Global Hazards Flashcards
Describe the volcanic eruption that occurs on constructive boundaries
On a constructive boundary two plates are pushed away from each other. The eruption is gentle. A shield volcano is created on a constructive boundary, the magma is more fluid than other boundaries.
Describe the eruption that occurs on destructive boundaries
On a destructive boundary two plates are pushed towards each other. The eruption is very violent. Composite volcanoes occur on a destructive boundary. The magma is much more vicious or sticky.
Oceanic crust
Thin (5-10km)
More dense (heavy)
Young (under 200 million years old)
Continental crust
Thick (30-200km)
Less dense (lighter)
Old (up to 3.8 billion years old)
Describe the inner core
Thick solid ball of iron (with some nickel)
Same temperature of the surface of the sun
Heaviest layer
Describe the mantle
Thick layer of rock (partly melted, partly solid)
Movement here moves above the crust
Describe the crust
The layer we live on
Light, thin skin of the rock around the earth
Around 8-65km thick
Describe the outer core
This is made up of liquid metal below the mantle
Describe how a Destructive plate boundary forms
Dense oceanic and less dense continental plates meet.
They lock together and pressure, energy and friction builds up. They eventually break free and the denser the oceanic plate is forced under (subducted) the continental plate. This huge release of energy is an earthquake. This also generates heat so the oceanic plate melts. The new magma rises through the continental plate, into the volcano.
Describe how a conservative plate boundary forms
Two plates move against each other (either in the same of opposite direction). They lock together and energy builds up. The energy is eventually released as ‘shockwaves’ sending energy out in 360 degrees. This energy causes the ground to shake. Energy reaches the surface, firstly at the ‘epicentre’. These earthquakes are very violent and powerful.
Describe how a constructive plate boundary forms
Two plates move apart due to convection currents. As they move apart a ‘gap appears’ in the crust. This movement of enormous plates creates an earthquake. Magma rises up through the gap and erupts. Eventually the new lava builds up and forms ridges either side of the gap. These are called ocean ridges. It happens on land, rift valleys are formed.
Describe how a collision plate boundary forms
Convection currents in the mantle move two plates towards each other. The ground ‘buckles’ and reshapes under this pressure. As they push, pressure and energy builds up. They are both the same density, so they collide, and push up against each other. This energy is eventually released as ‘shockwaves’ causing an earthquake to occur. Fold mountains are a feature of the boundary.
What is a hotspot?
- occurs away from plate boundary, when plate moves past a particularly hot part of the mantle
- hot magma rises and punches through weakness of crust causing volcanic eruption
Explain convection currents
- core heats magma in lower mantle, rises as hot material is less dense
- nears the crust a cools becomes more dense and sinks
- as sinks, drags or pulls plate with it
Composite volcano
- destructive boundary
- explosive eruption
- aa lava
- steep side, layers = ash and lava
- cone shape
Shield volcano
- constructive boundary
- magma is runny and less vicious, travels far
- quiet eruption
- pahoehoe lava
- gentle slope
Caldera volcano
- forms when volcano erupts so violently, magma chamber empties, crater collapses into itself
- new cone forms as magma rises again
Fissure volcano
- constructive boundary
- no cone to erupt from but lava erupts along a linear crack in crust
Earthquakes
- occur at all boundaries
- point in crust where plate jolts after locking is where eq begins (focus)
- seismic waves released in 360 degrees
- point directly above focus = epicentre (ground shaking will be worst here
- If the focus is deep wave lose more energy by the time they get to the epicentre
Primary impacts for Earthquakes
- ground shakes
- collapsing building
- death
- snapped water, gas and electricity pipes or cables
Secondary impacts for Earthquakes
- tsunamis
- homelessness
- looting (stealing)
- bereavement and grief
How can a tsunami be formed because of an earthquake?
- crust beneath ocean jolts up or down
- creates wave of enormous energy
- shaking causes water from below surface to rise up
- particles of rock shake to become fluids
- causing buildings and cars to sink
Earthquake building design (Taipei 101)
- skyscraper in Taiwan
- located 200m from a major faultline
- has ‘turned mass damper’ or pendulum that swings it the opposite way of ground movement
Earthquake early warning system - Shakealert
- app on smartphone allowing app to use gps
- identifies eq from p waves
- calculates how much ground will shake from p waves and following s waves
- sends warning with time warning about strengths of both waves
Low air pressure
- rising air
- cools
- condenses
- clouds
- rain
High air pressure
- sinking air
- no condensation meaning no clouds
- no rain
Drought definition
a prolonged period of low rainfall leading to a water shortage
Physical causes of droughts
dry high pressure weather systems block low pressure systems from arriving and bringing rainfall
La Nina
- more extreme storms
- more extreme droughts
- in normal locations
El Nino
- wind and pressure reversed to La Nina, so West gets wetter and East gets wetter
