AQA A-level Geography · 3.1.5

Plate tectonics

50 exam-style questions with answers for 3.1.5 Plate tectonics in AQA A-level Geography (spec 7037). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official AQA material.

All 50 questions and answers

Question 1 · Spec 3.1.5.2 · Earth structure
Describe the structure of the Earth. [4 marks]
Answer:
Crust: thin, solid, rocky outer layer (1); mantle: thick layer of hot, mostly solid rock that flows very slowly (1); outer core: liquid iron and nickel (1); inner core: solid, very hot iron and nickel (1).
Question 2 · Spec 3.1.5.2 · Earth structure
Distinguish between continental and oceanic crust. [3 marks]
Answer:
Continental crust is thicker, about 30–70 km, and oceanic crust is thinner, about 5–10 km (1); continental crust is less dense (granite) and oceanic crust is denser (basalt) (1); oceanic crust is younger than continental crust (1).
Question 3 · Spec 3.1.5.2 · Earth structure
Distinguish between the lithosphere and the asthenosphere. [2 marks]
Answer:
The lithosphere is the rigid outer layer made of the crust and uppermost mantle, broken into plates (1); the asthenosphere is the hotter, partly molten, weaker layer of mantle beneath on which the plates move (1).
Question 4 · Spec 3.1.5.2 · Earth structure
Describe the sources of internal energy in the Earth. [3 marks]
Answer:
Radioactive decay of elements such as uranium in the mantle and crust (1); residual heat left from the formation of the Earth (1); heat released as the liquid outer core crystallises onto the inner core (1).
Question 5 · Spec 3.1.5.2 · Earth structure
Explain how seismic waves provide evidence for the structure of the Earth. [3 marks]
Answer:
P waves travel through solids and liquids, but S waves only through solids (1); S waves are not detected on the far side of the Earth, which shows that the outer core is liquid (1); changes in the speed and direction of waves show boundaries between layers (1).
Question 6 · Spec 3.1.5.2 · Plate tectonic theory
Describe the theory of plate tectonics. [3 marks]
Answer:
The lithosphere is split into rigid plates (1); the plates move slowly over the semi-molten asthenosphere (1); most earthquakes and volcanoes occur at plate margins where plates interact (1).
Question 7 · Spec 3.1.5.2 · Plate tectonic theory
Name three major tectonic plates. [3 marks]
Answer:
Any three from: Pacific (1); North American (1); South American (1); Eurasian (1); African (1); Indo-Australian (1); Antarctic (1); Nazca (1).
Question 8 · Spec 3.1.5.2 · Plate tectonic theory
Describe the evidence used by Wegener for continental drift. [4 marks]
Answer:
The coastlines of South America and Africa fit together like a jigsaw (1); the same fossils, such as Mesosaurus and Glossopteris, are found on continents now far apart (1); rock sequences and mountain ranges match across the Atlantic (1); glacial deposits occur in tropical areas and coal in Antarctica, showing that climates have changed with position (1).
Question 9 · Spec 3.1.5.2 · Plate tectonic theory
Explain why Wegener's theory was not accepted at first. [2 marks]
Answer:
He could not explain what force could move continents (1); critics did not believe that continents could plough through the solid ocean floor (1).
Question 10 · Spec 3.1.5.2 · Plate tectonic theory
Explain how sea-floor spreading supports plate tectonic theory. [3 marks]
Answer:
New crust forms at ocean ridges as magma rises and cools (1); rocks are youngest at the ridge and older with distance from it (1); this shows the sea floor is moving apart, carrying the continents with it (1).
Question 11 · Spec 3.1.5.2 · Plate tectonic theory
Explain how magnetic striping supports sea-floor spreading. [3 marks]
Answer:
Iron minerals in cooling basalt line up with the Earth's magnetic field (1); the field reverses from time to time, producing bands of normal and reversed polarity (1); the bands are symmetrical on either side of the ridge, showing that crust formed there and spread outwards (1).
