Paper 1: geophysical hazards

Geography IB paper 1 option D: geophysical hazards SL/HL

The mohorovicic discontinuity

The mohorovicic discontinuity

AKA the Moho, the boundary between the crust and the mantle

Lithosphere

The sum of the Earth’s crust and the upper, most solid mantle

Sial

The upper layer of the lithosphere comprising of silica and aluminium ore

Sima

The lower layer of the lithosphere made out of silica and magnesium

Asthenosphere

The upper layer of the mantle below the lithosphere with relatively low resistance to plastic flow and convection currents.

Seismic waves

Elastic waves in the earth produced by an earthquake or other tectonic activity.

Subduction

The sideways/downwards movement of the edge of the plate of crust into the mantle beneath another plate

Conduction (heat)

The direct transmitssion of heat through the material of a substance

Convection

Movement in a fluid caused by the tendency of hotter, less dense material to rise and colder, denser material to sink due to gravity

Volcanic advection

The transfer of heat or matter by the flow of a fluid

Crust

The upper layer of the Earth consisting of oceanic and continental crust with seawater on top

Mantle

• The layer of the earth underneath the crust

• Molten

• Mostly silicates

• 2800km thick

• Temperatures of between 870 and 3700 degrees celsius

Outer core

• Layer of the earth between the mantle and inner core

• 2200km thick

• Liquid iron and nickel

• Temperatures of 3700-4300 degrees celsius

Inner core

• Innermost layer of the earth

• Solid iron and nickel

• Temperatures of 4300-7200 degrees celsius (hotter than the surface of the sun)

• 1300km thick

Mass movement

The process of erosion, transportation and accumulation of material that occurs on a slope due to gravitational forces

What is the case study for a mass movement event in a LIC?

Freetown, Sierra Leone (Aug 2017)

Mass movement event, Sierra Leone 2017 details

• Rapid-onset mudflow

• Followed three days of torrential rainfall

• The area had received almost triple the season’s average rainfall since July 1st

• Deforestation meant fewer trees to absorb water

• Waste was blocking drainage systems

What is the case study for a mass movement event in a HIC?

Pozano, Italy (Feb 2017)

Pozano, Italy (Feb 2017) mass movement event details

• Landslide

• Moving at around 1m/day for almost two weeks

• 7 million cubic metres of soil moved

• Triggered by saturation of slope triggered by meltwater from snow and intense rainfall (81mm between the 6th and 10th of February)

Shear stress

The forces attempting to pull a mass downslope

Factors increasing shear stress

• Removal of lateral support by undercutting

• Removal of underlying support

• Loading of slope

• Lateral pressure

• Transient stresses such as earthquakes or trees moving in the wind

Shear strength

The internal resistance of the slope

Factors decreasing sheer strength

• Weathering effects

• Changes in pore water (saturation, softening of material pressure)

• Changes in structure (remoulding, creation of fissures)

• Organic effects (burrowing of animals, growth and decay of plants)

What are the hard-engineering strategies to stop mass movement events?

• Terracing steep slopes

• Improving drainage

• Erosion control

• Use of restraining substances

What is an example of an earthquake event in an HIC?

Japan earthquake (Tonoku event, March 2011)

Japan earthquake (Tonoku event, March 2011) information

9.0 magnitude earthquake and tsunami

Relatively isolated and largely rural location

Wave heights reached 45m

Japan earthquake (Tonoku event, 2011) social impacts

• Killed between 15,000 and 20,000 people

• Flooded 561km²

• Fukushima power plant meltdown

• 46,000 buildings were destroyed

Japan earthquake (Tonoku event, 2011) economic impacts

• Losses of up to $300B (4% of GDP)

• Only took one year for economy to nearly be back to normal

• Rise in employment in construction-related jobs during rebuilding

• All of Japan’s 50 nuclear power plants were closed

Japan earthquake (Tonoku event, 2011) environmental impacts

• Over 4 million chickens died due to disruption in feed supply chain from overseas

• 23,600 hectares of farmland especially rice paddies were damaged

• 90% of fishing boats rendered unusable

What is a case study of an earthquake event in an LIC?

Haiti earthquake in 2010

One of the poorest countries in the world which had not experienced a comparable earthquake for 200 years

Magnitude 7.0

Haiti earthquake 2010 social impacts

• 200,000 people killed

• 300,000 injured

• 1.5 million people were displaced and by 2017, 55 thousand still lived in temporary camps

• 60% of government buildings and 80% of schools were damaged

• Main airport, ports and paved roads damaged

Haiti earthquake 2010 economic impacts

• Estimated of damage costs range between $8.5B and over $14B

• Damage was DOUBLE GDP!

• 1 in 5 jobs were lost because of damage to clothes manufacturing plants

• Government efforts to restore order were crippled because the quake hit the country’s capital Port-au-Prince

What are some strategies for protecting buildings against earthquakes??

• Seismic dampers

• Tuned mass dampers (big swinging ball in top of building)

• Shock absorbers in foundations

• Vibrating barrier (buried box full of springs)

• Retrofitting buildings

• Specially 3D-printed cement “architectures“ modelled on the claw of the mantis shrimp

What are the secondary hazards associated with earthquakes?

• Tsunamis

• Landslides and other mass movement events

• Transverse faults

• Liquefaction- when saturated soil or sand temporarily becomes quicksand

What are some strategies for defending against tsunumis?

• Tsunami action can be modelled in a lab including its effects on buildings etc

• Regular coastal defences such as sea walls may help

• The Fukushima power plant had the world’s highest sea wall but this was breached by the tsunami in 2011

What is the VEI?

• Volcanic Explosivity Index

• Analogous to the Richter scale for earthquakes

• It is a logarithmic scale from 0 to 8

• Measures the magnitude and intensity of eruption events

What are some secondary hazards associated with volcanoes?

