Unit 1A: The Challenge of Natural Hazards
Natural Hazards
A natural hazard is a natural process which could cause death, injury, or disruption to humans, or
destroy property and possessions. A natural disaster is a natural hazard that has actually happened.
Extreme events which don’t pose a thread to human activity are not hazards.
There are two main types of natural hazard: Geological and Meteorological
A geological hazard is caused by tectonic and land processes, such as volcanoes,
earthquakes, landscapes, and avalanches.
A meteorological hazard is caused by weather and climate, such as tropical storms, extreme
weather, and climate change.
Factors Affecting Risk
A hazard risk is the probability a natural hazard occurs.
Vulnerability:
The more people in areas exposed to natural hazards, the greater they will be affected by
one; so, the hazard risk is higher. Like a city at the base of a volcano (Naples).
Capacity to Cope:
The better a population can cope with an extreme event, the lower the threat. Such as how
HICs are better at coping with flooding as they can afford resources to do so.
Nature of Natural Hazards:
Type – some hazards are greater than others
Frequency – some hazards occur more than others, increasing risk
Magnitude – more severe hazards have a greater effect than less severe natural hazards
Tectonic Plates
The Earth’s surface is separated into tectonic plates; the core of the Earth is a ball of solid (inner) and
liquid (outer) iron and nickel. Around the core is the mantle, which is semi-molten rock which moves
very slowly. The outer layer of the Earth is the crust, divided into slabs called tectonic plates which
float on the mantle. There are two types of tectonic plate, oceanic and continental. Oceanic crust is
thinner (5-10km) and denser than a continental plate which is thicker (30-50km) and less dense. The
plates are moving though convection currents under the mantle. The places where plates meet are
called plate margins or plate boundaries.
Types of Plate Margin
Destructive Margins – Moving towards each other; e.g. along the west coast of South
America; if an oceanic and continental plates meet, the oceanic plate is forced down and
destroyed, creating volcanoes and ocean trenches often; if two continental plates meet,
they collide and form a mountain range.
, Constructive Margins – Moving away from each other; e.g. at the mid-Atlantic ridge; magma
rises to fill the gap and cools, creating new crust
Conservative Margins – Moving sideways past each other or the same direction at different
speeds; e.g. along the west coast of the USA; crust is neither created nor destroyed
Volcanoes and Earthquakes
Volcanoes
Volcanoes are found at destructive and constructive plate margins.
At a destructive plate margin, the oceanic plate goes under the constructive plate as it’s denser. The
oceanic plate is melted and destroyed, and a pool of magma forms and passes through cracks in the
crust (vents) which erupts onto the surface (now lava), forming a volcano.
At a constructive margin the magma rises into the gap and forms a volcano.
Some volcanoes also form over bits of the mantle that are very hot (hotspots) like in Hawaii.
When a volcano erupts, it emits lava and gases. Some emit a lot of ash, which can cover land, block
out the sun, and form pyroclastic flows.
Earthquakes
Earthquakes are caused by the tension that builds at all three types of plate margin.
Destructive Margin – tension builds when a plate gets stuck as it moves down past the other
into the mantle
Constructive Margin – tension builds along cracks within the plates as they move away from
each other
Conservative Margin – tension builds when the plates moving past each other get stuck
They eventually jerk past each other and send out shock waves, this is the earthquake. The shock
waves spread from the focus – the point in the Earth the earthquake starts. The nearer the focus the
more damage. The epicentre is the point on the Earth’s surface above the focus.
Earthquakes are measured using the moment magnitude scale, which measures the amount of
energy released by the earthquake (the magnitude). It is a logarithmic scale, meaning a magnitude 7
earthquake is ten times more powerful than a magnitude 6 earthquake. Magnitude 6 and under only
cause slight damage to buildings (although can be worse in very built up areas), magnitude 7 and
above can cause major damage.
