- Created by: Fflur Haf
- Created on: 04-05-19 16:14
What is a Natural Hazard?
A natural hazard is a threat to people or property.
1) A natural hazard is a natural process which can cause death, injury or disruption to humans, or destroy property and possessions.
2) A natural disaster is when the natural hazard actually happens.
3) Extreme events in which do not pose any threat to human activity are not counted as hazards (e.g. a drought in an uninhabited desert or an avalanche in Antarctica).
Two Types of Natural Hazards.
Geological Hazards - Caused by land and tectonic movements. Examples are volcanoes, earthquakes, landslides and avalanches.
Meteorological Hazards - Caused by weather and climate. Examples include tropical storms (other extreme weather), including heatwaves, cold spells and climate change.
Factors Affecting Hazard Risk.
Hazard risk is the likelihood that a natural hazard occurs. There are several factors affecting hazard risk:
Vulnerability - The more people that are in areas exposed to natural hazards, the greater the probability they will be affected by a natural hazard - so the hazard risk is higher.
Capacity to Cope - Natural hazards have to affect human activities to count as a hazard. The better a population can cope with an extreme event, the lower the threat. For example, higher income countries are better able to cope with flooding because they can afford to build defences, evacuate people in a disaster and repair damage afterwards.
Nature of Natural Hazards - Type: The hazard risk from some hazards is greater than others. E.g. tropical storms can be predicted and monitored, giving people time to evacuate to safety. But earthquakes happen very suddenly, with no warning, so it's much harder to protect people. Frequency: Some natural hazards occur more often than others, increasing the hazard risk. Magnitude: More severe natural hazards cause greater effects than less severe natural hazards. E.g. a magnitude 9.0 earthquake struck Japan in 2011 and killed over 15,000 people. When a 6.3 magnitude earthquake struck L' Aquila, Italy, around 300 people died.
The Earth's surface is made of huge floating plates that are constantly moving.
1) The core of the Earth is a ball of solid (inner core) and liquid (outer core) iron and nickel.
2) Surrounding the core is the mantle, which is semi-molten rock that moves very slowly.
3) The outer layer id the crust.
4) The crust is divided into slabs called tectonic plates. Plates are made of two types of crust:
- Continental - Thicker than the oceanic plate (30-50km) and less dense.
- Oceanic - Thinner (5-10km) and denser.
5) The plates are moving because of convection currents in the mantle underneath the crust.
6) The places where plates meet are called plate margins or plate boundaries.
Destructive Plate Margins
Destructive margins are where two plates are moving towards each other, e.g. along the west coast of South America.
Where an oceanic plate meets a continental plate, the denser oceanic plate is forced down into the mantle and destroyed. This creates a vent in the crust causing magma to come through, this often creates volcanoes and ocean trenches (very deep sections of the ocean floor where the ocean plate goes down).
Tension builds up when one plate gets stuck ad it's moving down past the other into the mantle.
Constructive Plate Margins.
Constructive margins are where two plates are moving away from each other, e.g. at the mid-Atlantic ridge, the convection currents also diverge. Magma rises from the mantle to fill the gap created by players moving apart and cools, creating new crust.
Tension builds up along cracks within the plates as they move away from each other.
Conservative Plate Margins.
Conservative margins are where two plates are moving sideways past each other, or are moving in the same direction but are different speeds, e.g. along the west coast of the USA. Friction occurs making the plates get stuck. The plates are made up of rock and have jagged edges and can catch on one another. When the pressure is released energy is sent out causing an earthquake.
Hotspots and Volcanoes.
Some volcanoes also form over parts of the mantle that are really hot, called hotspots, e.g. in Hawaii.
When a volcano erupts, it emits lava and gases. Some volcanoes emit lots of ash, which can cover land, block out the sun and form pyroclastic flows (superheated currents of gas, ash and rock).
Shockwaves, focus and epicentre.
The plates eventually jerk past each other, sending out shock waves (vibrations). Thes vibrations are the earthquakes.
The shock waves spread out from the focus - the point in the Earth where the earthquake starts. Near the focus, the waves are stronger and cause more damage.
The epicentre is the point on the Earth's surface straight above the focus.
The moment magnitude scale measures the amount of energy released by an earthquake.
The moment magnitude scale is logarithmic - so a magnitude 7 earthquake is ten times more powerful than a magnitude 6.
Magnitude 6 and below earthquakes normally only cause slight damage to buildings, although they can be worse in very built up areas.
