Tectonics

What happens at a Constructive plate margin?

• The 2 plates are moving apart

• This causes magma to rise up from the mantle and form new oceanic crust

• This normally happens under oceans

• It forms underwater volcanoes (some are so large you can see them above sea level such as Iceland)

What happens at a Destructive plate margin?

• The 2 plates are moving towards eachother

• The oceanic plate is being pushed under the continental plate as it is denser

• This forms a deep sea trench

• Oceanic crust is melted into magma by the mantle and rises along the fault lines to form volcanoes

What happens at Conservative plate margins?

• The 2 plates are sliding past eachother

• When the plates stick it causes tension to build up

• When this tension is released an earthquake occurs

• The crust is neither created nor destroyed

• Volcanic eruptions DO NOT occur

• (San Andreas fault line in Los Angeles)

What happens at Collision plate margins?

• The 2 plates are moving towards eachother BUT are both continental plates

• Neither plate can be subducted so the crust is crumpled upwards to form Fold Mountains (Himalayas)

What are Infra-plate Earthquakes?

Earthquakes in the middle of plates on fault zones where the tectonic plate is being squashed, forcing the pressure to be released through the cracks.

Energy travels up cracks in the plate and causes an earthquake

(They’re usually weaker, lower energy but they’re shallow focus)

What are Infra-plate Volcanoes?

A hotspot is a plume of super-heated magma in the mantle.

As the plate moves over the hotspot, volcanoes and new crust are created. The plate moves, but the hotspots remain stationary.

How do tectonic plates move?

Convection Cycles, Slab Pull, Ridge Push

What are the properties of the Lithosphere?

• ~100km thick (varies a lot)

• Strong, solid, rigid

• Divided into tectonic plates

What are the properties of the Asthenosphere?

• ~100km thick (varies)

• Several hundered km below surface

• Rock is close to melting point

• Solid mantle - can deform/ flow over long periods

What are the differences in Oceanic vs Continental crust?

Oceanic

• Solid + rigid

• 6-10 km thick

• balsatic rock

• ~3.0g/dm³ density

Continental

• 30-70km thick

• ~2.7g/dm³ density

• Solid + rigid

• mainly granatic rock

Diagram of the Earth:

What are Convection Cycles?

Hot magma rises, as it cools it sinks and moves apart.

What is Slab Pull?

• Subduction zone at destructive margin

• The further the subducted plate goes down, the more it will pull on the rest of the plate from the surface down into the mantle.

What is Ridge Push?

• Construcive plate margin

• The ocean ridge makes the plate heavier, gravity pulls down from the highest point.

• Convection currents open the gap in the crust, the ridge causes it to widen.

What evidence is there of Continental Drift?

Fossils of the same plant/ animal found on different continents

What evidence is there of Paleomagnetism?

• Rocks formed by underwater volcanoes in relation to Earth’s magnetic field

• Mapping suggested the migration of sea floor rocks

What evidence is there of Sea- Floor Spreading?

• Newest rocks near centre of Iceland and oldest at the coast

• Suggested the crust was splitting, expanding in certain places

What are the different forms of Seismic Waves?

• Body Waves

• Surface Waves

What are Body Waves?

Waves that travel from the focus of the earthquake

(Primary and Secondary)

They can travel through liquid (mantle) but not through solid (crust)

They do NOT shake the ground

(They then turn into L and R waves)

What are Surface Waves?

Waves that travel form the epicenter along Earth’s surface. They arive after body waves.

(Long and Rayleigh)

When and how much of an earthquakes energy is released?

95% of an earthquakes energy is released in the first 10 seconds

What is Liquefaction?

• The Earth shakes

• Water under the ground gains energy and begins to move upwards

• Water then penetrates through the sand/soil and onto the surface

What does the building code account for?

Earthquakes NOT Liquefaction

What are the consequences of Volcanic Activity?

• Pyroclastic Flow

• Tephra

• Lava Flows

• Volcanic Gases

• Lahars

• Jokulhaups

What type of Volcanoc does Pyroclastic Flow come from?

Stratovolcanoes

What are the characteristics of Pyroclastic flow?

• Hot → 200-700°C

• Fast moving → 100km/h

• Consists of rock fragments, pumice, ash

• Travels down volcano slopes

• VERY large (~8km wide and ~1km high)

What are the Harmful Effects of Pyroclastic Flow?

Burns, Asphyxiation

What is a recent example of a Pyroclastic Flow?

Mount Merapi (2010, Indonesia)

What type of volcanoes have Volcanic Gases?

Any

What are the characteristics of Volcanic Gases?

Water Vapour (H₂O), Carbon Dioxide (CO₂), Sulfur (SO₂, H₂S)

What are the Harmful effects of Volcanic Gases?

Irritation of the: eyes, nose, throat

Breathing difficulties

Asphyxiation

What is a recent example of Volcanic Gases due to an erruption?

Mount Nyiragongo (DR Congo, 2002 + 2021)

Which type of volcanoes do you find Lahars?

Stratovolcanoes

What are the Characteristics of Lahars?

• ~90°C

• 30-80km/h

• Follows river valleys

• Happens during or after rain

• It’s a mud flow of vlocanic material (rocky debris, water)

What are the Harmful Effects of Lahars?

Burial, Environmental damage, Infrastructure damage, High speed and force

What is a recent example of a Lahar?

Eyjafjallajökull (Iceland, 2010)

How does the UN define a Disaster?

“A serious disruption of the function of a community/ society involving widespred human, material, economic, or environmental losses and impacts, which exceeds the ability of the affected community or society to cope using its own resources.”

What is Insurance groups defiinition of Disaster?

“an economic loss of over $1.5 million.”

What is Degg’s Model of Disaster and Vulnerablity?

Hazardous event + Vulnerable population

What is Hazard Vulnerability?

The susceptability/ exposure to a degree of loss resulting from the occurance of a hazard.

What are some factors that affect Vulnerability?

• Demographics

• Population size/ density

• Development

• Governance

• Preparedness

• Infrastructure

• Communication

What is the Risk equation?

Risk (R) = Hazard (H) x Vulnerability (V) / Capacity to Cope (C)

What is the Pressure And Releaser model?

PAR model looks at underlying causes of a disaster. Based on the idea that a disaster happens when two opposing ‘forces‘ interact.

Vulnerability starts with Root Causes, through a series of Dynamic Pressures, these root causes can lead to Unsafe Conditions.

What is Resilience?

The ability to protect lives, livelihoods, and infrastructure from destruction, and to restore areas aftera natural hazard has occurred.

What factors into an Increase in Resilience?

• Good communication

• Pre-planning

• High quality health care

• Member of a Trade Bloc

• High GDP per capita

• Stringent building regulations

• Rehearsed emergency procedures

• Low doctor to patient ratio _{^{(D:P 1:10 > 1:1000)}}

• ‘Open’ political regime

What factors into a Decrease in Resilience?

• Government corruption

• Poor emergency services

• High population density

• Low access to education

• Foreign Debt repayments

• High rural to urban migration

• Lack of skills

• Unmaintained roads

• Energy insecurity

• High unemployment

• Rapid population growth