Natural Hazards

Revision

Plate tectonics

The core extends to about half of the radius of the Earth. It is made mostly from iron and nickel and is where the Earth’s magnetic field comes from. It is very dense. The temperature is high and the outer core is molten. Towards the centre high pressure makes the inner core solid. Intense heat is generated in the inner core by decay of radioactive elements like uranium. It s thinnest under the sea, and thickest on the continents.

The mantle extends outwards from the core to the crust: a distance of about 2,900 km. It is mostly a semi-molten liquid upon which the Earth’s crust floats. The heat coming from the core generates convection currents in the viscous mantle that cause the crust above to move.

The crust is the thin layer of rock at the surface upon which we live. •Eight elements make up over 98% of the Earth’s crust – although they are virtually entirely in the form of compounds.

The earth’s crust is made of about twelve plates. These are like big rafts floating on the semi-molten mantle. Convection currents within the mantle cause the plates to move. Although they only move about 2 cm per year, this can have huge effects over long periods of time. The map below shows the distribution of the world’s tectonic plates.

Laser beams can be used to detect plate movement.

Continental drift

Evidence for continental drift...

• There are similarities in the type and age of fossils found in Africa and South America

• They fit together like a jigsaw.• There are similarities in the rock

layers from Africa and South America.• There is evidence of related species

that definitely did not swim the Atlantic Ocean

• Rocks found in Britain were formed in desert conditions

Scientists think the continents were originally all together in a super-continent called Pangaea. Over millions of years they have drifted to their present positions on the floating tectonic plates

How do plates move?

1. The earths core is extremely hot due to radioactive processes

2. Heat from the core rises into the mantle

3. Convection currents in the mantle cause the semi-molten rock to move in a circular motion

4. Movements in the mantle drag the tectonic plates

Distribution of earthquakes and volcanoesVolcanoes and earthquakes occur at plate boundaries (where the tectonic plates meet). •Earthquakes occur at all plate boundaries irrespective of which direction the plates are moving in.•Volcanoes tend to occur where oceanic and continental plates are moving towards each other or where two oceanic plates are moving apart (where they form mid-ocean ridges).

Plate boundaries

•Oceanic plates move apart•Lava erupts•New crust is formed on the sea bed•Underwater volcanoes (e.g. mid-Atlantic ridge)•Gentle earthquakes

•Oceanic and continental plates move together•Heavier/denser oceanic crust is pushed down into the mantle•Ocean crust is melted and destroyed•Explosive volcanoes (e.g. St. Helens)•Violent earthquakes•Most hazardous boundaries

Subduction zone

•Tectonic plates move in different directions, or at different speeds.•Plates are locked together by friction•Pressure builds up until a plate breaks along a fault line•No volcanoes•Violent earthquakes

Collision margin •Continental plates move together•Plates are too ‘light’ to sink into the mantle•Plates buckle and fold to form mountains (e.g. Himalayas and the Alps)•Volcanic activity is rare•Violent earthquakes

EarthquakesEarthquake –the shaking and vibration of the Earth's crust due to movement of the Earth's platesMagnitude – The amount of energy that is given out during an earthquake.Focus – This is the point underground where the earth’s plates have moved.Epicentre – The point on the surface directly above the focus.Seismic waves – These are waves of force that travel through the earth. There are two main types of wave, P waves and S waves.• P waves are faster and can travel through solids and liquids•S waves are slower and can only travel through solids.Seismometer –An instrument used to measure the movement of the earth’s surface. A seismometer records the vibrations from earthquakes. Mechanical versions work by way of a large mass, freely suspended.Seismograph – A graph produced by data collected from the seismometer. This shows the shaking of the earth.Aftershocks – Aftershocks are smaller earthquakes formed as the crust around the displaced fault adjusts to the effects of the main shock. If an aftershock is bigger than 5.9 on the Richter scale then it is classed as an earthquake.

Some of these key features are labelled on the diagram below:

Factors that can affect the impact of earthquakes:

• Distance from the epicentre• Type of land- effects would be worse if city is built on a clay bed which

could amplify shock waves• Population density (rural or urban area). The more densely populated

an area, the more likely there are to be deaths and casualties.• Level of development (MEDC or LEDC) – MEDCs are more likely to have

the resources and technology for monitoring, prediction and response.• Communication - accessibility for rescue teams.• Time of day influences whether people are in their homes, at work or

travelling. A severe earthquake at rush hour in a densely populated urban area could have devastating effects.

