Waves and tides

Correct answer: A. Fine sediment can be transported easily

The governing concept is the relationship between current competence and particle size. Flowing water must exert enough shear stress to overcome the forces holding sediment on the bed. Fine particles generally require less force to be entrained than coarse gravel or large stones, so a strong tidal current can lift, suspend, and transport mud or fine sand. As current velocity falls, the material may settle and form tidal flats, bars, or other deposits; transport is therefore not guaranteed everywhere. Option A states the appropriate possibility without claiming that every particle will remain in motion. B incorrectly assumes automatic lithification, while C and D contradict the nature of tides and wind-generated waves.

Correct answer: B. Water level matters but low wave energy can limit erosion

The governing concept is that coastal erosion depends on several interacting controls rather than on water level alone. High tide raises the position at which waves and currents can reach the shore, and this can expose higher parts of a beach or cliff to marine action. However, erosion also requires sufficient wave energy, suitable rock or sediment conditions, and repeated hydraulic or abrasive force. If wave energy is low, the raised water may cause inundation or alter sediment movement without producing extreme erosion. Thus option B gives the balanced conclusion. Option A treats one factor as decisive, while C and D are physically unrelated and therefore cannot follow from the stated conditions.

Correct answer: D. Explain water depth and navigation timing through spring tide at full moon

The governing concept is the practical significance of spring tides. At full moon, the Sun, Earth, and Moon are approximately aligned, so solar and lunar gravitational effects reinforce each other and produce a relatively large tidal range. For a port, the resulting high-water stage can temporarily increase navigable depth over a channel or bar, allowing a vessel with greater draft to enter or leave at a suitable time. The exact operational decision still depends on local charts, channel depth, safety margins, and tidal predictions, but option D gives the correct examination strategy. A reverses spring and neap tides, while B and C ignore the stated physical and human-use relationship.

Correct answer: A. They can change landforms through both erosion and deposition

The governing concept is wave geomorphic work. As waves break and strike a shore, their energy can create hydraulic pressure in cracks, remove particles by abrasion, and weaken or transport coastal material. This produces erosional features such as cliffs, notches, caves, arches, and stacks where resistant rock is attacked along lines of weakness. The same wave system can move sand and pebbles; where transport capacity decreases, those materials are deposited to form beaches, bars, or spits. Therefore option A correctly includes both erosion and deposition. Wave action does not control the Moon’s motion, does not leave coasts unaffected, and does not merely create tidal range, so B, C, and D are unsuitable.

Correct answer: A. Joints can give waves pathways to affect weak zones

The governing concept is the interaction between lithology and rock structure. Hard rock generally resists weathering and wave attack more effectively than weak, poorly consolidated material, but hardness does not make it immune to erosion. Joints, faults, bedding planes, and other discontinuities provide pathways where water pressure can enter. Repeated wave impact compresses air and water in these openings, while abrasion enlarges the weakened surfaces. Blocks may eventually loosen and collapse, allowing a cliff or cave to develop even in resistant rock. Option A is therefore the subtle and correct conclusion. B uses an absolute claim, C ignores structural weakness, and D wrongly separates wave action from the nature of the shore.

Correct answer: A. Neap tide may reduce water-level range but storm-wave energy can be high

The governing concept is compound coastal risk: tidal range and wave energy are separate but interacting controls. Neap tides occur near the first and third lunar quarters, when the Sun and Moon pull at roughly right angles, so the tidal range is smaller than during spring tide. That smaller range may reduce the vertical tidal contribution to inundation, but it says nothing about the strength of a storm. Strong winds, long fetch, low atmospheric pressure, and wave setup can still produce powerful waves, beach erosion, overtopping, and flooding. Therefore option A gives the necessary balanced analysis. B and D make unjustified absolute claims, while C incorrectly prevents simultaneous consideration of tides and storm waves.

Correct answer: C. The Moon phase can reduce the tidal range, while the bay's shape can strengthen the local current

At first quarter, the Sun's and Moon's tidal effects partly counteract one another, so the tidal range is generally smaller; this is a neap-tide condition. Tidal range and current speed are not the same. A narrow or funnel-shaped bay and its channels can concentrate flow, so a local current may still be strong. Therefore C is the balanced conclusion.

Correct answer: A. Distance from Earth is very important to tidal effect

Tidal effect depends on both mass and distance, not simply on an object's size. The Moon is much less massive than the Sun but much closer to Earth. Tidal acceleration depends strongly on distance—approximately on its inverse cube—so the nearby Moon has the larger direct tidal effect on Earth's oceans. Therefore A gives the needed correction.

Correct answer: C. An elevated water level and energetic waves

High tide raises the starting sea level, while storm waves carry substantial energy toward the coast. Together, these conditions can increase flooding, erosion, and damage on a low coastal plain. Thus C correctly identifies the combined danger; a storm surge can add to it, but it is not needed to explain the conditions stated in the question.

