Geography-Natural hazards Flashcards

Terms Definitions
How do we classify hazards?
- By type-tectonic, atmospheric or geomorphological
- Scale
- Magnitude/strength
- Devastation/impact
- Frequency
- Location
When was the Kobe earthquake in Japan?
1995
How many people died in the Kobe earthquake?
5000
When was the earthquake in San Francisco in America?
1989
How many people died in the San Francisco earthquake?
57
What was another name for the San Francisco earthquake?
The Ioma Prieta earthquake
Why did more people die in the Kobe earthquake than in the San Francisco earthquake, despite both countries being developed?
- Kobe is more densely populated-multi-storey buildings collapsed easily in the earthquake
- The Kobe earthquake struck early in the morning when many were asleep, whereas the Ioma Prieta earthquake struck later in the afternoon
- The Superbowl match was held in the USA when the earthquake struck so many were at home watching, or staying at work late, instead of on the collapsed roads
- Many houses in San Francisco were made of wood which absorbs pressure well
- In Kobe, fires broke out, killing many, and they were hard to control
What factors affect the rate of flooding?
- Drainage- if there are a lot of tributaries, water will be collected efficiently and possibly cause flooding
- Heavy rainfall- unable to infiltrate ground so collects on surface
- Geology (rock type)- rocks like clay do not allow water through, whereas permeable rocks like limestone do
- Angle of slope- slopes cause water to flow off the surface, whereas flat land allows water to collect
- Previous weather- Previous rainfall could waterlog the ground and extreme heat or icy conditions can cause an impermeable surface
- Human interference- buildings/tarmac create an impermeable surface
What is a hydrograph?
A graph showing the discharge of a river, at a given point, over a period of time.
What is a storm hydrograph?
A graph that shows a rivers response to an individual rainfall event.
What is the DISCHARGE of a river?
The given amount of water in a river, at a given poin in time.
What is the discharge of a river measured in?
Cumecs (cubic metres per second)
What is the RISING LIMB of a hydrograph?
The period in which discharge increases.
What is the RECESSIONAL/FALLING LIMB?
The period in which discharge decreases.
What is the BASEFLOW?
Rainwater which has permeated the ground and seeped into the river.
What is the LAG TIME?
The time between peak rainfall and peak discharge.
What is the hydrograph like for a flashy drainage basin?
Steep
What is the drainage basin like for a flashy drainage basin?
Lots of tributaries.
What is the rock type like for a flashy drainage basin?
Impermeable, low infiltration, high surface run-off and high drainage density.
What is the soil like for a flashy drainage basin?
Thin soils, quickly saturated-decreased infiltration, greater surface run-off.
What is the relief like for a flashy drainage basin?
Steep slopes, faster surface run-off.
What is the vegetation like for a flashy drainage basin?
Moorland grass/heather-little interception, greater surface run-off.
What is the landuse like for a flashy drainage basin?
Urban, concrete and tarmac-impermeable, little storage, rapid run-off through drains.
What is the management like for a flashy drainage basin?
Land drainage pipes in arable areas increase throughflow.
What are the water demands for a flashy drainage basin?
Low demand.
What is the hydrograph like for a slow response drainage basin?
Gently sloping.
What is the drainage basin like for a slow response drainage basin?
Few tributaries.
What is the rock type for a slow response drainage basin?
Permeable, high infiltration, greater throughflow and groundwater flow.
What is the soil like for a slow response drainage basin?
Deeper soil-increased infiltration and less surface run-off.
What is the relief like for a slow response drainage basin?
Gentle slopes-increased infiltration, lower surface run-off.
What is the vegetation like for a slow response drainage basin?
Woodland/forest-high interception/evaporation, root systems absorb large amounts of water, increased water loss through transpiration.
What is the landuse like for a slow response drainage basin?
Rural areas-more interception/storage, reduced surface run-off.
What is the management like for a slow response drainage basin?
Dams built to store water and control discharge.
What are the water demands for a slow response drainage basin?
High demand-water extracted from boreholes and rivers.
What is a flood?
A flood occurs when a river overflows its banks-exceeds its bankfull discharge.
Where is Boscastle?
North Cornwall coast, previously a fishing village but now 90% of the economy is reliant on tourism.
When did the Boscastle flood take place?
16th August 2004
Why did the Boscastle flood occur?
- Two rivers meet-the Valency and the Jordan
- Close to the sea-heavy rainfall
- Lack of vegetation on the slopes
- Steep land and hills
- The bridge acted as a dam
- Boscastle's valley catchment area extends 9 square miles spanning inland onto Bodmin Moor, with steep-sided valleys and 'flashy' tributaries
- More 1400 millions litres of rain fell in just 2 hours on the afternoon of the 16th
What were the impacts of the Boscastle flood?
- Largest peacetime rescue in Britain
- 58 properties flooded and 4 demolished (including the Visitor Centre)
- Costs-£2 million
- 100 people airlifted to safety
- 84 cars wrecked and 32 washed away
- 4 footbridges on the Valency were washed away
How has Boscastle been managed since the flood?