• The time of year and climate will influence survival rates and the rate at which disease can spread.

How earthquakes are measured

The vibrations during an earthquake are measured/ predicted using a seismometer. This produces a seismograph

The Richter scale measures the strength or magnitude (amount of energy released) of an earthquake. The scale is shown below. It is a logarithmic scale and therefore each point on the scale is 10 times greater than the previous one. An earthquake measuring 6 on the Richter scale is therefore 10 times more powerful than an earthquake measuring 5 on the Richter scale.

Earthquakes can also be measured using the Mercalli Scale. The Mercalli Scale measures the amount of damage caused by the earthquake.

Richter magnitudes Description Earthquake effects Frequency of occurrenceLess than 2.0 Micro Microearthquakes, not felt. About 8,000 per day

2.0-2.9Minor

Generally not felt, but recorded. About 1,000 per day

3.0-3.9 Often felt, but rarely causes damage. 49,000 per year (est.)

4.0-4.9 LightNoticeable shaking of indoor items, rattling noises. Significant damage unlikely.

6,200 per year (est.)

5.0-5.9 Moderate

Can cause major damage to poorly constructed buildings over small regions. At most slight damage to well-designed buildings.

800 per year

6.0-6.9 Strong

Can be destructive in areas up to about 160 kilometres (100 mi) across in populated areas.

120 per year

7.0-7.9 Major Can cause serious damage over larger areas. 18 per year

8.0-8.9

Great

Can cause serious damage in areas several hundred miles across.

1 per year

9.0-9.9Devastating in areas several thousand miles across. 1 per 20 years

10.0+ Epic

Never recorded; see below for equivalent seismic energy yield. Extremely rare (Unknown)

Richter scale

Why would people live in earthquake-prone areas?

• They may have no/limited choice• At collision plate boundaries, hills and mountains are created, this attracts tourists, and is nice scenery.• Fertile soil - new soil is produced, richer in minerals and nutrients and plants grow better there

For example, Japan is very prone to earthquakes. However, people still want to live there as it is a wealthy country. And good jobs can be found there. Economic interests is one of the consideration for people when choosing places to live.

How to prepare the house for an earthquake:

• Secure heavy appliances to studs in the wall so that they are less likely to move

• Take all heavy objects of shelves, to prevent things from falling on your head

• Put latches on cupboards to prevent doors from swinging open

• Make sure all pictures, clocks, e.t.c hanging on the wall are securely screwed in, so there is no chance of them falling

• Have safety film put over your windows, glass can break easily in a severe earthquake

• Make sure all flammable liquids are placed on the lowest shelves of cupboards, or in a garage or garden shed.

What to do in an earthquake scenario:

• Move away from windows• Arrange a meeting point with

family• Protect your head• Turn off electricity• Check for fires• Hang onto door frame• Keep away from power cables• Keep away from trees• Stop driving• Get outside it possible• Turn off gas• Listen to the radio

Supplies you will need:

• Food• Water• Medical supplies• General supplies: batteries

portable radio e.t.c

Listening to the radio keeps people updated and informed about a coming earthquake, they would know if the needed to prepare or evacuate.

Comparing earthquakes in LEDCs and MEDCs

Kobe, Japan (MEDC) 1995 Haiti (LEDC) 2010

Magnitude 7.2 7.2

Deaths 6000 220000

Depth of focus 16km 12km

Time of day 5:46am 4:53pm

Reasons why there was more damage in Haiti:•Less money= less earthquake preparation materials purchased (earthquake proof buildings, radios, emergency kits)•Haiti was closer to the focus•Higher population density•Less emergency services with less equipment•Wasn’t expected•Daytime- people were out and about•Poor quality buildings •Disease was likely to spread more quickly

Effects of an earthquake

Primary• Direct death or injury• Damage to buildings and infrastructure

Secondary• Fires caused by ruptured gas mains• Death due to disease• Lack of food, water, shelter and medical facilities• Economic effects might include job losses and loss of

communication networks

LiquefactionLiquefaction happens because soft sediment often behaves like quicksand during an earthquake. This is because the shaking brings water to the surface. Buildings often topple over or sink into the ground as a result of this. The diagrams below show how liquefaction operates.

The Mexico City earthquake of 1985 was so bad because the city is built on old lake sediments and these had the effect of amplifying the shock waves.

