AQA A-level Geography · 3.1.2

Desert processes and landforms

50 exam-style questions with answers for 3.1.2 Desert processes and landforms in AQA A-level Geography (spec 7037). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official AQA material.

All 50 questions and answers

Question 1 · Spec 3.1.2.2 · Energy sources
Name the three main sources of energy in hot desert environments. [3 marks]
Answer:
Insolation (1); wind (1); runoff (1).
Question 2 · Spec 3.1.2.2 · Energy sources
Explain why insolation is important in desert geomorphology. [2 marks]
Answer:
Intense heating and cooling cause thermal stress that weathers rock (1); heating of the ground creates convection and winds that move sediment (1).
Question 3 · Spec 3.1.2.2 · Energy sources
Explain why wind is an effective geomorphological agent in deserts. [3 marks]
Answer:
There is little vegetation to protect the surface or slow the wind (1); sediment is loose and dry (1); winds are strong and often unobstructed across open surfaces (1).
Question 4 · Spec 3.1.2.2 · Energy sources
Explain why runoff is described as having an episodic role in deserts. [2 marks]
Answer:
Rain falls rarely and unpredictably (1); but when it does, flash floods have large amounts of energy and can change the landscape greatly in a short time (1).
Question 5 · Spec 3.1.2.2 · Sediment budgets
What is a sediment cell? [2 marks]
Answer:
A section of land or coast in which the movement of sediment can be studied as a system (1); with sources, transfers, stores and sinks of sediment (1).
Question 6 · Spec 3.1.2.2 · Sediment budgets
Define a sediment budget. [2 marks]
Answer:
The balance between sediment entering and leaving a sediment cell (1); a positive budget means gains exceed losses, a negative budget means losses exceed gains (1).
Question 7 · Spec 3.1.2.2 · Sediment budgets
Name three sources of sediment in a hot desert. [3 marks]
Answer:
Weathering of local bedrock (1); material carried by flash floods and ephemeral rivers (1); wind-blown sand and dust from elsewhere (1).
Question 8 · Spec 3.1.2.2 · Sediment budgets
Explain how a positive sediment budget affects a desert landscape. [2 marks]
Answer:
More sediment arrives than leaves, so stores such as dunes or alluvial fans grow (1); sediment accumulates, building depositional landforms (1).
Question 9 · Spec 3.1.2.2 · Sediment budgets
Explain why sediment budgets in deserts can change suddenly. [2 marks]
Answer:
Rare storm events produce flash floods that move large volumes of sediment quickly (1); strong winds can also remove or deposit large amounts of sand in a short time (1).
Question 10 · Spec 3.1.2.2 · Weathering and mass movement
Define weathering. [1 mark]
Answer:
The breakdown of rock in situ (where it lies) by physical, chemical or biological processes without movement.
Question 11 · Spec 3.1.2.2 · Weathering and mass movement
Distinguish between erosion and transportation. [2 marks]
Answer:
Erosion is the wearing away of the land surface and removal of material by agents such as wind and water (1); transportation is the movement of that eroded material from one place to another (1).
Question 12 · Spec 3.1.2.2 · Weathering and mass movement
Explain how thermal fracture weathers desert rocks. [3 marks]
Answer:
Rocks heat and expand by day and cool and contract at night (1); repeated expansion and contraction causes stress (1); cracks develop and the rock splits, especially where minerals expand at different rates (1).
Question 13 · Spec 3.1.2.2 · Weathering and mass movement
Explain how exfoliation occurs. [3 marks]
Answer:
The outer surface of rock heats up and expands more than the cooler interior (1); repeated heating and cooling, helped by moisture from dew, causes stress (1); curved sheets peel off, like the layers of an onion (1).
Question 14 · Spec 3.1.2.2 · Weathering and mass movement
Explain how granular disintegration occurs. [2 marks]
Answer:
Coarse-grained rocks such as granite have minerals that expand at different rates when heated (1); the grains loosen and fall away, producing sand (1).
Question 15 · Spec 3.1.2.2 · Weathering and mass movement
Explain how block disintegration occurs. [2 marks]
Answer:
Repeated heating and cooling stress rock along joints and bedding planes (1); large blocks break away from the rock mass (1).
Question 16 · Spec 3.1.2.2 · Weathering and mass movement
Explain how salt weathering breaks down desert rocks. [3 marks]
Answer:
Water containing dissolved salts enters pores and cracks in rock (1); the water evaporates, leaving salt crystals that grow and exert pressure (1); this forces the rock apart so grains and flakes break away (1).
Question 17 · Spec 3.1.2.2 · Weathering and mass movement
Explain how chemical weathering operates in deserts. [2 marks]
Answer:
Occasional rain and dew provide moisture for reactions such as hydration and oxidation (1); oxidation can colour rock surfaces red or brown, and water helps break down minerals slowly (1).
