OCR A-Level Geography Geographical debates (03), June 2025: Question 10

12 marks · Hard difficulty · Extended Response

Examine how volcanic eruptions can affect stores in the carbon cycle.

Practise this question

Question

Question text

10 Examine how volcanic eruptions can affect stores in the carbon cycle. [12]

Mark scheme

Show the mark scheme

Question Answer Mark Guidance

10 Examine how volcanic eruptions affect the carbon cycle. 12 Indicative

AO1 x6 content AO1 – 6

Level 4 (10-12 marks) AO2 x6 marks

Demonstrates comprehensive knowledge and understanding of Knowledge and understanding of the risks from

volcanic eruptions and the carbon cycle (AO1). volcanic eruptions and the carbon cycle could

potentially include:

Demonstrates comprehensive application of knowledge and • Volcanic eruptions

understanding to provide clear, developed and convincing • Lava, pyroclastic flows, gas emissions,

analysis that is fully accurate of how volcanic eruptions affect the tephra, ash, lahars, flooding

carbon cycle (AO2). • Carbon Cycle

• Inputs, stores, flows, outputs

This will be shown by including well-developed ideas about • Fast and slow carbon cycle

volcanic eruptions and the carbon cycle. • Spatial and temporal scales e.g.

global/regional/local and geological vs

There are clear and explicit attempts to make appropriate synoptic geomorphological.

links between content from different parts of the course of study.

AO2 – 6 marks

Level 3 (7-9 marks) Application of knowledge and understanding to analyse

Demonstrates thorough knowledge and understanding of how volcanic eruptions affect the carbon cycle could

volcanic eruptions and the carbon cycle (AO1). potentially include:

• Moving carbon from slow carbon cycle in

Demonstrates thorough application of knowledge and asthenosphere / mesosphere to fast carbon

understanding to provide clear and developed analysis that shows cycle on earth’s surface

accuracy of how volcanic eruptions affect the carbon cycle (AO2). • ↑ store of carbon dioxide in atmosphere after

eruption, vented from underground.

This will be shown by including well-developed ideas about • ↑ store of carbon in atmosphere with input of

either volcanic eruptions or the carbon cycle and developed ash from eruption – could last several years

ideas for the other focus. with higher VEI eruption and affect global

carbon cycle e.g. Pinatubo eruption

There are clear attempts to make synoptic links between the • Change in surface store of carbon as tephra

content from different parts of the course of study but these are spread over wide surface area extending from

not always appropriate. volcano including in seas + oceans

• Higher VEI index leading to larger change in

Level 2 (4-6 marks) store / flow e.g. impact of super volcanic

Demonstrates reasonable knowledge and understanding of eruptions.

volcanic eruptions and the carbon cycle (AO1). • Balance of the CO2 from eruption vs less

carbon emitted through cancellation of flights.

Demonstrates reasonable application of knowledge and

understanding to provide sound analysis that shows some

Mark Scheme June 2025

accuracy of how volcanic eruptions affect the carbon cycle (AO2).

This will be shown by including developed ideas about either

volcanic eruptions or the carbon cycle and simple ideas for the

other focus.

There are some attempts to make synoptic links between content

from different parts of the course of study but these are not always

relevant.

Level 1 (1-3 marks)

Demonstrates basic knowledge and understanding of volcanic

eruptions and the carbon cycle (AO1).

Demonstrates basic application of knowledge and understanding

to provide simple analysis that shows limited accuracy of how

volcanic eruptions affect the carbon cycle (AO2).

This will be shown by including simple ideas about volcanic

eruptions and the carbon cycle.

There are limited attempts to make synoptic links between content

from different parts of the course of study.

