OCR A-Level Geography Physical systems (01), June 2025: Question 3
33 marks · Hard difficulty · Extended Response
A multi-part question on dryland landscapes covering the formation of linear dunes, statistical analysis of canyon erosion rates, nivation hollow formation, and an evaluative essay on the impacts of water supply issues versus economic activity.
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Question text
Option C – Dryland Landscapes
(a) Explain the influence of flows of energy in the formation of a linear dune. [8]
(b) Study Table 3, which shows canyon erosion rates in a dryland landscape in China.
Table 3 Canyon erosion rates in a dryland landscape in China
Rate of erosion
Location
(m / year)
Xi’an 3.5
Yinchan 3.5
Milan 1.0
Hami 0.5
Turpan 2.0
Korla 3.0
Yinang 1.0
Kashi 0.7
Shache 2.8
Lhasa 1.6
(i) Using Table 3, calculate the mean rate of erosion.
Show your workings. [2]
(ii) The standard deviation for the rate of erosion in Table 3 is 1.11.
State what this indicates about the dispersion (spread) of the data set. [2]
(iii) Explain why standard deviation is a more accurate measure of dispersion (spread) than range
and interquartile range. [2]
(c) Study Fig. 3, a dryland landscape in Chad.
With reference to Fig. 3, explain the influence of one geomorphic process in shaping landform C
(nivation hollow). [3]
(d)* ‘Dryland landscape systems are influenced more by human activity, due to water supply issues,
than by economic activity.’
To what extent do you agree with this statement? [16]
Mark scheme
Show the mark scheme
Question Answer Mark Guidance
3 (a) Explain the influence of flows of energy in the 8 Indicative content:
formation of a linear dune. AO1 x8 AO1 – 8 marks
Knowledge and understanding of the reasons for the
Level 3 (6-8 marks) influence of flows of energy (e.g. kinetic, thermal,
Demonstrates thorough knowledge and understanding gravitational) in the formation of a linear dune could
of the influence of flows of energy in the formation of a potentially include:
linear dune. (AO1). • A linear dune is straight or slightly curved
• They form parallel to the bimodal wind which
This will be shown by including well-developed ideas pushes the sand in one direction
with a clear appreciation of the reasons for the
influence of flows of energy in the formation of a linear • Thermal energy from sun creates winds
dune. • Thermal energy can also dry and harden sand
making it easier to transport
Level 2 (3-5 marks) • Kinetic energy from the wind pushes sand by
Demonstrates reasonable knowledge and creep and saltation up the slope
understanding of the reasons for the influence of flows • Sand will be deposited on the slope as friction
of energy in the formation of a linear dune increased which reduces kinetic energy
This will be shown by including developed ideas with • Converging wind directions create two slip faces
some appreciation of the reasons of the influence of where kinetic wind energy builds up slope angle
flows of energy in the formation of a linear dune. • Gravitational potential energy increases as sand
accumulates on the slope therefore the slope
Level 1 (1-2 marks) angle increases until angle of repose is
Demonstrates basic knowledge and understanding of exceeded and energy is released as kinetic
the reasons for the influence of flows of energy in the energy in a mini avalanche
formation of a linear dune (AO1).
This will be shown by including simple ideas and with
no or limited appreciation of the reasons for the
influence of flows of energy in the formation of a linear
dune.
0 marks
No response or no response worthy of credit.
Question Answer 22 Mark Guidance
3 (b) (i) Study TABLE 3, which shows canyon erosion rates 2 AO3 - 2 marks
in a dryland landscape in China. Using TABLE 3, AO3 x2 1 x 1 (✓) for calculating the mean rate of erosion using
calculate the mean rate of erosion. Show your TABLE 3.
workings. 1 x 1 (✓) for showing workings.
