causes

Common at hot spots and constructive plate boundaries.

Low-viscosity basaltic lava flows long distances before cooling.

Repeated lava flows gradually build a broad volcano.

Features

Very wide, with gentle slopes.

Mainly made of layers of solidified lava.

Usually produces effusive eruptions.

Can grow to a very large size across a wide area.

C. Supervolcano

Causes

Large volumes of magma can accumulate beneath the crust.

Very large explosive eruptions can release enormous amounts of volcanic material.

After the magma chamber loses a large volume of magma, the ground above may collapse.

Features

Often forms a huge depression called a caldera, rather than a typical cone-shaped mountain.

Can produce extremely large explosive eruptions.

Eruptions can spread ash over very wide areas and affect climate.

Example: Yellowstone, USA. A supervolcano is commonly associated with an eruption of VEI 8.

VEI VOLCANIC EXPLOSIVITY INDEX

Two key factors: 

• Magnitude:  the amount of material erupted 

• Intensity:  the speed at which the material is erupted 

 

 

THE VOLCANIC EXPLOSIVITY INDEX (VEI) 

Combines intensity and magnitude into one number on a scale from 0 (the least explosive) to 8.  Each increase in number means an almost 10 fold increase in explosivity. 

 

The following factors are taken into account when assessing the explosivity of an eruption: 

• The volume of the material erupted 

• The height the material reaches 

• The duration in hours  

Main volcanic hazards

1. Lava flows-effusive

Molten rock flows downhill under gravity.

Usually moves slowly enough for many people to evacuate, but speed varies.

Can destroy homes, roads, farmland and infrastructure; fires can start where lava meets combustible materials.

Example: lava flows during the 2018 Kīlauea eruption in Hawaii.

2. Pyroclastic flows-explosive

Fast-moving mixtures of hot gas, ash and rock fragments that travel down a volcano.

Can move at very high speeds and reach extremely high temperatures.

Cause severe burns, breathing problems, destruction of buildings and rapid burial.

They are among the most dangerous volcanic hazards because escape may be difficult once a flow is underway.

3. Tephra and ash-explosive

Tephra is all solid material ejected into the air; ash is the finest fraction, smaller than 2 mm.

Ash can cause respiratory irritation, contaminate water, damage crops, reduce visibility and disrupt aviation.

Thick deposits can collapse roofs, particularly when wet.

Example: the 2010 Eyjafjallajökull eruption in Iceland disrupted European air travel.

4. Volcanic gas emissions-both

Volcanoes release gases including water vapour, carbon dioxide and sulphur dioxide.

Sulphur dioxide can irritate the respiratory system and contribute to acid rain and volcanic smog.

Carbon dioxide can accumulate in low-lying areas and displace oxygen.

Gas emissions may cause harm even when there is little lava or ash.

5. Lahars-often explosive

Fast-moving flows of water mixed with volcanic ash, soil and rock.

Can be triggered by heavy rainfall, melting snow or ice, or the sudden release of water.

Travel down valleys and river channels, burying settlements and damaging bridges and farmland.

Can occur during or long after an eruption.

6. Tsunamis-explosive

Can be generated by underwater or coastal volcanic explosions, caldera collapse, flank collapse or volcanic material entering the sea.

Waves can travel across oceans and flood distant coastlines.

Example: the 2022 Hunga Tonga–Hunga Ha'apai eruption generated tsunami waves.

7. Flooding caused by melting ice-both

Heat from an eruption can melt snow or glacial ice.

Meltwater may accumulate and then rush downhill as a sudden flood, known in Iceland as a jökulhlaup.

Flooding can carry sediment and debris, damage roads and bridges, and threaten settlements downstream.

Why volcanic hazards vary

Why volcanic hazards vary

Magma viscosity and gas content: influence whether eruptions are explosive or effusive.

Eruption size and duration: larger eruptions can produce more ash, lava and pyroclastic material.

Volcano shape and topography: steep slopes and valleys can channel pyroclastic flows and lahars.

Weather: wind spreads ash; heavy rainfall can trigger lahars.

Ice and water: can intensify flooding and explosive interaction with magma.

Population exposure: settlements close to the volcano or in valleys are more vulnerable.

