Key Idea: Topic 9.2 is about how extreme environments are physically shaped — and how to take a named landform and explain which process built it. It pulls together two contrasting cold/hot worlds: 9.2.1 — hot deserts: weathering breaks rock in place, wind (aeolian) action sandblasts and builds dunes, and rare but powerful water (fluvial) action carves wadis and lays down fans and playas. 9.2.2 — glacial & periglacial: moving ice plucks and abrades to carve corries, aretes and troughs, while in the periglacial fringe it is the freezing and thawing of water in permafrost (freeze-thaw, solifluction, frost heave) that does the work. This is an Option (Extreme environments), examined on Paper 1 — SL answers 2 options, HL answers 3 (same questions). Each option = a short structured question off a figure plus a [10] extended-answer essay (Examine / To what extent / Discuss).
🏜️ 9.2.1 — Hot desert processes and landforms
A hot desert is shaped by three families of process: weathering (rock broken in place), wind action (erosion by abrasion/deflation + deposition of dunes) and water action (rare flash floods that carve and deposit). Deserts look 'dry', but water still does a lot of the shaping. The data-response skill is reading a value off a figure — for example which dune type forms (sand supply + wind + vegetation) — then Explaining a named landform by its process chain.
Desert processes and the landforms they build
| Process family | What it does | Landforms it makes |
|---|---|---|
| Weathering (in place) | Heat, salt and water break rock where it sits — exfoliation, salt crystal growth, granular disintegration | Loose debris that feeds wind and water erosion |
| Wind erosion (aeolian) | Abrasion sandblasts rock near the ground; deflation lifts loose sand away | Rock pedestals, yardangs, deflation hollows, desert pavement |
| Wind deposition (aeolian) | Wind slows or hits an obstacle and drops its sand load; the dune then migrates | Sand dunes — transverse, longitudinal (seif), star, barchan |
| Water action (fluvial) | Rare flash floods erode steep valleys and deposit as the channel slows | Wadis/canyons, alluvial fans, playas (salt lakes) |
Key terms — hot deserts
- Weathering — the breakdown of rock in place (no transport), by heat, salt or chemical action.
- Aeolian action — wind erodes (abrasion, deflation), transports and deposits sand.
- Abrasion — wind-blown sand sandblasts rock; strongest near the ground where most sand is carried.
- Deflation — wind lifts and removes loose sand, lowering the surface into a hollow.
- Fluvial action — running water from flash floods erodes and deposits, even in deserts.
Tip: 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. A dune's type depends on sand supply, wind and vegetation — read it straight off the figure, then explain.
🏔️ 9.2.2 — Glacial and periglacial processes and landforms
Glacial landscapes are carved by moving ice: plucking (ice freezes onto rock and pulls it away) and abrasion (embedded rock grinds the bed like sandpaper) cut corries, aretes and U-shaped troughs. Periglacial landscapes are the cold fringe beyond the ice, underlain by permafrost. Here ice does not flow — the repeated freezing and thawing of water (freeze-thaw, solifluction, frost heave) builds the landforms. The corrie-aspect figure below is a typical Paper 1 stimulus.
Read the axis first. Most corries face the shaded, colder N–NE slopes where snow survives longest and ice can form and erode.
🔒 Interactive diagram
Explore the labelled diagram, charts and maps for this topic in study mode.
Glacial vs periglacial — process and landforms
| Setting | Process at work | Landforms it builds |
|---|---|---|
| Glacial erosion | Plucking + abrasion by moving ice; freeze-thaw feeds loose rock to the ice | Corrie (with tarn), arete, pyramidal peak (horn), U-shaped trough |
| Glacial deposition | Ice dumps its load of debris (till) as it melts | Moraine, drumlin, erratic |
| Periglacial | Freeze-thaw, solifluction and frost heave in permafrost — water freezing/thawing, not flowing ice | Patterned ground, solifluction lobes, pingos, thermokarst |
Key terms — glacial & periglacial
- Permafrost — ground frozen for two or more years; the surface active layer thaws each summer.
- Plucking — ice freezes onto rock and the moving ice pulls it away, eroding the bed.
- Abrasion — rock frozen into the ice grinds the bedrock smooth, like sandpaper.
- Freeze-thaw weathering — water in cracks freezes, expands ~9% and shatters rock into angular fragments.
- Solifluction — the waterlogged active layer creeps slowly downslope over frozen ground in summer.
- Mass balance — accumulation (snow gained) vs ablation (ice lost); it decides whether a glacier advances or retreats.
Heat from drilling, buildings and warm oil thaws the frozen ground; the thawed soil subsides and loses strength, so pipelines fracture and foundations tilt. This is why Arctic infrastructure (e.g. the Alaskan oilfields, Siberian towns) is raised on piles, insulated or refrigerated — not because the frozen ground is simply 'too hard to drill'.
✍️ IB-style questions
Explain how wind action produces two contrasting landforms in a hot desert.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
"Water, rather than wind, is the main force shaping hot desert landforms." To what extent do you agree?
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
✅ Quick self-check
Tap each card to reveal the answer.
What does weathering mean in a desert? The breakdown of rock in place (no transport), by heat (exfoliation), salt crystal growth or chemical action — it feeds loose debris to wind and water.
How does wind erosion form a rock pedestal? Wind carries most sand near the ground, so abrasion is strongest at the base — it wears the base thin while the top survives, leaving a mushroom shape.
How does a corrie form? Snow collects in a hollow → freeze-thaw + plucking steepen the back wall → abrasion deepens the floor → a rock lip and tarn remain.
Why do most corries face north or east? Those slopes are shaded and coldest, so snow survives longest and ice can form and erode there — the aspect chart shows the clustering.
Why does thawing permafrost damage Arctic pipelines? Heat from infrastructure thaws the frozen ground, which subsides and loses strength, so pipes fracture — hence raised, insulated piles.
🎯 Highest-yield exam reminders
Exam Tips
- Option C is on PAPER 1: a structured question off a figure PLUS a [10] extended answer per option (SL does 2 options, HL does 3 — same questions).
- Always pair the landform with its PROCESS CHAIN — naming alone scores little (wind abrasion near the ground → thin base → pedestal).
- Deserts: weathering = in place; wind builds dunes + pedestals/yardangs; water cuts wadis + builds fans/playas. Dune type = sand + wind + vegetation.
- Glacial = moving ice (plucking + abrasion → corries, aretes, troughs); periglacial = freeze-thaw of water in permafrost → patterned ground, lobes, pingos.
- Permafrost thaws when heated → subsidence → raised/insulated pipelines (NOT 'too hard to drill').
- On the [10] essay: develop two+ named landforms tied to processes, use NAMED places (Sahara, Death Valley, the Alps), weigh the processes, and end on a clear JUDGEMENT.