0 marks

No response or no response worthy of credit

Mark Scheme June 2025

SECTION C

How to answer it

OCR A-LEVEL GEOGRAPHY • PAPER 3 (SYNOPTIC DEBATES)

Volcanic Eruptions and Stores in the Carbon Cycle

What this question tests

Question: "Examine how volcanic eruptions can affect stores in the carbon cycle. [12]"

AO1 (6 marks): Knowledge and understanding of the carbon cycle (stores, fluxes, fast vs slow cycles) and volcanic hazards/processes (degassing, pyroclastic flows, ash/tephra distribution).
AO2 (6 marks): Application and analysis of how volcanic activity alters carbon stores across varying spatial scales (local to global), temporal scales (geological vs short-term atmospheric residence), and magnitude scales (VEI ratings, supervolcanoes).
Synoptic Linking: Explicit connections between Earth's Life Support Systems (Carbon Cycle) and Tectonic Hazards.

Question 10 Breakdown & Analysis

Total Marks: 12 (AO1: 6 marks, AO2: 6 marks) • Command Word: "Examine"

💡 Key Knowledge (AO1)

Carbon Stores: Lithosphere (slow cycle: ~100,000,000 PgC), Hydrosphere/Oceans (~38,000 PgC), Biosphere (~560 PgC), Atmosphere (~800 PgC).
Volcanic Transfer Flux: Eruptions move carbon stored in the upper mantle and asthenosphere/lithosphere (carbonates subducted and melted) directly into the atmospheric store via volcanic venting (CO₂ and volcanic gases).
Biomass & Soil Destruction: Pyroclastic density currents, lava, and tephra burn and bury terrestrial ecosystems, reducing the terrestrial biosphere store and transferring carbon to the atmosphere (combustion) and lithosphere (charcoal/fossilisation).
Ocean Carbon Store: Ash clouds rich in bio-available iron deposit nutrients onto ocean surface layers, causing diatom blooms (marine phytoplankton) that pull atmospheric carbon into the marine biotic pump.

🧠 Exam Technique (Command: "Examine")

Unpack Both Sides / Nuance: Do not just state "volcanoes add carbon to the air". Examine the scale and net direction of impacts on multiple stores (atmosphere, lithosphere, biosphere, oceans).
Categorise by Scale:
• Temporal: Instantaneous (degassing/combustion) vs Long-term (silicate weathering reducing atmospheric CO₂).
• Magnitude (VEI): Low-level effusive eruptions (Hawaii) vs massive plinian/super-eruptions (Pinatubo VEI 6, Toba VEI 8).
Aim for Level 4 (10–12 marks): The mark scheme requires "well-developed ideas" about both volcanism and the carbon cycle, accompanied by explicit synoptic connections.

✅ Well-Developed Exemplar Arguments (Level 4 Standard)

1. Lithosphere to Atmosphere (Venting): Subducted marine carbonates melt in the asthenosphere; during eruptions, CO₂ is outgassed into the atmosphere. Globally, subaerial volcanoes emit ~0.15–0.26 Gt CO₂/year. This is a vital pathway linking the deep geological slow cycle to the fast atmospheric cycle.
2. Biosphere Store Depletion: High-temperature pyroclastic flows and hot ash blankets (e.g., Mount St. Helens, 1980) incinerate forests, shifting carbon out of the terrestrial biospheric store into the atmospheric store via rapid oxidation.
3. Indirect Cooling & Reduced Photosynthesis: High VEI eruptions (e.g., Mt Pinatubo 1991) inject SO₂ and aerosols into the stratosphere. The resulting solar dimming reduces terrestrial plant photosynthetic sequestration, temporarily slowing carbon uptake into the biosphere.
4. Ocean Fertilisation (Biological Pump): Iron-rich basaltic tephra settling across nutrient-deficient ocean waters (HNLC zones) stimulates phytoplankton growth, accelerating carbon transfer from surface ocean waters into deep marine sediments.
5. Long-term Carbon Drawdown (Silicate Weathering): Over geological time, basaltic lava surfaces undergo chemical weathering ( CaSiO₃ + CO₂ → CaCO₃ + SiO₂ ), acting as an enormous net sink that removes carbon from the atmosphere back into sedimentary rocks.

