Fragile World

Question 1

1. Explain how evidence supports Plate Tectonic Theory

Answer 1

Evidence of plate tectonic theory is proven by the fact some continents fit together like a jigsaw puzzle. Eg. South America and South Africa. It is believed there was one continent called Pangea before continental drift, which occurs because of convection currents under the tectonic plates. Due to radioactive decay temperature in the core (5500c°) cause rocks in the mantle to heat up become less dense and rise. Without the core heating it the rocks in the asthenosphere become more dense cool and sinks back to the core which re-heats it. Evidence of this is During this powerful process the tectonic plates are slowly moved.

Or

One piece of evidence about geological patterns to prove plate tectonics is the facts that Antarctica has coal in it. Coal is formed in war environments around the equator so Antartica’s plate tectonic must have once been around the equator with high latitude like seen in Gondwana and now it has moved down with its plate due to continental drift caused by convection currents.

Fossils: animals such as mesosaurus was found in south africa and south america, these animals could not swim across continents

Question 2

2. Explain why earthquakes and volcanoes are found along plate boundaries

Answer 2

Earthquakes and volcanos are found along plate boundaries because of tectonic plates moving by convection currents driven by radioactive decay in the core.

• A convergent boundary occurs where two plates are pushing toward each other eg: Nazca Plate and the South American causes both big and small earthquakes and big and no volcanoes depending of the type of crust
• A divergent boundary marks two plates that are moving apart from each other eg: North American and Eurasian causes small volcanoes and small Earthquakes

-A transform boundary occurs where two plates slide past each other eg:
Pacific Plate and the North American causes large earthquakes e.g the san adres fault

Question 3

3. Explain how earthquakes and volcanoes occur at Destructive plate boundaries

Answer 3

At a destructive plate boundary

• Less dense Continental plate (e.g. South American plate) moves towards Oceanic plate.
• Denser Oceanic plate (e.g. Nazca plate) is forced below the continental plate
• Lighter continental crust remains at the surface but crumples into fold mountains e.g. Andes due to the subduction pushing the plate upwards
• Pressure builds up at the subduction zone – friction causes melting of oceanic plate and can cause earthquakes when friction is released. The eroded continental plate and sea water causes the magma to be high in silica and thus viscus.
• Molten rock (magma) builds up in the chambers. Because the magma is Less dense it rises up the fissure but the high viscosity means it solidifies on the way up
• when the pressure builds up magma escapes through a composite volcano

Question 4

4. Explain how earthquakes and volcanoes occur at Constructive plate boundaries

Answer 4

At constructive plate boundaries

• powerful convection currents within the mantel (heated by radioactive decay) are moving the 2 plates (N America and Eurasia plate) apart at 2cm a year
• A gap appears between the crust as the two plates start to diverge. The mantle starts to rise and consequently pressure decreases and the upper part of the mantle starts to melt
• Magma rises steadily through the gap and forms shield volcanoes (mostly submarine and small the volcanos are frequent but has low silica levels and is very runny so not dangerous)
• As the magma is cooled by the water it solidifies and sea floor spreading occurs and new crust is formed over the atlantic (this created the 16000km long mid-atlantic ridge). Islands like (iceland) are formed over millions of years

Question 5

5. Explain the effects of the Montserrat volcano (including facts)

Answer 5

Some major effects of the Monserrat volcano include primary social factors such as the population declined from 12000 to 3000 because of the risk. The GDP went down by 15% as most the people who stayed couldn’t afford to leave. An ageing population has been created as younger people have seen no economic future to return too

Plymouth (capital) under 12m of ash (social) – vegetation was damaged by the ash – however good soil fertility (economic) – health issue with silicosis for quartz in volcanic ash

Question 6

6. Explain why human and physical factors caused the Haiti earthquake to be so destructive

Answer 6

Hati has a conservative fault going through it which increased the likely hood for earthquakes one of which focus was shallow (8km - 10km form focus to epicentre) so their was no crust for the shock waves to dissipate into. The densely populated capital (per km2 <500 people) which was only 15kms from the high magnitude (7 on the richter scale) epicentre could have prepared for the earthquake.

During this time Hati was in 4.5bn dept and any country so poor is vulnerable to corruption. Hati is 160th worst country in terms of corruption which caused not enough attention to be payed to building codes such as seismic design. Low building quality like the slum Cité Soleil caused primary factors like 100,000 houses 45% of commercial buildings were destroyed when the earthquake struck. This had massive secondary social impacts such as 1.3 mil being homeless and no aid being able to get through the fallen buildings. This all lead to an increase in poverty from 50% to 80% total poverty.