Question 12 · Spec 3.1.5.2 · Plate tectonic theory
Explain why the oceanic crust is much younger than the continental crust. [2 marks]
Answer:
Oceanic crust is created at ridges and destroyed at subduction zones, so it is continually recycled (1); most is under 200 million years old, but continental crust is too buoyant to subduct and can be billions of years old (1).
Question 13 · Spec 3.1.5.2 · Plate tectonic theory
Describe how plate movement is measured today. [2 marks]
Answer:
GPS stations on plates record tiny movements each year (1); satellite radar and laser measurements track changes in ground position (1).
Question 14 · Spec 3.1.5.2 · Plate movement
Explain how convection currents move tectonic plates. [3 marks]
Answer:
Heat from the core and radioactive decay warms the mantle, making it less dense so it rises (1); cooler material sinks, setting up circulation (1); the movement drags the plates along the base of the lithosphere (1).
Question 15 · Spec 3.1.5.2 · Plate movement
Explain what is meant by ridge push. [2 marks]
Answer:
New lithosphere at an ocean ridge is hot and elevated (1); gravity makes it slide down the slope away from the ridge, pushing the plate (1).
Question 16 · Spec 3.1.5.2 · Plate movement
Explain what is meant by slab pull. [2 marks]
Answer:
At a subduction zone the cold, dense oceanic plate sinks into the mantle under its own weight (1); it pulls the rest of the plate behind it (1).
Question 17 · Spec 3.1.5.2 · Plate movement
Explain what is meant by gravitational sliding. [2 marks]
Answer:
Lithosphere slopes downwards from the ridge towards the subduction zone (1); the plate slides down this slope under the force of gravity (1).
Question 18 · Spec 3.1.5.2 · Plate movement
Explain why slab pull is thought to be the most important force moving plates. [2 marks]
Answer:
Plates attached to long, sinking slabs, such as the Pacific plate, move fastest (1); the weight of the dense, cold slab provides a stronger force than ridge push (1).
Question 19 · Spec 3.1.5.2 · Plate movement
Explain why plates move at different speeds. [2 marks]
Answer:
Plates attached to a subducting slab are pulled faster (1); plates with deep continental roots meet more resistance and move more slowly (1).
Question 20 · Spec 3.1.5.2 · Plate movement
Calculate how far a plate moves in 10,000 years at 4 cm per year. Give your answer in metres. [2 marks]
Answer:
4 × 10,000 = 40,000 cm (1); 40,000 cm = 400 m (1).
Question 21 · Spec 3.1.5.2 · Plate movement
The Atlantic is widening at 2.5 cm per year. Calculate how much wider it becomes in one million years, in kilometres. [2 marks]
Answer:
2.5 × 1,000,000 = 2,500,000 cm (1); = 25 km (1).
Question 22 · Spec 3.1.5.2 · Plate margins
Explain what is meant by a subduction zone. [2 marks]
Answer:
A place where a denser plate is forced down beneath another plate into the mantle (1); the descending plate melts and is destroyed (1).
Question 23 · Spec 3.1.5.2 · Plate margins
Explain why oceanic crust subducts but continental crust does not. [2 marks]
Answer:
Oceanic crust is denser than the mantle and than continental crust, so it sinks (1); continental crust is too buoyant to be pulled down (1).
Question 24 · Spec 3.1.5.2 · Destructive margins
Describe what happens at a destructive plate margin. [4 marks]
Answer:
A denser oceanic plate is subducted beneath a less dense plate (1); friction between the plates causes earthquakes (1); the plate melts and the magma rises to form volcanoes (1); a deep ocean trench forms at the surface (1).
Question 25 · Spec 3.1.5.2 · Destructive margins
Name three landforms found at destructive plate margins. [3 marks]
Answer:
Any three from: deep ocean trenches (1); young fold mountains (1); volcanoes (1); island arcs (1).
