1. HAZARDS
Combination of natural and human
processes. A hazard is an event with the
potential to damage human activity.

2. Structure of the Earth
• Inner Core
solid, iron and nickel
• Outer Core
molten, 5000 degrees
• Mantle
semi-solid, asthenosphere is upper mantle- 20km
thick
• Crust
divided into plates, combined with asthenosphere is
lithosphere, 80-90 km thick

3. Plates
• Plates are 7 large pieces of the lithosphere
• They float on asthenosphere and move through
convection currents
• Continental
30-70 km thick, light in colour (mainly
granite), composed of SIAL (silicon, aluminium), lighter
than oceanic, over 1500 million years old
• Oceanic
6-10 km thick, dark (mainly basalt), SIMA (silicon
magnesium), heavier than continental, younger than
continental (200 million years old)

4. Plate Tectonic Theory
• Alfred Wegener, German
• 1915
• Coastlines of South America and Africa- suggested continents were joined
together
• Originally one continent, Pangaea
• Split into 3 super continents which were later fragmented
• He could not prove why this happened, so theory was dismissed
• Sea floor spreading in Mid Atlantic Ridge brought his theory back to light
• Glacial deposits of similar ages in Brazil and West Africa
• Geologically corresponding mountains in US (Appalachian) and NW Europe
(incl. Scotland)
• Fossil remains of the Mesosauraus (270 million years extinct) found in South
Africa and Brazil
• Fossilised plants in India and Antarctica
• Palaeomagnetism shows periodically reversing magnetic fields (shown by sea
floor spreading)
• Earthquakes and Volcanic activity

5. Magnetic Striping
• Iron particles in solidified lava align with Earth’s
magnetic field
• Polarity
• Reversed regularly
• You can tell how old lava is by looking at its
polarity
• Palaeomagnetism
• Creates striped pattern
• Ocean crust spreading away from plate boundary

6. Destructive Boundaries
• Andean-type subduction
Oceanic beneath continental
Deep sea trench
Fold mountains
Deep focus Earthquakes
Steep-sided volcanoes
Nazca under South American plate – Andes Mountains, Peru-Chile trench, Nevado del Ruiz volcano
• Island Arcs
Oceanic and oceanic crusts
Steep-sided volcanoes formed
Shallow sea trench
Deep-focus earthquakes
South American under Caribbean plate formed Caribbean Islands, Soufriere Hills, Marianas Islands
• Continental collision boundaries
Two continental crusts colliding
Sediments between plates rise up to form fold mountains
Deep focus earthquakes
e.g. The Himalayas- Indo-Australian and Eurasian plates

7. Constructive Boundaries
• Ocean ridges
Sea floor spreading zones
Two areas of oceanic crust pulled apart
New ocean floor formed as lava fills gap
Shield volcanoes
Shallow focus earthquakes
e.g. Mid-Atlantic Ridge, Eurasian and North American plates
• Continental rifts
Rift valleys
Two areas of continental crust pulled apart
e.g. East African rift valley
Volcanoes are rare
Shallow focus earthquakes

8. Conservative Boundaries
• Plates sliding parallel to each other
• Friction and tension build
• Shallow focus earthquakes
• E.g. San Andreas Fault, California
• Pacific vs. North American plates
• Moving in same direction at different speeds
• Pacific is faster (5-9cm/year)
• Can cause transform faults

9. Hot Spots
• E.g. Hawaiian Islands
• Hot Spot within pacific plate
• Radioactive elements within mantle
• Magma rises to surface in plumes, forming small
shield volcanoes
• Hot spots are rooted, but the movement of the
pacific plate has caused Island Chains
• Only the volcano above the hot spot is active-
Mauna Loa
• Pacific plate is moving in a NW direction

10. Intrusive Volcanicity
• It’s what happens when the magma cools
before it reaches the surface
• Often exposed years later after erosion
• Batholiths are an example of a bubble of
solidified magma, often hundreds of
kilometres in diameter
• E.g. Dartmoor
• Dykes radiate from batholiths

11. Extrusive Volcanicity
• When magma reaches the surface
• Formation depends on type of lava
• Lava plateaux formed from fissure eruptions-
flat landscapes due to basic lava
• E.g. Antrim Plateau, NI
• Volcanic forms e.g. Volcanoes, Geysers and
Mud volcanoes

12. Volcanic shapes
• Shield- basic lava, short and wide
e.g. Mauna Loa, Hawaii
• Dome- viscous lava, tall and steep
e.g. Puy district, France
• Cinder cone
e.g. Paricutin, Mexico
• Composite cone- pyramid shape, layers of ash and lava
e.g. Mt Etna, Sicily
• Calderas- gas build up explodes and removes summit
Krakatoa, Indonesia