- Landuse zoning-low value car parks in high risk area
- Flood warning system planned
- New culvert on the River Jordan, extending 80m into the Valency
- Reducing global warming/greenhouse gas emissions
- Environmental Agency-flood prevention
Why is Bangladesh prone to flooding?
- Heavy monsoon rain causes summer flooding
- Deforestation-fewer trees to absorb/transpire water
- Trees cleared for fuel and grazing-contributes to greenhouse effect (less oxygen released-so more carbon dioxide)
- Bangladesh is 80% floodplain and delta
- Two huge rivers meet-the Ganges and the Brahmaputra
- During the 1980s, 120,000 wells were sunk-2.5cm subsidence per year
- 70% of land is less than 1m above sea level
- Silt blocks rivers and creates islands making discharge difficult
- Increased surface run-off leads to soil erosion and more silt raising river beds-the beds of the Brahmaputra rise 5cm a year
- In India, the Ganges has been diverted into the Hooghy channel for irrigation
- The Farraka dam reduces flow in the dry season but increases the deposition of silt which decreases channel capacity-in the rainy season water is let through causing floods
- Melting of snow from Himilayas adds to volume of water in summer months
What are the effects of flooding in Bangladesh?
- Rice crops ruined
- Many people drowned
- Many made homeless
- Dirty drinking water-disease
- Many bridges over the River Ganges swept away
- Railways swept away
- People bitten by poisonous snakes
How are floods in Bangladesh managed?
- Water purification tablets sent
- Plans to build 5000 emergency shelters
- Aid-Britain sent boats and helicopters, and millions of pounds of aid was sent
- River divided into sections
- Riverbanks strengthened
- Land drained before the monsoon season
What is a cyclone?
Cyclones are large rotating storms formed over water.
What are the features of a cyclone?
- Also known as hurricanes, willy willies and typhoons
- Large rotating storms
- Low air pressure
- Strong winds (>72 mph)
- 5-6 miles high and 300-400 miles wide
- Moves at 50 mph
Why is Bangladesh vulnerable to cyclones?
- Bangladesh lies north of the Bay of Bengal, where cyclones are funnelled between India and Myanmar
- Bangladesh lies adjacent to tropical seas with temperatures above 27 degrees, providing heat and moisture to drive the cyclone
- 70% oi land is low-lying and easily flooded by storm surges, and there are few places to escape
- Densely populated
- Storm surges easily breach earth embankments
- Little money for protection against cyclones-flimsy housing
- No telephones/radios-no warning of cyclones
What are the impacts of cyclones in Bangladesh?
- Injuries, disease, death
- Fishing boats damaged
- Farms destroyed, loss of land-food shortages
- Loss of cattle
- Flooding
- Storm surges
- Trees knocked down
- Contaminated land
When did Cyclone Sidr hit Bangladesh? (It also hit parts of India)
November 15th 2007
What category cyclone was it?
Category 5 with winds reaching a maximum of 260 km/h
What were the impacts of the cyclone in Bangladesh?
- Nearly 3500 died (although some charities estimated between 5000 and 10,000 deaths)
- $450 million of damage
- Tidal waves up to 3 metres high
- Tin shacks flattened, houses and schools blown away and enormous tree damage
- Much of the capital city of Dhaka was severely affected, as electricity and water services were cut and significant damage was reported there due to winds and flooding
- The entire cities of Patuakhali, Barguna and Jhalokati District were hit hard by the storm surge of over 5 metres
- Local agricultural industry devastated, as many rice crops,which have a December harvest,were lost-in many areas 95% of the rice crop was lost
- Shrimp farms and crops washed away
- 500,000 homes destroyed-millions left homeless
- Disease, such as dysentery, due to the shortage of drinking water
How was Cyclone Sidr managed?
- $140 million pledged in emergency aid
- Government tried to provide shelter and help with rebuilding, as well as setting up a programme to re-stock the country's farms with seeds and fertiliser
- However, many remote communities along the south-western coast were difficult to reach except by boat
- Saudi Arabia pledged $100 million in aid
- 18 Bangladesh Air Force helicopters and 5 Bangladesh Navy ships were immediately dispatched with food, medicine, and relief supplies for the hardest-hit areas
- World Vision released volunteers to help house more than 20,000 people left homeless
What are the hazards associated with cyclones?
- Storm surges
- Extreme weather
- Tornadoes
- Diseases such as dysentery and cholera
- Flooding
- Homelessness
- Starvation
- Orphaned children
- Flying debris
How are cyclones managed?
- Cyclone shelters can accommodate 1000 people-70 new ones have been built, paid for by overseas aid at the cost of £80,000 each
- Cyclone shelters are huge structures on stilts, so will be above floodwaters, and are build to withstand strong winds
- Earth embankments-new one constructed at Dhaka
- Tree-planting programmes-mangrove trees have been planted along the shoreline as they are able to survice in shallow, salty water
- Mangroves absorb the power of the storm surge waves and stabilise shifting silt, protecting the embankments
- Trees on land have been planted around buildings and roads to protect them from the power of the winds
- Community activities in cyclone shelters to get people used to them, especially women (some religious groups have been reluctant to allow women to mix with men)
- Education is provided on cyclone risk
- Radio warnings-radios provided by charities
- Bike messengers
- Cyclone dam
What are the 3 main hazards of cyclones?
