A Level Edexcel Tectonics Enquiry Question 1

[1.1A] What is the global distribution of earthquakes, volcanic eruptions and tsunamis?

Earthquakes:

- Most Earthquake zones are found at, or close to tectonic plate boundaries.

- About 70% of all earthquakes are found in the "Ring of Fire" in the Pacific Ocean.

Tsunami:

- The global distribution of a tsunami is fairly predictable in terms of source area, occurs at or close to tectonic plate boundaries where water is situated.

Volcanic Eruptions:

- These also occur at, or close to tectonic plate boundaries, with the exception of hotspots such as that by Hawaii.

[1.1A] What are the causes of earthquakes?

- Constructive plate boundaries only result in small magnitude earthquakes as there's not much friction or strain as the plates diverge away from each other.

- Transform plate boundaries have a large amount of friction, and when the energy is released, the shockwaves can be strong.

- A converging plate creates large amounts of friction and strain, and usually creates high magnitude earthquakes.

[1.1A] What are the causes of volcanoes?

- Volcanic activity is found at constructive plate boundaries, as mantle material moves upwards to fill the gaps left by diverging places.

- Volcanoes, can also be found in fold mountains because unstable mantle material and melted oceanic plate forced their way to the surface.

[1.1A] What are the causes of tsunamis?

- This is an upward or downward movement of the crust which disturbers mass of a seawater.

- It is associated with an undersea earthquake, and so is usually linked to a destructive plate boundary.

[1.1B] What is the distribution of plate boundaries?

Most plate boundaries are located around the coast, or in the sea. It's rare for there to be a plate boundary in land.

[1.1C] What are intra-plate processes?

This is when earthquakes can occur near the middle of plates.

- The cause isn't fully known, but it is believed the plates have pre-existing weaknesses become reactivated, causing seismic waves.

- For example, if solid crust has weakened over time and cracks under pressure.

- Small movements build up friction and strain over time, which is usually released small magnitude earthquakes.

[1.1C] How are volcanoes linked with hotspots from mantle plumes?

There can be volcanic activity near the centre of some plates (known as hotspots).

- This can be result of the upwelling of hot molten material from the core/mantle boundary.

- It could be also as a result of isolated plumes of convecting heat, called mantle plumes rising towards the the asthenosphere.

- As the tectonic plate moves over the hotspot, it can generate volcanoes.

[1.2A] What is the tectonic theory?

The lithosphere is split into seven larger plates, and they fit together in a constantly moving jigsaw of rigid lithosphere. They move slowly through continental drift, which is caused by convection currents.

[1.2A] What's the earth's structure?

Inner Core:

- Solid.

- Temperatures around 7000 degrees.

- Very dense.

Outer Core:

- Liquid.

- Temperatures from 4400 to 6100 degrees.

- Dense.

Mantle:

- Solid and liquid layers.

- Temperatures around 870 degrees.

- Less dense.

Crust:

- Solid.

- Less dense than the mantle.

- Temperature around 400 degrees.

[1.2A] What is the asthenosphere and lithosphere?

Asthenosphere:

- The asthenosphere is a dense but weak area located below the lithosphere. Between 100-400km below the surface.

Lithosphere:

The coolest and most rigid part of the earth, what we stand on. It is divided into 15 major tectonic plates.

[1.2A] How does mantle convection work?

This processes occur in the asthenosphere only.

1. Heat from inner core travels through mantle into asthenosphere.

2. Hot magma rises because it becomes less dense with heat (as particles spread out).

3. Magma is cooler at the top as it is further away from the heat source. It becomes more dense and sinks to the bottom.

4. Cooler magma is reheated, so it starts to rise again. Creating a loop called a convection current.

[1.2A] What is slab pull?

Slab pull is the pulling force exerted by a cold, dense oceanic plate plunging into the mantle due to its own weight. This occurs at destructive margins.

[1.2A] What is subduction?

This is when an oceanic plate is forced below continental plate, due to the oceanic plate being more dense than the continental plate. This occurs at destructive margins.

[1.2A] What is palaeomagnetism?

When new igneous rocks, including lavas cool form solid rock, the minerals align themselves with polarity after solidifying. It is the study of rocks.

- Geological records of magnetic directions are symmetrical either side of constructive plate boundaries, proving that oceanic crust has been diverging (moving apart) in places for a very long time.