• 3.5+3.5+1+0.5+2+3+1+0.7+2.8+1.6 / 10 ( ) or
19.6 / 10 ( )
• Mean value is 1.96 ( )
3 (b) (ii) The standard deviation for the rate of erosion in 2 AO3 – 2 marks
TABLE 3 is 1.11. State what this indicates about the AO3 x2 1 x 1 (✓) for general point about dispersion
dispersion (spread) of the data set. 2 x 1 (✓) for specific point about dispersion
• The sample suggests that approximately 68% of
the values ( ) lies in the range 0.85 – 3.07
(within 1.11 of the mean) ( )
• The sample is fairly spread out around the mean
/ limited clustering (✓) there are locations more
than one SD from the mean e.g. Kashi (0.7) (✓)
• The sample suggests that 6/10 or 60% of the
values ( ) lie within 1 SD of the mean / within
1.96 ( )
3 (b) (iii) Explain why standard deviation is a more accurate 2 AO3 – 2 marks
measure of dispersion (spread) than range and AO3 x2 1 x 1 (✓) for explanation of why standard deviation is
interquartile range. more accurate than the range
1 x 1 (✓) for explanation of why standard deviation is
• Standard deviation is more useful than the more accurate than the interquartile range
range which only uses the maximum and
minimum value so gives you limited information
about the spread of data ( )
• Standard deviation is more useful than the
range, as the range can be skewed by
outliers/anomalies’ ( )
• Standard deviation is more useful than the IQR
which only uses half the values / the middle 50%
of the data set ( )
• The range only uses the highest and lowest
values ( )
3 (c) Study FIG. 3, a dryland landscape in Chad. 3 Indicative content:
With reference to FIG. 3, explain the influence of AO2 x3 AO2 – 3 marks
ONE geomorphic process in shaping landform C For analysing Fig. 3 to explain the influence of ONE
(nivation hollow). geomorphic process in shaping landform C (nivation
hollow)
• Freeze thaw weathering occurs when melt water • Naming a geomorphic process of its own is not
seeps into cracks in the rock ( ) as it freezes it sufficient for a mark.
expands exerting pressure (DEV) causing the • A geomorphic process must be present within
rock to break up / disintegrate (DEV) the answer to achieve full marks.
• Pressure causes ice at the base to melt ( )
causing abrasion as weathered material scrapes
the floor (DEV), deepening nivation hollow /
removing more rock (DEV)
• Rill wash – weathered material is deposited in
meltwater streams ( ), abrasion deepens
channel allowing weathered material to move
(DEV), deepening nivation hollow (DEV)
3 (d*) ‘Dryland landscape systems are influenced more by 16 Indicative content
human activity, due to water supply issues, than by AO1 x8
economic activity.’ AO2 x8 AO1 – 8 marks
To what extent do you agree with this statement? Knowledge and understanding of human activity on
dryland landscape systems could potentially include:
AO1 • Human activity due to water supply issues
Level 3 (6-8 marks) o Dam construction altering flows of water,
Demonstrates thorough knowledge and understanding making discharge more consistent
of the influence of human activity on dryland landscape o Velocity reduced behind dams causing
systems. deposition in lake and sediment starvation
downstream
The answer should include accurate place-specific
• Economic activity in a dryland landscape system
detail.
o Tourism – off road driving, hiking, mountain
Level 2 (3-5 marks) biking, camping, quad biking
Demonstrates reasonable knowledge and o Damage to crytobiotic crusts, dune
understanding of the influence of human activity on equilibrium, increased dust storms and
dryland landscape systems. wind erosion
AO2 – 8 marks
The answer should include place-specific detail which
is partially accurate. Apply knowledge and understanding to analyse and
evaluate the extent to which dryland landscape systems
Level 1 (1-2 marks) are influenced more by human activity, due to water
Demonstrates basic knowledge and understanding of supply issues, than by economic activity. This could
the influence of human activity on dryland landscape potentially include:
systems. • Importance will vary depending on use of case
study
There is an attempt to include place-specific detail but • Economic activity has a greater influence as
it is inaccurate. hikers can damage crytobiotic crust with one
footstep and it takes 50 years to recover
0 marks
No response or no response worthy of credit. • Human activity due to water supply issues is
more influential as limiting floods causes sand
AO2 bars to disappear and sand bars at the edge of
Level 3 (6-8 marks) the flood plain degrade – the area affected by
Demonstrates thorough application of knowledge and the dam is significantly larger than a footprint on
understanding to provide clear and developed analysis crytobiotic crust
that shows accuracy. Includes a detailed evaluation that • Human activity due to water supply issues is
offers generally secure judgements, with some link more influential as wadis are shortened
between rational conclusions and evidence regarding significantly affecting the size of landforms over
the extent to which dryland landscape systems are a large area, as well as the loss of sand bars
influenced more by human activity, due to water supply which reduce the input of sand into dunes
issues, than by economic activity.
