Flashcards in Tectonics Deck (49)
- the lines where tectonic plates meet are called the plate boundaries.
Name the four types of plate boundary
- convergent (destructive)
- divergent (constrictive)
- transform (conservative)
- intra plate
Where do most powerful earthquakes occur?
Where do most volcanoes occur?
- intraplate (hotspots)
What are hotspot volcanoes and where do they occur?
- areas on the mantle where heat rises as a thermal plume from deep in the earth, low pressure and high heat in the tectonic plate leads to the melting of rock which rises through cracks as magma to form a volcano.
- form at intra plate boundaries
What is the mid Atlantic ridge and its hazards?
- divergent (constructive) plate boundary
- forms volcanic islands
Why are some at more risk to earthquakes than others?
- closer to plate boundaries
Difference between oceanic and continental plates
- oceanic underneath sea floor, dense basalt
- continental underneath land, less dense granite
Why do plates move?
- convectional currents
3 processes that occur at convergent boundaries
- volcanic activity
What is paleo magnetism and how does it help in the study of plate tectonics?
- the study of the magnetism in rocks induced by the earths magnetic field
- helped back up the continental drift hypothesis and its transformation into plate tectonics.
What is a locked fault?
- a fault hat isn't slipping as the frictional force is greater than the stress on the rock
- when it does slip can cause a larger earthquake
What is the Benioff zone?
- an inclined zone underneath convergent plate margins where the oceanic crust is subducted.
Hypocentre and epicentre
- hypocentre point within earth where earthquake originates
- epicentre pint on earth surface where earthquake originates
Intensity vs magnitude of earthquake
- intensity , severity of shaking assessed using modified mercalli scale
- magnitude, size of earthquake using Richter scale
Describe the three types of seismic waves
- arrives first, longitudinal, travels through solid rock and fluids.
- slower than p wave, transverse, only moves through solid rock
- only travels through surface of crust, fastest of surface waves, moves form side to side as it moves forward
- only travels through surface of crust, rolling motion, slower than love wave, ground moved up and down and side to side.
Secondary hazards associated with earthquakes
Seismic waves loosen rocks of steep slopes, loses cohesion and falls due to gravity.
Lowland areas where shaking sorts the ground material to the point where it acts as a fluid.
Describe how 3 primary volcanic hazards affect people
- Lava flows
Burns and covers everything in its path and when moving quickly can burn humans.
- emissions of gases or steam (phreatic eruption)
Can pollute water sources and cause mass fatalities as a large amount of co2 in the air reduces oxygen.
- pyroclastic flow
Rock fragments and hot gases, 900 degrees Celsius can cause death and destruction of cities e.g. Pompeii
What are jokulhlaups and why are they hazardous
- a jokulhlaup is a flood of meltwater issuing from underneath an ice cap or glacier, forming when a volcano erupts underneath the ice and melts the ice so it forms a lake.
- the water bursts out carrying blocks of ice, this can lead to it wiping out roads and bridges, e.g. Iceland main road along the south coast been cut and bridges washed away.
What is meant by vulnerability
- the weaknesses of people in a situation where they are exposed to risk e.g. A tectonic hazard.
What is meant by resilience
- the ability of a community to resist the impacts of a hazard by adapting and recovering
What is the hazard risk equation
risk = hazard x vulnerability
- an equation used to show the risk to people
What makes a hazard into a disaster
- the United Nations suggest 500 or more deaths is a disaster.
Name the 2 pressures in the pressure and release model
- (dynamic pressures)
Lack of skills
Lack of training
What are the main economic impacts of tectonic hazards
- damage to infrastructure
- halt to agricultural activities
- collapsed buildings less business higher unemployment less tax
Explain the possible link between the capacity of a country to cope with a hazard and its level of development
- urban governments of rapidly growing cities can plan ahead to reduce vulnerability
- poorer countries with poor governance such as Haiti have poor capacity and cannot reduce vulnerability
Why are the impacts of earthquakes generally greater than those of volcanoes
- fast speed of onset
- impacts larger area
What does VEI stand for and what does it measure
- volcanic explosivity index
- measures how explosive a volcanic eruption is using style of past activity, plume head and height of spreading.
Name the six characteristics commonly used in producing a tectonic hazard profile
- high magnitude
- speed of onset
- areal extent
- spatial predictability