13. Volcanic Eruptions
• Icelandic
gently flowing basalt lava from a fissure
• Hawaiian
basalt lava flowing from a central vent
• Vesuvian
violent explosion after long inactivity
• Kratatoan
violent eruption destroying entire cone base leaving crater
• Pelean
violent eruption with pyroclastic flows
• Plinean
violent eruption where lava and pyroclastic materials ejected e.g. Lava bombs

14. Distribution of Volcanoes
• Mainly found along mid-ocean ridges
e.g. Mid-Atlantic ridge- Iceland
• Near subduction zones
e.g. ‘Ring of Fire’- Nazca plate under South American plate
• Along rift valleys
e.g. African rift valley- Mt Kenya and Mt Kilamanjaro
• Over hot spots
e.g. Pacific ocean- Hawaiian islands

16. Effects of Volcanic Activity
Primary
• Lava flow – threat to farmland and infrastructure
• Tephra – solid material of varying size ejected into the atmosphere
• Pyroclastic flows – hot, gas-charged, high velocity flows of gas and tephra, respiratory problems
• Volcanic gases – mainly carbon dioxide, killed 1700 people in 1986 at Lake Nyos, Cameroon
Secondary
• Lahars – volcanic mud flows, e.g. Nevado del Ruiz in 1985
• Flooding – melting of ice caps and glaciers e.g. Grimsvotn, Iceland 1996
• Tsunamis – giant sea waves e.g. Krakatoa, 1883 killing 30,000 in Sumatra
• Volcanic landslides
• Climatic change – volcanic debris in the atmosphere reduces global temperatures

17. Hazard Management- Prediction
• Swelling ground (rising magma)
• Seismic activity (splitting rock)
• Groundwater (gets hotter)
• Emission of gases (from crater)
• Magnetic fields (change)
• Animal behaviour

18. Hazard Management - Protection
• Monitoring the volcano (leaves time for evacuation)
• Risk assessments (identifying those at greatest risk)
• Land use planning (avoid building in high-risk areas)
• Controlling lava flows (trenches, walls, dynamite, pouring water on slow moving lava to set)
• Technical and financial aid (for LEDW)

19. LEDC Eruption -Montserrat
• Soufriere Hills, Montserrat, Caribbean
• Dormant for 400 years
• July 1995, started steaming and small ash explosions
• 1996, pyroclastic flows, southern population in danger,
most had fled
• 1997, residents move back to south as volcano went
through a quiet phase
• June 1997- exploded, large pyroclastic flows destroyed
settlements (Plymouth, capital city) and killed 19

20. Montserrat Aftermath
• British dependency, UK government had to provide:
• Evacuation of 7000 inhabitants to Antigua/UK
• Resettlement of population from south to north of the
island
• Constructing temporary shelters in north
• Re-establish air and sea links to Montserrat
• Building permanent housing
• Providing farming areas in north
• Moving the capital from Plymouth to Salem
• It cost the government £100million+ to minimise
effects and introduce a 3-yeaer development plan

21. MEDC Eruption- Mt Etna
• Northern Sicily
• 3310m tall and 460 miles long
• Lies on destructive Eurasian and African plate boundary
• Theories to its existence include hot spot over European plate and
fractures in lithospheric slab
• Densely populated lower slopes due to banana, fig and pistachio
farming
• Skiing, cafe and cable car bring tourism
• Erupted in may 2008
• Lava travelled 6km
• 200 earthquakes
• Flank eruption (lava exposed on eastern side as opposed to crater)
• Artificial channels dug and water cooling used to divert lava from
villages

22. Etna Aftermath
• Activity continued for 6 months
• No deaths
• Sulphur dioxide found 3000 miles away
• Temporary closure of airport
• Dip in tourism
• Dip in economy (farmland ruined)

23. Benefits of Volcanoes
• Geothermal power - Iceland use this to heat greenhouses and
this enables it to be self-sufficient in most food stuffs
• Volcanic soils – lava weathers to produce fertile soils rich in
minerals. Farmers work at the low lopes of volcanoes such as Mt Etna,
Sicily
• Volcanic rocks – they make good building materials also pumice
• Tourism – tourists are able to climb to the crater of mount Vesuvius

24. Earthquakes
• An earthquake is oscillation of the earth’s crust
• Measured on a Richter scale (logarithmic)
• May also be measured on the Mercalli scale
• Triggered mostly by plate boundaries moving but also
by movement in fault lines, volcanic activity and
human activity (e.g. Drilling)
• Epicentre happens underground
• Focus is where it impacts on the surface
• Surface waves- Raleigh and Love
• Body waves- primary and secondary
• Easier to say ‘where’ than ‘when’

25. MEDC Earthquake
• Northridge, LA, 1994
• 6.7 on the Richter scale
• San Andreas fault line
• Focus was 18.4km deep
• 0430 am
• 57 deaths
• 1500+ injuries
• 11 main road closures
• 11,000 landslides triggered
• 20,000 homeless
• Many homes without gas, electricity and water
• 6,000 aftershocks
• $30billion worth of damage

