IELTS Reading: Sand Dunes Passage Explained with Answers & Analysis

“Sand Dunes” is a reading passage focused on Geography and Science—a common theme in the IELTS exam. This passage is particularly challenging due to the “Matching Headings” task, which requires the ability to quickly and accurately summarize the main idea of each paragraph. In this article, the ECE language center provides an in-depth analysis of the entire passage, complete with answers, detailed explanations, and a summary of key vocabulary to help you confidently tackle similar question types.

Reading Passage and Questions: Sand Dunes

Reading Content

(A) One of the main problems posed by sand dunes is their encroachment on human habitats. Sand dunes threaten buildings and crops in Africa, the Middle East, and China. Preventing sand dunes from overwhelming cities and agricultural areas has become a priority for the United Nations Environment Program. On the other hand, dune habitats provide niches for highly specialized plants and animals, including numerous rare and endangered species.

(B) Sand is usually composed of hard minerals such as quartz that cannot be broken down into silt or clay. Yellow, brown and reddish shades of sand indicate their presence of iron compounds. Red sand is composed of quartz coated by a layer of iron oxide. White sands are nearly pure gypsum. Sand with a high percentage of silicate can be used in glassmaking.

(C) The most common dune form on Earth and on Mars is crescentic. Crescent-shaped mounds are generally wider than they are long. The slipfaces are on the concave sides of the dunes. These dunes form under winds that blow consistently from one direction, and they also are known as barchans or transverse dunes.

(D) Radially symmetrical, star dunes are pyramidal sand mounds with slipfaces on there or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes. Straight or slightly sinuous sand ridges typically much longer than they are wide are known as linear dunes.

(E) Once sand begins to pile up, ripples and dunes can form. Wind continues to move sand up to the top of the pile until the pile is so steep that it collapses under its own weight. The collapsing sand comes to rest when it reaches just the right steepness to keep the dune stable. This angle, usually about 30-34°, is called the angle of repose. Every pile of loose particles has a unique angle of repose…

(F) The repeating cycle of sand inching up the windward side to the dune crest, then slipping down the dune’s slip face allows the dune to inch forward, migrating in the direction the wind blows. As you might guess, all of this climbing then slipping leaves its mark on the internal structure of the dune… This structure is called cross-bedding…

(G) Sand dunes can “sing” at a level up to 115 decibels and generate sounds in different notes… The tone of the sounds depended primarily on the size of the grains.

(H) Scientists performed a computer simulation on patterns and dynamics of desert dunes in laboratory. Dune patterns observed in deserts were reproduced. From the initial random state, stars and linear dunes are produced… which greatly helps them build a model to simulate a sand move.

Questions

Questions 27-34 (Matching Headings) Choose the correct heading for paragraphs A-H from the list below.

List of Headings

i. potential threat to buildings and crops despite of benefit

ii. the cycle of sand moving forward with wind

iii. protection method in various countries

iv. scientists simulate sand move and build model in lab

v. sand composition explanation

vi. singing sand dunes

vii. other types of sand dunes

viii. the personal opinion on related issues

ix. reasons why sand dunes form

x. the most common sand dune

27. Paragraph A
28. Paragraph B
29. Paragraph C
30. Paragraph D
31. Paragraph E
32. Paragraph F
33. Paragraph G
34. Paragraph H

Questions 35-36 (Multiple Choice)

35. What is the main composition of white sand made of according to the passage?

A. Quartz

B. Gypsum

C. Lime

D. Iron

36. Which one is not mentioned as a sand type in this passage?

A. Linear

B. Crescentic

C. Overlap

D. Star

Questions 37-40 (Summary Completion) Complete the summary using the list of words, A-J below.

Crescentic is an ordinary 37……………………….. on both Earth and Mars, apart from which, there are also other types of sand dunes. Different color of the sand reflects different components, some of them are rich in 38………………………… that can not be easily broken into clay. Sand dunes can “sing” at a level up to 115 decibels and generate sounds in different notes. Sand dunes can be able to 39………………………. at a certain level of sound intensity, and the different size of grains creates different 40………………………… of the sounds.