degrading them significantly
Level 2 (3-5 marks) • Glen Canyon 1963 damming of Colorado River
Demonstrates reasonable application of knowledge had biggest impact. Average daily flows
and understanding to provide sound analysis that exceeded 850 cumecs only 3% of the time
shows some accuracy. Includes a sound evaluation compared with 18% before 1963. At the same
regarding the extent to which dryland landscape time low flows became less frequent – flows of
systems are influenced more by human activity, due to less than 140cumecs occur 10% of the time
water supply issues, than by economic activity. compared to 18% prior to the dam
Judgements and conclusions are generalised, with
limited use of evidence Highest level likely to refer to dynamic equilibrium /
spatial / temporal variations.
Level 1 (1-2 marks)
Demonstrates basic application of knowledge and
understanding to provide simple analysis that shows
limited accuracy to provide an un-supported evaluation
that offers simple conclusions regarding the extent to
which dryland landscape systems are influenced more
by human activity, due to water supply issues, than by
economic activity.
0 marks
No response or no response worthy of credit.
Quality of extended response
Level 3
There is a well-developed line of reasoning which is
clear and logically structured. The information
presented is relevant and substantiated.
Level 2
There is a line of reasoning presented with some
structure. The information presented is in the most-part
relevant and supported by some evidence.
Level 1
The information is basic and communicated in an
unstructured way. The information is supported by
limited evidence and the relationship to the evidence
may not be clear.
How to answer it
Dryland Landscapes: Energy Flows, Statistics & Human Impacts
What This Question Tests
This exam question assesses core theoretical and quantitative components of Option C (Dryland Landscapes):
- Systems approach to landforms: Explaining how distinct energy forms (thermal, kinetic, gravitational potential) drive sediment flux and linear dune morphology ( AO1 ).
- Quantitative & statistical analysis: Calculating the arithmetic mean, interpreting standard deviation (σ) within real-world dryland datasets, and critically contrasting dispersion metrics ( AO3 ).
- Process geomorphology: Detailed mechanistic explanation of nivation hollow evolution via weathering and transport ( AO2 ).
- Synoptic evaluation (16-mark essay): Critically comparing the impacts of water management infrastructure against economic/recreational pressures on dryland dynamic equilibrium, supported by locational case studies ( AO1 & AO2 ).
Energy Flows in Linear Dune Formation
Explain the influence of flows of energy in the formation of a linear dune.
💡 Key Knowledge: Energy Forms as System Drivers
- Thermal Energy: Insolation generates differential atmospheric heating, producing persistent regional pressure gradients and prevailing wind systems. Thermal energy also desorbs moisture, drying sand grains to reduce cohesion.
- Kinetic Energy: Wind energy transfers shear stress to loose sand particles, driving transport via saltation, surface creep, and suspension. Friction with existing topography dissipates kinetic energy, triggering deposition.
- Converging Energy Vectors: Linear (seif) dunes develop under bidirectional/converging wind regimes. Wind shifts divert kinetic energy to alternating dune flanks, carving two steep slip faces.
- Gravitational Potential Energy: Grains accumulate on slip faces until the critical angle of repose (approx. 32°–34°) is exceeded. Instability converts stored gravitational potential energy into kinetic energy via grain slumping and grainfall avalanching.
🧠 Exam Technique & Mark Scheme Unpack
This question demands a systems perspective. Do not just narrate the appearance of a sand dune; explicitly name and trace the transformations between energy types.
- Level 3 (6–8 marks): Thorough knowledge of multiple energy flows (thermal → kinetic → potential → kinetic release) explicitly linked to linear dune morphology (elongated ridges, twin slip faces).
- Level 2 (3–5 marks): Sound description of wind transport, but only vague references to "energy" without classifying kinetic or gravitational components.
❌ Common Errors
- Describing a crescentic barchan dune instead of an elongated linear (seif) dune formed by converging winds.
- Failing to mention energy altogether, treating wind merely as "moving air" rather than a conduit of kinetic energy and frictional dissipation.
- Omitting gravity and angle of repose, missing the key energy transition from potential to kinetic energy during avalanching.
Calculation: Mean Erosion Rate
Using Table 3, calculate the mean rate of erosion. Show your workings.