Question 26 · Spec 3.1.5.2 · Destructive margins
Explain how a deep ocean trench forms. [2 marks]
Answer:
The subducting plate bends downwards into the mantle (1); a long, narrow, steep-sided trench forms, for example the Mariana Trench, nearly 11 km deep (1).
Question 27 · Spec 3.1.5.2 · Destructive margins
Explain how an island arc forms. [3 marks]
Answer:
An oceanic plate subducts beneath another oceanic plate (1); the subducting plate melts and magma rises (1); volcanoes build up from the sea floor to form a curved chain of islands, such as the Aleutians or the Marianas (1).
Question 28 · Spec 3.1.5.2 · Destructive margins
Explain how young fold mountains form. [3 marks]
Answer:
Sediments lie in a sea between two converging plates (1); the plates push together and compress, fold and uplift the sediments (1); the Andes formed this way along a subduction zone, and the Himalayas where two continental plates collided (1).
Question 29 · Spec 3.1.5.2 · Destructive margins
Describe what happens when two continental plates collide. [3 marks]
Answer:
Neither plate subducts because both are buoyant (1); the crust crumples, thickens and is uplifted into fold mountains (1); earthquakes are common but volcanoes are rare (1).
Question 30 · Spec 3.1.5.2 · Destructive margins
Explain the formation of the Himalayas. [3 marks]
Answer:
The Indo-Australian plate moves north and collides with the Eurasian plate (1); sediments from the sea between them are folded and thrust upwards (1); the collision continues, so the mountains are still rising and earthquakes are frequent (1).
Question 31 · Spec 3.1.5.2 · Destructive margins
Explain the formation of the Andes. [3 marks]
Answer:
The oceanic Nazca plate subducts beneath the South American plate (1); compression folds and uplifts the crust and sediments (1); magma from the melting plate rises to form volcanoes (1).
Question 32 · Spec 3.1.5.2 · Destructive margins
Explain why earthquakes at subduction zones occur at a range of depths. [3 marks]
Answer:
The subducting plate descends at an angle, down to several hundred kilometres (1); earthquakes occur along the plate as it sinks, in the Benioff zone (1); the earthquakes become deeper further from the trench (1).
Question 33 · Spec 3.1.5.2 · Destructive margins
Explain why volcanic eruptions at destructive margins are more explosive than those at constructive margins. [3 marks]
Answer:
Magma formed from melting subducted plate is rich in silica, so it is thick and sticky (1); gas becomes trapped, and pressure builds up (1); the gas is released violently, causing explosive eruptions (1).
Question 34 · Spec 3.1.5.2 · Constructive margins
Describe what happens at a constructive plate margin. [4 marks]
Answer:
Two plates move apart (1); magma rises to fill the gap and cools to form new crust (1); shallow earthquakes and frequent, fairly gentle eruptions occur (1); an ocean ridge or a rift valley forms (1).
Question 35 · Spec 3.1.5.2 · Constructive margins
Explain how volcanoes form at constructive margins. [3 marks]
Answer:
As plates pull apart, pressure on the mantle beneath falls (1); the hot rock partly melts to form runny basaltic magma (1); magma rises and erupts as lava, building new crust and volcanoes (1).
Question 36 · Spec 3.1.5.2 · Constructive margins
Explain how a rift valley forms on land. [3 marks]
Answer:
Plates pull apart and the crust is stretched (1); it fractures along parallel faults (1); the block between the faults drops down, forming a steep-sided valley such as the East African Rift (1).
Question 37 · Spec 3.1.5.2 · Constructive margins
Name one example of a constructive plate margin. [1 mark]
Answer:
The Mid-Atlantic Ridge, or the East African Rift Valley.
Question 38 · Spec 3.1.5.2 · Constructive margins
Explain why Iceland has high volcanic activity. [2 marks]
Answer:
It lies on the Mid-Atlantic Ridge, a constructive plate margin (1); it is also above a mantle plume, which supplies extra magma (1).