- Storm surges
- Strong winds
- Torrential rain
Why are storm surges a hazard?
- Cause 90% of deaths in cyclones
- Rapid rise in sea levels caused by cyclone winds 'pushing' sea water onto the coast-worsened if it coincides with high tide
- Can drown people and animals and destroy crops
Why are strong winds a hazard?
- Can exceed 250 km per hour, often reach 160 km per hour
- Can flatten whole neighbourhoods and uproot trees
- Cause flying debris
Why is torrential rain a hazard?
- Up to 250mm a day
- Usually follows strong winds
- Rivers overflow, causing flooding
- Floods leave contaminated water, causing disease
- Landslides
- Flash floods
- Sweep people/housing away
How should you prepare for a hurricane?
- Board up property and remove items from the outside
- Education
- Provision of aid
- Insurance
- Hurricane shelters
- Evacuation-10 hours needed
- National Hurricane Centre-Miami, Florida
- Engineering-hurricane resistant buildings-wind-resistant or raised
- Stop building in coastal areas at risk
- Predtion/warning system
- Monitorng satellites
- Hurricane hunters
Where do hurricanes and tropical storms occur?
- Over warm tropical seas with a temperature of over 27 degrees
- In the late summer/autumn when sea temperatures are highest
- Over vast areas of deep water
- In the Trade Winds belt, north and south of the equator
- Close to the Tropics of Cancer and Capricorn
- 5 degrees north and south of the equator
- Bay of Bengal-channelled between India and Myanmar, where the Indian Ocean is 27 degrees or more
- North America, especially Florida, as hurricanes build across the vast Atlantic ocean
- Australia, due to its situation in warm, tropical water
How do tropical storms form?
- Very moist, warm air rises rapidly from the surface of the sea
- On meeting colder air high in the atmosphere it condenses to form clouds
- If the sea is warm enough, the upward movement sucks in more warm air that evaporates more water and the storm builds
- Rising warm air rises fast causing towering clouds, heavy rainfall, and intense low pressure
- The low pressure sucks in air, causing very strong winds which spiral - clockwise in the northern hemisphere
- They spiral violently upwards driven by the rotation of the earth and are thrown outwards from the centre of the storm
- In the centre develops a calm 'eye where there are high temperatures and no cloud
- The strong Trade Winds drive the storm from East to West
- They lose their energy when they reach land or move into higher, cooler latitudes and the heat and moisture supply disappears
Can tropical storms be predicted?
- A specially adapted aeroplane is in use in the USA to fly through tropical storms as they form, collecting information to help predict the path
- Satellite images and advances in weather forecasting allow us to predict the speed and path of hurricanes better
- Still impossible to forecast them accurately
- Instead of trying to predict these storms, progress has been made in trying to prevent them-early warning systems, imrpoved coastal defences, better trained emergency services and reinforced buildings
What is drought?
Drought is a climactic hazard. In meteorological terms, it is a continuous or lengthy period without a significant amount of rain recorded.
What are the factors that affect the impact of drought?
- Temperature- affects evaporation and water demand
- Previous rainfall- affects the amount of water in the ground and surface stores
- Run-off rate- determines what water reaches stores or is quickly lost from the system
- Wealth- determines how well a country copes
- Population- affects demand for water
- Land use- affects how much water is needed e.g. urban or rural, farming or industry
What is desertification?
Desertification is the process by which a combination of human and climatic factors change fertile farming area to unproductive desert.
Where is the Sahel?
- The Sahel region of North Africa is a belt running from Mauritania in West Africa to Sudan in the East
- South of the Sahara desert
- Countries affected include Niger, Chad, Ethiopia and Burkina Faso
What is the total land area?
650,000 square km (twice the size of Britain
What are the human causes of desertification in the Sahel?
- Overgrazing- animal herds, which are too large, contrinually graze the same piece of land, destroying the plant roots so grass cannot regrow
- Deforestation- larger populations have higher fuel requirements so trees are felled and soil erosion increases as wind and rain erode exposed soil
- Population increase- high birth rates and an increased demand for food has led to overgrazing
What are the climatic reasons for desertification in the Sahel?
- Drought-periods of below average rainfall-between 1970 and 2000, the annual rainfall was only above the long term average ONCE
- High temperatures- higher rate of evapotranspiration and moisture loss from the soil
- Infrequent but intense rainfall- heavy showers cause soil erosion and rain is spread unevenly-Timbuktu in Mali receives 70% of it's annual rainfall in 2 months
Where is the village of Dali?
Central Niger on the edge of the Sahara desert.
What are the causes of desertification in the Sahel?
- Wind can easily erode the soil as trees have been removed to supply firewood for the increasing number of villagers
- Low yileds are caused by destruction of woodlands that used to shelter crops and stop soil erosion
- Population growth has caused overgrazing, over-cultivation and deforestation
- Populations of nearby Ethiopia and Sudan have increased by 300% (decreased death rates whilst birth rates have stayed high)
What are the impacts of desertification in Dali?