Monitoring and preparation: warnings and evacuation can reduce deaths but may not prevent damage.

Earthquake

An earthquake is the sudden release of energy stored in rocks, producing seismic waves that cause the ground to shake.

Focus hypocentre

Focus (hypocentre): the point inside the Earth where the earthquake begins.

Epicentre

Epicentre: the point on the Earth's surface directly above the focus.

Fault

Fault: a fracture in the Earth's crust along which movement occurs.

Magnitude

Magnitude: a measure of the energy released by an earthquake.

Intensity

Intensity: a measure of the observed shaking and damage at a particular location.

How earthquakes occur

How earthquakes occur

Tectonic plates move but friction may prevent rocks from sliding smoothly.

Stress builds up in the rocks.

When stress exceeds the strength of the rocks or frictional resistance, the fault slips.

Stored energy is released as seismic waves.

The waves cause ground shaking and may trigger secondary hazards.

Type of earthquakes and the cause and features

Shallow-focus earthquakes

Cause

Sudden movement along a fault releases built-up stress in the Earth's crust.

Common at constructive and conservative plate boundaries, and the shallow parts of destructive boundaries.

Features

Focus is 0–70 km deep.

Energy is released close to the Earth's surface.

Seismic waves travel a shorter distance to the surface, often causing more intense shaking near the epicentre.

Can cause severe damage to buildings and infrastructure near the epicentre.

Deep-focus earthquakes

Cause

Occur within cold, descending oceanic plates at destructive (subduction) boundaries.

Stress and sudden movement within the subducting plate cause energy to be released.

Features

Focus is 300–700 km deep.

Seismic waves travel further before reaching the surface.

Local shaking is often less intense than for a similar-sized shallow earthquake.

Can be felt over wide areas and still cause damage, depending on magnitude, geology and building vulnerability.

Different measures of assessing earthquake magnitude

Richter scale

Measure strength of quake

Measures earthquake magnitude using seismic wave amplitude.

Logarithmic scale: each whole-number increase represents 10 times greater wave amplitude.

Less reliable for very large earthquakes.

Moment Magnitude Scale (Mw)

it measures the strength of the quake by seeing how much the plates moved when the earthquake happened The more the plates moved, the bigger the strength of the quake.

Modified Mercalli Intensity Scale (MMI)

Measure both impact and strength of quake

Measures the intensity of shaking and the effects of an earthquake on people, buildings and the environment.

Has 12 levels, from I (not felt) to XII (total destruction).

Intensity varies between locations.

Effects of earthquakes on landforms and landscapes

Escarpments: vertical displacement along faults can create steep slopes separating areas of different elevation.

Rift valleys: tensional forces at divergent plate boundaries create parallel faults, causing the land between them to sink.

Fault scarps: sudden movement along a fault creates a steep step in the land surface.

Landslides: ground shaking can destabilise slopes, moving rock and soil downhill and reshaping the landscape.

Uplift and subsidence: fault movement raises or lowers sections of land.

Ground rupture: movement along faults creates cracks and displacements at the surface.

Main hazards generated by earthquakes

1. Ground shaking

Seismic waves move the ground, causing buildings, bridges and roads to vibrate or collapse. Damage depends on magnitude, depth, distance, duration, local geology and building quality.

2. Ground displacement

Movement along a fault can rupture the surface, offset roads and railway lines, and damage pipelines. This is particularly destructive where infrastructure crosses an active fault.

3. Liquefaction

Strong shaking increases water pressure between grains in loose, water-saturated sediment.

The sediment loses strength and behaves more like a liquid.

Buildings may tilt or sink; roads and underground pipes can be damaged.

Particularly likely in waterlogged sandy soils and reclaimed land.

4. Landslides and avalanches

Shaking destabilises steep slopes, triggering rockfalls, landslides or avalanches. These can bury settlements, block roads and rivers, and isolate communities.

5. Tsunamis

Large undersea earthquakes can suddenly uplift or lower the sea floor, displacing water.

Waves travel rapidly across the ocean and increase in height as they enter shallow coastal waters.

Coastal flooding can destroy buildings, ports and farmland and cause major loss of life.

