How do aeolian and fluvial processes shape dryland landscapes, and how does change threaten them?
The dryland landscape as a system shaped by climatic and tectonic controls; aeolian and fluvial (and weathering) processes; the erosional and depositional landforms they create; desertification and landscape change; and the human use and sustainable management of drylands.
An OCR A-Level Geography answer to the Dryland landscapes option in Landscape Systems, covering arid and semi-arid landscapes as systems, climatic and tectonic controls, aeolian and fluvial processes, weathering, the landforms of erosion and deposition (dunes, yardangs, wadis, alluvial fans, mesas), desertification and landscape change, and the human use and sustainable management of drylands.
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What this dot point is asking
OCR wants you to treat arid and semi-arid landscapes as systems, explain the climatic and tectonic controls and the aeolian, fluvial and weathering processes that operate, link those processes to landforms, account for desertification and landscape change, and evaluate the human use and sustainable management of drylands.
The answer
Drylands as systems: climatic and tectonic controls
The master control is climate: rainfall is low (often under 250 mm a year in true deserts), highly variable and frequently delivered in intense, short storms; evaporation is high; and diurnal temperature ranges are large, driving mechanical weathering. Tectonic controls shape the relief, with uplift creating the basin-and-range topography of many deserts and exposing resistant rock. Sparse vegetation is critical: with little plant cover to bind soil or intercept rain, surfaces are exposed to wind and to rapid, erosive overland flow. The system therefore swings between long dry periods of aeolian dominance and brief, geomorphologically powerful wet events.
Aeolian, fluvial and weathering processes
Aeolian processes are wind-driven: deflation removes fine, loose particles (sometimes lowering the surface to a stony desert pavement), and abrasion sandblasts rock close to the ground. Wind transports sediment by suspension (fine dust), saltation (bouncing sand) and surface creep (rolling coarse grains). Fluvial processes are episodic but potent: flash floods in ephemeral channels carry large sediment loads, eroding wadis and depositing fans where they leave confined channels. Weathering is dominated by mechanical types, thermal fracturing under large temperature ranges, salt crystallisation in pore spaces and limited freeze-thaw at altitude, with chemical weathering suppressed by the lack of moisture.
Landforms of erosion and deposition
Aeolian erosional landforms include ventifacts (wind-faceted stones), yardangs (streamlined ridges aligned with the prevailing wind) and deflation hollows. Aeolian depositional landforms are the dunes, barchans, seif, transverse and star dunes, whose form records wind regime and sand supply. Fluvial erosional landforms include wadis (dry valleys), canyons, mesas and buttes (flat-topped resistant remnants) and inselbergs (isolated residual hills). Fluvial depositional landforms include alluvial fans at mountain fronts, coalescing into a bahada, and playas (salt-flats where ephemeral lakes evaporate). Many landscapes are polygenetic, bearing the imprint of past wetter (pluvial) climates as well as present aridity.
Desertification, change and management
Desertification is land degradation in drylands, the spread of desert-like conditions at the margins, driven by physical drought and human pressure (overgrazing, overcultivation, deforestation for fuelwood, poorly managed irrigation causing salinisation). It is reinforced by positive feedback: lost vegetation reduces infiltration and raises albedo, suppressing rainfall and stripping more soil. Drylands are also changing through long-term climate shifts and increasingly through climate change, which alters rainfall reliability. Sustainable management includes water harvesting, drought-resistant crops, agroforestry, regulated grazing and large initiatives such as the Sahel "Great Green Wall", balancing the needs of growing populations against the fragility of the system.
Examples in context
Example 1. The Sahel, sub-Saharan Africa. The Sahel is the standard desertification case study, a semi-arid belt south of the Sahara where recurrent drought (notably the 1970s-80s) combined with rapid population growth, overgrazing and fuelwood collection to degrade soils and reduce productivity. The "Great Green Wall" initiative, a planned belt of restored vegetation across the continent, plus local water-harvesting and agroforestry (such as farmer-managed natural regeneration in Niger), illustrate sustainable management and the interplay of physical and human factors that the 16-mark questions target.
Example 2. The Mojave and Death Valley, southwestern USA. Death Valley shows the depositional and tectonic signature of drylands: a fault-bounded basin where ephemeral streams off the surrounding ranges build large alluvial fans that coalesce into bahadas, feeding a central playa (the Badwater salt-flat) where evaporation concentrates salts. Migrating sand at Mesquite Flat forms classic dunes, and wind-faceted ventifacts and desert pavement record aeolian processes. The basin-and-range setting demonstrates tectonic control on dryland relief and provides a contrasting, sparsely populated example for evaluation.
Try this
Q1. Define deflation and explain one landform it helps to create. [4 marks]
- Cue. Deflation is the wind removal of loose, fine sediment; by stripping fines it can lower the surface to a stony desert pavement, or contribute to deflation hollows.
Q2. Suggest two human activities that can cause desertification. [2 marks]
- Cue. Any two of: overgrazing, overcultivation, deforestation for fuelwood, poorly managed irrigation leading to salinisation.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR H481/01 (style)6 marksExplain how aeolian processes produce depositional landforms in dryland environments.Show worked answer →
A medium-tariff Levels-of-Response question (AO1 and AO2). Define aeolian processes as those driven by wind: erosion by deflation (removal of loose, fine sediment) and abrasion (sandblasting of rock near the surface), transport by suspension, saltation and surface creep, and deposition where wind energy falls. For AO2, explain that sand dunes form where saltating sand meets an obstacle or a fall in wind speed and accumulates; the dune migrates as sand is moved up the gentle windward slope and avalanches down the steeper leeward slip face, so dune shape records wind direction and sediment supply.
Reward candidates who name dune types and link them to controls: barchans (crescents in unidirectional winds with limited sand), seif dunes (linear, in variable winds) and star dunes (multidirectional winds). The strongest answers stress that aeolian deposition needs a dry, sparsely vegetated surface with abundant loose sand, which is why these landforms concentrate in arid cores rather than semi-arid margins.
OCR H481/01 (style)16 marksAssess the relative importance of physical and human factors in causing desertification at the margins of drylands.Show worked answer →
A 16-mark extended response across four Levels (AO1 and AO2). Physical factors include climate variability (drought cycles and declining, less reliable rainfall), the fragility of dryland soils and vegetation, and feedbacks such as reduced vegetation lowering infiltration and raising albedo. Human factors include overgrazing, overcultivation, deforestation for fuelwood and poor irrigation (causing salinisation), often driven by population growth and poverty, which strip the protective vegetation and expose soils to wind and water erosion.
A strong AO2 judgement weighs the two: physical drought may trigger degradation, but human pressure usually determines whether the land recovers or crosses a threshold into lasting desertification. Reward use of a located example such as the Sahel, and a supported conclusion, for example that the factors are interlinked, with human pressure amplifying climatic stress, rather than a simple ranking.
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Sources & how we know this
- OCR A-Level Geography (H481) specification — OCR (2016)