Volcanoes

A volcano is an opening in the ground where magma forces its way to the surface. Magma which reaches the earth's surface is called lava. Volcanoes can be:•active (erupting), •dormant (sleeping) •or extinct (no eruption for 10,000 years and unlikely to erupt again).

You need to know about two different types of volcano - composite volcanoes and shield (basic) volcanoes.

The magma chamber is a collection of magma inside the Earth, below the volcano.The main vent is the main outlet for the magma to escape.Secondary vents are smaller outlets through which magma escapes. The crater is created after an eruption blows the top off the volcano. An eruption occurs when pressure in the magma chamber forces magma up the main vent, towards the crater at the top of the volcano. Some magma will also be forced out of the secondary vent at the side of the volcano.

Composite Volcanoes

Composite volcanoes happen where the lava is acidic. The sticky acidic lava pours slowly down the side of the cone and cools quickly to produce a steep sided volcano. Alternate layers are formed because each eruption first produces rock fragments which are later covered by lava. This kind of volcano is found at destructive plate margins.

Ash and lava

Crater

Vent

Layers of ash and lava

Secondary cone Steep sides

Example: St Helens, USA

Shield (basic) volcanoes Shield volcanoes are enormous features built up only from layers of lava. They produce lots of lava but they tend not to erupt violently. Shield volcanoes form when the lava is basic (the opposite to acidic). You get these types of volcanoes along constructive plate margins and also where there are hotspots. Basic lava is runny so it flows quite a long way before it cools and becomes rock, this is what forms the gentle sides.

crater

VentLayers of lava

Gentle sides

Runny lava flow

Example: Mauna Loa, Hawaii

Predicting eruptions

Preparing for an eruption

•Creating an exclusion zone around the volcano.•Being ready and able to evacuate residents.•Having an emergency supply of basic provisions, such as food.•Funds need to be available to deal with the emergency and a good communication system needs to be in place.

Living with volcanoes

Fertile soilsVolcanic rocks are rich in minerals and when weathered, form fertile soils. These are ideal for growing crops

Geothermal energySteam from water heated by hot rocks below the surface drives turbines to generate electricity

Mineral extractionMany valuable minerals form when volcanic activity occurs

TourismVolcanic landscapes can have beautiful scenery that attracts many visitors

Raw materialsThe raw materials for many products come from volcanoes. These include building materials used in industry

Example: Iceland

Effects of a volcanic eruption

•Volcanic gases - All magma contains dissolved gases that are release during and between eruptions. These gases are mainly steam, carbon dioxide and compounds of sulphur and chlorine.• Lava flows - These are streams of molten rock.• Pyroclastic flows - These are high speed avalanches of hot ash, rock fragments and gas which move down the sides of a volcano. These flows occur when the vent area or ash column collapses.• Tephra - The explosive power of an eruption causes old lava to be blasted into tiny pieces and hurled into the air. The fragments are tephra.

Primary effects

Secondary effects• Lahars - These are mixtures of water, rock, ash, sand and mud that originate

from the slopes of a volcano. Lahars often happen because of heavy rainfall eroding volcanic deposits or heat from a volcanic vent suddenly melting snow and ice.

• Landslides - Heat from cooling magma can cause hydrothermal alteration of the rocks, turning sections of them into clay. This weakens the rocks and increases the risk of slope failures.

• Flooding - Explosive eruptions can change the surface areas around a volcano and disrupt drainage patterns, leading to long-term flooding.

• Food / water supply interrupted.• Homelessness.• Businesses forced to close.• Cost of insurance claims.• Unemployment.• Long-term issues with the tourism industry.

Mount St Helens erupted on May 18th 1980. This followed a period of activity which began in March 1980 with an earthquake measuring 4.0 on the Richter scale. There was 3 months of activity as magma rose inside the mountain, creating a large bulge on the north side of the mountain. This was due to a blockage in the main vent which prevented the magma rising through the vent in the normal way. The technical name for the bulge is a cryptodome.

Mount St. Helens 1980MEDC

On May 18th, an earthquake measuring 5.1 on the Richter scale caused a landslide on the northern flank of the volcano. This exposed the cryptodome and resulted in a sudden release of pressure and a huge eruption in the form of a lateral (sideways) blast.

