Geography Yr 9 Flashcards
Explain how evidence supports Plate Tectonic Theory
Pangea
Alfred Wegener
Jigsaw fit
Radioactive decay in the mantle drives convection currents which can move tectonic plates slowly
Fossils: animals such as mesosaurus was found in south africa and south america, these animals could not swim across continents
Geological patterns coal can only be found in dense jungle and it has been found in south america and Antarctica
Palaeomagnitism: every 100mill years iron particles switch from North to South and that can bring areas of land with them as they switch
Explain how earthquakes and volcanoes occur at Destructive plate boundaries
Continental and Oceanic crust collide
Oceanic is denser so it subducts and brings with it sand and silica
Continental buckles like a car bonnet after crash and creates fold mountains
Lots of friction in the subduction zone, melts oceanic plate
Rest of oceanic plate is melted in the magma chamber
The magma caused be friction rises because it is less dense
Magma is high in silica ( very viscous ) cools and gets blocked
Pressure builds
Massive, explosive volcano erupts 🤎🤎🤎🤎
Explain how earthquakes and volcanoes occur at Constructive plate boundaries
Powerful convection currents are moving two divergent plates apart
This is called sea floor spreading
Eg North American plate and Eurasian plate
As gap appears underwater, mantle moves upwards and as pressure decreases the lava starts to solidify
These are non violent because they have low silica levels
These create shield volcanoes
An example is the Atlantic ridge which stretches 16,000km
Explain the effects of the Montserrat volcano (including facts)
Pyroclastic flows Lahars Lava Ash Volcanic bombs
Characteristics of pyroclastic flows
Pyroclastic flows: clouds of hot gas and rock, spread laterally due to gravity, 1000 degrees, travel at 350mph
Characteristics of lahars
Lahars: mud which mixes with water, ash and volcanic material after eruption, thickness of cement, destroy everything in their path, scalding water, 30-50mph
Characteristic of lava
moves slowly, destroys everything in their path, 700-1200 degrees
Characteristics of ash
after initial explosion ash travels in air, starts fires and burns
Characteristics of volcanic bombs
Volcanic bombs: blasted out of volcano, larger that 60mm in diameter, acquire aerodynamic shapes as they cool in wind
Convection currents
In mantle powerful radioactive decay drives convection currents
In mantle, rock nearest the core heat, become less dense and rise
Temperatures in the upper mantle ( asthenosphere ) are cooler and rock cools
As it cools it becomes less dense and sinks downwards
This process happens agains and has the power to move continents
Why are earthquakes and volcanos found along plate boundaries
Volcanos and earthquakes are found along convergent ( destructive ) plate boundaries and divergent ( constructive ) plate boundaries
By how much did the population fall after the Montserrat volcano
The population fell from 12,000 to 3,000 due to risk
Three good effects after the Montserrat volcano
Tourism has increased after the National Geographic rated it the top trip of 2010
Volcanic ash has improved soil fertility
Volcanic ash was quarried and sold abroad and Montserrat now earns income from that
How many casualties was there
19 people died and 7 people were injured
What happened to large areas
Large areas including the capital Plymouth were buried under 12 meters of ash
How many villages were destroyed
12 villages and 2/3 buildings were destroyed
What happened to the health of crops and citizens of montserrat
Volcanic ash damaged and destroyed crops and vegetation
The ash carried quartz which if inhaled can cause a respiratory disease called silicosis
What were the physical factors of the Haiti earthquake
The focus was shallow ( 8 - 10km ) no t much ground for shockwaves to dissipate
The epicentre was right next to capital ( port-au-prince ) ( 15km southwest )
The earthquake was a magnitude of 7 on the richter scale
What were the physical factors of the Haiti earthquake
They were corrupt ( 160th worst country on corruption )
Citizens earned the equivalent to 85p a day
They violated the seismic code so their buildings were not earthquake safe
Port-au-prince was densely populated
The life expectancy was 60
They did not learn from previous earthquakes ( port-de-paix 1994 )
70% population is unemployed
Haiti has a debt of $4.5bln
