HAZARDS

Combination of natural and human processes. A hazard is an event with the

potential to damage human activity.

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

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)

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

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

Destructive Boundaries• Andean-type subductionOceanic beneath continentalDeep sea trenchFold mountainsDeep focus EarthquakesSteep-sided volcanoesNazca under South American plate – Andes Mountains, Peru-Chile trench, Nevado del Ruiz volcano

• Island ArcsOceanic and oceanic crustsSteep-sided volcanoes formedShallow sea trenchDeep-focus earthquakesSouth American under Caribbean plate formed Caribbean Islands, Soufriere Hills, Marianas Islands

• Continental collision boundariesTwo continental crusts collidingSediments between plates rise up to form fold mountainsDeep focus earthquakese.g. The Himalayas- Indo-Australian and Eurasian plates

Constructive Boundaries• Ocean ridgesSea floor spreading zonesTwo areas of oceanic crust pulled apartNew ocean floor formed as lava fills gapShield volcanoesShallow focus earthquakese.g. Mid-Atlantic Ridge, Eurasian and North American plates

• Continental riftsRift valleysTwo areas of continental crust pulled aparte.g. East African rift valleyVolcanoes are rareShallow focus earthquakes

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

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

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

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

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

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

Distribution of Volcanoes

• Mainly found along mid-ocean ridgese.g. Mid-Atlantic ridge- Iceland

• Near subduction zonese.g. ‘Ring of Fire’- Nazca plate under South American plate

• Along rift valleyse.g. African rift valley- Mt Kenya and Mt Kilamanjaro

• Over hot spotse.g. Pacific ocean- Hawaiian islands

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

Hazard Management- Prediction

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

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)

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

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

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

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)

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

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’

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

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

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

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

Multi hazard urban environmentMANY HAZARDS HAVE INTERRELATIONSHIPS

• Los AngelesEarthquakes- lies on fault lineRiver flooding- increased interception as well as heavy winter stormsCoastal flooding- heavy winter storms cause waves to pound coastDrought- high evapotranspiration and little rainfallWildfires- hot summers dry vegetation, and wind spreads fires more easilyLandslides/mudslides- fires remove vegetation, loosening groundSmog- due to intense car useCrime- highest in USA

• Mexico CityEarthquakes- 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 areaSinking ground- sediments in old lake bed on which the city lies are contractingCrime- 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.

Additional Clarification

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

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)

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

Destructive plate marginsoceanic-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

Destructive plate marginsoceanic-oceanic

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

Destructive plate marginscontinental-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

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