Summary of the “Sand Dunes” Passage

The passage provides an overview of sand dunes, covering the following aspects:

• (A): Sand dunes are both a threat to humans (encroaching on homes and crops) and an important habitat for various species.
• (B): Describes the chemical composition and minerals that create different sand colors.
• (C, D): Introduces the main types of sand dunes, including crescentic (the most common), star, and linear dunes.
• (E, F): Explains the physical mechanisms of dune formation (angle of repose) and their migration cycle with the wind.
• (G): Describes the phenomenon of “singing sand dunes” and the science behind it.
• (H): Reports on how scientists use computer simulations to study and replicate sand dune formation.

Key Vocabulary and Structures

1. Encroachment on (noun): The act of intruding or advancing beyond proper limits.
2. Niches (noun): Ecological roles or suitable habitats for specific organisms.
3. Crescentic (adjective): Having the shape of a crescent or a new moon.
4. Radially symmetrical (adjective phrase): Arranged around a central axis.
5. Sinuous (adjective): Having many curves and turns.
6. Angle of repose (noun phrase): The steepest angle at which loose material remains stable.
7. Laminations (noun): Thin layers or plates.
8. Resonate (verb): To produce or be filled with a deep, full, reverberating sound.

Answer Key and Detailed Explanations

Questions 27-34

27. Paragraph A ➞ i. potential threat to buildings and crops despite of benefit

• Explanation: Paragraph A highlights the dual nature of sand dunes: they are a “threat” to buildings and crops, yet they also provide beneficial habitats.

28. Paragraph B ➞ v. sand composition explanation

• Explanation: The entire paragraph is dedicated to explaining the composition of sand, including the minerals involved and the reasons for its varying colors.

29. Paragraph C ➞ x. the most common sand dune

• Explanation: The first sentence explicitly states: “The most common dune form on Earth and on Mars is crescentic.”

30. Paragraph D ➞ vii. other types of sand dunes

• Explanation: Paragraph D describes other types of dunes beyond the crescentic ones mentioned in paragraph C, specifically star and linear dunes.

31. Paragraph E ➞ ix. reasons why sand dunes form

• Explanation: Paragraph E explains the physical process of dune formation, from sand accumulation to collapsing under its own weight and stabilizing at the “angle of repose.”

32. Paragraph F ➞ ii. the cycle of sand moving forward with wind

• Explanation: Paragraph F describes the repeating “cycle” of sand moving up the windward side and slipping down, causing the dune to migrate forward.

33. Paragraph G ➞ vi. singing sand dunes

• Explanation: Paragraph G focuses entirely on “singing” sand dunes, describing their decibel levels, notes, and scientific causes.

34. Paragraph H ➞ iv. scientists simulate sand move and build model in lab

• Explanation: Paragraph H describes scientists performing “computer simulations” in a “laboratory” to build a model.

Questions 35-36

35. B. Gypsum

• Evidence (Paragraph B): “White sands are nearly pure gypsum.”
• Explanation: This sentence directly identifies the primary component of white sand.

36. C. Overlap

• Explanation: The passage mentions Linear, Crescentic, and Star dunes. “Overlap” is not mentioned as a type of sand dune.

Questions 37-40

37. B. shape

• Evidence (Paragraph C): “The most common dune form on Earth… is crescentic.”
• Explanation: “Form” is a synonym for “shape.”

38. G. minerals

• Evidence (Paragraph B): “Sand is usually composed of hard minerals such as quartz…”
• Explanation: The summary notes that sand is rich in “minerals.”

39. H. sing

• Evidence (Paragraph G): “Sand dunes can “sing” at a level up to 115 decibels…”
• Explanation: The passage uses the verb “sing” to describe the sound produced by the dunes.

40. D. tone

• Evidence (Paragraph G): “The tone of the sounds depended primarily on the size of the grains.”
• Explanation: Different grain sizes produce different “tones.”

Conclusion

The “Sand Dunes” passage is an excellent exercise for the Matching Headings skill, which requires you to quickly identify the main idea of each paragraph. An effective strategy is to skim the headings first, underline keywords, and then read each paragraph to find the best match rather than working strictly in order. We hope that with this detailed explanation and vocabulary list from ECE, you have gained valuable experience to conquer this challenging task.