Earthquakes – Effects and Responses
Effects
Primary effects of an earthquake include:
Buildings and bridges collapse; homes destroyed
Injuries and deaths caused by falling debris and buildings
Roads, railways, airports, and ports are damaged
, Electricity cables, gas, water pipes, and communication networks are damaged; supplies cut
off
Secondary effects of an earthquake include:
Leaking gas can be ignited; fires
Landslides and tsunamis; damage to buildings and people
Homelessness; more deaths
Shortage of clean water; disease spreads
As roads are blocked or damaged, aid and emergency vehicles can’t get through and trade is
harder
Businesses are damaged or destroyed, leading to unemployment and a loss of income;
reduced tourism
Repairs are very expensive and can weaken the economy
Responses
Immediate responses of an earthquake include:
Rescue people from trapped buildings and treat the injured
Recover dead bodies to prevent the spread of disease
Put out fires
Set up temporary shelters and supplies of food, water, electricity, gas, and communications
systems
Foreign governments or charities may send aid (supplies, equipment, financial donations, aid
workers)
Tech companies may set up disaster response tools which allow for damage to be recorded
and for people to confirm their safety (Google Crisis Response™)
Long-term responses of an earthquake include:
Rehousing those displaced
Repairing or rebuilding destroyed or damaged buildings, railways, roads, and bridges
Reconnect electricity, water, gas, and communications connections
Improve building regulations if necessary
Establish initiatives to help economic recovery (tourism)
Volcanoes – Effects and Responses
Effects
Primary effects of a volcano include:
Buildings and roads destroyed by lava and pyroclastic flows or heavy ash
People and animals injured by pyroclastic flow, lava flow, and falling rock
Crops damaged and water supplies contaminated by falling ash
People, plants, and animals suffocated by volcanic gases
Secondary effects of a volcano include:
Mudflows (lahars) form when volcanic material mixes with water (heavy rainfall/snow melt);
destruction, death, injury
, Flooding from hot rock, ash, and gas melting ice and snow on the volcano. Rock and ash can
clog up rivers and dams, making flooding worse
Transport networks are blocked so aid and emergency vehicles can’t get though and trade is
harder
Homelessness due to loss of income
Tourism can be disrupted straight after, but can often increase afterwards
Ash makes fields more fertile after it’s broken down
Recovery is very expensive and can be difficult on an economy
Responses
Immediate responses to a volcano include:
Evacuate before the eruption if it was predicted, ASAP if not
Provide food, water, and shelter for the evacuated
Treat the injured (e.g. falling debris or ash inhalation)
Rescue those cut off by damage to roads or bridges
Provide temporary electricity, gas, and communications
Foreign governments or charities may send aid (supplies, equipment, financial donations,
aid workers)
Tech companies may set up disaster response tools which allow for damage to be recorded
and for people to confirm their safety (Google Crisis Response™)
Long-term responses to a volcano include:
Repairs and rebuilding
Resettle affected people
Repair and reconnect roads, railways, power lines
Improve and update monitoring and evacuation plans
Boost the economy if possible (tourism)
Tectonic Hazards – Case Studies
Two tectonic hazards, one in an LIC, one in a HIC in different parts of the world
Tectonic Hazard in an LIC
Place: Nepal, one of the poorest countries in the world, with a HDI of 0.540 (145 th in the
world) and a GDP of $649 per annum
Date: 11:26 local time on Saturday 25th April 2015, with aftershock the next day and on the
12th May
Size: 7.8-7.9 on the Richter Scale
Plates: A collision (convergent) boundary between the Eurasian and Indian Plate
Primary effects
9000 deaths
2000 injured
3 million homeless when homes were destroyed
Natural Hazards
A natural hazard is a natural process which could cause death, injury, or disruption to humans, or
destroy property and possessions. A natural disaster is a natural hazard that has actually happened.
Extreme events which don’t pose a thread to human activity are not hazards.
There are two main types of natural hazard: Geological and Meteorological
A geological hazard is caused by tectonic and land processes, such as volcanoes,
earthquakes, landscapes, and avalanches.
A meteorological hazard is caused by weather and climate, such as tropical storms, extreme
weather, and climate change.
Factors Affecting Risk
A hazard risk is the probability a natural hazard occurs.
Vulnerability:
The more people in areas exposed to natural hazards, the greater they will be affected by
one; so, the hazard risk is higher. Like a city at the base of a volcano (Naples).
Capacity to Cope:
The better a population can cope with an extreme event, the lower the threat. Such as how
HICs are better at coping with flooding as they can afford resources to do so.
Nature of Natural Hazards:
Type – some hazards are greater than others
Frequency – some hazards occur more than others, increasing risk
Magnitude – more severe hazards have a greater effect than less severe natural hazards
Tectonic Plates
The Earth’s surface is separated into tectonic plates; the core of the Earth is a ball of solid (inner) and
liquid (outer) iron and nickel. Around the core is the mantle, which is semi-molten rock which moves
very slowly. The outer layer of the Earth is the crust, divided into slabs called tectonic plates which
float on the mantle. There are two types of tectonic plate, oceanic and continental. Oceanic crust is
thinner (5-10km) and denser than a continental plate which is thicker (30-50km) and less dense. The
plates are moving though convection currents under the mantle. The places where plates meet are
called plate margins or plate boundaries.
Types of Plate Margin
Destructive Margins – Moving towards each other; e.g. along the west coast of South
America; if an oceanic and continental plates meet, the oceanic plate is forced down and
destroyed, creating volcanoes and ocean trenches often; if two continental plates meet,
they collide and form a mountain range.
, Constructive Margins – Moving away from each other; e.g. at the mid-Atlantic ridge; magma
rises to fill the gap and cools, creating new crust
Conservative Margins – Moving sideways past each other or the same direction at different
speeds; e.g. along the west coast of the USA; crust is neither created nor destroyed
Volcanoes and Earthquakes
Volcanoes
Volcanoes are found at destructive and constructive plate margins.
At a destructive plate margin, the oceanic plate goes under the constructive plate as it’s denser. The
oceanic plate is melted and destroyed, and a pool of magma forms and passes through cracks in the
crust (vents) which erupts onto the surface (now lava), forming a volcano.
