Geography - Tectonic Hazards

lithosphere

cold, rigid, brittle

asthenosphere

hot, weak, plastic

mesosphere

hot but stronger due to high pressure

moho

boundary between solid crust and semi-solid mantle/asthenosphere

continental crust

less dense, thicker (30 - 75cm), older

oceanic crust

more dense, thinner (5 - 10cm), younger

pangea

made up of Laurasia and Gondwana land

continental drift theory

Alfred Wegner → theory was disregarded as unable to explain the mechanism behind the movement

evidence of continental drift

1. jigsaw fit of continents e.g. South America and Africa

2. location and mapping of volcanic activity

3. fossils of the same pre-historic aquatic animals have been found in continents that are now far apart (mesosauras = freshwater reptile in Africa + South America and Glossepten’s leaf = found in Antarctica + Australia but different climates and extinct nearly 220 millions years ago)

4. same rock sequences in Scotland + Canada

‘ring of fire’

most tectonically active area in the world

How did the thoery of plate tectonics evolve?

1. identification of mid-Atlantic ridge - mountains 1000 miles wide and 25—m high was discovered by 2 plates moving apart

2. echo sounders used to prove the crust and ocean floors found to be thinner

3. paleomagnetism - Earth’s magnetic field reverses every 400,000 years and lava preserves record of magnetic film at that time due to orientation of iron particles

4. Benioff zone - depth of EQs get larger the further away from the boundary/zone due to oceanic crust sinking

convection currents

heat transferring from one area to another

rising and sinking convection currents within the mantle allow the slabs of crust to float in the same direction as the diverging or converging currents in the asthenosphere

‘slab pull’ vs ‘ridge push’

• ‘slab pull’ = where the weight of a subducting plate ‘pulls’ the rest of the plate downwards into the mantle due to gravity

• ‘ridge push’ = due to mid-ocean ridges lying at higher elevation than the rest of the ocean floor, gravity causes the ridge to push on the crust that lies further away

convergent boundaries

plates moving towards each other (either destructive or collision)

destructive plate boundaries

either oceanic + continental or BOTH oceanic

the denser oceanic curst subducts beneath the less dense continental or oceanic plate. Due to high pressure and heat it melts and this magma rises through the continental or oceanic plate as is less dense, leading to VOLCANOES

friction in the Benioff zone between the plates creates stress and eventually rocks will fracture and slip, meaning EARTHQUAKES

e.g. Nazca Plate and South American Plate

submarine volcano

formed if two oceanic plates converge and when the magma cools, a volcanic island is built e.g. Indonesia

collision boundaries

continental and continental

creates fold mountains but NOT volcanoes as no new magma being created

stress created by the pressure causes rocks to fracture and therefore earthquakes are very common

e.g. Indian and Eurasian Plate

divergent boundaries

plates moving away from each other

constructive plate boundary when both oceanic plates

magma rises and cools as it enters the cooler ocean which forms submarine volcanoes and volcanic islands

forms new oceanic crust e.g. Mid Atlantic Ridge

constructive plate boundary when both continental

convection currents thin the crust causing it to begin to fracture, forming volcanoes as magma rises

causes continental crust to split apart forming more oceanic crust

e.g. East Africa being pulled apart

conservative boundary

plates moving in the same/opposite direction/rubbing together

EARTHQUAKES occur when stress is released due to sudden plate movement after locking together

e.g. North American plate and the Juan de Luca plate creating the San Andreas fault

shallow focus earthquakes

close to the surface

often more powerful as they don’t have time before losing their energy

focus (hypocentre)

origin of the earthquake

epicentre

lies directly above the focus

mantle plumes + hot spot volcanoes

occur when an area of the mantle experiences increased temperatures and therefore increased upwelling of magma beneath the crust

movement of plate above can cause a chain of volcanoes to form (the one directly above the plume is more active)

e.g. Hawaii

both continental and oceanic plates

Midlands EQ (2002)

• 4.8 on Richter scale

• epicentre = Dudley, west of Birmingham

• caused by movement along the old fault line known as the Malvern Lineament

intra-plate earthquakes

occur along faults (cracks in the earths lithosphere where sections of a plate are fractured) due to friction and the buildup of stress and pressure

shadow zone

the area of the Earth where seismograms cannot detect an earthquake since it does not receive any direct P or S waves (104-140 degrees)

P-wave (primary)

