GeographyISC Class 11 · Aeolian Landforms

Sand Dunes and Loess (ISC Class 11 Geography)

Updated 17 October 2026 · Fact-checked

Sand dunes are wind-deposited mounds with a gentle windward slope and steep slip face, migrating downwind. Barchan, longitudinal (seif), transverse, parabolic and star dunes differ in wind direction and sand supply. Loess is fine, yellowish, wind-blown dust laid down far from its source, as in northern China.

Wind climbs the gentle slope and drops sand over the steep slip face, so dunes migrate downwind; barchan horns point downwind, parabolic horns upwind.

Illustration drawn for QuestionBuddy.

Understand Sand Dunes and Loess

Dunes. Sand deposited where wind speed falls or an obstacle intervenes. A dune has a gentle windward slope and a steep leeward slip face; dunes migrate downwind.

Barchan: crescent with horns pointing downwind; one wind direction, limited sand on a hard surface; Thar, Sahara.
Longitudinal (seif): long ridges parallel to the wind; strong winds, moderate sand; Thar, Sahara, Australia, Arabia.
Transverse: long ridges at right angles to the wind; plentiful sand, moderate winds.
Parabolic: U-shaped, horns pointing upwind, anchored by vegetation; coasts and semi-arid margins.
Star: several arms, winds from several directions, very high (Sahara, Arabian Empty Quarter).

Shifting dunes threaten farms, roads and settlements; in the Thar they are stabilised by shelterbelts and by planting grasses and trees.

Loess. Very fine, yellowish, wind-blown silt laid in thick layers, often far from source.

Formation: winds lift fine dust from deserts or glacial outwash plains, carry it in suspension, and it settles where winds weaken or rain washes it down over thousands of years.
Characteristics: unstratified, porous, very fine; stands in vertical cliffs; easily gullied by water.
Examples: the Loess Plateau of northern China (dust from the Gobi and other deserts; the Hwang Ho takes its colour and name from loess); Mississippi valley and parts of central Europe, largely from glacial outwash.
Importance: fertile soils for intensive farming but highly erodible; cave dwellings in loess cliffs in China.

Migration. Time = distance / rate of movement.

Sand Dunes and Loess: key facts

Dune types: Barchan horns downwind
Seif parallel to wind
Transverse at right angles
Parabolic horns upwind
Star many arms
Dune migration: $T im e = d i s t an ce / r a t e ∣ S am e u ni t f or b o t h$
Loess: Fine wind-blown silt | Unstratified, porous, fertile, erodible
Control of dunes: Shelterbelts
Grass and tree planting
Stabilisation

Barchan	horns downwind
Seif	parallel to wind
Transverse	at right angles
Parabolic	horns upwind
Star	many arms

How to answer Sand Dunes and Loess questions

Questions ask for dune types (4 marks), loess (3 to 4 marks) or short migration sums.

1For dunes, give shape, wind direction, sand supply and a place.
2For loess, give source, transport, deposition and characteristics.
3For sums, convert km to m and divide by rate.
4Add effects and control measures for shifting dunes.

Sand Dunes and Loess in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Dune and road

Suppose a dune 900 m from a village road moves 12 m each year.

How long before it reaches the road?

Try it first, then show the solutionSolution

Time = 900 / 12 = 75 years.
Planting grass can slow it further.

Answer: 75 years.

Memory hook: Distance over speed.

Dust far away

Suppose a farmer notes thick yellow dust settling on a hill plain hundreds of kilometres from a desert.

Name the deposit and the transport mode.

Try it first, then show the solutionSolution

Fine silt carried in suspension settles as loess.
It forms fertile but erodible soil.

Answer: Loess carried in suspension.

Memory hook: Dust travels, then settles.

Tricks to remember Sand Dunes and Loess

Short memory aids. Say each one aloud once, then use it on a question the same day.

Barchan horns lead
Barchan horns point where the wind goes (downwind); parabolic horns point back upwind.
Use it when: Compare dune shapes.
Seif is a sword
Seif means sword: a long ridge parallel to the wind.
Use it when: Longitudinal dune.

Sand Dunes and Loess: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Dune identification · 1 mark · MCQBoard level

A long dune ridge parallel to the prevailing wind is a:
(a) barchan
(b) transverse dune
(c) seif dune
(d) parabolic dune

Try it first, then show the solutionSolution

Longitudinal.

Answer: (c) Seif dune.

Example 2: Loess definition · 3 marks · Short answerBoard level

Define loess and name two regions where it occurs.

Try it first, then show the solutionSolution

Fine, yellowish, wind-blown silt laid in thick layers.
Loess Plateau of northern China.
Mississippi valley (or central Europe).