The plume of ash erupted for more than 9 hours. It spread north-eastwards, eventually reaching 30 kilometres into the sky. 540 million tonnes of ash were pushed into the atmosphere and noticeable ash fell on 11 American states. Just three days after the eruption, air pollution monitoring systems detected ash in east coast cities such as New York (over 4000 kilometres away). The ash circled the globe in 17 days. The blast zone covered over 700 square kilometres and left a lunar landscape. Trees were flattened and ash covered the area.

Mount St Helens is a mountain in the Cascades range in North West USA. The Cascades have formed because the area is a destructive plate margin. The Juan de Fuca plate (oceanic) is being subducted under the North American plate (continental).

Primary effects of the Mount St Helens eruptionAsh column of over 80,000 feet in height.Pyroclastic flows moving at up to 670 miles per hour flattened over 600 square kilometres of forest.Poisonous gases released. Secondary effects of the Mount St Helens eruption Glaciers melted on the volcano, mixing with ash and mud to form lahars.200 homes, 27 bridges, 15 miles of railway and 185 miles of roads were destroyed.7000 big game animals perished (deer, elk and bear). People across north-western America were told to stay indoors and wear gauze masks.The ash made roads slippery and reduced visibility. Many roads were closed, trains halted and aircraft grounded.Fish, in some hatcheries, perished as ash fell into lakes and streams, clogging their gills and raising the temperature of the water. Crops were destroyed, or subsequently produced low yields, because ash settled on leaves, impeding photosynthesis. Electricity supplies were interrupted and sewers were blocked, and the ash damaged car engines. The town of Yakima, as an example, some 150km away, was blanketed in 1.5cm of ashSkies were turned grey as far away as as Spokane, Washington State, 400km away.57 people lost their lives in the blast, including 84-year-old Harry Truman who had refused to evacuate his lodge near Spirit Lake.

Chances Peak, Montserrat, 1995-97 LEDC

Montserrat is a small island in the Caribbean. There is a volcanic area located in the south of the island on Soufriere Hills called Chances Peak. Before 1995 it had been dormant for over 300 years. In 1995 the volcano began to give off warning signs of an eruption (small earthquakes and eruptions of dust and ash). Once Chances Peak had woken up it then remained active for five years. The most intense eruptions occurred in 1997.

During this time, Montserrat was devastated by pyroclastic flows. The small population of the island (11,000 people) was evacuated in 1995 to the north of Montserrat as well as to neighbouring islands and the UK.

Despite the evacuations, 19 people were killed by the eruptions as a small group of people chose to stay behind to watch over their crops.Volcanic eruptions and lahars have destroyed large areas of Montserrat. The capital, Plymouth, has been covered in layers of ash and mud. Many homes and buildings have been destroyed, including the only hospital, the airport and many roads.

Earthquakes and volcanoes in LEDCs

• Communication systems may be underdeveloped, so the population may not be well educated about what to do in the event of a volcanic eruption or an earthquake.

• Construction standards tend to be poor in LEDCs. Homes and other buildings may suffer serious damage when a disaster occurs.

• Buildings collapsing can cause high death tolls.• Evacuation and other emergency plans can be difficult to put into action

due to limited funds and resources.• Clearing up can be difficult. There may not be enough money to rebuild

homes quickly and safely. Many people could be forced to live in emergency housing or refugee camps.

Tropical storms

Tropical storms are large areas of intense low pressure and extreme depressions.

On a satellite image, a tropical storm will show as a huge, swirling mass of cloud.

The eye (calm area, no wind) is at the centreThe track is the path taken by a tropical storm

FormationThese storms occur over water in areas where the sea surface temperature is at least 27 degrees.

Essentially, this means that they form between the Tropic of Cancer and the Tropic of Capricorn (hence the name 'tropical' storm).

They rarely occur within 5 degrees either side of the equator because the Coriolis force is too weak here.

Formation in detail...

Tropical storms use warm, moist air as fuel. That is why they form only over warm ocean waters near the equator. The warm, moist air over the ocean rises rapidly upward from near the surface and becomes saturated with evaporated moisture. This means that there is less air left at the surface (i.e. low pressure). Air from surrounding areas with higher air pressure pushes in to the low pressure area to try to equalise the pressure. Then that “new” air becomes warm and moist and rises, too. As the warm air continues to rise, the surrounding air swirls in to take its place. Trade winds cause the moist air to spin inwards. As the warmed, moist air rises and cools off, the water in the air forms towering cumulonimbus thunderclouds (because there is a huge amount of condensation). The whole system of clouds and wind spins and grows, fed by the ocean’s heat and water evaporating from the surface.