- 40 years ago, Malam Garba and his brother harvested 700 baskets of millet from their fields (a surplus)
- The village was surrounded by trees, where antelope, monkeys and squirrels were hunted
- There was enough dead wood without cutting down more for firewood
- Today, Malam Garba farms an area 3 times greater but harvests only 1/7th of the millet he used to
- An area the size of Luxembourg is lost to desertification each year in Niger
Where is Burkina Faso situated?
- Burkina Faso landlocked nation in West Africa
- It is surrounded by six countries: Mali, Niger, Benin, Togo, Ghana and Côte d'Ivoire
What is the population of Burkina Faso?
10 million
What is the GDP per capita in Burkina Faso?
$1300 (£2 per day)
What is the area of Burkina Faso?
275,000 square km
What are the problems in Burkina Faso?
- Poor and losing money
- Only 15% of land can be farmed
- Only 0.19% of crops are permanent
- It is part of the Sahel which suffered through the West Sahel drought
How is desertification being dealt with in Burkina Faso?
- Stone walls/afforestation
- Stones are removed from teh land and used to build low walls follwing natural contours
- A ditch is dug alongside the wall and tree saplings are planted in it
- Soil being eroded by the wind collects against the walls and any rainfall runs into the ditch
- Trees grow, further protecting the land
What are the natural causes of bush and forest fires?
- Drought- fires peak in drought/dry conditions
- Drainage- even wetlands become susceptible after drainage
- Climate change- the El Nino phenomenon can cause drought-an upsurge of warm water in the Pacific ocean causes a change in weather patterns and delays the rainy season (Human causes such as global warming also contribute to this)
- Intense heat- temperatures of over 40 degrees can cause plant litter to ignite
- Lightning- 100 strikes to the Earth per second-major natural cause
What are the human cause of bush and forest fires?
- Arson/careless disposal of cigarettes
- Timber speculation- deliberate forest fires to overcome laws about clearing timber for sale or to create a source of cheap, damaged timber
- Selective logging- can create artificially dry forests by opening up the canopy (especially in tropical rainforests)
- Artificial fire suppression- stopping minor fires allows the build-up of flammable material
- Land clearing- quest for increased pasture (e.g. for ranching) and traditional 'slash and burn' technique (e.g. in Indonesia, during dry/windy conditions)
When did forest fires break out in Australia?
January 1994
Why did fires break out in Australia?
- Very dry, early summer between October and January-plant litter was very dry
- Intense daytime heat (over 40 degrees) caused plant litter to ignite
- Lightning
- Accidental littering of cigarettes
- Arson
What were the impacts of the forest fires in Australia?
- 4 people killed
- 200 homes destroyed
- Fires affected south-east Australia around Sydney and threatened the city
- Worst affected area was the Royal National Park-98% of land was burned
- Vegetation destroyed, air polluted, water supplies reduced, communications disrupted and electricity supplies cut
- In Western Sydney, visibility was just 3.5 km
- Hundreds evacuated from the north of the city
When were there forest fires in Indonesia?
1997
What caused the forest fires in Indonesia?
- Most fires were started deliberately for commercial interests-and worsened by heavy logging
- 'Slash and burn' agriculture
- Conditions unnusually dry due to the El Nino phenomenon
What were the impacts of the forest fires in Indonesia?
- Thailand nearly sued for lost income
- Orangutans died
- 2 million hectares of forest/land destroyed-led to food shortages
- Homelessness
- Economy wrecked
- Mass evacuation
- 70 million were affected by smog and it made 50,000 ill
- Air pollution index exceeded 800 (a day's exposure to an API of 200-300 is equivalent to smoking 20 cigarettes)
- Haze blocked out the sun affecting the ripening of fruits and causing an airplane to crash, killing 234 people
- Death/injury
- More than $3 billion in losses for 1997 alone
- Total losses for 1997-8 could be $5-6 billion including loss of timber, biodiversity and plantations, as well as health effects
- Coffee production declined 40% and palm oil harvests declined 30%
What is the global distribution of forest fires?
- On either side of the equator where temperatures get very high
- Forest fires generally occur in hot and forested parts of the world, for example, Australia, Indonesia and Africa (Rwanda, Tanzania, the Congo and Senegal)
- The forested areas of the United States and Canada are also susceptible to wildfires-the climates are sufficiently moist to allow the growth of trees, but feature extended dry, hot periods
- Fires are particularly prevalent in the summer and fall, and during droughts when fallen branches, leaves, and other material can dry out and become highly flammable
- Wildfires are also common in grasslands and scrublands, for example, Savannah areas in Brazil, where forest fires were caused by land clearance
What is the structure of the Earth?
The earth consists of four concentric layers: inner core, outer core, mantle and crust.
What is the inner core like?
The inner core is in the centre of the earth and is the hottest part of the earth. The inner core is solid. It is made up of iron and nickel with temperatures of up to 5500°C.
What is the outer core like?
