Landform Development by Wind Action and Glaciation

21 questions

Question 1Question

Which of the following landforms is created by wind abrasion cutting into steep-sided, narrow ridges and furrows aligned parallel to the prevailing wind direction in arid regions?

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Answer: Yardang

Answer

Yardang is created by wind abrasion eroding parallel bands of hard and soft rock aligned in the direction of the prevailing wind.
A Yardang is formed when wind abrasion undercuts and sculpts rocks into long, narrow, steep-sided ridges separated by furrows, aligning parallel to the direction of the prevailing wind in desert landscapes.

Step-by-Step Solution

1
Analyze the process and geological arrangement described in the stem.
The process is wind abrasion operating parallel to prevailing winds in arid conditions.
Differentiation between desert landforms relies on rock orientation (vertical vs horizontal) and process direction.
2
Distinguish between Yardang and Zeugen based on rock strata alignment.
Yardangs develop where vertical bands of hard and soft rocks lie parallel to wind direction, creating narrow ridges and furrows.
Zeugen require horizontal strata where wind abrades jointed hard rocks into tabular blocks.
3
Identify and reject distractors from non-aeolian domains.
Oxbow lakes originate from fluvial action and moraines from glacial deposition.
Landform classification requires isolating the active agent of erosion or deposition.

Key Concept

Aeolian Erosional Landforms and Rock Strata Orientation
Estimated Time:1m 0s
Question 2Question

Arrange the following stages of alpine glacial landform evolution in sequential order from the initial pre-glacial hollow to the final alpine peak landform.

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Answer

The correct sequence begins with the formation of a nivation hollow, followed by its enlargement into a bowl-shaped cirque, the sharpening of dividing rock walls into an arête by adjacent cirques, and culminates in the formation of a pyramidal peak by three or more converging cirques.
Alpine glacial landscapes evolve systematically from small localized hollows to complex high-relief landforms. Snow accumulates in hillside depressions where freeze-thaw weathering creates a nivation hollow. As ice thickens and begins rotational movement, plucking and abrasion transform the hollow into a deep, bowl-shaped cirque. When neighboring cirques erode headward towards each other, their dividing rock wall is carved into a narrow, sharp-edged arête. Finally, when three or more cirques erode into the same mountain block from different directions, their intersecting headwalls isolate a steep, horn-like pyramidal peak.

Step-by-Step Solution

1
Identify the initial weathering and accumulation process.
Freeze-thaw action and snow gathering produce a nivation hollow in a shallow mountain slope depression.
Glacial landform development begins with pre-glacial nivation in minor depressions.
2
Identify the primary landform created by active glacial scouring.
Rotational movement of glacier ice scours out an armchair-shaped cirque with a steep headwall and basin floor.
Plucking and abrasion deepen and expand the nivation hollow into a true cirque.
3
Determine the feature created between two adjacent expanding cirques.
Headward erosion from two opposite or neighboring cirques leaves a narrow, steep ridge known as an arête.
An arête requires pre-existing cirques eroding toward one another.
4
Determine the peak landform formed when multiple cirques meet.
When three or more cirques erode headward around a single mountain summit, they leave a sharp pyramidal peak.
This represents the apex of mountain glacial erosion.

Key Concept

Evolutionary sequence of erosional alpine glacial landforms from cirque development to pyramidal peak isolation.
Question 3Question

Match each physical geography feature below with its corresponding process and landform type.

Click a left item, then click its matching right item

Items

Yardang
Barchan
Cirque
Moraine

Matches

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Answer

Yardang matches Aeolian erosional landform produced by wind abrasion; Barchan matches Aeolian depositional crescent-shaped sand dune; Cirque matches Glacial erosional armchair-shaped hollow; Moraine matches Glacial depositional ridge composed of unsorted till.
Each feature is correctly matched to its active agent (wind or moving ice) and whether the process involved is erosional or depositional.

Step-by-Step Solution

1
Identify the primary erosional wind landform
Yardang corresponds to wind abrasion acting on alternating rock strata.
Yardangs are distinct wind-eroded ridges found in arid environments.
2
Identify the primary depositional wind landform
Barchan corresponds to crescent-shaped sand deposition.
Barchans develop under wind action where sand supplies are moderate and winds blow from a single direction.
3
Identify the primary erosional glacial landform
Cirque corresponds to the steep-walled, armchair-shaped mountain hollow.
Cirques are created at the source of mountain glaciers by freeze-thaw weathering and ice plucking.
4
Identify the primary depositional glacial landform
Moraine corresponds to ridges composed of unsorted glacial till.
Moraines are formed when glaciers deposit rock debris as they melt or retreat.