[1.2A] What is seafloor spreading?

The formation of new areas of oceanic crust, which occurs through the upwelling of magma at mid-ocean ridges and its subsequent outward movement on either side.

[1.2B/C] What is the Benioff zone?

This is the zone where earthquakes occur. This is a zone of earthquake activity created by the friction between the two plates.

[1.2B] What processes occur at destructive (convergent) plate boundary between the continental and oceanic plate?

- The denser oceanic plater subducts below the continental, and slab pull occurs.

- Friction is created between the two plates as they subduct in the Benioff zone, creating seismic activity.

- The oceanic crust is melted as it subducts into the asthenosphere.

- The extra magma causes pressure to build up.

- This pressurised magma can force itself through weak areas in the continental plate.

- Rarely, explosive, high pressure volcanoes may form.

- Fold mountains can also occur here when sediment is pushed upwards during subduction.

[1.2B] What processes occur at destructive (convergent) plate boundary between the oceanic and oceanic plate?

- The heavier plate subducts leaving an ocean trench, but also fold mountains will occur here.

- The built up pressure causes underwater volcanoes, which bursts through oceanic plates.

- Lava cools and creates new land called island arcs.

[1.2B] What processes occur at collision (convergent) plate boundary between the continental and continental plate?

- Both plates are not as dense as oceanic, so lots of pressure builds.

- Ancient oceanic crust is slightly subducted, but the continental crust does not subduct.

- Pile up of continental crust on the lithosphere, forming fold mountains.

[1.2B] What processes occur at constructive (divergent) plate boundary between the oceanic and oceanic plate?

- Magma rises in between the gap left by two plates separate, forming new land when it cools.

- Less explosive underwater volcanoes form as the magma rises.

- New land forming on the ocean floor by lava filling the gaps is known as sea flood spreading.

[1.2B] What processes occur at constructive (divergent) plate boundary between the oceanic and continental plate?

- Any land in the middle of the separate is forced apart, causing a rift valley.

- Volcanoes forms where the magma rises.

- The gap will most likely fill with water and separate completely from the main island.

[1.2B] What processes occur at transform (conservative) plate boundary between the continental and continental plate?

- The parallel plates move on different direction.

- No plates are destroyed.

- When these plates moved, a lot of a pressure and friction is built up, causing frequent earthquakes.

- On the continental crust, fault lines can occur where the group is cracked by the movement,

[1.2B] What type of rock is oceanic and continental?

Oceanic:

- Low density rock, mainly basalt, thin and newly created.

Continental:

- High density rock, mainly granite, thick and old.

[1.2B] Which plate margin is the most destructive and why?

Continental + Continental:

- They have shallow focuses, meaning the energy is able to reach the land quite quickly.

- Creates a small infrequent number of very shallow earthquakes.

- Oceanic + Oceanic have a range of focus depths, as do Oceanic+ Continental.

[1.2C] What is the focus and epicentre of an earthquake?

Focus:

- The focus is the point underground where the earthquake originates from.

Epicentre:

- The epicentres the area above ground directly above the focus.

[1.2C] What is the type of seismic activity at a constructive, destructive and a transform plate boundary?

Constructive:

- Shallow focus, usually low magnitude (5-6).

- This is the same for oceanic + oceanic and continental + continental.

Destructive:

Oceanic + Continental:

- Range of focal depths from shallow to 700km along the Benioff zone. Often high in magnitude (8-9).

Oceanic + Oceanic:

- Range of focal depths from shallow to 700km along the Benioff zone. Moderate to high magnitude (7-9).

Continental + Continental (Collisions)

- Shallow to intermediate focal depth. Moderate magnitude (6-8).

Tranform:

- Shallow focus, moderate magnitude. (6-8)

[1.2C] What are the different types of volcanoes?

Composite Volcanoes:

- Wide base and a narrow top.

- Crater also known as a caldera.

- Have ash clouds and a pyroclastic flows.

- Occurs at subducting plate boundaries.

Shield Volcanoes:

- Form at a hotspot where plates are pulling apart.

- Wider than they are tall.

- Not explosive.

- Much gentler slope on sides.

[1.2C] What is the volcanic activity at a constructive, destructive and a transform plate boundary?

Constructive:

- Effusive eruptions, low VEI scale (1-3).

Destructive:

Oceanic + Continental:

- Explosive, moderate to high VEI scale (5-6).