The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel. It is still extremely hot here, with temperatures similar to the inner core.
What is the mantle like?
The mantle is the widest section of the earth. It has a diameter of approximately 2900km. The mantle is made up of semi-molten rock called magma. In the upper parts of the mantle the rock is hard, but lower down, nearer the inner core, the rock is soft and beginning to melt.
What is the crust like?
The crust is the outer layer of the earth. It is a thin layer between 0-60km thick. The crust is the solid rock layer upon which we live.
There are two different types of crust: continental crust, which carries land, and oceanic crust, which carries water.
What is the asthenosphere?
The soft zone in the upper mantle, on which the plate of the lithosphere move.
What is the lithosphere?
The crust and upper-most mantle.
Why do plates move?
- Tectonic plates are constantly moving
- The plates 'float' on the mantle, generally moving just a few cm a year
- This movement is caused by convection currents generated by the hot temperatures within the Earth
- The source of heat for convection currents is radioactive decay deep within the Earth
How do convection currents work?
- Convection currents are formed when a liquid (in this case magma) is heated ang begins to rise
- As it gets nearer the Earth's surface it cools and sinks back down to the bottom of the mantle, where it is heated again-creating a convection current
- The plates that rest on top of the mantle move a few cm a year due to the movement of magma in the mantle, caused by convection currents
What is continental drift?
The movement of plates which over millions of years has caused continents to split apart and collide, so changing the relative position of the continents and oceans.
What are plate margins?
Plate margins are the places where tectonic plates meet-these are areas of great crustal stress and activity due to the movement of the plates.
What are the 3 types of plate boundary?
1. Destructive margins
- Subduction zones
- Collision zones
2. Constructive margins (divergent plate margins)
3. Conservative margins
(transform boundary)
What is the oceanic crust like?
- Mainly basalt
- Between 5 and 10 km thick
- Very dense
- Frequently being destroyed and replaced so younger
What is the continental crust like?
- Mainly granite
- Between 25 and 90 km thick
- Less dense than oceanic crust and does not sink
- Older
What is a subduction zone?
- Destructive margin
- Occurs when an oceanic plate moves towards a continental plate
- As the two plates are pushed together, the heavier and denser oceanic plate sinks below the lighter continental plate to form a subduction zone, and the associated ocean trench
What hazards are associated with subduction zones?
- Earthquakes due to the increase in friction and pressure between the two plates
- Volcanoes because the oceanic plate melts as it sinks and the liquid magma formed rises to form a volcano
What landforms are associated with subduction zones?
- The rising of liquid magma alongside the collision of the plates can push up fold mountains such as the Andes
- Sometimes the magma rises offshore from a continent and islands will form following the line of the ocean trench-these are called ocean arcs due to the shape of them-Japan is one example
Name an example of a subduction zone.
- In the West of South America, the oceanic Nazca plate meets the South American continental plate
- The heat from the mantle and friction from contact between the plates has caused the oceanic Nazca plate to melt giving rise to a volcano
- The Andes fold mountains and the Peru-Chile ocean trench have formed as a result
What is a collision zone?
- A destructive margin
- These occur where two continental crusts collide
- Both plates 'buckle', as they are the same density, and are forced up into mountains
What is a hazard related to collision zones?
- Earthquakes e.g. Latur in India in 1993
What is a landform associated with collision zones?
Mountains
Name an example of a collision zone.
- The plate carrying India, the Indo-Australian plate, has collided with the larger Eurasian plate
- Once there was an ancient sea called Tethys between the two land masses
- As the plates moved together the sea disappeared and the sea bed was pushed up and buckled to form the world's highest mountain range-the Himilayas
What is a divergent plate margin?
- A constructive margin
- Occurs when two plates move away from each other
- Most commonly occurs in the middle of oceans
- Magma rises, filling the gap in the oceanic crust, known as a mid-oceanic ridge
What hazards are associated with divergent plate margins?
- Volcanoes
What landforms are associated with divergent plate boundaries?
- Mid-oceanic ridge
- When magma builds up above the surface of the ocean, volcanic islands form e.g Iceland and Surtsey
Name an example of a divergent plate margin.
- The Mid-Atlantic Ridge
- The North Amrican plate is moving apart from the Eurasian plate, so the Atlantic Ocean is slowly widening
What is a transform boundary?
- A conservative margin
- Occur where plates move alongside each other
- Crust is neither created nor destroyed and no new landforms appear
What hazard is associated with transform boundaries?
- Earthquakes due to the release of strain as the plates rub past each other
Name an example of a transform boundary.
- The San Andreas Fault in California
- It marks the junction of the North American and Pacific plates
- Both plates are moving northwards but at different speeds
- Instead of slipping smoothly past each other, they tend to 'stick'
- The pressure builds up until suddenly the plates jerk forwards sending shock waves to the surface and triggering a sudden earthquake
What is the world distribution of earthquakes?
- Occur in narrow belts
- Follow all types of plate margin
- Are near volcanoes
- Are particularly concentrated around the Pacific Ocean
- West coast of North and South America stretching out into the Pacific
- Centre of the Atlantic Ocean
- Along the south of the Eurasian plate, running through southern Europe and Asia
- East coast of Africa
What is the world distribution of volcanoes?
