Erosional and depositional landforms created by various agents

The governing concept is differential fluvial erosion. When a river flows across alternating hard and soft rock, the softer rock is worn away more quickly. A steep step develops, and water plunges over it as a waterfall; continued erosion may also create a plunge pool and retreat the fall upstream. Thus option B is correct. The other options describe deposition or agents that do not chiefly produce ordinary river waterfalls.

Correct answer: C, a narrow and deep valley. A gorge is a long, deep, and narrow valley with very steep sides or nearly vertical walls. It is commonly produced when a river cuts downward into the land for a long period, especially where the slope is considerable and the river’s vertical erosion is strong. The important identifying features are depth, narrowness, and steep sides, not the presence of sand or its location near the coast. Option A describes a broad valley, which is generally associated with wider lateral erosion, gentler slopes, or deposition and does not match the defining shape of a gorge. Option B is not a recognised geomorphological category because a gorge is classified by its form, not by whether its floor contains sand. Option D is a coastal landform, whereas a gorge is primarily a fluvial valley. Memory cue: “gorge” means a river-cut passage that is deep, narrow, and steep-walled.

The governing concept is lateral river erosion and deposition. In a relatively gentle-gradient river, faster flow erodes the outer bank while slower flow deposits sediment on the inner bank. Repetition of this process creates large, looping bends called meanders. Hence option D is correct. A delta forms near a river mouth, a moraine is deposited by a glacier, and a cave is generally associated with solution or erosion in rock rather than a winding river course.

Natural levees are depositional landforms built along river banks. During floods, water spreads beyond the channel and quickly loses energy near the banks, causing relatively coarse sand and silt to settle first. Repeated floods gradually raise the banks into low ridges. Thus option A is correct. Ocean floors, glacier beds, and desert interiors may contain other deposits, but they are not the usual locations of river natural levees.

A cirque, also called a corrie or cwm, is a bowl-shaped hollow carved by glacier ice near the head of a mountain valley. Plucking and abrasion enlarge the hollow, while ice movement and weathering steepen its back and side walls. Hence option C is correct. Sea waves mainly shape coasts, wind forms dunes and some erosional hollows, and groundwater commonly produces caves or sinkholes rather than cirques.

The correct answer is A: deposition of debris carried by a glacier. A glacier is a slowly moving mass of ice that can transport rock fragments, clay, sand, and soil. The debris may travel on the glacier’s surface, inside the ice, or along its bottom. When the glacier slows, melts, or reaches its end, the material is deposited and forms a moraine. Depending on its position, it may be called a lateral moraine along the side, a medial moraine where two glaciers meet, or a terminal moraine at the glacier’s front. A is correct because it includes both essential ideas: glacial transport and deposition. B is wrong because evaporation of seawater can leave salts behind but does not form a moraine. C describes river erosion, not glacial deposition. D refers only to groundwater drops and cannot explain a broad accumulation of unsorted rock debris. Memory cue: a moraine is the load that moving ice carries and leaves behind.

A drumlin is an elongated, smooth, streamlined hill made mainly of glacial till. Its blunt end generally faces the direction from which the ice came, while its tapered end points down-ice. This distinctive tear or spoon shape results from glacial movement and deposition. Hence option B is correct; the other choices describe neither a standard drumlin nor a glacial depositional hill.

An esker is a long, narrow and often winding ridge composed mainly of sand and gravel. It forms when meltwater streams flow through tunnels beneath or within a glacier and deposit sediment in those channels. After the ice melts, the sedimentary ridge remains visible. Therefore option A is correct. A sea cliff and mushroom rock have different agents, while a cave roof is not an esker.

A sea cliff is a steep coastal rock face produced mainly by persistent wave erosion. Waves strike the lower part of the coast, exploit joints and weak layers, and cut a wave notch; continued undercutting causes the upper rock to collapse and leaves a retreating cliff. Thus option C is correct. The other choices involve river, glacial or wind processes rather than direct marine erosion.