The strength of a tropical storm is measured using the:

Measuring tropical storms

Tropical storms usually weaken when they make landfall (i.e. hit the land) because they are no longer being fed by the energy from the warm ocean waters. In the northern hemisphere they track (i.e. move) westwards due to the Coriolis effect

Physical effects of a tropical storm

Primary•high winds, •torrential rain and •storm surges at landfall (more about this one later on). •There may also be localised tornadoes and waterspouts. SecondarySecondary effects of tropical storms are very wide-ranging. We tend to divide them into social, economic and environmental effects

Social effects• There are likely to be food and water shortages.• As a result of extensive flooding, people may catch water-borne

diseases. This may eventually lead to death.• Communities are displaced from their homes, and may be broken

up if the area is not restored. Many people are made homeless.• People suffer from stress due to loss of possessions and housing.• There may be looting of properties - domestic and commercial.• People may lose their jobs if they work in an industry that has

been badly affected.• If insurance premiums rise in the future, some people may not be

able to afford them and will consequently not be financially protected against future storms.

• People might be stranded due to flooding - this will cause trauma.

• Electricity lines might be blown down and, as a result, people could be without power supplies.

• Roads and other infrastructure such as railways may be destroyed. This can lead to communication problems.

Economic effects• There are the obvious costs of repairing any damage

caused.• There will be structural damage to buildings and they

may have to be pulled down and rebuilt. This is very costly. Other buildings may have broken windows, chimneys etc.

• Insurance claims will be made, and this may cause the cost of insurance premiums to rise in the future.

• Whilst businesses are closed, earnings (and profits) will be lost.

• Crops may be damaged and exports lost. These may be a key source of income for the local economy.

• Oil prices may increase (this was a significant effect in the aftermath of Hurricane Katrina).

Environmental effects

• A huge amount of water is released in a tropical storm so there will be extensive flooding.

• Flooding might led to sewer systems being flushed out and spreading disease.

• Sensitive ecosystems may be destroyed and plant and animal habitats lost.

• Sea fish are often killed because of silting, and freshwater fish may be killed in storm surges.

• Fishing boats and other craft may be damaged.• Crops and livestock may be damaged or destroyed.• Mudslides become common because the soil is saturated. They

will flow quickly down hillsides and may bury houses, crops and livestock (or even people).

Storm surgesStorm surges occur where the sea level along a shoreline rises as the result of a storm. This is shown in the diagram below.

There are two main causes of storm surges (described below and shown on the accompanying diagram): 1. The eye pile. The low pressure draws the water beneath it upwards to form the eye pile. It gets dragged along with the eye. The eye pile grows in height as it is forced into shallower water. It splats onto the land as the storm makes landfall. 2. Wind-blown water. Zonal winds push the water in the same direction that they are moving. If the winds blow long enough and hard enough, the water banks up and floods the land when the winds blow onshore.

PreparationMost countries affected by tropical storms now have education programmes to raise awareness on preparing for storms. There is an annual Hurricane Preparedness Week in the USA when schools, businesses and families are all encouraged to plan for possible strikes in the forthcoming hurricane season. Leaflets, posters and school lessons are common ways of spreading the message. New technologies - such as Twitter are also being used to educate people.

People living in areas affected by tropical storms are encouraged to have a hurricane emergency kit on standby and also to have thought in advance about how they will protect their home and belongings. This might include boarding up windows and doors. In MEDCS, people may also be able to afford windproof tiles, water-resistant windows and strengthened building structures

People in LEDCs may not be able to afford this kind of protection. However, simple but cheap measures can be put in place to ensure that people are well prepared for tropical storms. These include educating people (particularly women) about what to wear in case they have to swim, building homes on stilts, building cyclone shelters and training local people to organise others in an evacuation.

Forecasting hurricanes

Rich MEDCs, such as the USA, can invest in technology to predict the general area in which hurricanes will strike. This technology is not so readily available to LEDCs, although many countries receive information from organisations such as the Joint Typhoon Warning Centre (Pacific) or National Hurricane Centre (Atlantic) to help them prepare for storms. The track of a tropical storm is affected by a great many fators, so they are very unpredictable. Forecasters have a 20-25% chance of knowing exactly where a tropical storm will hit 48 in advance of landfall. Forecasts are made available to residents on the internet so that they can make decisions about whether they need to evacuate. This is obviously a much more useful means of communication in an MEDC where the percentage of residents with internet access is much higher than in LEDCs. Indeed, one of the major problems in preparing for a strike in an LEDC is communicating with the people in an area that is likely to be affected as the infrastructure may well be poorly developed.