Key Concept

Classification of landforms by geomorphic agent (wind vs glacier) and process (erosion vs deposition)
Question 4Question

Match each landform feature with its corresponding process of formation and distinct structural characteristic.

Click a left item, then click its matching right item

Items

Yardang
Roche Moutonnée
Barchan
Drumlin

Matches

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Answer

Yardang matches with aeolian wind abrasion producing parallel ridges; Roche Moutonnée matches with glacial erosion combining stoss-side abrasion and lee-side plucking; Barchan matches with aeolian deposition forming a crescent dune with downwind horns; Drumlin matches with glacial deposition molding subglacial till into an oval hill.
Each feature is correctly linked to its primary geomorphic agent (wind or ice), process (erosion or deposition), and distinct structural geometry.

Step-by-Step Solution

1
Classify each landform by agent of erosion or deposition.
Yardang and Barchan are aeolian (wind-formed) features; Roche Moutonnée and Drumlin are glacial (ice-formed) features.
Categorizing by geomorphic agent reduces potential matching combinations.
2
Differentiate between erosional and depositional mechanics for the aeolian pair.
Yardangs are formed by wind abrasion carving rock, while Barchans are depositional sand dunes.
Process mechanics distinguish landforms shaped by wind action.
3
Differentiate between erosional and depositional mechanics for the glacial pair.
Roche Moutonnée is an asymmetrical bedrock outcrop shaped by plucking and abrasion, whereas a drumlin is an elongated hill formed by deposited glacial till.
Morphological orientation relative to ice flow distinguishes glacial landform types.

Key Concept

Classification of landforms by process (abrasion, plucking, deposition) and agent (wind vs. glacier)
Question 5Question

Which of the following landforms is formed by glacial deposition and is characterized as an elongated, streamlined, teardrop-shaped hill of unsorted till with its blunt end pointing towards the direction of ice advance?

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Answer: Drumlin

Answer

Drumlin
The correct answer is the drumlin. Drumlins are smooth, elongated, teardrop-shaped hills of unstratified glacial till deposited and shaped under moving ice. The steep, blunt end (stoss side) faces the direction from which the glacier advanced, while the gently sloping tail (lee side) points in the direction of ice movement.

Step-by-Step Solution

1
Identify the primary agent and process specified in the stem
The landform is formed by glacial deposition (ice carrying and dropping sediment).
Differentiating between erosional and depositional features narrows down glacial landform classifications.
2
Analyze the physical shape and orientation of the landform described
An elongated, teardrop-shaped hill composed of unsorted till with a steep blunt stoss side facing ice advance and a tapered lee side.
This specific morphology uniquely identifies a drumlin.
3
Distinguish from non-glacial and erosional distractors
Roche moutonnée is erosional, oxbow lake is fluvial, and scree slope is caused by weathering and mass wasting.
Eliminating features of other geological agents confirms the correct answer.

Key Concept

Glacial Depositional Landforms (Drumlins)
Estimated Time:50s
Question 6Question

In arid regions, wind action causes severe erosion through different mechanics. Which landform is created when wind abrasion selectively undercuts the base of a rock outcrop more rapidly than its top due to sand particles being carried close to the ground?

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Answer: Mushroom rock

Answer

Mushroom rock (also known as a pedestal rock)
Wind abrasion in deserts is most effective close to the ground where wind-borne sand particles are concentrated. When an isolated rock mass is exposed to this sandblasting action, the lower portion erodes significantly faster than the upper part, creating a distinctive mushroom rock (pedestal rock).

Step-by-Step Solution

1
Identify the primary agent and mechanism described in the question
The agent is wind (aeolian process) using wind abrasion (sandblasting action near ground level).
Wind action carries the heaviest abrasive tools (sand grains) close to the surface, typically within 1 to 1.5 meters above the ground.
2
Analyze the structural outcome of ground-level undercutting on an isolated rock
The base of the rock undergoes maximum erosion while the top remains wider and less eroded.
Differential erosion leaves a narrow stalk supporting a wider cap rock, forming a pedestal or mushroom shape.

Key Concept

Aeolian Abrasion and Landform Development
Question 7Question

Arrange the stages of barchan dune formation in an arid environment in sequential order from initial sand accumulation to the fully developed landform.

