The big idea: A hot desert is shaped by three groups of processes: weathering (rock broken in place), wind action (aeolian — wind erodes, transports and deposits sand), and water action (fluvial — rare but powerful flash floods).
Deserts look 'dry', but water still does a lot of the shaping. The big Option C skill is to take a named landform and explain which process made it — and to weigh wind against water in a markband essay.
Key terms for desert landforms
- Weathering — the breakdown of rock in place (no movement), by heat, salt or water.
- Aeolian (wind) action — wind erodes (abrasion, deflation), transports and deposits sand.
- Abrasion — wind-blown sand sandblasts rock, wearing it away (a wind-erosion process).
- Deflation — wind lifts and removes loose sand, lowering the surface into a hollow.
- Fluvial (water) action — running water from flash floods erodes and deposits, even in deserts.
- Aeolian deposition — wind drops its sand load, building sand dunes where it slows.
Wind vs water — the deal-breaker: Wind shapes the erosion features (rock pedestals, yardangs, deflation hollows) and builds dunes.
Water (rare flash floods) carves wadis and canyons and deposits alluvial fans and playas. Most desert landscapes are made by both — which is why the [10] essay asks you to weigh them.
How this is tested: Paper 1 Option C opens with a data-response. One recurring stimulus is a triangular (ternary) graph of the three things that control which sand dune forms — the amount of sand, the wind strength/direction, and the vegetation. You Identify the dune type for a given mix, or Estimate a percentage off an axis. Read each axis carefully and quote the value.
A sand dune forms by aeolian deposition: wind carries sand, hits an obstacle or slows down, and drops its load. The dune then migrates as sand is blown up the gentle windward slope and slips down the steep leeward slope. The type of dune depends on the sand supply, the wind, and how much vegetation anchors the sand.
| Conditions on the graph | Dune type that forms | Why |
|---|---|---|
| Lots of sand, one steady wind direction | Transverse (ridges across the wind) | Plentiful sand piles into ridges at right angles to the wind |
| Limited sand, strong wind | Longitudinal / seif (long, parallel ridges) | Little sand is stretched into long ridges aligned with the wind |
| Moderate sand, winds from several directions | Star dune (radiating arms) | Shifting winds pile sand into a central peak with arms |
| Some sand + some vegetation to anchor it | Barchan / crescentic (horns point downwind) | Vegetation and an obstacle fix sand; horns trail downwind |
Reading the triangular graph: Each corner = 100% of one control (sand, wind, vegetation). Follow the gridlines from a plotted point back to each axis. To Estimate a value, read where the point sits on that axis (e.g. the lowest sand needed for transverse dunes is about 35%, accept 30-40%).
Study smarter, not longer
Most students waste 40% of study time on topics they already know. Our AI tracks your progress and optimizes every minute.
Try Smart Study Free7-day free trial • No card required
Three families of process shape a desert. Weathering breaks rock in place; wind erosion then sandblasts and lowers the surface; water erosion (rare flash floods) carves and deposits. Each makes its own landforms — name the process, then the landform it builds.
| Process | How it breaks rock |
|---|---|
| Exfoliation (thermal) | Huge day-night temperature swings expand and contract the rock surface, so outer layers peel off like onion skins |
| Granular / block disintegration | Different minerals expand by different amounts when heated, loosening grains or whole blocks |
| Salt crystal growth (haloclasty) | Salty water seeps into cracks; as it evaporates, growing salt crystals prise the rock apart |
| Chemical weathering (hydrolysis) | The little dew/water that is present reacts with minerals, slowly rotting and weakening the rock |
Wind-erosion landforms (aeolian)
- Rock pedestal / mushroom rock — abrasion is strongest near the ground (most sand is carried low), so the base is worn thin while the top survives.
- Yardang — abrasion grooves softer rock into long, streamlined ridges aligned with the wind.
- Deflation hollow — deflation lifts and removes loose sand, lowering the surface into a basin.
- Desert pavement — deflation blows the fines away, leaving a surface of stones too heavy to lift.
Water-formed landforms (fluvial)
- Wadi / canyon — a flash flood erodes a steep, dry valley that only holds water briefly.
- Alluvial fan — as a flooded channel leaves the mountains onto flat ground it slows and dumps a fan of sediment.
- Playa / salt lake — flood water collects in a basin and evaporates, leaving a flat salt crust.
- Mesa & butte — flat-topped uplands left when water (helped by weathering) strips the softer rock around a hard cap.
Always pair the landform with its process: Marks come from the process chain, not the name. Wind abrasion is strongest near the ground -> it wears the base of a rock thin -> a mushroom-shaped pedestal. Name the landform, then explain the process step by step.
How this is tested - the [10] essay: Paper 1 Option C ends with a 10-mark markband essay, usually weighing water against wind (or asking how important one process is) in shaping desert landforms.
Top band needs: accurate terms, two or more landforms each tied to a process, named deserts as evidence, a weighing of the two processes (including over time), and a clear conclusion.
Named deserts to use as evidence: Sahara / Sahel — vast ergs (sand seas) of wind-built dunes, but also fossil wadis cut by wetter past climates (pluvials). Atacama (Chile) — one of the driest places on Earth; salt playas and salt weathering dominate. Death Valley (USA) — classic alluvial fans and the Badwater salt playa from flash floods. Name a desert + a feature, not just 'a hot desert'.
Markband marks: (1) Tie each landform to its process (wadi <- flash flood; dune <- aeolian deposition). (2) Anchor to a named desert (Sahara, Atacama, Death Valley). (3) Weigh water and wind, then end on an explicit judgement that answers the question.