A Level Geography Tectonic Hazards

Divergent

Whereby two plates pull apart from each other and cause low magnitude earthquakes eg. Dead Sea

Destruction (ocean +ocean)

Frequent earthquakes. Not as bad as ocean+continetal doe. Violent eruptions from curving chains of volcans. E.G Hawaii 2018

Convergent/Destructive

Whereby two plates are moving towards each other, with one subducting under the other due to the subducted plate being of higher density. Causes frequent eruptions and earthquakes eg. Andes Mountains

Destructive (Ocean+continental)

High magnitudinal and frequent earthquakes. Due to long friction+pressure along the subduction zone. Frequaent + violent composite volcanoes. Nazca + South atlantic- chile 2010

Conservative

High magnitude earthquake, shallow focal depth, Highly destructive.+ no volcanic erruption. Pacific Plate. San Andreas fault. 6.9 magnitide in 1689.

Collision

zones where two (continent+continent) tectonic plates converge, leading to mountain building and seismic activity. No volcanic erruption+ high magnitude earthquakes. South Americam earthquake. 2014. 4.9 magnitude.

Constructive

Generally shallow. Low magnitude 5.0 ish. Small and effusive erosions, Low lava and gas but very high viscosity. E.G. Mid atlantic ridge

Conservative

Whereby two plates slide against each other and can cause large earthquakes due to locked faults and elastic rebound theory. eg. San Andreas Fault

Lithosphere

Crust

Asenthosphere

Mantle

Sea Floor Spreading

Occurs at divergent plate whereby new oceanic crust forms from volcanic activity and moves away from ridge. eg. Mid-Atlantic Ridge

Radioactive decay

Process in earths core which releases heat to drive convection currents and causes tectonic activity

Hotspot volcanoes

Volcanoes that form within a plate caused by the existence of mantle plumes

Subduction zone

Whereby two plates are moving together and the denser plate will descend underneath the less dense plate

Locked fault

A fault that is not slipping and can build up pressure that is released in the form of an earthquake and cause cause high magnitude earthquakes due the the elastic rebound theory. eg. Indian Ocean Tsunami

Paleomagnetism

Technique used to track the geological history of plates

Focus

The point within the lithosphere where energy from an earthquake is released

Epicentre

Point directly above focus on the earths surface

P waves

Vibrations caused by compressions at more than 8km/s. Not as destructive

S waves

Vibrations at right angles at about 4km/s. Relatively destructive

L waves

Vibrations along a horizontal plain. Relatively destructive

Secondary effects of earthquakes

Hazards which can occur as a result of earthquakes

Landslide

Occur when soil covering plate moves and causes 70% of earthquake related deaths in the Philippines

Tsunamis

Occur when ocean floor violently displaces water and caused the Boxing Day Tsunami (2004) killed around 250,000 people

Fire

Caused by electric and gas cables breaking from the force of an earthquake and caused 90% of damage in 1906 San Francisco earthquake

Liquefaction

Buildings on top of soil sink due to saturation of sand particles and caused extensive damage in Niigata, Japan (1964) earthquake.. Roads cracked, water mains burst, and buildings tilted or sank. Emergency services were delayed, and rebuilding costs increased significantly due to ground instability.

Basic volcanic eruption

Low silica, low viscosity, low explosivity and high temperature

Intermediate volcanic eruption

Higher silica, higher viscosity, more explosive, less viscous, spews tephra and lower temperature

Acid volcanic eruption

High silica, highly viscous, highly explosive, spews tephra and pyroclastic flows and lowest temperature

Pyroclastic flows (Primary Hazard)

Large, thick clouds of up to 1000 degrees thfurat cause most volcanic related deaths. eg. Killed 60 at Mt. St Helens eruption (1890)

Tephra (Primary Hazard)

Material ejected from volcanoes that creates dust

Lava flows (Primary Hazard)

Fast moving lava that, if it of low viscosity, can travel further and cause a danger to human life. eg. 22% of Iceland died of famine in 1873 after lava flows destroyed crops

Volcanic gases (Primary Hazard)

Volcanoes release, water vapour, CO2, SO2 and Carbon Monoxide which can be dangerous. eg. CO2 killed 1700 people in Cameroon in 1986

Lahars (Primary Hazard)

Mudflows created by heavy rain covered in volcanic material. eg. Mt. St Helens (1980) destroyed 200 homes

Jokulhaups (Primary Hazard)

Floods caused by eruptions that melt surrounding glaciers eg. Iceland eruption (1996) caused '20-30 years of damage'

Composite volcano

Super-volcano with steep cones and highly acidic. eg. Mt. Fiji

Fissure vent volcano

Large crack extending the radius of volcanoes with basic lava. eg. Hawaii

Shield volcano

Low viscosity, slow build up and basic lava. eg. Hawaiian Islands

Acid dome volcano

Highly viscous, created from a dome within lava and acidic. eg. Mt Pelee eruption 1902 which killed 30,000

Cinder cone volcano

Formed by rock fragment cooling from gas explosives, intermediate lava eg. North America

Risk formula

(hazard x exposure x vulnerability)/manageability

Risk definition

The exposure of people to a hazardous event

Components of hazard-risk relationship

Unpredictability, lack of alternatives, dynamic hazards, cost-benefit, 'Russian roulette' reaction

Tectonic event definition

A hazard that adversely effects people

Vulnerability definition

The ability of a community to cope with the impacts of a disaster

When do hazards become disasters?

When 100+ people are killed or injured

Resilience definition

A country's ability to resist, absorb and recover from the impacts of a disaster

PAR model

Disasters occur at the intersection of vulnerability and risk

Degg's model

Shows the interaction between hazards, disaster and human vulnerability, although doesn't show magnitude or locational factors affecting hazard

Hazard profiles

Measures magnitude, speed of onset, duration, areal extent, spatial predictability and frequency of disaster in a subjective manner

Factors affecting exposure to tectonic hazards

Development levels, population density, recovery speed, degree of urbanisation and uninsured losses

Factors affecting development (economic)

Institutions, technology, infrastructure, building regulations, income levels

Factors affecting development (non-economic)

Education, healthcare, housing quality

Importance of governance

Governance affects quality of infrastructure and mitigative measures in place (hazard management cycle) as well as preparedness to deal with hazard and aftermath

Importance of geographical factors

Degree of urbanisation, community spirit, population density and isolationism affects ability of aid in immediate aftermath of disaster to be effective as well as the number of people at risk

Importance of magnitude and intensity

Magnitude and intensity scales can attempt to quantify how powerful a disaster is, although some of these such as the Mercalli Scale are highly subjective. Higher intensity disasters may mean even a developed, well-governed country may remain in relief stage of Park's Model for longer

Factors affecting hazard response

Degree of preparedness, infrastructure, economic wealth, governance, accessibility, hazard type, topography

Disaster mitigation strategies

Modify hazard (defences), modify losses (aid, insurance) and modify vulnerability/resilience (building regs, hazard predictions etc)

OFZ

Ocean Fracture Zone. Earthquake activity along mid

CFZ

Continental Fracture Zone. earthquake activity along mountain range zones

Pacific Rings

A major area in the basin of the Pacific Ocean where a large number of earthquakes and volcanic eruptions occur.

Intra Plate

earthquake occurrences that happen within tectonic plates rather than at their boundaries.

Crustal Fractioning

The process where different minerals separate out from cooling magma, causing the Earth's crust to become chemically different over time (e.g. more silica-rich).

Focal Depth

The depth at which an earthquake originates within the Earth, measured from the Earth's surface to the hypocenter of the seismic event.