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Answer

The correct sequence begins with sand encountering an obstacle and depositing, followed by the formation of a sand mound with a leeward slip face, the extension of lateral horns downwind by wind eddies, and finally the migration of a mature crescent-shaped barchan dune.
The correct sequence follows the physical progression of aeolian deposition: wind-blown sand first accumulates around an obstacle, forms an asymmetrical sand mound with a leeward slip face, develops two downwind-pointing horns as marginal sand moves faster than the center, and ultimately becomes a mobile crescent barchan dune.

Step-by-Step Solution

1
Identify the initial trigger for wind deposition.
Sand carried by saltation is trapped by an obstacle on the desert surface.
Aeolian deposition requires a physical barrier or reduction in wind energy.
2
Determine the initial structural dune development.
Sand accumulates into an asymmetrical mound with a gentle windward side and steep leeward slip face.
Sand accumulates on the windward slope and avalanches down the leeward side when it exceeds the angle of repose.
3
Trace the development of characteristic lateral features.
Lighter sand loads at the lateral margins move faster downwind, forming two pointed horns.
Eddy currents and lower resistance at the edges push the sides forward faster than the thick central core.
4
Identify the final landform state.
A fully formed crescent-shaped barchan dune migrates in the direction of the prevailing wind.
Ongoing wind action continually recycles sand over the crest, causing the entire dune to advance.

Key Concept

Barchan Dune Formation and Aeolian Deposition Processes
Question 8Question

Which of the following landforms is created primarily by wind deposition in arid environments?

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Answer: Barchan dune

Answer

The barchan dune is a landform formed by wind deposition in arid environments.
The barchan dune is a characteristic crescent-shaped dune formed by aeolian deposition where wind direction is dominant and sand supply is moderate.

Step-by-Step Solution

1
Identify the primary geomorphic agent requested in the question stem.
The agent specified is wind (aeolian process) operating in an arid environment via deposition.
Differentiating between erosional and depositional aeolian landforms is necessary to isolate the correct feature.
2
Evaluate the landform choices based on their active process and shaping agent.
Barchans are crescent-shaped sand dunes formed when wind deposits sand grains. Oxbow lakes and levees are fluvial landforms created by running water, while scree slopes are produced by mechanical weathering and mass wasting.
Classifying each landform eliminates fluvial and mass wasting distractors.

Key Concept

Aeolian Depositional Landforms
Estimated Time:45s
Question 9Question

Arrange the following geomorphic stages in the correct sequential order describing the evolution of a pre-glacial river valley into a steep-sided glacial trough (U-shaped valley).

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Answer

The correct sequential order of landform development is: 1. A pre-glacial stream carves a V-shaped valley with interlocking spurs -> 2. Climatic cooling causes snow accumulation, feeding a valley glacier that occupies the river channel -> 3. Basal plucking and active lateral abrasion truncate the interlocking spurs -> 4. Glacial retreat exposes a wide, flat-floored U-shaped trough flanked by truncated spurs and hanging tributary valleys.
The correct order begins with pre-existing fluvial landforms (V-shaped valley with interlocking spurs), followed by valley glacier occupation, active glacial modification (truncation of spurs and wall steepening via abrasion and plucking), and culminates in the post-glacial exposure of a flat-bottomed U-shaped trough with hanging tributary valleys.

Step-by-Step Solution

1
Identify the initial fluvial topography.
Establish that a V-shaped valley created by stream action with interlocking spurs exists first.
Glacial troughs form by modifying pre-existing river valleys rather than creating new channels from flat terrain.
2
Determine ice accumulation and valley occupation.
A valley glacier fills the pre-existing V-shaped river path.
Glacial ice must occupy the conduit before glacial erosion processes can begin.
3
Analyze the active erosion phase during peak glaciation.
Glacial plucking and abrasion shear off interlocking spurs and steepen valley sides.
Ice cannot bend around interlocking spurs like river water; instead, it cuts directly through them.
4
Identify the post-glacial landscape features upon ice retreat.
Exposure of a steep-sided, flat-floored U-shaped trough with hanging valleys.
Deglaciation reveals the modified valley cross-profile created by ice action.

Key Concept

Glacial Trough Evolution
Estimated Time:2m 0s
Question 10Question

In a glaciated mountain region, a massive main-trunk glacier erodes its valley far deeper than smaller feeder glaciers. Upon deglaciation, the tributary valleys remain perched high above the main trough floor, typically featuring plunging waterfalls. Which landform does this description represent?