When landfall has been forecast, action needs to be taken. This might include boarding up windows and doors, or evacuating the area. A mandatory evacuation is where the authorities command everyone in an area to leave. It is vital to ensure that only those peole who are in the danger area try to leave - otherwise the road system will get clogged up and people will be put at greater risk.

How to act in a hurricane situation

Hurricane Katrina, New Orleans, USA MEDC

Hurricane Katrina struck in August 2005. It tracked over the Gulf of Mexico and devastated most of the coastline from Louisiana to Alabama (see map below). It arrived as a category 4 storm with winds of over 140 mph and a storm surge of approximately 6 metres. The city of New Orleans was very badly affected because it is mostly below sea-level and is surrounded by water. The city was protected by defence walls called levees. However, the levees were overwhelmed by the extra water from the storm surge and rainfall, and many collapsed allowing water to flood into the city. About 80% of the city was flooded to depths of up to 6 metres.

The National Hurricane Centre predicted accurately where Hurricane Katrina would make landfall and how strong it would be....

This gave people the opportunity to prepare for the storm. The mayor of New Orleans ordered people to evacuate the city. About 80% of the city's residents did so, but about 20% remained. The majority of these were in the poorest areas of the city (people had little access to transport so couldn't leave in many cases).

Over 10,000 people sought refuge in the city's Super dome football stadium. Conditions here deteriorated quickly - food and water soon ran out and the toilet facilities were inadequate. The atmosphere in the stadium was described as 'very tense and unsafe'.

•More than 80% of the city was submerged with floodwater and over 1200 people drowned. •Approximately 1 million people were made homeless and thousands of businesses were destroyed. •Thousands of jobs were lost and millions of dollars lost in tax income. •There was a lot of looting. Criminal gangs roamed the streets, looting homes and businesses and committing other crimes.•Major highways were disrupted and some major road bridges were destroyed. •Agricultural production was badly damaged by the tornadoes and also by flooding. •Cotton and sugar-cane crops were flattened.•Hurricane Katrina didn't just impact people in the USA. Many offshore oil facilities were damaged and supplies of oil were reduced. This caused the price of oil to rise on the global markets and the price of petrol in the UK rose as a result.•Estimates suggest that Hurricane Katrina has cost over $300 billion. This makes it one of the costliest hurricanes ever to hit the USA.

Effects

Oooooh dear....

Cyclone Sidr, Bangladesh LEDC

Cyclone Sidr formed in the central Bay of Bengal and quickly strengthened to reach sustained winds of 160 mph, making it a category 5 storm. The storm eventually made landfall in Bangladesh on November 15, 2007. It weakened quickly after landfall. The Joint Typhoon Warning Centre predicted the scale and location of landfall and so people were forewarned. Government officials were recalled from their weekly leave. Ports were closed. There was mass-scale evacuation of the coastal area, much of which is land below sea-level. The image below shows the storm surge prediction for the area. 2 million people were evacuated to emergency shelters. Over 40,000 Red Crescent volunteers were deployed to order residents in the 15 affected provinces into special cyclone and flood shelters (see image below). Relief organisations distributed seven-day emergency disaster kits of food, blankets and clothing for evacuated families.

Coastal districts of Bangladesh faced heavy rainfall as an early impact of the cyclone. The damage in Bangladesh was extensive, including tin shacks flattened, houses and schools blown away and enormous tree damage. The entire cities of Patuakhali, Barguna and Jhalokati District were hit hard by the storm surge of over 5 metres. About a quarter of the world heritage site Sunderbans were damaged. Researchers said mangrove forest Sunderban will take at least 40 years to recover itself from this catastrophe. Much of the capital city of Dhaka was also severely affected, as electricity and water service were cut and significant damage was reported there due to winds and flooding. The local agricultural industry was also devastated, as many rice crops — which have a December harvest — were lost

Effects

Tropical storms in the futureScientists are not agreed about how and why the distribution of tropical storms might change. The exam specification says that you must be able to 'explain why the distribution and frequency of tropical storms may change' and that you should include the impact of climate change in your explanation. However, as good geographers you will need to keep an open mind as to whether or not climate change is really at the heart of any changes to the intensity and distribution of tropical storms.