- Occur in long, narrow belts
- Are found most often at destructive plate margins, especially around the Pacific Ocean-The Pacific Ring of Fire
- Coincide with constructive margins e.g. Iceland and Surtsey
- West coast of North and South America
- Centre of the Atlantic Ocean
- South coast of Europe and Western Africa
Where is the Nyiragongo earthquake situated?
In the Viunga mountains, in the Congo.
When did Nyiragongo erupt?
17th January 2002
What type of volcano is Nyiragongo?
Stratovolcano-steep-sided cones formed from layers of ash and lava flows which erupt explosively.
How tall is Nyiragongo?
3500m
What is the main crater of Nyiragongo like?
It is 250m deep, 2km and sometimes contains a lava lake. Due to rainfall, many of Nyiragongo's craters sometimes have lakes in them-they glow different colours because of the minerals in the volcano.
What caused the eruption of Mount Nyiragongo?
- Volcanism at Nyiragongo is caused by the rifting of the Earth's crust where two parts of the African plate are breaking apart
- A hot spot is probably also partly responsible for the great activity at Nyiragongo
- Nyiragongo is associated with the East African Rift and is part of the Virunga Volcanic Chain
- An 13km fissure opened in the southern flank-it spread in a few hours from 2800 to 1550m elevation
- There were small tremors and earthquakes which worsened the tears in the crust
- Before the eruption, temepratures around the volcano increased
What happened during the eruption at Nyiragongo?
- Before the volcano started there was increased seismic activity and small earthquakes, which made the tears in the crust bigger
- Lava streamed from three spatter cones at the end of the fissure and flowed in a stream 200 to 1000m wide and up to 2m deep through Goma, a city on the Congo's eastern border with Rwanda
- Immediately after the eruption stopped, a large number of earthquakes were felt around Goma and Gisenyi, causing buildings to collapse
- The lava was very liquid, making it fast-flowing-up to 60mph
What were the impacts of the eruption at Nyiragongo?
- 45 people died in the eruption from asphyxiation by carbon dioxide and buildings collapsing due to the lava and earthquakes
- Overall about 100 people died
- 15% of Goma was destroyed, elaving 120,000 homeless
- 16,000 homes were destroyed
- 400,000 people had to be evacuated
- More than 40 schools disappeared
- Much of the food that was growing was destroyed
- People used tree branches to erect temporary shelters
- Lava streams covered 1/5 of the town
- The smoke and ash emitted from the volcano hung over Goma for weeks after the eruption
How is Nyiragongo managed?
- Japan and America were worried when people started living on Nyiragongo so set up monitors and gave financial aid
- $35 million was received for shelter, sanitation and medical aid
- Some money was used to fund more research into monitoring the volcano
- In the eruption, lava reached Lake Kivu-this raised fears that the lava might cause gas-saturated waters deep in the lake to suddenly rise to the surface, releasing lethally large amounts of carbon dioxide and methane
- This did not happen, but volcanologists continue to monitor the area closely
Can volcanoes be predicted?
- Earthquakes- before an eruption there is often an increase in the number and strength of tremors as the magma rises through the Earth's crust-the foci of these tremors rises towards the surface as well
- Ground changes- the movement of magma underground often deforms the volcano and bulging is common, as is the opening up of cracks
- Lasers are used to measure changes, while fixed tiltameters measure any change in the tilt of the slope
- Radar images from satellites can also penetrate vegetation and measure surface changes accurately
- Ground temperatures- Can be measured by satellite and often increase as magma rises and lava appears-snow and ice sometimes melt
- Environmental changes- Can trigger changing gas emissions, with the amount of sulphur, chlorine and water vapour varying in the weeks prior to an eruption, and animals often behave strangely
- Past volcanic history- geological studies of previous volcanic deposits and historical records can provide clues
When did Mount St Helens erupt?
May 18th 1980
Where is Mount Etna located?
In the sparsely populated Cascade Mountains in north-west USA. It had been inactive for 123 years, but in 1980 the most powerful volcanic eruption in 60 years worldwide occurred.
What caused the eruption?
- It was caused by the rising of magma where the oceanic plate, the Juan de Fuca, decends underneath the continental North American plate
- The resulting friction caused heat which melted the destroyed oceanic crust into magma
- Over time the build up became so great that it forced its way to the Earth's surface
What signs were there that an eruption was going to take place?
- On the 20th of March there was an earthquake of 4.0 on the Richter scale
- On the 25th of March there were 47 earthquakes in just 12 hours
- Over the next month or so, a small explosion formed a new crater 70m across, steam was ejected, there were ground shakes (possible caused by the movement of magma and gas)
- On the 12th of April, a 100m high, 2km in diameter bulge appeared on the side of the volcano-the bulge grew 1.5m a day
- Snow and ice melted on the mountain
- Local animals behaved strangely
What finally triggered the eruption?