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Answer: Hanging valley

Answer

Hanging valley
A hanging valley forms when a main trunk glacier erodes its valley floor much deeper than smaller tributary glaciers. When the ice melts, the floor of the tributary valley is left suspended high above the main glacial trough, often giving rise to waterfalls.

Step-by-Step Solution

1
Analyze the landform features described in the stem
The landform is located in a glaciated mountain valley, sits elevated above the main valley floor, and creates waterfalls where streams flow out of it.
Main trunk glaciers possess far greater volume and erosive capacity than tributary glaciers, gouging the main trough much deeper.
2
Identify the specific geological feature and rule out non-glacial processes
Differential ice erosion between main and tributary glaciers forms a hanging valley. Oxbow lakes and deltas are river features, while scree slopes result from mass wasting.
Perched tributary troughs created by differential glacial deepening are uniquely classified as hanging valleys.

Key Concept

Hanging Valley Formation in Glacial Troughs
Estimated Time:1m 0s
Question 11Question

Match each physical landform listed on the left with its precise developmental process and structural characteristics under aeolian or glacial action on the right.

Click a left item, then click its matching right item

Items

Yardang
Zeugen
Roche Moutonnée
Drumlin

Matches

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Answer

Yardang matches with the aeolian erosional ridge formed on vertically tilted strata parallel to prevailing winds; Zeugen matches with the flat-topped ridge formed on jointed horizontal cap-rock; Roche Moutonnée matches with the asymmetric erosional bedrock hill exhibiting a gentle smoothed stoss side and steep plucked lee side; Drumlin matches with the streamlined depositional mound of till exhibiting a steep blunt stoss side and tapering lee tail.
The matching correctly pairs each landform with its exact agent (wind vs glacier), process (abrasion/plucking vs deposition), and structural orientation (vertical vs horizontal strata, stoss vs lee slope profiles).

Step-by-Step Solution

1
Analyze aeolian erosional landforms by structural strata orientation
Identify that Yardangs form on vertically aligned rock bands, whereas Zeugen form on horizontally bedded strata with jointed cap-rocks.
Differential wind abrasion attacks structural weaknesses based on whether strata inclination is vertical or horizontal.
2
Differentiate glacial erosional landforms from depositional landforms
Identify Roche Moutonnée as an erosional bedrock feature formed by combined abrasion and plucking, and Drumlin as a depositional feature composed of unsorted glacial drift.
Erosional glacial landforms sculpt solid bedrock, while depositional glacial landforms aggregate till under moving ice mass.
3
Examine stoss-and-lee slope polarity for Roche Moutonnée versus Drumlin
Confirm that a Roche Moutonnée has a gentle stoss slope up-ice and a steep lee slope down-ice, whereas a Drumlin has a steep stoss side up-ice and a gentle tapering lee tail down-ice.
Glacial ice abrades the up-ice side of bedrock obstacles (Roche Moutonnée) but deposits and molds till heavily on the advancing up-ice side of drumlins.

Key Concept

Structural and Process Mechanics in Aeolian and Glacial Landform Development
Estimated Time:2m 0s
Question 12Question

In an arid environment, wind deflation selectively removes loose, fine-grained sediments until a continuous armor of polished, coarse pebbles covers the desert floor. In contrast, in areas where wind abrasion attacks alternating horizontal strata of hard and soft rocks near the surface, deep parallel furrows are gouged out, leaving standing ridges of resistant rock. Which pair of aeolian features describes these respective erosion landforms?

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Answer: Desert pavement and yardangs

Answer

The combination of desert pavement and yardangs correctly identifies the described aeolian erosional features.
Desert pavement is formed when wind deflation carries away fine sand and silt, leaving a concentrated layer of heavy pebbles on the desert surface. Yardangs are elongated, steep-sided ridges carved out by wind abrasion operating on alternating belts of hard and soft rocks aligned parallel to the prevailing wind direction.