Correct answer: D. Deposition can occur, and particle size affects the energy needed for transport

Coarse pebbles need more energy to be moved than fine sediment. As wave energy falls, the water may no longer be able to transport them, so they can settle. Decreasing energy does not make deposition impossible; it can favour deposition of coarse particles. Therefore D is correct.

Correct answer: A. Weak, jointed rock allows waves to erode more effectively

Rock structure affects how it responds to wave energy. Joints and cracks provide weaknesses where water pressure and sediment abrasion can loosen rock. Repeated wave action can widen the cracks and remove fragments, so weak, jointed rock may erode faster than more resistant rock under similar wave conditions. Therefore A is correct.

Correct answer: A. Wave energy can increase because greater wind speed can transfer more energy

The governing concept is wind-wave generation. Fetch is the uninterrupted distance over which wind blows, and duration is the length of time for which it acts. If both remain constant, increasing wind speed increases the stress and energy transferred from the atmosphere to the sea surface. Stronger wind can therefore produce larger, steeper and more energetic waves, although the exact response also depends on whether the sea has reached a fully developed state and on local conditions. Option A is the only conclusion supported by the changed variable. Options B, C and D either contradict wave-generation physics or concern unrelated processes.

Correct answer: C. Sediment sorting according to particle size

The governing concept is sediment sorting by wave energy and particle size. When waves break and lose energy near a shore, they cannot transport every grain equally. Coarse pebbles require stronger competence and are commonly deposited nearer the zone where wave energy falls sharply, while finer sand can remain suspended longer and may be carried farther before settling. This systematic arrangement of particles from coarse to fine is called sorting. Option C correctly names the process. Option A is unrelated to the grain pattern, option B requires a sudden large-scale displacement of seawater, and option D has no geomorphic connection. The observation therefore indicates selective deposition by wave action.

Correct answer: B. A tide is a periodic rise and fall of water level, whereas a current is a relatively continuous flow of water

The governing distinction is the form and timescale of water movement. A tide is a periodic change in sea level, expressed as high tide and low tide, and is driven mainly by the gravitational effects of the Moon and Sun along with Earth’s rotation. An ocean current is a more sustained, directed movement of seawater from one place to another. Currents may be influenced by wind, density differences caused by temperature and salinity, pressure gradients, and Earth’s rotation. Thus option B correctly separates vertical or level change associated with tides from horizontal transport associated with currents. The other options are either absolute, scientifically false, or confuse causes with phenomena.

Correct answer: C. Tsunami

The governing concept is the origin of the disturbance that generates the wave. An undersea earthquake can abruptly displace the seafloor and the overlying water column, launching long-wavelength waves that travel rapidly across the ocean. As these waves enter shallow coastal water, their speed decreases and their height may increase greatly, producing destructive inundation; this phenomenon is called a tsunami. Spring and neap tides are periodic sea-level changes controlled mainly by the relative positions of the Sun, Moon and Earth, not by earthquakes. Ordinary wind-generated waves are produced by atmospheric wind stress at the sea surface. Therefore option C is the correct cause-based classification.

Correct answer: B. Concentration of water by the coastal shape

The governing concept is the interaction between astronomical forcing and coastal geometry. The Moon and Sun establish the basic tidal forcing, but the observed tidal range at a particular coast is also shaped by local bathymetry and the form of the shoreline. A narrow, funnel-shaped bay can progressively concentrate incoming tidal water and restrict its lateral spread. Under suitable conditions, this produces a much larger rise and fall of water level toward the head of the bay, an effect associated with tidal amplification and resonance. Option B identifies the relevant supporting factor. The Moon’s colour, fish migration and cloud weight do not provide a mechanism capable of producing this systematic increase in tidal range.

Correct answer: C. Coordinating water depth, current direction and tide timing

The governing concept is safe navigation under changing tidal conditions. A large tidal range means that the vertical distance between high and low water is substantial, so the available depth in a channel can change significantly during a tidal cycle. A strong tidal current can alter a vessel’s speed over ground, drift it sideways, increase turning difficulty and affect berthing or departure. Operators therefore need reliable tide predictions, actual water-depth information, current direction and speed, vessel draught, and an appropriate operating window. Option C combines the essential factors. The other choices do not help determine under-keel clearance, vessel control or the timing of safe movement, so they cannot be operational priorities.

Correct answer: B. Water level matters, but low wave energy can limit erosion

The governing concept is that coastal erosion depends on several interacting controls rather than on tidal height alone. A high tide raises the water level and may allow waves to reach a higher part of the shore or attack the base of a cliff. However, if wave energy is low, the waves have less capacity to detach, transport and abrade sediment. Erosion may therefore occur, but its rate and intensity can be limited unless other factors, such as strong currents, weak material, storms or human interference, contribute. Option B gives the balanced conclusion. Option A treats one factor as decisive, while C and D contradict the meaning of high tide and basic gravitational physics.