A wave-cut platform is a gently sloping, relatively flat rock surface at the foot of a sea cliff. Repeated wave attack cuts a notch into the cliff, and the cliff retreats, leaving the former shore surface exposed between tides. Therefore option B is correct. It is a coastal erosional landform, not a desert, glacial or river-source feature.

A sea cave develops when waves repeatedly attack a weak zone, crack or joint in a coastal cliff. Hydraulic pressure and the impact of sediment enlarge the opening until a hollow passage forms in the rock. Hence option A is correct. Wind deposition creates dunes, river sediment creates fluvial deposits, and glacier ice is associated with glacial landforms rather than sea caves.

The correct answer is B: a sea cave eroded from both sides. Waves repeatedly strike a rocky headland, especially along cracks and weak joints. Hydraulic pressure and abrasion enlarge these openings into a sea cave. If erosion continues through the headland and the cave opens from one side to the other, the remaining rock above the opening forms a sea arch. The usual sequence is crack or notch, cave, arch, and finally stack when the arch roof collapses. A is wrong because a floodplain is a river deposition feature. C is wrong because a moraine is sediment deposited by a glacier. D is wrong because a sand dune is formed mainly by wind deposition. Memory cue: waves cut caves, caves become arches, and collapsed arches leave stacks.

The correct answer is A: an eroded sea arch. A sea stack is an isolated pillar or column of resistant rock standing near a coast. The sequence begins when waves attack lines of weakness in a coastal cliff or headland. Cracks enlarge into caves. Continued wave erosion may cut through the headland and form an arch. The roof of the arch eventually becomes weak and collapses, leaving a separate rock pillar offshore or close to the shore; this is the stack. Further erosion may reduce it to a low stump. A is therefore correct. B, a river delta, is sediment deposited where a river enters a sea or lake, not a coastal rock pillar. C, a barchan, is a crescent-shaped dune made by wind-blown sand. D, a cave drip deposit such as a stalactite forms from mineral-bearing groundwater inside a cave. Memory cue: crack → cave → arch → stack → stump.

A beach is a coastal depositional landform formed when waves lose energy and leave sand, gravel, pebbles or shell fragments along the shore. The balance between wave action, sediment supply and currents controls its shape and size. Therefore option A is correct. Glacial cutting, groundwater solution and river incision are erosional processes associated with different environments, not the primary formation of a beach.

A spit is a narrow, elongated ridge of sand or shingle attached to the coast at one end and extending into the sea or across part of a bay. It develops mainly when longshore drift transports sediment along the shoreline and wave energy decreases, causing deposition. Therefore, option B is correct; the other options are glacial, river-eroded, or groundwater-related landforms.

The correct answer is C: wind. A mushroom rock, also called a pedestal rock, commonly forms in a dry region through wind abrasion. Wind-blown sand is concentrated close to the ground, so the lower part of an exposed rock receives more repeated impacts than the upper part. The base is therefore worn and narrowed faster, while the upper portion remains relatively broad. Over a long period, the rock develops a mushroom-like shape. C is correct because wind is the main agent producing this selective abrasion. A, a river, usually cuts channels, valleys, potholes, and deposits alluvium; it does not normally create this characteristic pedestal shape. B, a glacier, can form moraines, U-shaped valleys, and other glacial landforms, but not the usual mushroom rock. D, groundwater, may dissolve soluble rock and form caves or sinkholes. The key clue is stronger sand abrasion near the ground: narrow base, wider top.

A yardang is a streamlined, elongated ridge carved in bedrock by wind erosion, usually in a dry desert environment. Winds carrying sand abrade softer rock more rapidly, while harder layers resist erosion and remain as raised ridges. Option A is therefore correct. A river-deposited island, glacial lake, and sandy sea coast are formed by deposition or glacial and marine processes, not by this characteristic wind erosion.

The correct answer is A: wind deposition. Wind transports sand by rolling, bouncing, or carrying grains close to the ground. When wind speed decreases, or when vegetation, a stone, or another obstacle interrupts the flow, the sand settles. Repeated settling builds a mound or ridge called a sand dune. B is wrong because river erosion is caused by flowing water and produces channels, valleys, and related features. C is wrong because glacial erosion is caused by moving ice. D is wrong because groundwater solution dissolves soluble rock, especially limestone, and is associated with karst features. A useful distinction is that wind erosion removes or moves sediment, while wind deposition builds dunes when the sediment is dropped.