Question 18 · Spec 3.1.2.2 · Weathering and mass movement
Explain why chemical weathering is less important in deserts than in humid areas. [2 marks]
Answer:
Chemical reactions need water, which is scarce in deserts (1); low rainfall means weathering products are not easily dissolved and removed (1).
Question 19 · Spec 3.1.2.2 · Weathering and mass movement
Describe mass movement in hot deserts. [2 marks]
Answer:
Rockfalls, landslides and debris flows occur on steep slopes (1); they are often triggered by flash floods or weathering that weakens rock (1).
Question 20 · Spec 3.1.2.2 · Wind processes
Distinguish between deflation and abrasion. [2 marks]
Answer:
Deflation is the removal of loose, fine particles by wind (1); abrasion is the wearing away of surfaces by wind-blown particles striking rock (1).
Question 21 · Spec 3.1.2.2 · Wind processes
Describe how wind transports sediment by suspension, saltation and surface creep. [3 marks]
Answer:
Suspension: very fine dust and silt are carried in the air (1); saltation: sand grains bounce along the surface in short hops (1); surface creep: larger grains roll or are pushed along the ground (1).
Question 22 · Spec 3.1.2.2 · Wind processes
Explain why saltation is the most important process of wind transport of sand. [2 marks]
Answer:
Sand grains are too heavy to stay suspended but light enough to be lifted briefly (1); impact of saltating grains dislodges others and causes creep, which also drives abrasion (1).
Question 23 · Spec 3.1.2.2 · Wind processes
Explain when wind deposition occurs. [2 marks]
Answer:
When wind speed falls or the wind meets an obstacle such as a rock or vegetation (1); sediment can no longer be carried and settles, forming dunes or sheets of sand (1).
Question 24 · Spec 3.1.2.2 · Wind processes
Suggest three factors that affect the amount of wind erosion. [3 marks]
Answer:
Wind speed (1); the amount of vegetation cover (1); the size and dryness of the sediment (1).
Question 25 · Spec 3.1.2.2 · Wind processes
Explain why surfaces covered by large stones suffer less wind erosion. [2 marks]
Answer:
Large stones are too heavy for the wind to lift (1); they armour the surface and protect finer particles below (1).
Question 26 · Spec 3.1.2.2 · Water processes
Distinguish between exogenous, endoreic and ephemeral water sources in deserts. [3 marks]
Answer:
Exogenous: rivers such as the Nile that rise outside the desert and flow through it (1); endoreic: rivers that drain inland to a basin or lake with no outlet to the sea (1); ephemeral: streams that flow only briefly after rain (1).
Question 27 · Spec 3.1.2.2 · Water processes
Explain how sheet flooding occurs. [2 marks]
Answer:
Heavy rain falls on hard, dry ground that cannot absorb water quickly (1); water spreads as a thin, unconfined sheet, carrying fine sediment across the surface (1).
Question 28 · Spec 3.1.2.2 · Water processes
Explain how channel flash flooding occurs. [3 marks]
Answer:
Intense rain over hard, dry ground produces rapid runoff (1); water becomes concentrated in channels such as wadis (1); it rushes along with high energy, often carrying large boulders, then disappears within hours (1).
Question 29 · Spec 3.1.2.2 · Water processes
Explain why flash floods can transport large amounts of sediment. [2 marks]
Answer:
They have high velocity and large discharge for a short time (1); there is plentiful loose weathered material and little vegetation to resist erosion (1).
Question 30 · Spec 3.1.2.2 · Water processes
Compare the roles of wind and water in shaping desert landscapes. [3 marks]
Answer:
Wind acts frequently but moves mainly fine material (1); water acts rarely but with great energy, so is more effective at moving coarse material and cutting channels (1); both depend on little vegetation and loose sediment (1).
Question 31 · Spec 3.1.2.3 · Aeolian landforms
Explain how deflation hollows form. [3 marks]
Answer:
Wind removes loose, fine sediment from the surface (1); this lowers the ground until a hard layer or the water table is reached (1); the hollow may deepen and widen, as in the Qattara Depression (1).
Question 32 · Spec 3.1.2.3 · Aeolian landforms
Explain how desert pavement forms. [3 marks]
Answer:
Wind removes fine sand and dust by deflation (1); stones too heavy to move are left behind and concentrated (1); they fit together to form a protective surface of interlocking pebbles over finer material (1).
Question 33 · Spec 3.1.2.3 · Aeolian landforms
What is a ventifact and how does it form? [2 marks]
Answer:
A stone or rock shaped, polished or faceted by wind-blown sand (1); by abrasion on its windward faces (1).
Question 34 · Spec 3.1.2.3 · Aeolian landforms
Explain how yardangs form. [3 marks]
Answer:
Wind-blown sand abrades rock made of alternating hard and soft layers (1); weaker rock is cut into troughs, leaving ridges of more resistant rock (1); the ridges are streamlined and aligned parallel to the prevailing wind (1).