Tsunamis can also result from underwater landslides and volcanic activity.

6. Flooding

Earthquakes can damage dams and water infrastructure, divert rivers, or trigger landslides that temporarily block river channels. Failure of a blockage or dam can cause sudden flooding downstream.

Why people choose to live in tectonically active locations

Fertile soils: volcanic ash weathers to form nutrient-rich soils suitable for farming.

Geothermal energy: volcanic areas can provide energy for electricity and heating.

Tourism: volcanoes attract visitors, creating jobs and income.

Mineral resources: volcanic areas can contain valuable minerals.

Employment and family ties: people may already live there and depend on local jobs, land and communities.

Low-cost land: some people settle in hazardous areas because housing or farmland is more affordable.

Impacts of volcanic eruptions

Deaths and injuries: lava, pyroclastic flows, ash and lahars can kill or injure people.

Displacement: homes can be destroyed or evacuated, forcing people to leave.

Infrastructure damage: roads, bridges, power supplies and water systems can be damaged.

Economic losses: businesses, farms and tourism may be disrupted; rebuilding is expensive.

Environmental impacts: vegetation and habitats can be destroyed, while ash and gases pollute air and water.

Positive impacts: volcanic ash can improve soil fertility, and eruptions may create new landforms and future tourism opportunities.

Economic, environmental and political impacts on the country

Economic: repair costs, loss of income, unemployment and disruption to trade; longer-term recovery can create jobs.

Environmental: destruction of habitats and farmland, air and water pollution, and changes to the landscape.

Political: governments must organise evacuations, provide emergency assistance and fund reconstruction. Their response can affect public trust.

Why people choose to live in tectonically active locations

Employment: cities and industries provide jobs despite earthquake risk.

Economic opportunities: ports, trade, tourism and industry attract people.

Fertile land: tectonic activity can contribute to productive agricultural landscapes.

Family and cultural ties: people may have lived in the area for generations.

Limited alternatives: people may lack the money or resources to relocate.

Impacts people experience as a result of earthquake activity

Ground shaking and displacement: buildings, roads and bridges can collapse or crack.

Deaths and injuries: falling buildings, debris and damaged infrastructure can cause casualties.

Liquefaction: water-saturated sediment loses strength, causing buildings to sink or tilt.

Landslides and avalanches: shaking destabilises slopes and can bury settlements or block roads.

Tsunamis: undersea earthquakes can displace seawater and flood coastal settlements.

Flooding: damaged dams, water pipes or tsunami waves can cause flooding.

Homelessness: damaged homes force people into temporary shelters.

Disease and shortages: damaged water supplies and transport networks can limit access to clean water, food and healthcare.

Economic, environmental and political impacts on the country By earthquake

Economic: damage to businesses and infrastructure, reduced productivity, unemployment and expensive reconstruction.

Environmental: landslides, altered landscapes, coastal flooding and damage to ecosystems.

Political: emergency response, rescue operations, rebuilding and possible criticism of government preparedness.

Long-term effects: national debt can increase, investment may fall, and communities may take years to recover.

5a. Strategies to manage hazards from volcanic activity

Attempts to mitigate against the event

Lava diversion channels: direct lava away from settlements and infrastructure.

Barriers and earth embankments: can slow or redirect some lava flows.

Monitoring: seismometers, gas measurements, ground deformation and satellite observations help identify changes in volcanic activity.

Hazard maps: identify areas at risk from lava, ash, pyroclastic flows and lahars.

Attempts to mitigate against vulnerability

Community preparedness: teach people what to do during an eruption.

Evacuation plans: identify evacuation routes, shelters and safe areas.

Public warnings: alert people when volcanic activity increases.

Education: explain volcanic hazards and how to respond.

Land-use planning: restrict building in high-risk areas where possible.

Attempts to mitigate against losses

Rescue operations: emergency services search for and assist people affected.

Emergency shelters: provide temporary accommodation for evacuees.

Emergency relief: provide food, clean water, medical treatment and essential supplies.

Government and international aid: provide funding and resources for recovery.

Reconstruction: repair homes, roads, utilities and public services.

