TECTONICS - everything else Flashcards
what is a divergent plate margin?
- divergent plates move apart
- make new land
- cause holes where magma spits through the crust
- gentle volcanic eruptions which have runny lava rather than explosive lava
what is another name for a divergent plate margin?
constructive
how are divergent plates formed?
convection currents cause the plates to move apart
- as they move the magma wells up from the mantle to form new plate
Explain the processes that take place at divergent plate boundaries (4)
Divergent plate boundaries are when two plates move away from each other. The plates move due to convection currents in the mantle. The movement can cause a gap called a mid-oceanic ridge. Magma rises to fill the gap, thus creating new land. Where magma builds up above the surface of the ocean, volcanic islands form. If a constructive (divergent) margin is found on the land a rift valley will be formed.
what is a destructive plate margin for continental and oceanic and how is it formed?
- dense oceanic plate subjects under the continental plate (becomes subduction zone)
- magma rises due to convections currents and heat
then rises through the cracks in the continental crust - pressure builds and may cause volcanic eruption
- as plates such together continental is squashed and forced upward
- creates fold mountains
- lava solidifies to create volcano
what is a destructive plate margin for continental and continental and how is it formed?
- When continental plates collide head on with other continental plates, the result is upheaval!
- Similar densities – neither plate is subducted
- Gradual forward movement of each plate creates extreme pressures= earthquakes
- Over time, the rock strata (layers) become folded, and rise to create mountain ranges
what is the conservative plate margin and how is it formed?
when plates move oppositely or at different paces/angles
• As the plates slide horizontally past each other pressure builds up in the rocks either side of the fault
• Fault surface often rough – friction creates large strains along the faults
• An earthquake happens when the built up pressure and energy are released in a sudden, jerky movement
how do you define what type of volcano it is?
activity levels
- Active: have erupted in the last 80 years - Dormant: resting but may erupt in the future - Extinct: dead and will not erupt again
what are characteristics of a shield volcano?
- broad peak
- wide long slopes
- runny lava
- gentler eruptions
- gentle slopes
- on a constructive plate boundary
what are characteristics of a composite volcano?
- cone shape, steep sides
- has main vent and secondary vents
- big lava flow of andesitic sticky magma
- volcanic bombs, so flying rock etc
- ash cloud
- has alternate layers of ash and lava
- violent eruptions
difference between andesitic and basaltic magma
- andesitic is lower in temp, more acidic and very sticky
- basaltic is high in temp, non-acidic and very runny and fluid
what is another name for a composite volcano ?
stratovolcano
where are shield volcanoes found?
divergent plate boundaries
where are composite volcanoes found?
convergent, where oceanic plate subducts
what is another name for convergent plate boundary?
destructive - oceanic and continental
what is an earthquake?
- a violent shaking of the earths crust
how are earthquakes measured?
- They are measured by something called the Richter scale, this is based on the energy levels or the strength (table to the side)
- The Mercalli scale measures how much damage is caused by the earthquake based on observations, it basically measures its impact on people.
how is The Richter scale used?
Open ended scale indication the strength of an earthquake measured by a seismograph, its an actual scientific measurement.
how is the Mercalli scale used?
- A scale from roman numerals 1 -12, used to indicate the impact and effects of an earthquake.
why do earthquakes and volcanoes cause more damage in LEDC’s than MEDC’s?
- LEDC’s dont have resources to cope
- bad buildings and infrastructure
- no buildings regs
- poverty
- government has little money to deal with it
- MEDC’s have more resources, more stable government etc
- have building regs and better things
what is the focus of an earthquake?
- point at which the rock moves
where do the seismic waves of an earthquake start?
start at the focus
what is the epicentre of an earthquake?
directly above the focus on the earth’s surface
what are management techniques for volcanoes and earthquakes?
prediction and preparation
how do they predict a volcano?
volcanologists
- seismometers
- thermal imaging
- gas samples and sensors
how do they prepare for a volcano?
detailed planning
- exclusion zones
- evacuation
- basic provisions
- good communication systems
how do they predict earthquakes?
they aren’t easy to predict
- they can measure the vibrations and plate movement but its still not super reliable
how do they prepare for an earthquake?
- training people, earthquake drills
- emergency kits
- earthquake proof buildings
- roads and bridges that are earthquake proof
what increases as the river progresses?
discharge channel width channel depth velocity load quantity
what decreases as the river progresses?
load particle size
bed roughness
gradient of the river
