World at Risk: Global Hazard Patterns

  • Created by: Sophie
  • Created on: 30-03-15 14:54

Climate Change Response Indicators

  • Date of arrival and departure of various migrant birds compared to average dates
  • Date of budding of trees or development of catkins
  • Appearance of various species from hibernation
  • Breeding period of various resident birds
  • Changing levels in rivers, lakes and water supply
  • Change in agricultural practice, e.g. the dates of harvests
  • Changes in gardening practice, e.g. the mowing periods for household lawns
  • The length of the Scottish ski season and closure of ski lifts
  • Number and date of summer wildfires
  • Date of first appearance of various species, both plants and animals, eg frogspawn in ponds, and snowdrops
  • Number and age of vineyards in the UK
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Plate Tectonics

1. Crust a) Oceanic Crust, a layer consisting mainly of basalt, averaging 6-10 km in thickness. At deepest has a temp. of 1200 C. Young, less than 200mn. Denser. 
b) Continental Crust, mostly granite, up to 70km thick. The crust and the rigid top layer of the mantle are collectively known as the lithosphere. Old, more than 1500mn. Lighter

2. Mantle Composed mainly of silicate rocks, rich in iron and magnesium. Apart from the rigid top layer, the rocks in the remainder, the asthenosphere are kept in a semi molten state. Extends to a depth of 2900km where temp. may reach 5000 C. This generates convection currents.

3. Core Iron and nickle, and is the size of Mars. Outer core semi molten, inner is solid. Temp 6200 C.

•The lithosphere (the Earth’s crust and the rigid upper part of the mantle) is divided into 7 large and several smaller plates. •The plates, which are rigid, float like rafts on the underlying semi-molten mantle  (called the asthenosphere) and are moved by convection currents. •Convection currents are generated by hotspots within the asthenosphere which cause magma (molten material) to rise towards the earth’s surface.  These currents can cause the plates above to move together, apart or side by side.  

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Local Area

Chalk of the Chiltern Hills which slope towards the Thames valley in the south. Has an extensive underlain aquifer which is prone to groundwater flooding. Marlow, for example, has a local flood risk which is made worse when levels are high in the Thames. Groundwater flooding following periods of prolonged rainfall is a key risk across this area and high groundwater levels lead to high flows in the watercourses for many weeks and months. Local flooding in urbanised areas (e.g. Chesham and High Wycombe) can be made worse during high runoff from the Chalk. 

February 2009: Extensive flooding affecting roads in southern Buckinghamshire (Marlow, and Little Chalfont) following heavy rain and a sustained period of high groundwater levels.

There are nearly 30,000 properties across the four Districts which could be at risk of local flooding to a depth greater than 0.3m in an event with a 1 in 200 (0.5%) annual chance or less of occurring. The primary concentration of these properties is predicted to be in Aylesbury, High Wycombe, Amersham/Chesham and Marlow.

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Distrubition of Earthquakes

Not only primary hazard causing shaking, but also secondary, triggering landslides and tsunamis. The main earthquake zones are clustered along plate boundaries. The most powerful earthquakes are associated with destructive or conservative plate boundaries

DESTRUCTIVE: An oceanic plate and a continental plate move towards each other

E.g. Alongside South America is the Nazca Plate (oceanic ) and the American Plate (continental) Also the Philippines, Eurasian plate subducting under the Philippines plate
The heavier, more dense oceanic plate is forced under the continental plate. As it sinks below the continental plate the oceanic plate melts due to friction in the subduction zone.
The crust becomes molten called magma, where it is stored in the magma chamber before being forced through vents and cracks to the surface of the Earth, sometimes causing a volcanic eruption. 
The movement of the oceanic plate is not smooth. Due to friction the plate gets stuck. Pressure then builds up. The plate will eventually slip sometimes causing an earthquake.
When the pressure is released the point at which it is released is called the focus The ground surface immediately above shakes The point on the surface where the maximum damage occurs is the epicentre

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Distribution of Earthquakes


Two plates of oceanic crust are moving towards each other
The denser of the two will be subducted
e.g. This has formed the volcanic islands of Indonesia.
As one plate moves under the other they can get stuck. This causes pressure to build up.
When the pressure becomes too much the plates jerk past each other, causing an earthquake.
Sometimes the magma rises offshore to form an island arc of volcanic islands eg Caribbean islands and Japan

Collision - Two continental plates move towards each other
They are of equal density so there is no subduction
The rocks are forced upwards to form fold mountains
E.g. The Indian and Eurasian plates are moving together forming the Himalayas and Mount Everest is slowly growing
Earthquakes occur in these locations- Large areas of countries can be affected by these shallow highly damaging earthquakes eg India and Iran
There is no volcanic activity in these locations
The Kashmir earthquake of 2005 occurred in this way