📐 Step-by-Step Calculation
Dataset (m/year): 3.5, 3.5, 1.0, 0.5, 2.0, 3.0, 1.0, 0.7, 2.8, 1.6 (n = 10)
- Sum the raw values (Σx):
3.5 + 3.5 + 1.0 + 0.5 + 2.0 + 3.0 + 1.0 + 0.7 + 2.8 + 1.6 = 19.6 - Divide by total sample count (n = 10):
Mean = 19.6 / 10 = 1.96 - State the final value with correct units:
Mean = 1.96 m/year
✅ Model Answer & Mark Breakdown
Workings: 19.6 / 10 [1 mark]
Correct Value: 1.96 m/year [1 mark]
Tip: Always retain exact decimals provided by the calculation unless the question specifies rounding.
Interpretation of Standard Deviation
The standard deviation for Table 3 is 1.11. State what this indicates about dispersion.
✅ Model Answer (Full 2 Marks)
- General Dispersion Point: A standard deviation of 1.11 indicates a moderate-to-wide spread of canyon erosion rates around the mean of 1.96 m/year, demonstrating substantial spatial variability across Chinese dryland locations [1 mark].
- Specific Statistical Context / Calculation: Approximately 68% of normally distributed data lies within ±1 standard deviation ( 1.96 ± 1.11 = 0.85 to 3.07 m/year ). In this dataset, exactly 6 out of 10 locations (60%) fall within this interval, with notable outliers sitting beyond 1 SD such as Kashi (0.7 m/year) below and Xi'an/Yinchan (3.5 m/year) above [1 mark].
🧠 Exam Technique: Securing 2/2
Examiners award 1 mark for stating that data is moderately spread/dispersed around the mean, and 1 mark for quantifying this dispersion using the boundaries: Mean ± 1 SD = [0.85 – 3.07] or citing that 6/10 (60%) of locations fall inside this range.
Comparing Measures of Dispersion
Explain why standard deviation is a more accurate measure than range AND interquartile range.
✅ Model Comparative Points
- SD vs Range: Standard deviation takes account of every individual data point in the distribution, whereas the range utilizes only the two extreme values (maximum − minimum), making range highly susceptible to distortion by singular anomalies or outliers [1 mark].
- SD vs Interquartile Range (IQR): While IQR eliminates extreme outliers by measuring the spread of the middle 50%, it ignores the remaining half of the dataset. Standard deviation is superior because it assesses the dispersion of the entire dataset while weighting variations mathematically relative to the central mean [1 mark].
❌ Common Errors
- Only explaining why SD is better than the range, forgetting to explain why it is more complete than the interquartile range.
- Vaguely stating that standard deviation is "more reliable" or "harder to calculate" without referencing the inclusion of all values versus extremes only or middle 50% only.
Geomorphic Process in Landform Evolution
With reference to Fig. 3, explain the influence of ONE geomorphic process in shaping landform C (nivation hollow).
🧠 Examiner Requirement
You must select and thoroughly develop only ONE process. Naming the process alone scores 0 marks; all 3 marks are awarded for explaining the physical chain of cause and effect.
Option A: Freeze-Thaw Weathering (Gelifraction)
- Meltwater from snow patches infiltrates micro-cracks, joints, and bedding planes in the bedrock beneath and surrounding the patch.
- Sub-zero temperatures cause water to freeze and expand by approximately 9% in volume, exerting strong hydrostatic pressure on rock fissures.
- Repeated diurnal freeze-thaw cycles shatter and disintegrate the bedrock, continuously enlarging and steepening the backwall of the hollow.
Option B: Basal Abrasion / Meltwater Fluvial Wash
- Basal Abrasion: Overlying snow/firn weight induces pressure melting at the base; rotational sliding of ice laden with angular rock fragments scours the bedrock floor, deepening the depression.
- Rill Wash / Solifluction: Seasonal meltwater streams wash fine, weathered regolith downslope out of the hollow, evacuating sediment and maintaining the depression.
Evaluative Essay: Water Supply vs Economic Activity
‘Dryland landscape systems are influenced more by human activity, due to water supply issues, than by economic activity.’ To what extent do you agree with this statement?