Direct answer: A, by dissolving limestone. Rainwater absorbs carbon dioxide from the atmosphere and soil, forming a weak carbonic-acid solution. As this groundwater passes through cracks, joints, and bedding planes in limestone, it slowly dissolves the soluble rock. Small cracks become wider, then develop into underground passages, chambers, and caves. Later, dissolved minerals may be deposited inside the cave when water loses carbon dioxide, producing features such as stalactites and stalagmites. B is wrong because blowing sand is a wind process. C is wrong because glacier movement is an ice-related process, not chemical solution of limestone. D is wrong because sea waves mainly shape coastal rocks and do not explain typical inland limestone caves. The key chain is: rainwater plus carbon dioxide, weak acid, limestone solution, widening cracks, and cave formation.

The correct answer is B: karst topography. A sinkhole is a closed depression in the ground, often formed in areas underlain by soluble limestone. Groundwater moves through cracks and dissolves the rock, creating underground openings. The surface may gradually subside or collapse into these openings, producing a sinkhole. A is wrong because wind deposition forms dunes and other sandy deposits. C is wrong because a moraine is an accumulation of sediment carried and deposited by a glacier. D is wrong because a sea beach is a coastal accumulation of sand or gravel. The key connection is soluble rock plus groundwater solution: caves, sinkholes, and other karst features commonly occur together.

Direct answer: A, from the cave roof. A stalactite is a mineral deposit that hangs downward from the ceiling of a limestone cave. Water seeps through limestone and carries dissolved calcium carbonate. When a drop reaches the cave roof, some carbon dioxide escapes, so a small amount of calcite is left behind. Repeated dripping and deposition gradually lengthen the formation downward. B is wrong because a river bed is shaped by flowing water and does not provide the cave-ceiling setting needed for a stalactite. C is wrong because a sea coast is mainly affected by marine erosion and deposition. D is wrong because a dune top consists of wind-deposited sand. The useful memory cue is that stalactite contains “c,” as in ceiling; it hangs from the ceiling. A stalagmite, in contrast, rises from the cave floor.

Direct answer: A, from the cave floor. A stalagmite is a mineral deposit that builds upward on the floor of a limestone cave. Rainwater takes in carbon dioxide while passing through soil and becomes mildly acidic. It dissolves a small amount of calcium carbonate from limestone. When the water drips onto the cave floor, carbon dioxide may escape and calcium carbonate is deposited. Repeated dripping gradually builds a cone or mound upward. B is wrong because a sea cliff is shaped mainly by wave erosion, not by cave-floor mineral deposition. C is wrong because a glacier mouth is related to ice and meltwater. D is wrong because a river source is the beginning of a stream and is not the setting for this cave feature. Memory cue: stalagmite has a “g” that can remind you of ground; it grows from the ground. Stalactite hangs from the ceiling.

The governing concept is the relationship between river velocity, carrying capacity, and deposition. In the lower course, the channel generally has a gentler gradient and the river’s energy and speed decrease. It can then carry less sediment, so sand, silt, and clay settle on the bed, banks, or floodplain. Hence option A is correct. Freezing, wind blockage, and disappearing rocks are not the normal causes of lower-course deposition.

The governing concept is the distinction between erosion and deposition. A gorge is a deep, narrow valley produced mainly when a river cuts downward and removes rock, so option C is correct. A delta and a beach are depositional features formed when transported sediment accumulates. Loess is also a wind-deposited blanket of fine sediment. Thus the gorge is the only clearly erosional landform among the choices.

The governing concept is deposition by different geomorphic agents. A sand dune forms when wind loses energy and deposits sand in a mound or ridge, so option B is correct. A sea cliff is mainly cut by wave erosion, a gorge by river erosion, and a cirque by glacial erosion. Although these agents and settings differ, the key test is whether material is being removed or deposited; only the dune represents deposition here.