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Distribution of Earthquakes


Both volcanoes and earthquakes occur at constructive plate boundaries
Two plates move away from each other (diverge) due to convection currents in the asthenosphere Molten magma rises to fill the gap and forms new oceanic crust through volcanic activity
Eg North American plate is moving away from Eurasian plate so Atlantic ocean is getting 3cm larger – USA and Europe are moving apart Mid oceanic ridges are formed eg The Mid Atlantic Ridge Islands may be visible above the water’s surface as islands eg Iceland
Earthquakes occur here due to friction and pressure release.
There are many earthquakes here.
These earthquakes tend to be shallow and low magnitude as lava rises.
Most (not Iceland!) tend to be under the sea (submarine) so pose little hazard to humans.
The plates do not move apart in a uniform way – some parts move faster than others. This causes pressure to build up. When the pressure becomes too much, the plate cracks, making a fault line and causing an earthquake. Further earthquakes may also occur along the fault line once it has been created.

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Distribution of Earthquakes


Earthquakes also occur at Conservative boundaries
A conservative boundary occurs where two plates are moving past each other laterally
The two plates get locked together in places and pressure builds up. As with destructive boundaries, this causes the plates to jerk past each other (or to crack forming fault lines) releasing the energy as an earthquake
For example, the Pacific plate is moving past the North American plate.
Many earthquakes occur along this boundary and its fault lines, e.g. The San Andreas Fault runs through California.
These earthquakes are often shallow and some are very high magnitude.


A small minority of earthquakes occur within plates, usually involving the reactivation of ancient faultlines eg Shropshire, UK 
Also earthquakes can occasionally occur due to human activity such as dam and reservoir building, which increase the weight and therefore stress on the land.  Earthquakes then can happen where there is no record of earthquakes.
Eg Killari, India (1993)10,000 killed by an earthquakes caused by dam construction.

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Earthquake Effects

Kobe 7.4, Japan, 17th January 1995, Philippines, Pacific and Eurasian Plate

35000 people injured.

Buildings and bridges collapsed despite their earthquake proof design.
Buildings destroyed by fire when the gas mains fractured.

316000 people left homeless and refugees moved into temporary housing.

Kashmir 7.6, Pakistan, 8th October 2005, Indian and Eurasian Plate

Buildings collapsed.
79,000 people were killed.
Landslides, and large cracks appeared in the ground.
Broken sewerage pipes contaminated water supplies and spread disease.
People died of cold during the harsh winter

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Distribution of Volcanoes


Constructive plate boundaries – most of the magma that reaches the earths surface wells up as volcanoes at ocean ridges, such as the mid Atlantic ridge.
These volcanoes are mostly on the sea floor and do not represent major hazards except on islands like Iceland. Rift valleys are also present where continental crust is being stretched eg East African Rift valley has 14 active volcanoes which can produce big explosions.   The East African Rift is a geological zone where continental plates in Eastern Africa have developed a tectonic plate boundary. A rift is a fracture in Earth's surface that widens over time. This is a part of the larger Great Rift Valley, where the African Plate is in the process of dividing into two new tectonic plates called the Somali Plate and the Nubian Plate.

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Distribution of Volcanoes


Destructive plate boundaries – some 80% of the worlds most active volcanoes occur along destructive boundaries. When oceanic plates are sub ducted beneath continental plates, explosive volcanoes, such as Mt St Helens, are formed.
The ‘Ring of Fire’ around the pacific has many such volcanoes, including those in the Philippines  HOTSPOTS: Volcanoes can occur far away from any plate boundaries, e.g. in Hawaii These volcanoes are thought to be caused by in localised areas of the lithosphere where there is a high heat flow and where magma is rising from a large chamber beneath the crust as a plume.  As a lithospheric plate moves over the hotspot a chain of volcanoes forms.   Areas like Hawaii are called volcanic hotspots

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Volcano Effects

Mount St Helens 1980

Hot ash and gas destroyed forests and logging camps.

63 people were killed, mainly by poisonous gases.
Lahars (mudflows of ash and water) covered an extensive area surrounding the volcano.
Ash blocked rivers destroying popular fishing sites and causing flooding. This in turn destroyed crops and livestock.

Flooding destroyed communications such as road and railway bridges.
Sediment carried downstream ruined barge transport on the Columbia River.