• travel in a linear fashion (parallel to the flow of particles )

• fastest moving wave (6km/s)

• travel though solids and liquids

• body wave and can travel through anything (from crust to core)

• travel in a push and pull motion

S-wave (seconday)

• travel 3km/s

• can only travel through solids not liquids (cannot go through outer core)

• particles vibrate perpendicular to the direction of the wave

• body wave

L-wave (surface/rayleigh)

• complex rolling motion (ground moves up and sideways)

• can only travel through the surface (solid) and energy decreases with distance from epicentre

• slowest velocity

• responsible for most structural damage and sometimes visible

seismograms

the velocities of all seismic waves are variable and dependent upon the density and composition of the rocks through which they travel (higher density = higher velocity)

seismographs

an inert weight is attached by a spring, which acts as a shock absorber which keeps the pen stationary whilst the rest of the instrument moves

Mercalli scale

records intensity or damage caused and is based on observations by those who experienced the event and the scale of resulting damage (I - XII)

Richter scale

assigned numbers in a logarithmic scale from 1 to 9.9 (increases 10x strength for each one e.g. 10x difference between a level 4 and 5 EQ)

Moment Magnitude Scale

measures the size of earthquakes in terms of energy released (same scale as Richter scale)

How to accurately pinpoint the epicentre of earthquakes

1. figure out the lag time between the arrival of P and S waves

2. using s = d/t, a distance between the epicentre and recording station is produced giving a possible radius

3. using multiple recording stations, the possible radius’ would overlap giving the epicentre p

primary effects of EQs

1. ground shaking → measured using a seismometer

2. ground rupturing → occurs when the EQ movement along a fault actually breaks the surface

secondary effects of EQs

1. damage to structures → depends upon building materials (metal = effective, bricks and concrete = can’t cope), underlying geology and age of building

2. building collapse e.g. Haiti - 250,000 collapsed

3. liquefaction → ground water migrates toward the surface causing sediment to behave like quicksand e.g. LA - Loma Prieta EQ

4. landslides → destabilises soil pulled down by gravity

5. tsunamis → EQ occurring underwater e.g. 10ft waves after Haiti

6. fires → may break gas pipes which leak gas and so any sparks would ignite

7. avalanches → destabilises snow

Bam (2003) - impacts + responses

• 6.8 magnitude yet destroyed 70% of buildings

• 26,271 deaths and 500 missing (even 3 months later

• high death toll as people asleep

• cut electricity, water supplies and phone services

Responses

• 40+ countries sent aid

• emergency centres set up as main hospital collapsed

• long term cost of reconstruction = $1 billion

Haiti EQ (2010) - impacts + responses

• 7.0 magnitude

• 170,000 deaths + 250,000 buildings collapsed

• one of worlds poorest countries

Responses

1. planeloads of water, food, tents, medicine and rescue equipment to Port-au-Prince

2. mass graves created to stop spread of disease

3. Nepal aid workers defecated in river causing 5000 further deaths from cholera

Paso Rables EQ (2003) - impacts + responses

• 3 deaths and 40 badly injured as high agricultural design

• 7.1 magnitude yet less deaths than Bam

• 75,000 homes and businesses lost power but restored rapidly

Response

• low destruction so little responses

Nepal EQ (2015) - impacts + responses

• 7.8 magnitude

• 9000 deaths and received many aftershocks

• 7000 schools + hospitals destroyed

• 25% loss of electricity

• harvests almost completely lost with a massive drop in tourism

• catalysed avalanche on Mt Everest killing 300

• Kathandu is population dense

Responses

• made 16 transitional shelters for hundreds of thousands of people who became homeless

• 500 million Nepall rupees for relief from government

• preparedness undermined as government buildings lost

causes of tsunamis

1. the continental crust and oceanic crust lock together causing the continental crust to be dragged downwards (if destructive boundary)

2. eventually the force of movement overcomes friction and the overlying crust is sprung upwards, displacing large volumes of water

3. coastal uplift - tsunami travels in both directions

4. wave approaches land causing its energy to compress into a smaller space, so gains height

characteristics of tsunamis (x5)

1. travel at speeds of up to 400-500 mph in deep ocean but only 100mph in shallow

2. can reach up to 100 feet or more and crash inland

3. shallow water = slows down, short wavelength but large height

4. deep water = faster, long wavelength but flat

5. waves retreating is a sign that a tsunami is approaching

Indian Ocean tsunami

• 230,000 deaths (deadliest tsunami)