Question 39 · Spec 3.1.5.2 · Conservative margins
Describe what happens at a conservative plate margin. [3 marks]
Answer:
Two plates slide past each other, in different directions or at different speeds (1); friction locks the plates, so pressure builds up (1); a sudden release causes large earthquakes, but there are no volcanoes and crust is neither created nor destroyed (1).
Question 40 · Spec 3.1.5.2 · Conservative margins
Name one example of a conservative plate margin. [1 mark]
Answer:
The San Andreas Fault in California, or the Alpine Fault in New Zealand.
Question 41 · Spec 3.1.5.2 · Plate margins
Compare constructive and destructive plate margins. [3 marks]
Answer:
Plates move apart at constructive margins and together at destructive margins (1); crust is created at constructive margins and destroyed at destructive margins (1); constructive margins have shallow earthquakes and gentle eruptions, destructive margins have deeper earthquakes and explosive eruptions (1).
Question 42 · Spec 3.1.5.2 · Magma plumes
Explain what is meant by a magma plume or hotspot. [3 marks]
Answer:
A column of unusually hot rock rising from deep in the mantle (1); it melts the crust above, producing volcanoes away from plate boundaries (1); examples are Hawaii and Yellowstone (1).
Question 43 · Spec 3.1.5.2 · Magma plumes
Explain how the Hawaiian island chain formed. [3 marks]
Answer:
The Pacific plate moves north-west over a fixed hotspot (1); volcanoes form above the plume and become extinct as the plate carries them away (1); islands are older and more eroded to the north-west, and the Big Island is the youngest and still active (1).
Question 44 · Spec 3.1.5.2 · Magma plumes
Name two hotspots other than Hawaii. [2 marks]
Answer:
Any two from: Yellowstone (1); Iceland (1); Réunion (1); the Galápagos (1); the Canary Islands (1).
Question 45 · Spec 3.1.5.2 · Distribution
Describe the global distribution of earthquakes and volcanoes. [3 marks]
Answer:
They are concentrated in narrow belts along plate boundaries (1); the Pacific Ring of Fire is the largest, with the Alpine–Himalayan belt and the mid-ocean ridges also active (1); few occur away from plate boundaries, except above hotspots (1).
Question 46 · Spec 3.1.5.2 · Distribution
Explain why the Pacific Ring of Fire has so many earthquakes and volcanoes. [3 marks]
Answer:
It is a horseshoe-shaped zone around the Pacific Ocean (1); the Pacific plate and others are being subducted along most of its length (1); it contains about three-quarters of the world's active volcanoes and most of its earthquakes (1).
Question 47 · Spec 3.1.5.2 · Distribution
Explain why earthquakes sometimes occur away from plate boundaries. [2 marks]
Answer:
Stress from plate movement is transferred through the plate (1); this can reactivate old faults within a plate, such as at New Madrid in the USA (1).
Question 48 · Spec 3.1.5.2 · Human use
Explain how people benefit from living near plate margins. [3 marks]
Answer:
Geothermal energy provides heat and electricity, for example in Iceland (1); volcanic soils are fertile for farming (1); mountains and volcanoes provide minerals and tourism (1).
Question 49 · Spec 3.1.5.2 · Constructive margins
Describe the main features of an ocean ridge. [3 marks]
Answer:
A chain of underwater mountains formed by rising magma (1); a rift valley along the crest where plates are pulling apart (1); the ridge is offset by transform faults, and shallow earthquakes and volcanic activity are common (1).
Question 50 · Spec 3.1.5.2 · Constructive margins
Explain how hydrothermal vents form along ocean ridges. [2 marks]
Answer:
Seawater seeps down through cracks in the crust and is heated by magma (1); the hot water rises, carrying dissolved minerals that are released at vents known as black smokers (1).

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