Step-by-Step Solution

1
Identify the first process and landform described in the stem.
The selective removal of fine particles by wind deflation leaving coarse pebbles creates a desert pavement (also known as reg or hamada lag deposit).
Wind deflation removes sand and dust, concentrating larger pebbles into an armoring surface layer.
2
Identify the second process and landform described in the stem.
Differential wind abrasion carving out soft rock strata to leave prominent parallel ridges forms yardangs.
Abrasion by wind-blown sand carves out linear furrows in soft rock, leaving ridges aligned parallel to the prevailing wind direction.
3
Compare candidate options to eliminate features formed by other geomorphic agents.
Options featuring oxbow lakes, river terraces, or scree slopes belong to fluvial action or mass wasting, leaving desert pavement and yardangs as the only valid aeolian landforms.
Ensures precise attribution to wind action rather than running water or mass movement under gravity.

Key Concept

Aeolian Erosional Landforms and Mechanics
Estimated Time:1m 30s
Question 13Question

Arrange the following stages in the development of a desert oasis resulting from wind action in the correct sequential order from earliest to latest.

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Answer

The correct sequence begins with persistent wind deflation scouring away dry sand, followed by the continuous deepening of the hollow down to the water table level. Exposure of groundwater moisture halts further wind deflation, enabling vegetation to colonize and form an oasis.
Wind deflation acts as the primary excavation mechanism, removing dry surface sand to create a depression. As the hollow deepens, it eventually meets the subterranean water table. Moisture from the water table acts as a natural limit to aeolian erosion because damp sand cannot be lifted by wind currents. Once water is available at the surface, vegetation takes root, completing the formation of a desert oasis.

Step-by-Step Solution

1
Identify the initial wind erosion mechanism
Strong wind deflation removes fine, unanchored sand particles from an arid surface hollow.
Deflation is the primary aeolian process responsible for lowering land surfaces in dry regions.
2
Trace the deepening of the landform
The deflation basin deepens vertically until it intersects the underground water table.
Wind can continuously excavate dry, loose sediment as long as it remains unanchored.
3
Determine the physical threshold that stops erosion
Moisture from exposed groundwater binds sediment particles, arresting further deflation.
Wet soil particles adhere together and are too heavy for wind currents to lift.
4
Identify the biological colonization stage
Plants establish around the permanent moisture source, completing the oasis landform.
Exposed water in an arid basin provides the necessary conditions for plant life to take root.

Key Concept

Formation of deflation hollows and oases by aeolian processes
Question 14Question

In a glaciated highland environment, when three or more adjacent cirques erode headwards into a single central mountain mass, which landform is created at the summit?

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Answer: Pyramidal peak

Answer

Pyramidal peak
A pyramidal peak (also known as a glacial horn) is formed when three or more cirques erode headward towards a central mountain point, leaving a sharp, steep-sided triangular peak.

Step-by-Step Solution

1
Identify the agent of erosion and regional setting.
The process described is glacial erosion (plucking and frost action forming cirques) in a highland region.
Cirques are steep hollows formed by arm-chair shaped glacial accumulation.
2
Analyze the spatial erosion pattern.
When three or more cirques develop back-to-back around a single peak and erode backwards into the mountain mass, a sharp, horn-shaped mountain peak is left behind.
This central remnant peak bounded by steep arêtes is defined geographically as a pyramidal peak.

Key Concept

Glacial Highland Erosional Features
Estimated Time:45s
Question 15Question

In arid geomorphology, both Zeugen and Yardangs represent wind-eroded ridge-and-furrow landforms. Which of the following structural characteristics distinguishes the formation of a Zeugen from that of a Yardang?

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Answer: Zeugen develop in horizontal strata of alternating hard and soft rocks cut by joint patterns.

Answer

Zeugen develop in desert environments characterized by horizontally bedded strata of alternating hard and soft rock cut by joint systems.
Zeugen formation relies on horizontal rock strata where an upper resistant cap-rock covers a softer underlying rock layer. Mechanical weathering opens vertical joints, allowing wind abrasion to scour deep furrows and leave flat-topped ridges.

Step-by-Step Solution

1
Analyze the structural arrangement of rocks in Zeugen formation.
Zeugen require tabular, flat-lying (horizontal) layers of resistant rock overlying less resistant rock with joints exposed to weathering and wind abrasion.
Wind abrasion deepens joint cracks into narrow furrows, leaving flat-topped ridges of hard rock standing above soft rock bases.
2
Compare Zeugen rock structure with Yardang rock structure.
Yardangs develop where rock strata are vertically aligned or steeply dipping parallel to the direction of prevailing winds, whereas Zeugen develop from horizontal strata.
Distinguishing rock layer orientation (horizontal vs vertical alignment) is key to differentiating these two wind-eroded landforms.