- An earthquake at 8.30 am on the morning of the 18th of May
- It was 5.1 on the Richter scale, and occurred about a mile beneath the volcano
- This caused the bulge to slide forward
- A landslide of rock, ice and soil moved north at 250km/h, suddenly releasing pressure over the magma
- A vast explosion resulted, sending a cloud of gas and volcanic ash (called a nuée ardente) into the air, devastating the area north of the volcano
What was the effect of the eruption on the landscape?
- 2.7 km cubed of rock was displaced from the volcano
- All vegetation 21km north of the volcano was levelled
- Volcanic deposits (up to 150m deep) were left from the landslide and (up to 5m deep) from the lava flows
What effects did the eruption have on farming?
- The volcanic deposits eventually increased soil fertility
- In the short term, though, flooding led to losses of crops and livestock in the valleys
- The ash ruined an estimated 12% of crops, especially fruit and alfalfa
What effects did the eruption have on forestry?
- With such a large area of forest to the north flattened, together with logging camps, the livelihood of loggers was devastated
- Some 10 million trees were replanted
What effects did the eruption have on fishing?
- Lava flows and ash clogged channels and raised water temperatures
- Fish died and 250km of prime salmoon and trout rivers were lost
What effects did the eruption have on tourism?
- Media interest both during and after the eruption attracted tourists to the area
- Roads around the volcano had to be closed before the eruption, as tourists were attracted by the hazard
- In 1993, a tourist centre was openeda at Mount St Helens attracting more than 1 million visitors per year
What effects did the eruption have on people?
- Because of the warnings and monitoring of the volcano, most people were evacuated to a safe distance
- However, 63 still died, most from the poisonous gases that accompanied the eruption
- Fortunately, it was an area of low-density population, with only a few logging camps and tourist lodges
How was Mount St Helens managed?
- As the volcanic activity had been building for 2 months, it meant that scientists were on hand to monitor events
- However, they were still amazed at the scale of the eruption
- Precautions were taken to ensure a high level of safety
- Towns near to Mount St Helens were evacuated and barriers were built around the volcano to create an exclusion zone that no one was permitted to enter
What was the effect of volcanic gas released in the eruption?
- By 2 days after the eruption, volcanic gas cloud covered the continent
- By early June, ash ahd blown around the whole world
What was another effect of the eruption?
Hundered of small forest fires were started by hot ash.
What is the structure of a volcano?
A volcano consists of a vent, a pipe, a crater and a cone:

1. Vent- a small opening at the Earth's surface
2. Pipe- a passageway in the volcano in which magma rises through to the surface during an eruption
3. Crater- a bowl-shaped depression at the top of a volcano where material like lava, ash and other pyroclastic materials are released
4. Cone- formed from solidified lava, ashes and cinder-layers of lava and ash build up to create a steep-sided cone
What are the types of volcano?
There are 5 main types:

1. Composite or strato- steep-sided cones formed from layers of ash and lava-they are explosive
2. Shield- gently sloping cone formed from layers of lava-typically non-explosive, but produce fast-flowing lava that can travel many miles
3. Cinder cones- cones formed from cinders, whcih are small jagged pieces of rock-they can be explosive and the small cinders are acttered everywhere in the eruption
4. Spatter cones- formed of molten lava ejected from a vent-as spatter is not fully solid when it lands, the individual deposits are very irregular in shape and weld together as they cool
5. Composite volcanoes- formed by alternating layers of lava and rock fragments-often explosive
What hazards are associated with volcanoes and why are some volcanoes more dangerous than others?
1. Lava viscosity- if the lava is thin (less viscous) it will travel more quickly, allowing less time to escape
2. Pyroclastic flows- super-heated clouds of hot ash and rock which can travel faster than 100km/h
3. Gas- can cause explosive eruptions if it expands quickly-can lead to acid rain, contamination of water supplies and poisoning of people in the area
4. Lahars- a mixture of water (often from melting snow) and ash/rock, which run down the slopes of the volcano, and can reach high speeds
5. Landslides- volcanoes can trigger large masses of rock to slide down their slopes-these can change into a lahar if water is added
How can the impacts of a volcano be reduced?
- Monitoring allows simple precautions to be taken
- Warnings can be broadcast on TV/radio
- Evacuation drills can be carried out for those living in the danger zone
- Lava flows can be slowed or diverted by hosing them with water or using bull-dozers to pile up cooled lava into barriers
What is an earthquake?
The sidden shaking or trembling of the Earth's crust, caused by a sudden release of tectonic strain-as plates try to move, pressure builds up under the rocks, and eventually ruptures causing an earthquake.
What are the features of an earthquake?
- Usually occur on plate boundaries of along fault lines, although they can be triggered by human activities such as mining
- Shakin/trembling of the ground
- Shock waves caused by sudden movement
- The vibrations which occur during an earthquake, are usually sent out as seismic waves, and can be detected by a seismograph
- The source of an earthquake is called the focus-earthquakes with a focus close to the surface are most damaging
- The epicentre, is the point on the Earth's surface, directly above the focus-the epicentre of an earthquake is affected first and suffers the most damage
- Earthquakes sometimes cause tsunamis
What is the Richter scale?
