Paper 1: geophysical hazards

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

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

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

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

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

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

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

The direct transmitssion of heat through the material of a substance

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

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

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

• The layer of the earth underneath the crust

• Molten

• Mostly silicates

• 2800km thick

• Temperatures of between 870 and 3700 degrees celsius

• Layer of the earth between the mantle and inner core

• 2200km thick

• Liquid iron and nickel

• Temperatures of 3700-4300 degrees celsius

• Innermost layer of the earth

• Solid iron and nickel

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

• 1300km thick

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

Freetown, Sierra Leone (Aug 2017)

• 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

Pozano, Italy (Feb 2017)

• 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)

The forces attempting to pull a mass downslope

• 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

The internal resistance of the slope

• 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)

• Terracing steep slopes

• Improving drainage

• Erosion control

• Use of restraining substances

Japan earthquake (Tonoku event, March 2011)

9.0 magnitude earthquake and tsunami

Relatively isolated and largely rural location

Wave heights reached 45m

• Killed between 15,000 and 20,000 people

• Flooded 561km²

• Fukushima power plant meltdown

• 46,000 buildings were destroyed

• 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

• 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

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

• 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

• 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

• 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

• Tsunamis

• Landslides and other mass movement events

• Transverse faults

• Liquefaction- when saturated soil or sand temporarily becomes quicksand

• 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

• 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

• Lava flow and pyroclastic flow

• Landslides

• Glacial outburst flood

• Lahars (a type of mudflow containing pyroclastic material)

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

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

• Monitoring seismic activity (seismicity)

• Changing SO2 emissions indicate magma moving underground

• Ground deformation

• Thermal monitoring of underground magma flows

2010 eruption of Eyjafjallajokull (E15), Iceland

A composite volcano (aka stratovolcano)

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

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

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

• 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

2018 eruption of Krakatoa (Indonesia)

A composite volcano (stratovolcano)

• 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

• 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

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

• Sea turtles were harmed

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

• Coastal agricultural areas were flooded with salt rendering them unusable

• 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)

• 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

• 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

• 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

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)

The spot the Earth’s surface directly above the epicentre

The underground spot where earthquake activity originates

• 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

• 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)

• Quantitative measure of earthquake magnitude

• Logarithmic scale with base factor 10

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

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

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

Primary waves caused by an earthquake

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

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

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