Magnitude 7 and above can cause major damage and deaths.
Earthquakes - Primary Effects
Earthquakes have primary and secondary effects:
Primary effects of an earthquake are the immediate impacts of the ground shaking.
- Buildings and bridges collapse, and homes are destroyed.
- People are injured killed by collapsed buildings and falling debris.
- Roads, railways, ports and airports are damaged.
- Electricity cables, gas and water pipes and communications network are damaged, cutting off supplies.
Earthquakes - Secondary Effects
Secondary effects happen later on, often as a result of the primary effects.
- Earthquakes can trigger landslides and tsunamis - these destroy more buildings and cause more injuries and deaths.
- Leaking gas can be ignited, starting fires.
- People are left homeless and could die, e.g. from the cold.
- There's a shortage of clean water and a lack of proper sanitation - this makes it easier for diseases to spread.
- Due to blocked or destroyed roads, aid and emergy vehicles can't get through, and trade is difficult.
- Businesses are damaged or destroyed, causing unemployment and lost income, and tourists can be put off visiting the area.
- Repairs and reconstruction can be very expensive, so can weaken a country's economy.
Earthquakes - Immediate Responses.
Some effects of earthquakes have to be dealt with immediately to stop further loss of life, injuries or damage to property;
- Rescue people trapped by collapsed buildings, and treat injured people.
- Recover dead bodies to prevent the spread of disease.
- Put out fires.
- Set up temporary shelters for people whose homes have been damaged or destroyed.
- Provide temporary supplies of water, food, electricity, gas and communications systems if regular supplies have been damaged.
- Foreign governments or charities may send aid workers, supplies, equipment or financial donations to the area affected.
- Tech companies may set up disaster response tools, allowing damage to be recorded and people to confirm their safety, e.g. Google Crisis Response service.
Earthquakes - Long-Term Responses.
Others are dealt with in the longer term;
Long-term responses -
- Re-house people who lost their homes.
- Repair or rebuild damaged buildings, roads, railways and bridges.
- Reconnect broken electricity, water, gas and communications connections.
- If necessary, improve buildings regulations so that buildings are more resistant to damage from earthquakes.
- Set up initiatives to help economic recovery, e.g. by promoting tourism.
Volcanoes - Primary Effects.
People living near a volcano can be seriously affected if it erupts - and not all the effects happen straight away. If an eruption does occur, there are lots of ways that people respond to try and help those affected.
Primary effects -
- Buildings and roads are destroyed by lava flows and pyroclastic flows. Buildings may also collapse if enough ash falls on them.
- People and animals are injured or killed by pyroclastic flows, lava flows and falling rocks.
- Crops are damaged and water supplies are contaminated when ash falls on them.
- People, animals and plants are suffocated by volcanic gases.
Volcanoes - Secondary Effects.
Secondary effects -
- Mudflows (also called lahars) from when volcanic material mixes with water, e.g. from heavy rainfall or snowmelt. Mudflows and landslides cause more destruction, death and injury.
- Flooding can be caused by 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 or destroyed so aid and emergency vehicles can't get through, and trade is difficult.
- People are left homeless. Damaged or destroyed businesses cause unemployment and loss of income.
- Tourism can be disrupted straight after an eruption - but often it can increase afterwards with tourists interested in seeing volcanoes.
- Ash makes fields more fertile once it's broken down.
- Recovering after an eruption can take a very long time and cost a huge amount of money, weakening a country's economy.
Volcanoes - Immediate Responses.
Immediate responses -
- Evacuate people before the eruption, if it was predicted, or evacuate as soon as possible after the eruption starts.
- Provide food, drink and shelter for evacuated people.
- Treat people injured by the eruption, e.g. from falling debris or ash inhalation.
- Rescue anyone cut off by damage to roads or bridges.
- Provide temporary supplies of electricity, gas and communications systems if regular supplies have been damaged.
- Foreign governments or charities may send aid workers, supplies, equipment or financial donations to the areas affected.
- Tech companies may set up disaster response tools allowing damage to be recorded and people to confirm their safety, e.g. Google Crisis Respons service.
Volcano - Long-Term Respinses
Long-term responses -
- Repair and rebuild if possible, or resettle affected people elsewhere.
- Repair and reconnect infrastructure (roads, rail, power lines and communications networks etc.).
- Improve, repair and update monitoring and evacuation plans.
- Boost the economy if possible, e.g. by attracting tourists to see the volcano and its effects.