Oceanic + Oceanic:

- Explosive, moderate to high VEI scale (5-6).

Continental + Continental (Collisions)

- Usually none.

Tranform:

- Usually none.

[1.3A] What are the characteristics of primary and secondary waves?

Primary:

- Can travel through solid, liquid and gases.

- Primary waves are first to arrive at recording stations.

- Move back and forth, vibrates in direction of travel.

Secondary:

- Arrive at the recording station after primary waves.

- Only travels through solids.

- Up and down movement.

[1.3A] What are the characteristics of a love and rayleigh wave?

These are surface waves which travel through the top of the crust.

Love:

- Moving the ground from side to side, horizontal motion, as it moves forward.

- Faster than Rayleigh waves.

- Rolling motion producing vertical ground movement.

- Arrive last.

Rayleigh:

- Have an elliptical motion.

- Most destructive.

- Causes the surface to move up and down.

[1.3A] How can earthquake waves cause the primary hazards, crustal fracturing and ground shaking?

Crustal Factoring:

- Shockwaves travel fast through solid rock. This causes stress to the rock, which will eventually fracture the rock. (Primary waves)

- Can result in faults.

Ground Shaking:

- Shockwave ground movements include pushing and pulling (p wave), and up and down (S wave), and side to (side). This all happens quickly and causes ground shaking.

- Buildings that are no aseismic may only survive some types of shaking, and will be damaged.

[1.3A] What secondary hazards can be generated as a result of earthquake waves?

Landslides:

- Where there is steep slopes and unconsolidated material, shockwaves loosen rock and cause it to move downslope under the influence of gravity.

- Landslides may destroy infrastructure and hit settlements.

Liquefaction:

- This occurs as a result of ground shaking particularly in areas that consists of loose, unconsolidated material that is also waterlogged.

- Causes building to tilt or collapse.

[1.3B] What primary hazards can volcanoes cause?

- Lava flows, pyroclastic flows, tephra and ash falls, gas eruptions.

[1.3B] What is a tephra and ash fall?

- The smallest fragments erupted from a volcano are called ash. They are blasted into the air, and can be carried around the planet.

- This is when pieces of volcanic rock and ash are blasted into the air.

- This can cause serious damage to buildings, vegetation, pollute water sources.

- Disrupt flights.

- Happens in composite volcanoes.

[1.3B] What is a gas eruption?

A gas eruption involves the eruption of carbon dioxide and sulphur dioxide.

- Sulphur dioxide can result in acid rain which damages buildings.

- Poisonous and can poison people and animals.

- Occurs in composite volcanos.

[1.3B] What is a lava flow?

This is molten magma that is erupted from volcanoes and flows down the sides until it cools.

- People usually get out of the way, so deaths can be preventable.

- Settlements are not protected, and can be set on fire.

- Occurs in both composite and shield volcanoes.

[1.3B] What is a pyroclastic flow?

- This is a dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing downslope at great speed. Found in composite volcanoes.

- It travels down the sides of volcanoes, and in speed of up to 700km/h.

- Any buildings, or people in the way are destroyed through incineration or poisoning.

- Destroyed the town of Plymouth in Monsterrat in 1997.

- Occurs in composite volcanoes.

[1.3B] What are secondary hazards of volcanoes?

Lahars, jokulhlaups.

[1.3B] What is a lahar?

A lahar is a combination of rock, mud and water, which travels quickly down the sides of volcanoes.

- Found at composite volcanoes.

[1.3B] What is a jokulhlaup?

It is a flood that is caused by a volcano erupting underneath a glacier causing it to melt.

- Creates huge volumes of meltwater.

[1.3B] What are the three types of lava and characteristics?

Basaltic:

- The hottest lava.

- Gentle, effusive.

- Found in ocean hot spots, shield volcanoes.

Andesitic:

- Hot, but not as hot as Basaltic (800-1000)

- Slow flow

- Composite cone volcanoes, subduction zones.

Rhyolitic:

- Coolest (650-800)

- Thick and stiff.

- Very violent.

[1.3C] How are tsunamis formed?

This happens when an undersea earthquake occurs at a subduction zone which may cause a rapid movement of the seabed vertically. If this movement is up or down, then a column of seawater above the epicentre is displaced, creating a powerful wave motion.

- Creates high waves, and quick waves.