❌ Common Misconceptions & Examiner Traps

Overestimating Modern Emissions: Claiming volcanoes emit more CO₂ than humans. Modern anthropogenic emissions (~36 Gt CO₂/year) dwarf subaerial volcanic emissions (~0.2 Gt CO₂/year) by over 100 times.
Treating the Atmosphere as the Only Store: High-scoring students examine multiple stores (biosphere, hydrosphere, lithosphere), not just the atmospheric carbon store.
Confusing Gases: Attributing global cooling directly to CO₂ instead of sulfur dioxide (SO₂) aerosols, or confusing the ozone hole with the carbon cycle.
Ignoring VEI Variations: Failing to differentiate between small basaltic eruptions and catastrophic explosive caldera eruptions.

📐 Comparative Scale & Flux Synthesis (Synoptic Evaluation)

Quantitative Contrast for Level 4 AO2:

Volcanic Flux: Approximately 0.15 to 0.26 Gt CO₂ yr⁻¹ (geological background rate).
Anthropogenic Flux: Approximately 36 Gt CO₂ yr⁻¹ (fossil fuels + land use changes).
Supervolcanic Events (e.g., Siberian Traps / Deccan Traps): Flood basalt volcanism released thousands of gigatonnes of carbon over millennia, altering the oceanic and atmospheric stores sufficiently to trigger mass extinction events (Permian-Triassic).
Short-term Human Offsets: Major explosive events (e.g., Eyjafjallajökull 2010) shut down European airspace, saving ~2.8 million tonnes of CO₂ emissions from aircraft fuel—an interesting indirect human feedback on the atmospheric store.

📋 Examiner Diagram Description (Recommended Synoptic Flow Diagram)

How to draw a Level 4 synoptic carbon-volcano link:
1. Central Hazard Event: A volcano box labelled with VEI Rating (1–8) and primary hazards ( CO₂ degassing, Tephra/Ash, Pyroclastic flows ).
2. Flow Arrow 1 (To Atmosphere): Arrow pointing upward to an "Atmosphere Store" box labelled "Direct degassing of deep mantle/subducted carbonates (+0.2 Gt/yr)".
3. Flow Arrow 2 (To Biosphere): Downward/outward arrow to "Biosphere Store" showing two opposite effects: Destruction of vegetation (combustion releases C) vs Solfataras/fertile volcanic soils supporting rapid regrowth over decadal time.
4. Flow Arrow 3 (To Hydrosphere): Wind-blown ash plumes falling into the ocean box showing "Nutrient input (Fe²⁺) → Phytoplankton bloom → Deep ocean sedimentation".
5. Flow Arrow 4 (Long-Term Lithosphere): Arrow showing atmospheric CO₂ combining with rainwater for "Chemical weathering of basaltic rocks → bicarbonate runoff → marine limestone storage".

Mark Scheme Level Summary:
Level 4 (10–12 marks): Comprehensive AO1 and AO2. Clear analysis of fast and slow carbon cycles, multiple stores (atmosphere, biosphere, ocean, lithosphere), variation by eruption size/VEI, and explicit synoptic links between tectonics and carbon cycling.
Level 3 (7–9 marks): Thorough AO1 and AO2. Well-developed ideas on one topic (e.g., volcanism) and developed on the other (carbon cycle). Mentions 1–2 stores with accurate mechanisms.
Level 2 (4–6 marks): Reasonable AO1/AO2. Descriptive of eruptions with simple references to CO₂ in the atmosphere.
Level 1 (1–3 marks): Basic, isolated points. Generalised assertion that "volcanoes release smoke and carbon".

Topics

Topic 1.2 Earth’s Life Support Systems · Topic 3.5 Hazardous Earth · 1.b. The carbon and water cycles are systems with inputs, outputs and stores. · 2.b. Volcanic eruptions generate distinctive hazards.

Question and mark scheme from the OCR A-Level Geography examination, Geographical debates (03), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.