S4 Geography Practice Paper: Plate Tectonics, Earthquakes And Volcanoes (12 Questions, 100 Marks, 75 Minutes)

S4 Geography Practice Paper: Plate Tectonics, Earthquakes and Volcanoes (12 questions, 100 marks, 75 minutes)

2026-11-09

HKDSE Geography: Plate Tectonics, Earthquakes and Volcanoes

12 questions, 100 marks, 75 minutes on plate boundaries, sea-floor spreading, earthquake waves, seismic risk, magma viscosity, lahars and the Pacific Ring of Fire.

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Instructions: This paper has three sections, A, B and C. Answer all questions. Total marks: 100. Time allowed: 75 minutes.

Show all working. Answers without working earn no method marks. Write down a formula before substituting numbers.

Give numerical answers to three significant figures unless stated otherwise, and state the correct units.

Spend about 30 minutes on Section A, then use the remaining time for the seismic-wave calculations in Section B and the volcanic hazard questions in Section C.

Section A　Plate Tectonics and Plate Boundaries

Section A: Read each question and write concise, accurate answers.

#	Question	Answer and marking notes
1	(a) State three main pieces of evidence for the theory of plate tectonics. (b) Explain how convection in the mantle drives plate movement. (c) Explain why plate boundaries are the main zones of earthquakes and volcanoes.	(a) Three lines of evidence: matching continental margins and fossils, symmetrical magnetic stripes on the ocean floor, and earthquakes and volcanoes concentrated in narrow belts (1 mark each, 3 marks). (b) Mantle convection drags the lithospheric plates sideways; upwelling pushes plates apart at ridges and downwelling pulls plates into the mantle at subduction zones (3 marks). (c) Rocks at boundaries are fractured, faults are active and magma rises easily, so stress release and magmatism are concentrated there (3 marks).
2	(a) Distinguish between constructive, destructive and conservative plate boundaries. (b) State one landform or feature commonly found at each type. (c) Give one example of a destructive plate boundary.	(a) Plates move apart at constructive boundaries, collide with subduction at destructive boundaries, and slide past each other at conservative boundaries (3 marks). (b) Constructive: mid-ocean ridge and rift valley; destructive: trench, fold mountain belt or island arc; conservative: transform fault (3 marks). (c) Example: the Andes along the west coast of South America, where the Nazca Plate subducts beneath the South American Plate (3 marks).
3	The sea floor on both sides of a mid-ocean ridge spreads at 5 cm per year. (a) Calculate the distance spread on one side after 1 million years, in kilometres. (b) Calculate the increase in the total width of the ocean basin after 10 million years, in kilometres. (c) Explain why magnetic stripes are symmetrical about the ridge.	(a) 5 cm equals 0.05 m; 0.05 times 1,000,000 equals 50,000 m, that is 50 km (3 marks; conversion must be shown). (b) 500 km on each side, so 1,000 km in total (3 marks). (c) Rising magma at the ridge cools and records the prevailing magnetic direction; as the floor moves away, normally and reversely magnetised stripes form in mirror image on both sides (2 marks).
4	Hong Kong lies inside the Eurasian Plate, far from plate boundaries, yet faults exist in its territory. (a) Explain why seismic activity in Hong Kong is weak. (b) Explain how earthquakes can still occur within a plate. (c) Suggest two measures to reduce the seismic risk of buildings.	(a) Hong Kong is hundreds of kilometres from plate boundaries, far from subduction and collision zones, so accumulated tectonic stress is small (3 marks). (b) Old faults exist within the plate; changes in the regional stress field can reactivate them and produce shallow earthquakes (3 marks). (c) Two measures: stronger seismic design and piling in buildings; avoid siting critical facilities near active faults and carry out regular seismic inspection (3 marks).

Section B　Earthquakes, Seismic Waves and Seismic Risk

Section B: Show all working and state the correct units.