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Distribution of Landslides

Landslides are the 7th biggest killer with over 1,400 deaths per year, ranking above both volcanoes and droughts. Most places that are vulnerable to landslides are mountainous areas, often after abnormally heavy rain and/or seismic activity. Human factors also play a part. Deforestation of hill sides, eg SE Asia, and building upon hill slopes, eg Hong Kong, are problematic if there are heavy rains. Snow avalanches are concentrated in high mountainous areas such as Rockies of N America, S. Alps of N Zealand. Avalanches tend to occur on slopes that are more than 35 degrees. On average 40 deaths occur in Europe and 100 in North America from avalanches. Recent research has reported that global warming may be increasing avalanche activity.   However trends in deaths have slowed due to better management.

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Distribution of Drought

Variations in the movement of the Inter-tropical Convergence Zone. As the ITCZ moves north and south through Africa, it brings a band of seasonal rain. In some years, high-pressure zones expand and block the rain-bearing winds. In Southern Ethiopia and Somalia, where farmers depend for food on rain-fed agriculture, famines may result if the summer rains never arrive.

El Nino can bring major changes to rainfall patters. In particular it can bring drought conditions to Indonesia and Australia.

Changes in mid-latitude depression tracks. In temperate regions, depressions bring large amounts of rainfall. However, if blocking anticyclones form and persist, depressions are forced to track further North, leading to very dry conditions

Failure of crops
Loss of livestock
Population migration – refugees etc
Economic impacts (especially in LEDCS) 

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Distribution of Flooding

Regional scale high magnitude floods are frequent in India, Bangladesh and China.

Atmospheric processes, including monsoon rainfall and cyclones. In temperate climates, a series of depressions sometimes brings prolonged heavy rainfall.

Intense rainfall sometimes associated with thunderstorms can lead to localised flash flooding. 

El Nino can bring devastating floods as in Mozambique in 2006.

Rapid snowmelt can add water to an already swollen river system.

Developing countries: Flooding may lead to deaths by drowning and diseases, destruction of food crops and infrastructure and loss of homes

Developed countries: Disrupts transport and infrastructure, damages livelihoods and creates high insurance costs

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Distribution of Storms

Tropical cyclones are huge storms with strong winds and torrential rain.
They are between 200-700 km in diameter
They develop above sea water that is 26°C or higher. As warm, moist air rises and condenses, it releases energy which increases wind speed.
Tropical cyclones lose strength when they move over land because the energy supply from the warm water is cut off
Most cyclones occur between 5° and 20° north and south of the equator – more than 30° away from the equator the water isn’t warm enough for cyclones to occur
They tend to move westwards due to the east-west winds in the tropics. For example, the trade winds move tropical cyclones westwards across the Atlantic Ocean towards the Caribbean Sea
Cyclones spin because of the Coriolis effect (the force that deflects the path of winds due to the Earth’s rotation). This effect is also why they move away from the equator.
Cyclones do not occur 0-5° either side of the equator because the Coriolis effect is not strong enough to make them spin.
Tropical cyclones are also known as hurricanes (when the occur in the Atlantic Ocean or Caribbean Sea) and typhoons (when they occur in the Pacific Ocean).

Storms cause heavy rain leading to floods and mudslides, high wind velocity and very low central pressure leading to storm surges and coastal flooding.

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Disaster Hotspots

Exposure to risk from two or more hazard groups and also high level of vulnerability.

Likely to be where plate boundaries intersect with major storm belts in areas of high human concentration in low or medium developed countries.

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Lower-middle income country
91 million (density 240 per km2, 2000 per km2 in Manila)
GDP per capita
Mountainous country, with crowded coastal lowlands. Consists of 7,000 islands, many very small, spread over latitudes between 5 and 20 degrees north.

Typhoons are the main hazard (20 per year)
Volcanic eruptions are explosive with dangerous lahars
Earthquakes are common (100% of the country at risk)
Occasional droughts associated with El Nino Years
Landslides common in mountainous areas
Densely populated, rapidly developing country
Vulnerability increased by poverty, deforestation, poor land management and rapid urbanisation

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Wealthiest state of the USA
40 million
GDP per capita
Coastal area contains the huge conurbations of LA, San Francisco and San Diego

Earthquakes are the main risk. Large shallow earthquakes occur along the swarm of faults associated with the San Andreas fault-a conservative plate boundary.
River floods occur in El Nino years, and droughts and wildfires in La Nina years.
Fogs occur in the SF Bay area
Landslides are a frequent secondary hazard from floods or earthquakes.
Coping capacity is high in this wealthy area, with much high-tech disaster preparedness, and state-wide drills
Economic costs of major disasters are high, especially if disaster strikes in a megacity

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