• displaced millions from their home - forced to live in temporary shelters or with host families

• loss of jobs and income for thousands in fishing and tourism industry

• agricultural loss e.g. rice paddies and fish reserves destroyed

• tourism showed sharp decline

• reached Thailand, Indonesia etc. (51m high)

Hunga Tonga volcano

• 4 deaths whilst 84,400 affected by volcanic ash fall and tsunami waves

• contaminated water supplies

• 600 structures destroyed or severely damaged

• 80% population affected

• caused an estimated US$90.4 million in damages (18.5% of Tonga’s GDP)

• agricultural loss - destroyed crop lands and reduced crop yields

• tourism industry hindered due to damages and fear

fissure volcano

linear volcanic vent through which lava erupts, usually without an explosion (gentle slopes + basaltic lava)

shield volcano

volcano with gently sloping sides due to layers of solidified basaltic lava

dome volcano

roughly circular mound-shaped volcano with steep convex slopes from thick, fast cooling andesitic lava

cinder cone volcano

a steep, conical hill consisting of layers of fine ash and cooled andesitic lava

composite cone volcano

a volcano with layers of solid andesitic lava and fine ash with not only the central vent but also side vents

caldera volcano

an extremely explosive volcanic crater which is usually formed by a major explosion leading to the collapse of the mouth of a volcano

basaltic lava

• low silica content and erupts at highest temperatures (1000 - 1200 degrees)

• very low viscosity and fast flows with high density (effusive)

• rates of 100km/hr and flows around 50km from source

• found near oceanic hotspots e.g. Hawaii

andesitic lava

• higher in aluminum and silica

• temperatures are lower (800 - 1000 degrees) - more viscous

• found at destructive subduction margins e.g. Mt Edna or in the Andes

rhyolitic lava

• high silica content and high viscosity (10x slower than basaltic lava)

• high gas and ash rich (pyroclastic)

• lower temperatures (650 - 800 degrees)

• explosive eruptions

• found at continental hotspots due to mantle plume melting e.g. Yellowstone

tephra as a primary hazard of volcanoes

any solid material ejected from a volcano e.g. ash or volcanic bomb

the size of the particles that fall out are largest near the volcano and get progressively smaller

lava as a primary hazard of volcanoes

quite predictable and rarely leads to death despite being fast-flowing

can impact infrastructure, destroy crop land and tourist facilities

main secondary hazard = fires

pyroclastic flows as a primary hazard of volcanoes

contains extremely hot gas, ash, lava and dust which can reach 800 degrees and travel at 200km/hr e.g. Mt St Helens destroyed 15km3 of timber

volcanic gases as a primary hazard of volcanoes

include CO2, CO, H2, SO2 and Cl2 which are greenhouse gases - can be deadly e.g. emissions of CO2 from Lake Nyos in Cameroon suffocated 1700 people

lahars as a secondary hazard of volcanoes

mudflows of wet volcanic debris and are a hazard of vulcanism

caused when heavy rainfall turns new ash deposits into fast flowing mud rivers or if pyroclastic flow meets a river or snow e.g. Mt St Helens

Johulhlaups as a secondary hazard of volcanoes

glacial outburst floods

caused if a subglacial volcano erupts causing the overlying ice to melt producing huge quantities of water which leads to flooding e.g. Grimsvotn in Iceland

fires as a secondary hazard of volcanoes

hot magma and volcanic bombs may cause wildfires, destroying wildlife and nature etc.

Lake Nyos, Cameroon (1986)

• released vast amounts of CO2 killing 1700 people due to suffocation

• due to a landslide hitting the lake (which lies above a pocket of magma) causing a large cloud of CO2 to be emitted

• killed 3500 livestock

Mt St Helens, USA (1980)

• destructive plate boundary between Juan de Fuca and the North American plate

• VEI of 5 - only 57 deaths due to remote place and when the volcano collapsed, it focused the blast laterally toward the north

• pyroclastic flows caused extensive damage, rhyolitic lava caused large explosion and ash caused suffocation

Kilauea, Hawaii (2018)

• almost continually active since 1983 with effusive eruptions

• 0 deaths but injured 23

• 700 houses destroyed and SO2 released

• insurance increased 6x

Nevada del Ruiz, Columbia (1985)

