plate techtonics and Christchurch Flashcards
Risk
Is the probability of a hazard happening and creating a loss of lives
Vulnerability
describes the risk of exposure to hazards combined with an inability to cope with them
Resilience
the degree to which the environment can absorb a hazardous even
3 ways to increase capacity to cope
- having emergency evacuation
- using earthquake proof buildings
- land use planning
2 Social impacts of the Christchurch earthquake
- 184 people were killed and over 1500 injured in 2011 quake
- 4 months after the earthquake around 50,000 Christchurch residents had moved permanently to other parts of NZ or Australia. (worse sense of community)
(however in the long term there was a net increase in population do to employment opportunities in recovery)
2 economic impacts of the Christchurch earthquake
- Some potential tourists may not travel to Christchurch now as the rugby World Cup could no longer be hosted (no multiplier effect)
- Total loss to the NZ economy was estimated as £16 billion, which is about 13% of GDP
2 Responses to the Christchurch earthquake
- Christchurch used land use planning with
The Green Zone – about 100,000 houses located here and these are likely to be rebuilt. However they are ‘rebuilt better’ – to reduce the impact of liquefaction the foundations are strengthened and piles can be driven 25m down to reach solid ground.
· Red zone – the worst affected residential areas – many along the valley slopes of the River Avon close to the inner city. Land in this area suffered badly from Liquefaction. The government agreed to buy over 5000 of the worst affected properties or the land on which they were built.
- In the first few months much of the CBD of Christchurch was converted into a complex of shipping container boxes, each replacing services like shops, banks and fast food outlets
focus
where the pressure from underground is released
epicenter
the point on the ground directly above the focus
Constructive plates
they move apart
destructive plates
two plates move towards each other resulting in the denser of the two plates to subduct causing friction
——–>
Conservative plates
Plates move in the same direction at different speeds. Friction the to get stuck. As pressure builds over time its can rebound and cause an earthquake.
- ————————->
- —————>
how does sea floor spreading occur
ocean ridges
Seafloor spreading occurs at divergent plate boundaries.
1. As tectonic plates slowly move away from each other, heat from the mantle’s convection currents makes the crust more plastic and less dense.
- The less-dense material rises, often forming a mountain or elevated area of the seafloor.
- Eventually, the crust cracks. Hot magma fueled by mantle convection bubbles up to fill these fractures and spills onto the crust. This bubbled-up magma is cooled by frigid seawater to form igneous rock. This rock (basalt) becomes a new part of Earth’s crust.
how do volcanos occur at subduction zones
- oceanic crust is melted when submerged into the magma
- as it is light and dense it rises up back into the continental crust
- these volcanoes are much more upright as the lava is andesitic which is more viscous and more explosive
example of composite volcanoes
mt Șt helens in North America
steep sided
where is the ring of fire
around the Pacific Ocean as it is a destructive plate boundary
what type of plate boundary do rift valley’s formed
the occur at continental constructive plate boundaries
eg east African Rift Valley
These valleys are formed when the lithosphere stretches, causing it to fracture. The land between these faults then collapse into deep, wide valleys which are separated by upright blocks of land called horsts
how are ocean ridges formed
The Ocean Ridge is formed when magma rising between diverging plates of the lithosphere cools and forms a new layer of crust.
slab pull
This is simply the weight of the tectonic plate being subducted (pulled) below the overlying plate dragging the rest of the plate along behind it.
ridge push
heat expelled by the magma expand the lithosphere and asthenosphere at the ridge, pushing them the surrounding ocean floor.
explain the process of liquefaction
- Liquefaction occurs when compacted sediments loses strength as a result of the stress such as shaking during an earthquake
- material that is usually solid acts like a liquid
- this loss of structure can cause damage to building as it acts like quicksand
why was the preparation in Christchurch poor
The government was unaware of the plate boundary as the the boundary was covered by alluvium and therefore seismometers could not detect tectonic movement
how do island chains form
- island arcs are long chains of activity volcanoes (Hawaiian islands)
- A hotspot is caused by a concentration of heat energy at the core of the Earth which is constantly heating the mantle above,
- creating rising magma plumes through the cracks and a volcano may be caused
- as the pacific plate moves at a northwesterly direction hotspot goes over more areas more volcanoes form
features of shield volcanoes shield volcanoes formed
- usually form at constructive plate boundaries
what is a hazard
a potential risk to life or property
examples of a land feature of a continental continental constructive plate boundary
- east African Rift Valley
as the Somali plate moves apart from the African plate continental crust stretches and as it becomes weaker it drops down to create a valley.
magma can penetrate and form volcanoes
examples of destructive plate boundaries in oceanic oceanic
Mariana island
examples of constructive plate boundaries in oceanic oceanic
mid Atlantic ridge
examples of destructive continental continental
Himalayas