Answer: Fine wind-blown dust; northern China and the Mississippi valley.

Example 3: Migration sum · 4 marks · Long answerHarder board level

A barchan 2.4 km from a highway advances 16 m a year. A shelterbelt reduces its rate to 4 m a year. Find the time to reach the highway in each case.

Try it first, then show the solutionSolution

2.4 km = 2,400 m.
Without shelterbelt: 2,400 / 16 = 150 years.
With shelterbelt: 2,400 / 4 = 600 years.
The shelterbelt gives 600 - 150 = 450 extra years.

Answer: 150 years without; 600 years with.

Example 4: Barchan and parabolic · 4 marks · Long answerHarder board level

Distinguish between barchan and parabolic dunes on shape, horns, wind and vegetation.

Try it first, then show the solutionSolution

Barchan is crescent-shaped; parabolic is U-shaped.
Barchan horns point downwind; parabolic horns point upwind.
Barchan forms with one wind direction on a hard surface and limited sand; parabolic forms where vegetation anchors sand.
Examples: Thar for barchans; coasts and semi-arid margins for parabolic.

Answer: Barchan: crescent, horns downwind, bare surface; parabolic: U-shaped, horns upwind, anchored by plants.

Example 5: Loess problem · 5 marks · Case-basedHOTS / competency

Case: A loess plateau has fertile farms, but gullies cut deeply each rainy season. (a) Name two properties of loess that explain this. (b) Explain how loess is formed. (c) Suggest two ways to limit erosion.

Try it first, then show the solutionSolution

(a) It is fine, unstratified and porous, so water erodes it into gullies.
(b) Wind lifts fine dust, carries it in suspension and drops it where wind weakens.
(c) Plant vegetation and terrace slopes.

Answer: (a) Fine and porous (b) wind-borne dust settles (c) vegetation and terracing.

Where students lose marks in Sand Dunes and Loess

The slips examiners see most often, and what to write instead.

Mistake: Reversing barchan horns
Direction mixed.
Wrong working
Barchan horns point upwind
Right working
Barchan horns point downwind
Do this: Barchan horns point downwind.
Usually costs: 1 mark.
Mistake: Writing loess is stratified
Confusion with sediments.
Do this: Loess is unstratified and porous.
Usually costs: 1 mark.
Mistake: Unit slip in migration
km and m mixed.
Do this: Convert km to m.
Usually costs: 1 mark.

Exam tips

List dune types with wind direction and a place.
Mention loess examples with the region.
Show unit conversion in sums.
Include control measures for shifting dunes.

Practice questions on Sand Dunes and Loess

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Star dunes form where winds blow from:
(a) one direction
(b) two opposite directions
(c) several directions
(d) the sea only
Hint
Star-shaped arms.
Answer
(c) Several directions.
Q2 · 3 marks · Short answerHarder board level
A dune advances 20 m a year and is now 1.5 km from a village. How long until it arrives?
Hint
Distance over rate.
Answer
1.5 km = 1,500 m; 1,500 / 20 = 75 years.
Q3 · 4 marks · Long answerHarder board level
Explain why shifting dunes are a hazard in the Thar and how they are controlled.
Hint
Farms, roads; shelterbelts.
Answer
Shifting dunes bury farms, roads and settlements. They are stabilised by planting shelterbelts and grasses and trees.
Q4 · 3 marks · Short answerHarder board level
Explain why the Hwang Ho is known as the Yellow River.
Hint
Loess.
Answer
The river flows across the Loess Plateau of northern China; it carries a heavy load of yellowish loess dust, which gives it its colour and name.
Q5 · 4 marks · Case-basedHOTS / competency
Case: Two sites show different dunes: crescents on a hard gravel plain with one steady wind, and U-shaped dunes with grass cover near the coast. (a) Name both. (b) Explain the difference in sand supply or surface. (c) Which is stabilised by vegetation?
Hint
Barchan and parabolic.
Answer
(a) Barchan and parabolic. (b) Barchans form with limited sand on a hard surface; parabolic dunes form where vegetation anchors sand. (c) The parabolic dune.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Slip face is on which side?Show answer
Leeward side.
2.Loess is?Show answer
Wind-blown silt.
3.Seif is another name for?Show answer
Longitudinal dune.
4.Which dune has several arms?Show answer
Star dune.
5.Major loess area?Show answer
Northern China.

Sand Dunes and Loess: frequently asked questions

Do dunes move?

Yes, downwind.

Is loess fertile?

Yes, but easily eroded.

Where are barchans common in India?

The Thar desert.