Why are opinions divided? Satellite technology has only been used to monitor tropical storms since the late 1960s. Before this, accounts from ships' logs, aeroplane research flights, and simple weather recording instruments were used. Some scientists have argued that the number and strength of tropical storms in the past may have been greater than was actually recorded at the time. They also claim that there may have been some tropical storms occurring that we did not know about as they did not make landfall. The graph below shows the storm history of named tropical storms in the North Atlantic. It is divided into two periods - pre-satellites and post-satellites.

Why do people think that climate change will lead to more tropical storms? As you already know, tropical storms form where the temperature of the water exceeds 27 degrees. Global warming is causing a rise in the ocean temperatures, and this will mean that ocean temperatures will exceed 27 degrees for longer periods of time and increase the sea surface area that tropical storms would be able to form on.

As a result, the tropical storm season will last longer, this would widen the distribution and increase the frequency of hurricanes.

The 'natural cycle' viewpoint An alternative viewpoint is that there is a natural cycle of variations in the number of tropical storms and that this is not linked to global warming. A natural cycle is a series of events that happen over and over again. the AMO is a 20-20 year fluctuation between warmer and cooler than average ocean temperatures in the North Atlantic Ocean. We are currently in the warm phase of the AMO. Some scientists argue that this is why we are experiencing increased tropical storm activity. The graph below shows a clear cyclical pattern in AMO values.

Are tropical storms becoming more destructive? In terms of the damage they cause, tropical storms do seem to be getting more destructive. 6 out of the 10 costliest hurricanes in the USA have happened since 1990. Why might this be? Firstly, more people are living near the coast. As tropical storms' effects are concentrated in coastal areas, this means that more people are living in danger zones. There has been much more building in these areas in recent years - so when a hurricane strikes, there is more infrastructure in its way and for it to damage! The value of property at the coast has increased rapidly, so the costs of clear-up have increased too.

El Nino El Niño is a climate phenomenon affecting the Pacific, Atlantic and Indian Oceans, occurring approx every 3-7 years. Officially, it is a sustained sea surface temperature greater than 0.5°C more than normal across the central tropical Pacific Ocean. It is explained very clearly on the BBC Bitesize website - http://www.bbc.co.uk/learningzone/clips/ocean-currents-and-winds-el-ni-o-and-la-ni-a/1504.html

Normally, trade winds blow west and slightly north across the Pacific Ocean, causing surface water, warmed by the sun, to 'pile up' at the western end so that the sea surface is about half a metre higher here. The warm water means surface temperature is about 8 degrees higher. Sometimes the normal trade winds relax. This is the start of an El Niño. The warm pool of water in the Western Pacific is released. It 'floats' because it is less dense than the cold water around it, and flows across the surface of the ocean back east towards South America. In general, El Nino events are characterised by more tropical storms in the eastern Pacific and less in the Atlantic, Gulf of Mexico and Caribbean Sea.

There is some uncertainty as to what will happen to El Nino as the planet warms. 3-5 million years ago the carbon dioxide in the atmosphere was significantly higher than it is now. During this time the El Niño conditions we consider exceptional now were much more frequent, perhaps even normal. The Met Office has suggested than an increase in carbon dioxide in the atmosphere will increase the frequency and intensity of El Niño. This may well be a cause of an increase in global sea surface temperatures.

Wild fires

A wildfire is an unplanned, unwanted wild land fire, including unauthorized human-caused fires.

WildfiresThe main causes of wildfires are:

• Hot temperatures• Farming• Lightning• Arson• Campfires• Volcanic eruptions• Discarding lit cigarettes• Sparks from trains• Drought

Things that can worsen the effects of wildfires:

•Size of fuel•Energy content of fuel•Arrangement of fuel (how compact)•Wind velocity •Recent weather (dry weather = more dry fuel)

Preparation – For the house•Keep your roof, gutters, and yard free of flammable debris such as dried leaves, dead branches, and garbage. •Cover house vents with wire mesh.( Vents can allow embers and flaming debris to enter a home and ignite it )

•Choose safety glass for windows and sliding glass doors.Windows allow radiated heat to pass through and ignite combustible materials inside. Dual- or triple-pane thermal

glass, and fire resistant shutters or drapes, help reduce the wildfire risk. You can also install non-combustible awnings to shield windows and use shatter-resistant glazing.