• killed 23,000 in town of Armero (40km away)

• VEI 3 but led to melting of 20% of snow and ice at the summit causing lahars

• infrastructure destroyed and cost of response was 20% of GDP

Volcanic Explosivity Index (VEI)

• given as a number based on the amount of material ejected from the eruption (scale of 1-8)

• super eruption = VEI 8

• an increase of 1 on the VEI is a 10x increase in explosivity

• volume of products, eruption cloud height and qualitative observations used

hazard

a naturally occurring process or event that has the potential to affect people

vulnerability

the ability to anticipate, cope with, resist and recover from a natural hazard

disaster

an event that causes significant social, environmental and economic damage

resilience

the ability to protect lives, livelihoods and infrastructure from destruction, and to restore areas after a natural hazard has occurred

hazard risk equation

risk = (vulnerability x hazard) / resilience

the ‘Pressure-release model’

• underlying causes of a disaster based on the idea that a disaster happens when two opposing forces interact

• vulnerability is a process that starts with dynamic pressures which are political and economic systems that control who has power in a society and who has access to resources

example of PAR mdoel

poor (root cause), don’t spend time or money enforcing building regulations (dynamic pressures), leads to poorly built infrastructure (unsafe living conditions)

factors that increases vulnerability

1. level of education e.g. people per doctor

2. government policies

3. location of country e.g. landlocked

4. landscape of a country (geology)

5. infrastructure

6. magnitude of disaster

7. wealth (GDP)

8. climate - worse weather = worse infrastructure

9. quality of healthcare system

10. preparation/monitoring levels

11. coastal or low-lying

12. access to clean water

13. population density = more people = greater vulnerability

primary effects of Haiti EQ

• 316,000 deaths and more than 1 million made homeless

• 1 in 5 jobs lost, 30,000 commercial buildings collapsed

• port destroyed, road and rail links blocked meaning hard to spread aid

• sea levels in the local area changed, some parts of land sinking into water

secondary effects of Haiti EQ

• 5000 people in a refugee camp died of cholera as a UN force from Nepal defecated in upland rivers

• looting and sporadic violence observed due to delay in disease distribution

• transport links destroyed and damage to communication and electrical networks

How have root causes led to unsafe living conditions in Haiti?

1. magnitude 7 + relatively shallow increased ground shaking

2. epicentre only 24km from Port-au-Prince which is the most densely populated city in Haiti (2 million people)

3. developing country - poor and limited resources

4. 80% Haitians lived in poverty (slum-like housing densely packed and poorly constructed)

5. high level of corruption so no building regulations

6. deforestation led to loose soil e.g. landslides

7. lack of disaster preparation

8. rapid urbanisation rates leading to overpopulation

hazard profiles

they compare the physical processes that all hazards share, and help decision makers to identify and rank the hazards (help compare across hazards)

advantages of hazard profiles

1. compare physical processes that all hazards share

2. helps rank and compare hazards

3. allows for specific management to be considered

4. identifies hazards that require the most resources and attention

disadvantages of hazard profiles

1. reliability when comparing different events is limited

2. difficulty comparing across hazards

3. for planning it is better to consider hazards as individual hazards

trends in disasters

1. World Meteorological organisation say number of disasters over last 50 years increased fivefold but number of deaths fallen by 2/3

2. increased due to weather disasters from climate change and easier to record disasters

3. death rates fallen from improvements in planning, prediction and reaction as well as better infrastructure, healthcare and education etc.

4. biological disasters e.g. Covid19

World Data for disaster trends (x5)

1. number of deaths from disasters has decreased from over 500,000 in 1920 to around 50,000 in 2010

2. total amount of economic damage is increasing but dictated by disasters in HICs as spend more

3. severity of hurricanes set to increase 2-11%

4. economic inflation means cost cannot represent how destructive a hazard was as may be different

5. responsible for 0.1% deaths in the world (45,000 per year)

how does climate change affect the frequency/hazard of disasters

as weather warms and ice melts, the release of ice can trigger EQs as well as remove support from the slopes which may lead to landslides which can destabilise the magma chamber and trigger an eruption

temperature increase also contributes to the increase in droughts, fires, tropical storms etc.