26. LEDC Earthquake
• Gujarat, NW India, Jan 2001
• Epicentre was Bhuj
• Collision boundary- Indian and Asian plates
• Intraplate earthquake (didn’t happen on boundary)
• Focus was 17km deep
• 7.9 in Richter scale
• 30,000 deaths
• 160,000 injuries
• 1 million homeless (90% homes destroyed)
• 800,000 buildings damaged
• All 4 hospitals were destroyed
• Heritage was destroyed e.g. Forts, palaces, temples
• Communications disrupted (power lines down)
• Looting
• 80% water and food supplies damaged
• Widespread diarrhoea and gastroenteritis
• $5.5 billion in damages

27. Tsunami
• A tsunami is a large ocean wave which is
caused by sudden motion on the ocean floor
• This is usually caused by an earthquake
• Pacific ocean accounts for 80% tsunamis
• Oceanic under continental plate

28. Boxing Day Tsunami
• 26th December 2004
• 9.0+ on Richter scale
• Sumatra, Indonesia
• India plate under Burma plate
• 275,000 deaths
• Affected 10 countries
• Aceh was worst-affected
• Aid was slow to reach the region
• Minimal secondary deaths
• School uniforms for children
• 60% of fishermen back to work 1 year on, catching 70% of previous years’ capacity
• The war-torn region now sees less violence from the opposing sides since the
tsunami
• 100,000 houses pledged, one year on and only 20,000 are finished
• Restoration of livelihood and water/sanitation were the focus of spending
• Indonesia was granted one third of the total aid contribution

29. Multi hazard urban environment
MANY HAZARDS HAVE INTERRELATIONSHIPS
• Los Angeles
Earthquakes- lies on fault line
River flooding- increased interception as well as heavy winter storms
Coastal flooding- heavy winter storms cause waves to pound coast
Drought- high evapotranspiration and little rainfall
Wildfires- hot summers dry vegetation, and wind spreads fires more easily
Landslides/mudslides- fires remove vegetation, loosening ground
Smog- due to intense car use
Crime- highest in USA
• Mexico City
Earthquakes- Cocos plate subducted under North American plate (last earthquake in 1985, 8.1 on Richter)
Smog- worst air quality in the world, old cars running in a small area
Sinking ground- sediments in old lake bed on which the city lies are contracting
Crime- increased by 80% in the 90’s, few crimes are solved
Reasons for Mexico City linked to unconstrained growth, meaning many poorly-built structures are erected,
only to easily fall down in an earthquake/landslide. 40% of people live in informal settlements there.

30. Additional Clarification
• 31: Oceanic Ridges
• 32: Sea floor spreading
• 33: Destructive boundaries (OC)
• 34: Destructive boundaries (OO)
• 35: Destructive boundaries (CC)
• 36: Fold mountains

31. Oceanic Ridges
• E.g. Mid Atlantic Ridge
• 1000km wide
• Result of sea-floor spreading
• 10-15mm/year
• Shallow-focus earthquakes due to transform
faults which cause sideways slipping
• Volcanic activity occurs
• Forms submarine volcanoes (sometimes rise
above sea-level, shield shape)

32. Sea Floor Spreading
• Constructive plate margins
• Space between diverging plates
• Filled with basaltic lava
• New crust continually being formed
• Youngest part of Earth
• Form mid oceanic ridges and rift valleys
• E.g. Jordan- East Africa 5500km

33. Destructive plate margins
oceanic-continental
• Oceanic plate goes under continental (heavier)
• Subduction
• Ocean trench
• Fold mountains
• Oceanic plate melts in Benioff zone
• Magma oozes up through plate and forms volcanoes
(andesitic lava)
• Island arc may occur here
• Triggers earthquakes
• e.g. Nazca vs. South American plates
• Andes, Peru-Chile trench, Cotopaxi volcano and Ecuador
earthquake of 1906 were formed this way

34. Destructive plate margins
oceanic-oceanic
• Ocean trenches
• Subduction
• Submarine volcanoes
• Island arc
• Earthquakes
• E.g. Pacific vs. Philippine plate
• Marianas trench, Island of Guam formed

35. Destructive plate margins
continental-continental
• Little subduction due to low density
• Fold mountains as two masses push upwards
• Shallow focus earthquakes may be triggered
• E.g. Indo-Australian vs. Eurasian plate
• Sediments from the Sea of Tethys rose to form
Himalayas
• India at risk of earthquakes, e.g. Gujarat, 2001

36. Fold Mountains
• Formed by Destructive plate margins (but not
ocean-ocean)
• Have anticline and synclines (folded rocks)
• Volcanic areas (e.g. Andes)
• Huge areas of overfolds
• Uplifted central areas e.g. Altiplano, Andes
• Earthquakes
• Highly weathered and eroded features e.g.
valleys, gorges, glaciers