💡 AO1: Core Empirical Evidence & Case Studies
1. Water Supply Infrastructure (e.g., Glen Canyon Dam & Lake Powell, Colorado River):
- Dams trap sediment (90%+ reduction in suspended load downstream), starving desert canyon systems of alluvial deposits.
- Loss of high-discharge spring floods suppresses natural formation of sandbars and sand terraces in canyon wadis.
- Flow regulation alters dynamic equilibrium: flows exceeding 850 cumecs dropped from 18% of the time to 3%; low flows below 140 cumecs dropped from 18% to 10%.
- Irrigation runoff causes extensive secondary salinisation and groundwater table depletion in arid basins.
2. Economic & Recreational Activities (e.g., Mojave / Sonoran Deserts):
- Off-road vehicles (OHVs), quad biking, and excessive hiking crush fragile cryptobiotic (biological soil) crusts composed of cyanobacteria, lichens, and mosses.
- Crust destruction reduces shear threshold velocity of soil, multiplying wind erosion and producing severe dust storms.
- Recovery time for biological soil crusts spans 50 to 250 years, causing persistent land degradation.
- Open-cast mineral extraction and commercial pastoralism lead to severe devegetation and accelerated gullying.
🧠 AO2: Criteria for High-Level Evaluation
Top-band answers ( Level 3 & Level 3 , 13–16 marks) structure their evaluation around clear spatial and temporal scales:
- Spatial Scale: Water supply infrastructure (e.g., dams, mega-aqueducts) has systemic, basin-wide geomorphic impacts altering fluvial and aeolian sediment supply for hundreds of kilometres downstream. In contrast, recreational and tourism impacts are often spatially localized along trails, corridors, and honeypots.
- Temporal Persistence & Thresholds: Damming causes an immediate, permanent shift in hydrology and sediment regimes. However, crushing cryptobiotic crusts triggers long-term soil vulnerability that persists for centuries, disrupting dynamic equilibrium even after human activity ceases.
- Interconnectedness: Economic growth (agriculture, urbanization like Las Vegas or Phoenix) is what drives the demand for water infrastructure. Separating them is artificial; economic expansion necessitates water diversion.
❌ Common Pitfalls in This 16-Marker
- Pure description without comparison: Describing damming in one paragraph and tourism in another without directly weighing which has a greater geomorphic influence.
- Neglecting landscape / geomorphic systems: Writing purely about socioeconomic impacts (e.g., "farmers earn less money") rather than physical processes (sediment flux, sandbar attrition, crust erosion, albedo changes, dynamic equilibrium).
- Unbalanced argument: Agreeing 100% with the statement without evaluating how severe biological crust destruction can be over wide desert expanses.
Structure for a 16/16 Mark Essay
- Introduction: Define dryland landscape systems and dynamic equilibrium. Set out your thesis: while water supply interventions exert the most pervasive macro-scale hydrologic and sedimentological alterations, economic activities create profound micro-to-meso-scale destabilisation of surface crusts.
- Theme 1 – Water Supply Issues: Analyze dam construction (e.g., Glen Canyon Dam on the Colorado River). Detail the trapping of sediment, loss of peak flow pulses, and degradation of downstream wadis/sandbars.
- Theme 2 – Economic Activities: Analyze off-road recreation, mining, and grazing in dryland ecosystems. Detail the physical pulverisation of cryptobiotic crusts, the dramatic decrease in wind threshold velocity, and increased aeolian deflation.
- Synoptic Synthesis (Scale & Reversibility): Explicitly weigh the two forces using evaluative criteria (spatial extent, recovery time, permanent vs episodic disturbance).
- Conclusion: Deliver an unambiguous, substantiated final verdict explaining the extent to which you agree with the proposition.
Topics
1.1.3 Option C – Dryland Landscapes · 1.1.1 Option A – Coastal Landscapes · 1.1.2 Option B – Glaciated Landscapes · Topic 1.2 Earth’s Life Support Systems · 2.a. Dryland landscapes develop due to a variety of interconnected climatic and geomorphic processes. · 3.b. Periglacial landforms can exist as a result of earlier colder periods. · 4.a. Water supply issues can cause change within dryland landscape systems. · 4.b. Economic activity can cause change within dryland landscape systems. · Topic-specific skills 1.a–4.b
Question and mark scheme from the OCR A-Level Geography examination, Physical systems (01), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.