Key Concept

Structural differences between Zeugen and Yardang landform development
Estimated Time:1m 0s
Question 16Question

Match each geomorphic landform listed on the left with its corresponding formation process and characteristic feature on the right.

Click a left item, then click its matching right item

Items

Ventifact
Drumlin
Bergschrund
Seif dune

Matches

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Answer

Ventifact matches with 'A rock or pebble faceted, grooved, and polished by wind abrasion'; Drumlin matches with 'A streamlined, elongated hill of unstratified till shaped by glacial deposition'; Bergschrund matches with 'A deep fissure formed near the headwall where moving glacier ice pulls away from stagnant ice or rock'; Seif dune matches with 'A steep-sided longitudinal sand ridge aligned parallel to the prevailing wind direction formed by aeolian deposition'.
Each feature corresponds to its specific agent and mode of formation: Ventifacts are produced by wind abrasion on rocks; Drumlins are depositional hills of glacial till; Bergschrunds are cracks formed by moving glacial ice near headwalls; and Seif dunes are depositional sand ridges parallel to prevailing winds.

Step-by-Step Solution

1
Identify the agent of erosion or deposition for each landform.
Ventifact and Seif dune are created by wind action (aeolian), while Drumlin and Bergschrund are created by glacial action.
Categorizing by geomorphic agent reduces the matching search space.
2
Distinguish between erosional and depositional features for wind landforms.
Ventifact is an erosional feature produced by wind abrasion; Seif dune is a depositional feature resulting from sand accumulation.
Ventifacts represent wind sculpting, whereas Seif dunes represent wind accumulation.
3
Distinguish between erosional/fracture and depositional features for glacial landforms.
Drumlin is a sub-glacial depositional hill of till; Bergschrund is a structural crevasse/crack in the glacial headwall area.
Drumlins consist of till laid down under moving ice, while bergschrunds mark tension fractures near cirque headwalls.

Key Concept

Classification of aeolian and glacial landforms by agent and process (erosional vs depositional).
Estimated Time:1m 30s
Question 17Question

A field geologist observes a glaciated bedrock feature characterized by a smooth, gently inclined side facing the direction of ice advance and a steep, jagged slope on the down-flow side. Which landform and primary evolutionary process are described?

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Answer: Roche moutonnée formed by glacial abrasion and plucking

Answer

Roche moutonnée formed by glacial abrasion and plucking
The correct answer identifies a roche moutonnée, an asymmetrical bedrock hill formed by glacial erosion. As moving glacial ice encounters a resistant rock obstacle, friction and debris at the glacier base abrade and smooth the up-ice (stoss) slope. On the down-ice (lee) slope, pressure release and refreezing of meltwater cause the ice to pluck out loose jointed rock blocks, leaving a steep, jagged cliff.

Step-by-Step Solution

1
Analyze the landform profile relative to ice movement direction.
The feature exhibits an asymmetrical slope with a smooth up-ice (stoss) side and a craggy down-ice (lee) side.
Slope asymmetry and orientation relative to ice flow are critical diagnostic criteria for glacial landforms.
2
Identify the erosional mechanisms responsible for the profile.
Abrasion smooths the stoss slope under heavy basal ice pressure, while plucking pulls away fractured bedrock on the lee side where pressure is reduced.
The combination of glacial abrasion and plucking acting on solid bedrock uniquely creates a roche moutonnée.
3
Distinguish this feature from depositional glacial and non-glacial landforms.
A drumlin has an inverted profile (steep stoss, gentle lee tail) and consists of deposited till rather than eroded bedrock, while terraces and pedestals originate from fluvial or aeolian/weathering action.
Eliminating options based on material composition and process origins confirms the correct choice.

Key Concept

Roche Moutonnée Formation and Glacial Erosional Processes
Question 18Question

During glacial retreat, unsorted and unstratified rock debris carried by a glacier is deposited directly by the melting ice to form ridges along the edges and snout of the glacial valley. Which of the following landforms is formed by this process?

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Answer: A moraine

Answer

A moraine is the correct landform formed by the direct deposition of unsorted glacial till during ice retreat.
Moraines are formed when glaciers retreat and deposit unsorted rock fragments and sediment (till) directly onto the landscape. Depending on their position relative to the glacier, they form lateral, medial, or terminal ridges.