Question 35 · Spec 3.1.2.3 · Aeolian landforms
Explain how zeugen form. [3 marks]
Answer:
A resistant caprock overlies softer rock (1); joints are widened by weathering and abrasion cuts into the soft rock beneath (1); this leaves tabular ridges of resistant rock protecting the softer rock below, which can reach tens of metres high (1).
Question 36 · Spec 3.1.2.3 · Aeolian landforms
Describe the shape of a barchan dune. [2 marks]
Answer:
Crescent-shaped with the horns pointing downwind (1); a gentle windward slope and a steep slip face on the lee side (1).
Question 37 · Spec 3.1.2.3 · Aeolian landforms
Explain how barchan dunes form and move. [3 marks]
Answer:
They form where sand supply is limited and wind is from a fairly constant direction (1); sand is blown up the gentle windward slope by saltation and avalanches down the slip face (1); this transfers sand forward, so the dune migrates downwind (1).
Question 38 · Spec 3.1.2.3 · Aeolian landforms
Explain how seif dunes form. [3 marks]
Answer:
They form where there is a plentiful sand supply and winds blow from two directions at an angle (1); sand accumulates in long, sinuous ridges (1); the ridges lie roughly parallel to the resultant wind direction and can stretch for many kilometres (1).
Question 39 · Spec 3.1.2.3 · Water landforms
Describe the features of a wadi. [2 marks]
Answer:
A steep-sided, flat-floored dry valley cut by water (1); usually dry but occupied by flash floods after rain, with a floor of coarse debris (1).
Question 40 · Spec 3.1.2.3 · Water landforms
Explain how bahadas form. [3 marks]
Answer:
Streams leave steep mountain valleys onto flat plains (1); they lose energy and water, and deposit their sediment in fan-shaped alluvial fans (1); neighbouring fans spread and merge into a continuous gentle apron called a bahada (1).
Question 41 · Spec 3.1.2.3 · Water landforms
Describe and explain the formation of pediments. [3 marks]
Answer:
Gently sloping rock surfaces at the foot of a mountain front, often with a thin veneer of sediment (1); formed as sheet floods and streams planate (erode laterally across) the rock (1); and as weathering and slope retreat push the mountain front back (1).
Question 42 · Spec 3.1.2.3 · Water landforms
Explain how playas form. [3 marks]
Answer:
Water collects in an enclosed (endoreic) basin after rain (1); it forms a temporary lake that evaporates quickly (1); leaving a flat bed encrusted with salts and fine sediment (1).
Question 43 · Spec 3.1.2.3 · Water landforms
Explain how inselbergs form. [3 marks]
Answer:
They are isolated, steep-sided hills of resistant rock standing above a plain (1); surrounding rock is weathered and eroded as pediments extend and slopes retreat (1); the resistant mass is left behind as a residual hill, such as Uluru (1).
Question 44 · Spec 3.1.2.3 · Landscapes
Explain how process, time and landform are related in a desert mountain landscape. [3 marks]
Answer:
Weathering and flash floods erode mountains and deposit debris as fans and bahadas (1); over time, slopes retreat and pediments widen (1); eventually only residual inselbergs remain on a wide, gently sloping plain (1).
Question 45 · Spec 3.1.2.3 · Landscapes
Describe the characteristics of a sand sea (erg) landscape. [2 marks]
Answer:
Large areas covered by sand dunes of several types (1); formed where there is a large sand supply and strong winds, with few rock outcrops (1).
Question 46 · Spec 3.1.2.3 · Landscapes
Explain why different landforms dominate different parts of the same desert. [2 marks]
Answer:
Local differences in rock type, relief and sand supply control which processes operate (1); wind dominates in open sandy areas, and water dominates near mountains and in basins (1).
Question 47 · Spec 3.1.2.3 · Field data
Describe how the shape and movement of a coastal sand dune could be investigated in the field. [3 marks]
Answer:
Measure the dune profile using ranging poles and a clinometer along a transect (1); record wind speed and direction with an anemometer and compass (1); measure sand grain size and sorting at several points to link to the processes (1).
Question 48 · Spec 3.1.2.3 · Aeolian landforms
What is meant by the term aeolian? [1 mark]
Answer:
Relating to the action of the wind.
Question 49 · Spec 3.1.2.3 · Water landforms
Distinguish between a bahada and a pediment. [2 marks]
Answer:
A bahada is a depositional landform made of merged alluvial fans of sediment (1); a pediment is an erosional rock surface sloping gently from a mountain front, with only a thin cover of debris (1).
Question 50 · Spec 3.1.2.3 · Landscapes
Suggest why some desert landforms do not match the present climate. [2 marks]
Answer:
Some features, such as large wadis, were cut by rivers during wetter (pluvial) periods in the past (1); present rainfall is too low to create them, so they are relict features that survive in the dry climate (1).

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