•Prepare for water storage; develop an external water supply such as a small pond, well or pool•Mow the lawn regularly•Listen to the radio regularly•Creating a 30 foot zone of fire-resistant space around your home will help prevent fires from starting near or spreading to your home.

Primary Effects

•Loss of life and injury to people and animals who are caught in the flames.•Destruction of property and possessions (this is getting more severe as more and more people live in the urban-rural fringe)•Burning of vegetation and crops.•Huge amounts of smoke released.

Secondary Effects

•Health problems for people as a result of the smoke and ash.•Loss of jobs and incomes for agricultural workers whose animals/crops are destroyed.•Decline in the tourist industry, leading to loss of jobs.•Homelessness.•Insurance premiums rise.•Access to recreational areas is restricted.•Soil erosion and landslides because there is less vegetation to bind the soil together.•Loss of habitats for animals may lead to extinction.

Managing the effects

What is meant by wildfire intensity?Fire intensity is a measure of the rate of heat released by a fire. It includes both radiant and

convectional heat.

What is a wildland urban interface?The wildland urban interface can be found in every part of the country where people live in

areas with vegetation near houses and little clearance. In ever-greater numbers, people are moving to these types of areas, sometimes as vacation homes and cabins, but more often as primary residences.

What are the Santa Ana winds?The Santa Ana winds are strong, extremely dry offshore winds that characteristically sweep

through Southern California and northern Baja California in late fall and winter. They can range from hot to cold, depending on the prevailing temperatures in the source regions, the Great Basin and upper Mojave Desert. The winds are known for the hot dry weather (often the hottest of the year) that they bring in the fall, and are infamous for fanning regional wildfires.

What is a firebreak?Controlled burning/back burning. Starving fire of fuel by using a drip torch (fuel canister

which is alight, like a long lasting match). Fires sometimes jump over controls and start again.

Random questions...

What are three man made causes of wildfires?•Arson •Discarding lit cigarettes•Farming

What are three natural causes of wildfires?•Lightning•Drought•Hot temperatures

What does Smokey bear do?Smokey bear is aimed to increase public awareness of wildfires

Mount Carmel wild fireWhat caused the fire?2010 spring and summer months were exceptionally hot, followed by unusually warm autumn and dry conditions formed dry and combustible fuel (timber). This increased and worsened the effects of the wildfire, but was not the cause. The wind also increased the speed of the spread of the fire.It became clear that this fire did not start due to natural causes and police began to investigate, there were 3 possible causes:•On December 3rd Israel Police suggested that the fire was caused by a bonfire lit by local residents that got out of hand, after not being extinguished properly. •December 4th, police arrested two adolescent brothers from the Druze town of Isfiya on suspicion of having caused the fire through carelessness.•I am not 100% sure about this possible cause - ‘Druze Member of Knesset Ayoob Kara, a resident of Isfiya near where the fire broke out, had said on the evening of 2 December that he had received information that the fire was a terror act. MKs Ya'akov Katz and Michael Ben-Ari also cited the possibility that the fire was an act of terrorism and called for an investigation.’However, the investigation was solved, as on 6 th December, a 14 year-old resident of Isfiya admitted to starting the fire without intending to. After smoking a hookah, he had thrown a lit coal into an open area and was shocked and worried when a fire broke out, that he returned to school without telling anyone what he had done .

Burned area 12,000

Buildings destroyed 74

Fatalities 43

Injuries Dozens

•Turkey, Greece and America both sent aircrafts filled with chemical retardants to help fight the flames. •The Israel Fire and Rescue Services firefighters attempted to contain the blaze by back burning (controlled burning wood around the fire), and were had support from the Israel Police.• Israel Defense Forces (IDF) sent heavy ground equipment from nearby military bases, including fire trucks, water tanks, cranes and bulldozers. The IDF used an unmanned aerial vehicle to collect information from above (take photos e.t.c)

Wildfire frequency/intensity in the future

• Many experts have argued that global warming will increase the number of wildfires and the areas in which they occur.•Higher temperatures dry out vegetation so it is more likely to catch fire.•Heat waves are associated with a higher number of fires.•We seem to be getting periods of wetter weather followed by periods of drier weather - in wet periods, vegetation grows quickly and in dry periods fires spread very rapidly.•We might be getting more storms - hotter temperatures lead to more intense evaporation, producing more lightning and leading to more lightning strikes.•Wildfires give out lots of carbon dioxide, which itself intensifies the greenhouse effect and leads to global warming.