• Lava flow and pyroclastic flow

• Landslides

• Glacial outburst flood

• Lahars (a type of mudflow containing pyroclastic material)

What is tephra?

Fine pieces of rock, glass and minerals (less than 2mm in diameter) that contribute to the ash cloud and acid rain following a volcanic event

Give an example of a volcanic eruption that cooled the earth

The 1991 eruption of mount pinatubo (the Philippines) emitted so much sulfur dioxide into the atmosphere that global temperatures were lower than average for over a year

How are volcanic eruptions predicted?

• Monitoring seismic activity (seismicity)

• Changing SO2 emissions indicate magma moving underground

• Ground deformation

• Thermal monitoring of underground magma flows

What is the case study of a volcanic eruption in an HIC?

2010 eruption of Eyjafjallajokull (E15), Iceland

What type of volcano is E15?

A composite volcano (aka stratovolcano)

2011 eruption of Eyjafjallajokull (E15), Iceland social impacts

• 700 people were evacuated (no deaths), many farms and properties were destroyed and many tourists were stranded in Iceland because flights were grounded

2011 eruption of Eyjafjallajokull (E15), Iceland economic impacts

• Hotel owners and airlines lost out on millions of dollars’ worth of income because of the grounded flights

2011 eruption of Eyjafjallajokull (E15), Iceland economic impacts

• For a period less CO2 was being emitted due to grounded flights

2011 Eyjafjallajokull (E15) eruption profile

• The eruption was caused by rising lava constantly being cooled by the glacier above

• A glassy mix of ice and rock exploded high into the atmosphere where it was caught in a jetstream

• This occured along the constructive plate boundary of the mid-Atlantic ridge

• It had an estimated VEI of 4

What is the case study of a volcanic eruption in an LIC?

2018 eruption of Krakatoa (Indonesia)

What type of volcano is Krakatoa?

A composite volcano (stratovolcano)

2018 Krakatoa eruption profile

• VEI of six

• Occurred along the Pacific rim of fire at the convergence of the Pacific, Eurasian and Philippine plates (convergent boundary)

• The volcano lost 2/3 of its volume

Social impacts of the 2018 Krakatoa eruption

• The deadliest volcanic eruption of the c21st to date, killing minimum 437 people

• Over 14,000 people injured

• Thousands living in camps

• The eruption triggered a tsunami that did not activate early warning systems

• 600 homes damaged by tsunami alone

• Red cross called in

Economic impacts of the 2018 Krakatoa eruption

• Damage to coastal fishing communities, roads, bridges, coastal defences and tourism facilities

Environmental impacts of the 2018 Krakatoa eruption

• Sea turtles were harmed

• All biodiversity on Anak Krakatoa (the island) was wiped out

• Coastal agricultural areas were flooded with salt rendering them unusable

Features of a shield volcano (aka basaltic dome)

• Gentle slope- long lava flows

• Low and wide cone shape

• Made of basalt

• Less violent eruptions with shorter intervals in between events

• Found on constructive boundaries

• eg. Kīlauea (Hawaii)

Features of a cinder cone volcano (aka scoria cone)

• Steep, cone-shaped hills

• Small (100-400m tall) but form extremely fast on convergent plate boundaries

• Bowl shaped craters at peak

• Most common type of volcano

• Explosive, gas-charged ‘strombolian‘ eruptions of basaltic lava

• eg. Volcán de Parícutin, Mexico

Features of a composite volcano

• Tall, steep-sided volcanoes

• Found on destructive plate boundaries

• Violent eruptions with a range of lava compositions

• Can develop secondary ‘parasite‘ volcanoes

• Lava is viscous and solidifies quickly

• eg. Vesuvius, Pompeii, 79 AD

Features of a fissure vent volcano (aka volcanic/eruptive fissures)

• Occur at constructive boundaries

• Produced by eruptions occur along elongated fissures (a few m wide but km’s long) not a central vent

• Usually found connected to shield volcanoes

• Non-explosive; eruptions are usually VEI 1 at worst

• Basaltic lava

• eg. Mount Etna, Italy

Jökulhlaups

Megafloods that occur when volcanoes erupt beneath glaciers and ice caps, creating huge volumes of meltwater (common in Iceland and associated mainly with cinder cone volcanoes)

Focus

The spot the Earth’s surface directly above the epicentre

Epicentre

The underground spot where earthquake activity originates

What are some human triggers of earthquakes?

• Underground nuclear weapons testing (eg. Nevada, 1968)

• Fracking (eg. 2.3 magnitude earthquake in Lancashire 2011)

• Construction of large dams (eg. Rocky Mountains in the 1960s)

• Since 1970 at least 20% of UK earthquakes have been man-made

What is the difference between earthquake intensity and earthquake magnitude?

• Magnitude- measure of the amount of energy released (the same wherever you are)

• Intensity- measure of the shaking and damage caused by the quake (differs from location to location depending on proximity and geology)

What is the Richter scale?

• Quantitative measure of earthquake magnitude

• Logarithmic scale with base factor 10

• From 0-2 (not felt by people) to 8 or above (total devastation)

What is the Mercalli scale?

A measure of earthquake intensity based on the observations of people who experienced it

From I (not felt) to XII (devastation nearly total)

Seismic P-waves

Primary waves caused by an earthquake

They travel fast in a longitudinal fashion causing the earth to compress

Seismic S-waves

Secondary waves caused by an earthquake

They travel more slowly than P-waves

They are transverse waves that shake the ground up and down and from side to side

CANNOT travel through molten rock or liquids

Seismic Reyleigh waves

Waves caused by earthquakes which roll along the ground moving the ground up, down and side-to-side in the same direction the wave is moving

Comparable to waves in a lake/ocean