At a constructive margin the magma rises into the gap and forms a volcano.
Some volcanoes also form over bits of the mantle that are very hot (hotspots) like in Hawaii.
When a volcano erupts, it emits lava and gases. Some emit a lot of ash, which can cover land, block
out the sun, and form pyroclastic flows.
Earthquakes
Earthquakes are caused by the tension that builds at all three types of plate margin.
Destructive Margin – tension builds when a plate gets stuck as it moves down past the other
into the mantle
Constructive Margin – tension builds along cracks within the plates as they move away from
each other
Conservative Margin – tension builds when the plates moving past each other get stuck
They eventually jerk past each other and send out shock waves, this is the earthquake. The shock
waves spread from the focus – the point in the Earth the earthquake starts. The nearer the focus the
more damage. The epicentre is the point on the Earth’s surface above the focus.
Earthquakes are measured using the moment magnitude scale, which measures the amount of
energy released by the earthquake (the magnitude). It is a logarithmic scale, meaning a magnitude 7
earthquake is ten times more powerful than a magnitude 6 earthquake. Magnitude 6 and under only
cause slight damage to buildings (although can be worse in very built up areas), magnitude 7 and
above can cause major damage.
Earthquakes – Effects and Responses
Effects
Primary effects of an earthquake include:
Buildings and bridges collapse; homes destroyed
Injuries and deaths caused by falling debris and buildings
Roads, railways, airports, and ports are damaged
, Electricity cables, gas, water pipes, and communication networks are damaged; supplies cut
off
Secondary effects of an earthquake include:
Leaking gas can be ignited; fires
Landslides and tsunamis; damage to buildings and people
Homelessness; more deaths
Shortage of clean water; disease spreads
As roads are blocked or damaged, aid and emergency vehicles can’t get through and trade is
harder
Businesses are damaged or destroyed, leading to unemployment and a loss of income;
reduced tourism
Repairs are very expensive and can weaken the economy
Responses
Immediate responses of an earthquake include:
Rescue people from trapped buildings and treat the injured
Recover dead bodies to prevent the spread of disease
Put out fires
Set up temporary shelters and supplies of food, water, electricity, gas, and communications
systems
Foreign governments or charities may send aid (supplies, equipment, financial donations, aid
workers)
Tech companies may set up disaster response tools which allow for damage to be recorded
and for people to confirm their safety (Google Crisis Response™)
Long-term responses of an earthquake include:
Rehousing those displaced
Repairing or rebuilding destroyed or damaged buildings, railways, roads, and bridges
Reconnect electricity, water, gas, and communications connections
Improve building regulations if necessary
Establish initiatives to help economic recovery (tourism)
Volcanoes – Effects and Responses
Effects
Primary effects of a volcano include:
Buildings and roads destroyed by lava and pyroclastic flows or heavy ash
People and animals injured by pyroclastic flow, lava flow, and falling rock
Crops damaged and water supplies contaminated by falling ash
People, plants, and animals suffocated by volcanic gases
Secondary effects of a volcano include:
Mudflows (lahars) form when volcanic material mixes with water (heavy rainfall/snow melt);
destruction, death, injury
, Flooding from hot rock, ash, and gas melting ice and snow on the volcano. Rock and ash can
clog up rivers and dams, making flooding worse
Transport networks are blocked so aid and emergency vehicles can’t get though and trade is
harder
Homelessness due to loss of income
Tourism can be disrupted straight after, but can often increase afterwards
Ash makes fields more fertile after it’s broken down
Recovery is very expensive and can be difficult on an economy
Responses
Immediate responses to a volcano include:
Evacuate before the eruption if it was predicted, ASAP if not
Provide food, water, and shelter for the evacuated
Treat the injured (e.g. falling debris or ash inhalation)
Rescue those cut off by damage to roads or bridges
Provide temporary electricity, gas, and communications
Foreign governments or charities may send aid (supplies, equipment, financial donations,
aid workers)
Tech companies may set up disaster response tools which allow for damage to be recorded
and for people to confirm their safety (Google Crisis Response™)
Long-term responses to a volcano include:
Repairs and rebuilding
Resettle affected people
Repair and reconnect roads, railways, power lines
Improve and update monitoring and evacuation plans
Boost the economy if possible (tourism)
Tectonic Hazards – Case Studies
Two tectonic hazards, one in an LIC, one in a HIC in different parts of the world
Tectonic Hazard in an LIC
Place: Nepal, one of the poorest countries in the world, with a HDI of 0.540 (145 th in the
world) and a GDP of $649 per annum
Date: 11:26 local time on Saturday 25th April 2015, with aftershock the next day and on the
12th May
Size: 7.8-7.9 on the Richter Scale
Plates: A collision (convergent) boundary between the Eurasian and Indian Plate
Primary effects
9000 deaths
2000 injured
3 million homeless when homes were destroyed