Step-by-Step Solution

1
Identify the primary agent of erosion and deposition described in the scenario
The process involves melting ice and glacial retreat, placing the feature under glacial depositional landforms.
Glacial deposition is distinct from running water (fluvial) or gravitational mass wasting processes.
2
Analyze the material characteristics and geometry of the landform
The material is unsorted rock debris (till) forming ridges along the glacial margins and snout.
Glaciers deposit unsorted debris (till) directly, which accumulates into ridges known as terminal, lateral, or medial moraines.
3
Evaluate the options to rule out non-glacial processes
Oxbow lakes and river deltas are formed by running water in river systems, while scree slopes are formed by mechanical weathering and mass wasting under gravity.
Only moraines fit the definition of direct deposition of unsorted till by a glacier.

Key Concept

Glacial Deposition and Till Landforms
Estimated Time:1m 0s
Question 19Question

In glaciated highland regions, frost action and glacial movement progressively transform mountain slopes into distinctive alpine landforms over time. Arrange the following geomorphic stages in the correct chronological order of their evolutionary sequence, from the initial process to the final landform.

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Answer

The correct sequence of glacial landform evolution is: (1) Snow accumulation and nivation in a mountain hollow, (2) Deepening into an armchair-shaped cirque by rotational ice flow and plucking, (3) Headward erosion of adjacent cirques into a central mountain mass, and (4) Isolation of a sharp pyramidal peak.
Alpine glacial landscape evolution begins with perennial snow accumulation and freeze-thaw nivation in mountain depressions. As ice builds up, rotational sliding and basal plucking deepen these hollows into armchair-shaped cirques. When three or more surrounding cirques erode headward into the same central mountain summit, the narrowing dividing ridges converge to leave a sharp, steep-sided pyramidal peak.

Step-by-Step Solution

1
Identify the initial process
Snow accumulates in a pre-existing depression, where freeze-thaw action (nivation) disintegrates rock.
Glacial erosion starts with snow accumulation and freeze-thaw weathering before a full glacier forms.
2
Determine the formation of the cirque basin
Ice accumulation produces rotational movement, plucking the backwall and scouring the hollow floor.
Plucking steepens the backwall while abrasion deepens the basin, creating a classic cirque.
3
Trace multi-directional headward erosion
Three or more cirques located on different sides of a mountain erode headward toward the summit.
Backwards erosion narrows the dividing rock ridges into knife-edge arêtes.
4
Identify the final residual landform
A steep, horn-like pyramidal peak is left isolated at the junction of the converging arêtes.
Continuous cirque recession from all sides meets at a central point, forming a horn/pyramidal peak.

Key Concept

Evolutionary sequence of alpine glacial erosional landforms from nivation hollows to pyramidal peaks.
Question 20Question

In arid regions, mushroom rocks (pedestal rocks) typically exhibit a narrow, undercut base beneath a broader cap rock. Which geomorphic factor explains why wind abrasion is most severe within the lowest one meter of the rock structure?

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Answer: Abrasive sand grains transported by saltation are too heavy to be lifted high and bounce mainly near ground level.

Answer

The maximum rate of wind abrasion occurs near the base of rock outcrops because sand grains moved by wind travel mainly by saltation within the lowest meter above the surface.
Wind abrasion requires abrasive tools, specifically sand grains. In desert environments, wind transports coarse sand primarily via saltation—a process where grains bounce along the ground, rarely rising above 1 meter. Consequently, the greatest density of abrasive impacts occurs near the base of an outcrop, wearing it away faster than the upper portion and producing the characteristic mushroom or pedestal shape.

Step-by-Step Solution

1
Identify the primary process responsible for shaping mushroom rocks in arid environments.
Mushroom rocks (gours) are shaped primarily by aeolian abrasion (sandblasting of solid rock by wind-borne grains).
Understanding the agent and process sets the framework for analyzing the vertical distribution of erosion.
2
Analyze the mode of transport and elevation range of abrasive particles.
Wind carries fine dust in suspension high into the air, but heavy sand grains move by saltation (bouncing) and stay below 1 to 2 meters.
The concentration of hard, sharp sand tools is highest near the surface.
3
Determine why undercutting occurs specifically near the base.
Because abrasive sand is concentrated in the lowest meter, maximum rock removal happens near the ground, producing a narrow pedestal.
This explains the differential erosion rate between the base and the upper rock cap.

Key Concept

Wind Abrasion and Saltation Mechanics
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Landform Development by Wind Action and Glaciation Practice Questions — JAMB UTME | Examkin