#	Question	Answer and marking notes
5	(a) Distinguish between focus, epicentre and epicentral distance. (b) Distinguish between earthquake magnitude and intensity. (c) Explain why one earthquake can produce very different intensities at different places.	(a) The focus is the point underground where rupture starts, the epicentre is the point on the ground directly above it, and epicentral distance is the distance from the epicentre to the station (3 marks). (b) Magnitude measures the energy released, calculated from instrument records, and is a single value; intensity describes shaking and damage at a place and varies from place to place (3 marks). (c) Distance attenuation, soft-soil amplification, building structure and site conditions all differ, so intensity differs (2 marks).
6	A station records P waves and S waves. The P wave travels at 7 km per second and the S wave at 4 km per second. The station is 210 km from the epicentre. (a) Calculate the arrival times of the two waves. (b) Calculate the time difference. (c) Another station records a time difference of 45 seconds; calculate its distance from the epicentre.	(a) P wave: 210 divided by 7 equals 30 seconds; S wave: 210 divided by 4 equals 52.5 seconds (3 marks). (b) 52.5 minus 30 equals 22.5 seconds (2 marks). (c) Let the distance be d; d divided by 4 minus d divided by 7 equals 45, so 3d divided by 28 equals 45, giving d equals 420 km (3 marks).
7	(a) Compare P waves, S waves and surface waves in terms of motion and speed. (b) Explain why S waves cannot pass through liquids. (c) Explain why surface waves cause the greatest damage to buildings.	(a) P waves are longitudinal, with particle motion parallel to travel, and are fastest; S waves are transverse, with motion perpendicular to travel, and are slower; surface waves travel along the ground and are slowest (3 marks). (b) Liquids cannot support shear stress, so transverse waves cannot pass through them (2 marks). (c) Surface waves have large amplitude and long period, their energy is concentrated near the surface, and they readily resonate with buildings (3 marks).
8	(a) Explain how an earthquake early-warning system works. (b) Explain how land-use planning reduces earthquake damage. (c) Suggest two drill measures suitable for schools.	(a) The system uses the travel-time gap between the fast P waves and the later, damaging shaking to issue an automatic alert, slowing trains, parking lifts and prompting people to take cover (3 marks). (b) Schools and hospitals are sited on firm rock, high-density development is kept off soft soils and active faults, and open refuge space is reserved (3 marks). (c) Two measures: regular evacuation drills; anchoring shelves and cabinets and marking escape routes (3 marks).

Section C　Volcanoes, Volcanic Landforms and Hazard Management

Section C: Refer to the information given and answer in full sentences.

#	Question	Answer and marking notes
9	(a) Compare basaltic, andesitic and rhyolitic magmas in silica content and viscosity. (b) Explain how viscosity affects the style of eruption. (c) Explain why rhyolitic magma erupts more violently.	(a) Basaltic magma has the lowest silica content and viscosity; andesitic is intermediate; rhyolitic has the highest silica content and viscosity (3 marks). (b) Low viscosity lets gas escape quietly, giving effusive eruptions; high viscosity traps gas until pressure builds up, giving explosive eruptions (3 marks). (c) Rhyolitic magma is so viscous that gas cannot escape; pressure builds to a very high level before release, so eruptions are violent and often generate pyroclastic flows (2 marks).
10	A lahar flows down a valley at 20 m per second. A village lies 12 km from the crater. (a) Calculate the time the lahar needs to reach the village, in minutes. (b) Villagers need 5 minutes to evacuate; state whether the warning time is sufficient, with reasons. (c) Suggest one monitoring method that could extend the warning time.	(a) 12 km equals 12,000 m; 12,000 divided by 20 equals 600 seconds, that is 10 minutes (3 marks). (b) The warning time is 10 minutes against 5 minutes needed for evacuation, leaving a margin of 5 minutes, so it is sufficient (3 marks). (c) Install seismometers and GPS ground-deformation monitoring near the crater, and monitor gas emissions, to detect rising magma earlier (2 marks).
11	(a) State two hazards caused by volcanic eruptions. (b) State two benefits of volcanic regions. (c) Explain why volcanic soils are usually fertile.	(a) Two hazards: pyroclastic flows and lahars destroy villages; ash disrupts aviation and crops; lava flows destroy facilities (any two, 3 marks). (b) Two benefits: geothermal power and hot-spring tourism; fertile volcanic soil for farming; volcanic rock as building material (any two, 3 marks). (c) Weathered ash and lava release potassium and phosphorus, so the soil is rich in minerals and well drained (2 marks).
12	(a) Describe the distribution of the Pacific Ring of Fire. (b) Explain why volcanoes are concentrated along this belt. (c) Explain why Hong Kong has no active volcanoes.	(a) The belt rims the Pacific, running from New Zealand through Japan and the Aleutians to the west coast of South America in a horseshoe shape (3 marks). (b) Most of the belt is a subduction zone: oceanic plates descend into the mantle, friction generates heat and hydrous minerals release water, lowering the melting point of the mantle and producing magma (3 marks). (c) Hong Kong sits inside the Eurasian Plate, far from boundaries, with thick and stable crust and no pathway for magma ascent (2 marks).

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