Correct answer: B. Deposition may be limited because sediment availability is limited

Deposition is governed by two linked conditions: transporting energy must fall sufficiently, and sediment must be available at the place where the energy falls. When waves lose energy, their ability to carry sand and other particles decreases, so deposition becomes possible. However, a distant sediment source may supply little material to that coast, especially if the transport route is interrupted or the source is not connected effectively. Therefore low energy alone does not guarantee a large deposit. Option B is correct because it recognises the limiting role of sediment supply. Option A is too absolute: high deposition cannot be assured without abundant material. Option C confuses deposition with tides, and option D incorrectly treats ordinary energy loss as a tsunami-generating mechanism.

Correct answer: B. A tidal current is tide-driven water flow, while waves can drive sediment transport

The governing distinction is between a current and a wave. A tidal current is the horizontal movement of seawater associated with the rising and falling of the tide; it can flow landward during flood tide and seaward during ebb tide. A wave, in contrast, is mainly a moving form of energy generated commonly by wind, although water particles often move in orbital or oscillatory paths rather than travelling forward with the wave as a whole. When waves break obliquely on a shore, their energy can move sand along the coastline, producing littoral or longshore transport. Thus option B correctly distinguishes tide-driven water flow from wave-driven sediment movement. Option A erases an important process difference, while C and D are unrelated descriptions.

Correct answer: C. Change in the sediment-transport pathway

The governing concept is littoral transport: the direction in which waves approach a coast influences the direction of the alongshore component of sediment movement. If wind direction changes, the waves generated by that wind may approach the shore at a different angle. Their breaking force then has a changed component parallel to the beach, so sand may be transported along a new pathway. Where the available energy falls or the transport pathway is interrupted, deposition can begin at a different location. Option C identifies this chain of cause and effect accurately. Option A is irrelevant because the Moon’s apparent phase or size is not the stated control. Option B is not implied, since tides may continue normally, and option D is physically impossible for a coastal deposition situation.

Correct answer: B. Neap-tide conditions can limit ship movement

The governing concept is the relationship between lunar phase, tidal range, and navigation. During the third-quarter phase, the Sun and Moon are approximately at right angles relative to Earth. Their tidal effects partly counteract one another, so a neap tide occurs and the difference between high and low water is relatively small. If the port already has limited depth, the lower water level associated with the tidal cycle can reduce the under-keel clearance available to ships. Consequently, larger vessels may need to wait for a more favourable tide or use a restricted loading condition. Option B is therefore the suitable conclusion. Option A describes the opposite spring-tide situation, while C and D introduce unrelated or physically false explanations.

Correct answer: A. Combined water-level and wave-energy risk

The governing hazard concept is the compounding of separate coastal influences. A spring tide produces a relatively large tidal range because the solar and lunar tidal forces reinforce one another. This can make the background or starting water level higher than during a neap tide. Cyclonic conditions can simultaneously generate powerful waves, storm surge, and onshore water movement. When these effects occur together, waves may reach farther inland, erosion can intensify, and flooding or damage to coastal infrastructure can become more severe. Option A is correct because it recognises both the elevated water-level component and the wave-energy component. Options B, C, and D do not describe the immediate coastal hazard produced by the stated combination and therefore cannot guide suitable risk assessment.

Correct answer: A. Limited fetch can restrict wave growth despite long duration

Wave development depends chiefly on wind speed, the length of uninterrupted water surface over which the wind acts, called fetch, and the duration of that action. A long duration gives wind more time to transfer energy, but the wave field cannot grow without limit if the fetch is short. Once the waves have used the available fetch, the restricted distance limits further energy input and limits their eventual height and development. Therefore option A is the best conclusion: a controlling factor can constrain growth even when another factor is favourable. Option B is false because ordinary wind waves do not automatically become tsunamis. Options C and D confuse wind-wave development with tidal or lunar processes, which are governed by different mechanisms.

Correct answer: A. Wave energy may be high, but resistant rock can slow erosion

The governing concept is the interaction between process energy and material resistance. An exposed coast generally receives waves with less shelter, so wave attack and the energy delivered to the shoreline may be substantial. However, erosion is not controlled by energy alone. Resistant, coherent rock can withstand abrasion, hydraulic pressure, and repeated wave impact more effectively than weak or fractured material. Consequently, the rate of cliff retreat or coastal erosion may remain slow even under energetic wave conditions, although joints, weathering, and wave-cut notches can eventually weaken the rock. Option A correctly combines high exposure with geological resistance. Option B denies the meaning of an exposed coast, C wrongly assumes immediate erosion, and D ignores the direct role of rock strength in determining coastal response.