how does population increase affect the frequency/hazard of a disaster

more than half the population live in cities → densely packed and poor conditions, increasing by 80 million a year

how does sea level rise increase the frequency/hazardous of a disaster

increase tsunami and hurricane hazard as amplifies it and increases magnitude

how does social media increase the frequency/hazardous of a disaster

e.g. Twitter sending alerts once marked by official accounts like the Police

mega disasters

large scale disasters either spatially, economically or socially which often require international support

Eyjafjallajokul eruption, Iceland (2010) x7

1. composite volcano - VEI 3 but produced large volume of very fine ash which combined with easterly blowing winds, blew ash across Europe

2. phreamagmatic eruption - cool water from glacier above and magma mixed creating vast volumes of ash which disrupted air travel (airlines lost £130 million a day, 17,000 flights cancelled during first day)

3. near shutdown of agricultural sector in Kenya causing refrigerate storehouses to fill up + 5000 staff temporarily laid off

4. led to some UK citizens to sail their own boats across the English Channel to pick up stranded tourists (150,000)

5. 2.8 million tonnes less of CO2 was released

6. Nissan plant in Japan had to stop producing cars as one part from Ireland so couldn’t import it

7. World Bank estimate African countries lost $65 million due to loss of exports

Japanese Tohoku tsunami (2011) x8

1. agriculture accounts for 3-4% of Japan’s employment and seawater contamination affected rice crops for years

2. magnitude 9 EQ + no deaths BUT triggered tsunami 40m high and travelled 10km inland killing 19,747 (5000 aftershocks + Japan have regular EQ drills and emergency SMS system)

3. more than 120,000 buildings destroyed and $235 billion spent (worlds costliest disaster) - 39,000 evacuees whilst 1000 still in temporary housing in 2021

4. level 7 nuclear meltdown and release of radioactive material as electrical power + backup generators were overwhelmed so lost cooling abilities

5. UK temporarily stopped their power plants

6. 200,000 residents evacuated due to Fukushima powerplant

7. main Tohoku Expressway was closed for 3 months and 20,000 people stranded

8. Japanese docks, ships and household items arrived on US and Canadian shores for years (5 million debris)

9. tsunami broke the Sulzberger ice shelf in Antarctica

multiple hazard zones

places where a number of physical hazards combine to creates an increased level of risk for a country's and its population

‘disaster hotspot’ e.g. Philippines

general info on Philippines (x12)

1. population = 106 million

2. more than 7000 islands

3. average GDP is $8100 (relatively low = LIC)

4. 25.4% agriculture sector

5. life expectancy = 70 years

6. high levels of deforestation

7. 0.8 doctors per 1000 people

8. unemployment rate = 2.41%

9. population below poverty line = 16.7%

10. rapidly urbanising era e.g. Manilla - 2000 people per square km

11. mountainous landscape means limited space for urbanisation → cramped housing near coast

12. found within the Pacific ‘ring of fire’

floods in Philippines

• 38 events since 1990 and 1147 killed

• ‘flash floods’ caused by EQ, typhoons etc.

• e.g. 2006 EQ - triggered a flood due to material from the Parker volcano entering the Maughan lake

typhoons in the Philippines

• on belt of SE Asian typhoons

• 6-7 per year

• e.g. Typhoon Haiyan (worst tropical storm to reach land = category 5)

earthquakes in the Philippines

• 24 major EQs since 1990

• e.g. 2006 EQ - killed 15 and damaged 800 buildings - triggered landslide from the Parker volcano into the Maughan lake = FLOOD

volcanoes in the Philippines

• 25 major eruptions with 1,700,000 people affected and 3000 deaths

• e.g. Mount Pinatubo - ash spread over 100km radius with 20 million tonnes of material ejected - triggered by a 7.7 magnitude EQ (killed 1600 in Manilla) - typhoon meant rain and ash swelled on roofs causing collapse and mudslides

landslides in the Philippenes

• e.g. Guinsaugan landslide (2006) - killed 1150 people and engulfed a whole village - caused by 70cm of rain over 10 days combined with a 2.6 magnitude EQ + deforestation causing destabilisation of slopes

droughts in the Philippenes

• e.g. Geneva drought (2016) - caused by significantly increasing temperatures and not enough rain

• left 43% of the country in drought with 1 farmer dying and 13 injured due to the conditions

• crop yields decreased as not enough water

3 characteristics of tropical revolving storms

1. strong winds - over 100mph except within the eye where winds = 0mph

2. storm surge - raised sea levels that move with the storm (coastal flooding)

3. heavy rain leads to flooding