- It measures the size of earthquakes
- The Richter magnitude test scale designates a single number to represent the size of an earthquake
- It measures from 1-10 positively and negatively and is assigned by calulating the horizontal amplitude from zero on a seismometer
What is the Mercalli scale?
- It measures the intensity of an earthquake on the surface of the Earth, people, natural objects and any manmade strutures like buildings
- It is measured on a scale of 1-12, with 1 being a very weak earthquake and 12 being one that causes total devastation
When was the Asian tsunami?
December 26th 2004
What countries were affected by the Asian tsunami?
India, Sri Lanka, Indonesia, Malaysia, the Maldives, Bangladesh, Myanmar, Thailand, Madagascar, Somalia, Kenya, Yemen, South Africa, the Seychelles, Tanzania, Andaman and Nicobar.
What caused the Asian tsunami?
- Tsunamis are generated when the sea floor abruptly deforms and vertically displaces the overlying water
- Such large vertical movements of water occur at plate boundaries
- Subduction earthquakes are particularly effective in generating tsunamis
- The 2004 tsunami was triggered when the biggest earthquake in 40 years, measuring 9.0 on the Richter scale, hit between the Australian and Eurasian plates in the Indian Ocean
- The earthquake caused the sea floor to rupture and send a huge wave, 4500km wide, across the ocean over 7 hours
What were the warning signs of the tsunami?
The only sign to people that the tsunami was coming was that the waterline suddenly retreated exposing hundreds of metres of seabed
What were the impacts of the tsunami on people?
- Death toll-220,000
- Most deaths in the provinces of Aceh and Sumatra in Indonesia
- 500,000 were made homeless
- Many thousands missing
What were the economic impacts of the tsunami?
- Affected shipping in the Malacca Straits by changing the depth of the seabed and by disturbing navigational buoys and old shipwrecks
- New navigational charts won't be ready for months or years
What were the environmental impacts of the tsunami?
- Severe damage was inflicted on many ecosystems-mangroves, coral reefs, forests, coastal wetlands, sand dunes and on vegetation, rock formations, plant/animal biodiversity and groundwater
- The spread of solid and liquid waste and industrial chemicals, water pollution and the destruction of sewage collectors and treatment plants threaten the environment even more
How can tsunamis be managed and predicted?
- A Tsunami Warning System is a system to detect tsunamis and issue warnings to prevent loss of life and property
- It requires a network of sensors to detect tsunamis and a communications infrastructure to issue timely alarms to permit evacuation of coastal areas
- These systems depend on the fact that while tsunamis travel between 500 and 1000km/h in open water, earthquakes can be detected almost immediately as they travel with a speed of 4km/s
- This gives time for a possible tsunami forecast to be made, and warnings to be issued to threatened areas, if warranted
- Unfortunately, there is not yet a reliable model to correlate earthquakes to tsunamis so alarms raised measuring only seismic waves are only warnings
- To be sure, tsunami waves should be observed in open water, as far out as possible by the coast, using real-time operating seafloor observatories
When did the Kobe earthquake erupt?
17th January 1995
What time did the earthquake strike Kobe?
5.45 am
Where did the earthquake strike?
- South Japan (Pacific Ocean)
- 14km beneath the northern part of Awaki Island in Osaka Bay
- Epicentre close to Kobe, Kyoto and Osaka
What did the Kobe earthquake register on the Richter scale?
7.2
How long did the earthquake last?
20 seconds
How far did the ground move in the earthquake?
- 18cm horizontally
- 12 cm vertically
What caused the Kobe earthquake?
- Kobe lies on the Nojima fault
- Destructive plate margin
- The heavier oceanic Phillippine plate is forced under the lighter continental Eurasian plate
- The sudden movement of the plates caused an earthquake
What were the short term effects of the Kobe earthquake?
- Nearly 6500 dead
- 35,000 injured
- Over 300,000 people evacuated
- Nearly 175,000 houses collapsed
- 3 hospitals ruined
- 35 schools destroyed
- More than 275,000 communication lines down
- More than 300,000 homeless
- Water, gas, and electricity interrupted
- Transport network wrecked
- Nearly 200 berths at Kobe and Ashiya damaged
- More than 600 aftershocks felt worldwide by 8pm that evening
What were the long term effects of the Kobe earthquake?
- 10 billion yen in damage (£43 million)
- Population fell by 33,000
- More than 5500 buildings destroyed by fire needed rebuilding
- Businesses closed
- Bridge connecting Port Island to the mainland came down
- Jobs created to rebuild the city
How is the earthquake risk in Kobe being managed?
- Injecting liquid into faults
- Rolling weights on roofs
- Shutters on windows
- Reinforced foundations
- Rubber shock absorbers
- Motion instruments installed
- Rescue drills practised
- Education-signs, leaflets, lessons in school
- Earthquake Memorial Park
- Open areas for pedestrian evacuation
- Residential Earthquake Insurance Scheme
- Funding levels increased
- Research programmes into seismology, earthquake engineering and disaster management
- Research project to map active faults
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