IELTS Reading Test Academic 240 – Sand Dunes
You should spend about 20 minutes on Questions 1-13 which are based on IELTS Reading Test Academic 240 – Sand Dunes Reading Passage Below:-
Sand Dunes
{A} One of the main problems posed by sand dunes is their encroachment on human habitats. Sand dunes move by different means, all of them aided by the wind. 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 the 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. Sandstone is created by sand, mixed with lime, chalk, or some other material that acts as a binding agent, that is deposited in layers at the bottom of a sea or other area and pressed together into the rock by the great pressure of sediments that are deposited on top over thousands or millions of years.
{C} The most common dune form on Earth and on Mars is crescentic. Crescent-shaped mounds are generally wider than they are long. The slip faces 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. Some types of crescentic dunes move more quickly over desert surfaces than any other type of dune. A group of dunes moved more than 100 meters per year between 1954 and 1959 in China’s Ningxia Province, and similar speeds have been recorded in the Western Desert of Egypt. The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than 3 kilometers, are in China’s Taklamakan Desert.
{D} Radially symmetrical, star dunes are pyramidal sand mounds with slip faces on three or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes. Star dunes grow upward rather than laterally. They dominate the Grand Erg Oriental of the Sahara. In other deserts, they occur around the margins of the sand seas, particularly near topographic barriers. In the southeast Badain Jaran Desert of China, the star dunes are up to 500 meters tall and maybe the tallest dunes on Earth. Straight or slightly sinuous sand ridges typically much longer than they are wide are known as linear dunes. They may be more than 160 kilometers (99 mi) long. Some linear dunes merge to form Y-shaped compound dunes. Many forms in bidirectional wind regimes. The long axes of these dunes extend in the resultant direction of sand movement. Linear loess hills known as pahas are superficially similar.
{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, depending upon the properties of the material it’s made of, such as the grain size and roundness. Ripples grow into dunes with an increase in wind and sand input.
{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. The image on the right shows a fossil sand dune structure preserved in the Merced Formation at Fort Funston, Golden Gate National Recreation Area. The sloping lines or laminations you see are the preserved slip faces of a migrating sand dune. This structure is called cross-bedding and can be the result of either wind or water currents. The larger the cross-bedded structure, however, the more likely it is to be formed by wind, rather than water.
{G} Sand dunes can “sing” at a level up to 115 decibels and generate sounds in different notes. The dunes at Sand Mountain in Nevada usually sing in a low C but can also sing in B and C sharp. The La Mar de Dunas in Chile hum in F while those at the Ghord Lahmar in Morocco howl in G sharp. The sounds are produced by avalanches of sand generated by blowing winds. For a while, it was thought that the avalanches caused the entire dune to resonate like a flute or violin but if that were true then different size dunes would produce different notes. In the mid-2000s, American, French, and Moroccan scientists visiting sand dunes in Morocco, Chile, China, and Oman published a paper in the Physical Review Letters that determined the sounds were produced by collisions between grains of sand that caused the motions of the grains to become synchronized, causing the outer layer of a dune to vibrate like the cone of a loudspeaker, producing sound. 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 the laboratory. Dune patterns observed in deserts were reproduced. From the initial random state, stars and linear dunes are produced, depending on the variability of the wind direction. The efficiency in sand transport is calculated through the course of development. Scientists found that sand transport is the most efficient in the linear transverse dune. The efficiency in sand transport always increased through evolution, and the way it increased was stepwise. They also found that the shadow zone, the region where the sand wastes the chance to move, shrinks through the course of evolution, which greatly helps them build a model to simulate a sand move.
You should spend about 20 minutes on the following questions, which are based on the reading passages on the following pages.
Questions 1-8
Reading passage A-H
Choose the correct heading for paragraphs A-H from the list below. Write the correct number, i-x, in boxes 1-8 on your answer sheet.
| List of Headings (i) potential threat to buildings and crops despite the 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 type |
Question 1:- Paragraph A
Question 2:- Paragraph B
Question 3:- Paragraph C
Question 4:- Paragraph D
Question 5:- Paragraph E
Question 6:- Paragraph F
Question 7:- Paragraph G
Question 8:- Paragraph H
Question 9-10
Answer questions 9-10 and choose the correct letter A B C or D.
Question 9:- What is the main component of white sand made according to the passage?
(A) Quartz
(B) Gypsum
(C) Lime
(D) Iron
Question 10:- Which one is not mentioned as a sand type in this passage?
(A) Linear
(B) Crescentic
(C) Overlap
(D) Star
Questions 11-14
Complete the summary using the list of words, A-J below.
Write the correct letter, A-J in boxes 37-40 on your answer sheet.
|
Crescentic is an ordinary……...11.……..on both Earth and Mars, apart from which, there are also other types of sand dunes. Different colors of the sand reflect different components, some of them are rich in………12………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 ……...13.…….. at a certain level of sound intensity, and the different size of grains creates different ………14.…….. of the sounds. |
| A quartz | B shape | C pressure | D tone | E protection |
| F category | G minerals | H sing | I lab | J direction |
Answers IELTS Reading Test Academic 240 – Sand Dunes
| 1 | I | 8 | IV |
| 2 | V | 9 | B |
| 3 | X | 10 | C |
| 4 | VII | 11 | B |
| 5 | IX | 12 | G |
| 6 | II | 13 | H |
| 7 | VI | 14 | D |