Strategies to manage hazards from earthquakes

Attempts to mitigate against the event

Land-use zoning: restrict development in areas at high risk from earthquakes, liquefaction or landslides.

Hazard mapping: identify active faults and areas vulnerable to ground shaking.

Monitoring and early-warning systems: detect earthquake waves and provide a few seconds of warning before stronger shaking arrives in some locations. Earthquakes cannot currently be predicted accurately enough to give reliable long-term warnings.

Attempts to mitigate against vulnerability

Earthquake-resistant building design: use reinforced concrete, steel frames, cross-bracing and flexible foundations where appropriate.

Retrofitting: strengthen older buildings to reduce the risk of collapse.

Building regulations: enforce construction standards in earthquake-prone areas.

Public education: teach people to protect themselves during shaking.

Drills and evacuation plans: practise emergency responses in schools, workplaces and communities.

Attempts to mitigate against losses

Insurance: helps households and businesses pay for damage and rebuilding.

Search and rescue: emergency teams locate and rescue trapped survivors.

Emergency medical care: treat injuries and prevent further deaths.

Emergency shelters and supplies: provide temporary accommodation, food and clean water.

Reconstruction funding: governments and aid organisations support rebuilding.

Infrastructure planning: improve the resilience of roads, bridges, water supplies and electricity networks.

How and why have the risks from tectonic hazards changed over time including:

Changes in the frequency and impacts of tectonic hazards over time

Earthquake frequency: the number of earthquakes detected has increased partly because monitoring networks have improved; this does not necessarily mean more earthquakes are occurring.

Volcanic monitoring: better monitoring can provide earlier warnings and allow more people to evacuate.

Population growth: more people living in hazard-prone areas can increase the number exposed to danger.

Urbanisation: expanding cities can increase potential losses when buildings and infrastructure are vulnerable.

Improved technology: satellite monitoring, warning systems and better construction can reduce deaths and damage.

Climate and environmental conditions: heavy rainfall can increase landslide and lahar risks around volcanoes, while sea-level rise can worsen the impacts of coastal tsunamis and flooding.

Economic development: wealthier countries often have more resources for monitoring, preparedness and reconstruction, although they can still suffer substantial economic losses.

Degree of risk and the disaster risk equation

Hazard: a potentially damaging natural event, such as an earthquake or volcanic eruption.

Exposure: the people, buildings and infrastructure located in the affected area.

Vulnerability: how susceptible people and assets are to harm.

Capacity to cope: the ability to prepare for, respond to and recover from the event.

A commonly used version of the disaster risk equation is:

Disaster risk =Hazard × Exposure × Vulnerability / Capacity to cope

Risk increases when the hazard, exposure or vulnerability increases.

Risk decreases when the capacity to prepare, respond and recover improves.

A powerful earthquake may cause fewer deaths in a well-prepared country than a smaller earthquake in a country with weak buildings and limited emergency services.

Possible future strategies to cope with tectonic risks

Improve earthquake-resistant building standards and retrofit vulnerable buildings.

Expand volcano monitoring and earthquake early-warning systems.

Improve hazard maps and land-use planning.

Educate communities and practise evacuation procedures.

Improve emergency services, healthcare and rescue capacity.

Increase access to insurance and emergency funding.

Strengthen international cooperation to share monitoring data, expertise and resources.

The relationship between disaster and response: the Park model

The Park model shows how a community's quality of life changes during a disaster and its recovery.

Pre-disaster: quality of life is relatively stable.

Impact: the hazard strikes, causing quality of life to fall sharply.

Relief: emergency services provide rescue, medical treatment, food, water and shelter.

Rehabilitation: essential services and daily activities begin to return.

Reconstruction: homes, infrastructure and the economy are rebuilt.

Recovery: quality of life returns towards its previous level or may improve if reconstruction makes the area more resilient.

Factors affecting recovery:

Wealth and availability of funding.

Effectiveness of government and emergency services.

Level of damage and number of people affected.

Availability of international aid.

Quality of reconstruction and preparedness for future hazards.

More developed countries often recover faster because they have greater resources, stronger infrastructure and better emergency services.

Less developed countries may experience longer recovery because funding, healthcare and infrastructure are more limited.