Waves and tides

Coastal deposition occurs when waves lose enough energy that they can no longer carry all the sediment they were transporting. The released material may accumulate as beaches, bars, spits, or other depositional features, depending on currents and shoreline shape. Two conditions are especially important: a supply of movable sediment and a reduction in transporting power. Option D includes both conditions and is therefore correct. High-energy waves usually increase erosion and transport rather than deposition, so A is unsuitable. Option B lacks sediment and has excessive energy, while C is not a normal coastal depositional condition.

Correct answer: A, coastal erosion. Energetic waves repeatedly attack coastal rock through hydraulic action and abrasion. Water and compressed air can force their way into cracks, while sand, pebbles, and other transported material scrape and wear the rock. Over time, this removes or weakens coastal material, which is the process called coastal or marine erosion. B is a possible landform result of prolonged erosion, but it names a feature rather than the process asked for, so A is more precise. C is unrelated to wave action and requires an astronomical alignment. D describes sediment settling from river flow, not repeated removal of hard rock by sea waves. Memory cue: erosion is the wearing-away process; a sea cliff is one possible product of that process.

The relevant astronomical relationship is the position of the Sun, Moon, and Earth. At the first-quarter and third-quarter phases, the Sun and Moon are approximately at right angles as viewed from Earth. Their gravitational effects act in partly different directions, so they do not combine to produce the greatest tidal range. Instead, the difference between high and low tide is relatively small; this condition is called a neap tide. Therefore option B is correct. Spring tides occur near the new moon and full moon, when the forces align more nearly. A tsunami is caused by sudden seafloor displacement, not by the lunar phase, and wind is not the defining cause of ordinary tides.

When the Sun and Moon are approximately at right angles relative to Earth, their tidal-producing forces act in different directions rather than reinforcing one another. This arrangement occurs near the first-quarter and third-quarter Moon and produces a smaller difference between high and low tide, known as a neap tide. Options A, B, and C are therefore consistent with the governing concept. Option D is the wrong answer because spring tides and their larger tidal ranges occur near the new moon and full moon, when the Sun, Earth, and Moon are more nearly aligned. The question asks for the incorrect association, so D must be selected.

The governing concept is tidal range, which is the vertical difference between high-water level and low-water level. At new moon and full moon, the Sun, Earth, and Moon are approximately aligned, so the gravitational effects of the Sun and Moon reinforce one another. This produces a spring tide, whose high tides are higher and low tides are lower than usual; therefore the tidal range is greater. Option A correctly links the observed large range with a spring tide. A neap tide occurs near the quarter phases and reduces the range, so B is incorrect. Wind and sea colour do not explain the regular lunar tidal pattern.

The strongest distinction is the governing cause and the type of movement. Tides are broad, periodic rises and falls of sea level produced mainly by the gravitational pull of the Moon and, to a lesser extent, the Sun, together with Earth–Moon motion. Ordinary surface waves are usually generated when wind transfers energy to the water surface; the water mostly oscillates while wave energy travels forward. Thus option B gives the scientifically useful comparison. A is geographically false, because waves and tides are not restricted in that way. C confuses ordinary waves with tsunamis, and D ignores their different primary causes.

The governing concept is wave origin. Ordinary wind waves are produced mainly by energy transferred from moving air to the sea surface. A tsunami is a long-wavelength sea wave or wave train generated when a large volume of seawater is suddenly displaced, commonly by an undersea earthquake, submarine landslide, volcanic eruption, or, less commonly, another major disturbance. Therefore its origin and scale differ from those of ordinary wind waves, although both are forms of wave motion. Option C correctly identifies sudden seafloor disturbance as one important cause. A and D deny its marine nature, while B incorrectly confuses a tsunami with a tidal phase.

The governing planning principle is that tidal range changes the depth of navigable water. In a port or shallow channel, low tide may reduce the available depth below a vessel’s safe draught, while high tide may provide more under-keel clearance. A large range therefore requires tide tables, depth measurements, suitable sailing windows, and sometimes controlled entry or departure times. Option A correctly connects navigation scheduling with changing water level. Sea colour, fish sounds, and language have no direct role in determining channel depth or safe vessel movement, so options B, C, and D are irrelevant distractors.

The governing concept is the changing alignment of the Sun, Earth, and Moon. At new moon and full moon, the Sun and Moon pull in approximately the same line, so their tidal forces reinforce one another. The result is a spring tide, with a relatively large tidal range. At the first- and third-quarter phases, the Sun and Moon are approximately at right angles as viewed from Earth, so their effects partly counteract one another and the tidal range is smaller; this is a neap tide. Therefore option B is correct. The other choices reverse or deny this established relationship.

The governing concept is differential coastal erosion. Rock strength controls resistance, while wave energy supplies repeated impact, pressure changes, abrasion, and hydraulic action. Where weak or fractured rock meets powerful waves, cracks can widen, particles can be removed, and cliffs or shore platforms can retreat more rapidly over time. The exact rate also depends on rock structure, wave exposure, tides, weathering, and sediment protection, but the expected direction of change is accelerated erosion. Therefore option A is correct. Wave energy does not stop spring tides, and ordinary coastal erosion does not directly alter a river source or remove seawater’s salinity, making B, C, and D unsuitable.

The governing concept is wave-driven littoral, or longshore, transport. When wind direction changes, the waves may approach the shoreline at a different angle. The swash then carries sediment obliquely up the beach, while backwash tends to move downslope, producing a net movement parallel to the coast. A changed wave angle can therefore alter both the direction and amount of sand transported, so option A is correct. Tides are controlled mainly by lunar and solar gravity and do not always end because wind changes. The Moon cannot collide with Earth as a normal coastal response, and the sea does not lose all its water. Thus the realistic result is a change in sediment transport.

A sound comparison of ocean-water movements must use their causes, the way water moves, and their effects. Waves are mainly oscillatory surface movements generated by wind; tides are periodic rises and falls of sea level caused chiefly by the gravitational pull of the Moon and, to a lesser extent, the Sun; currents are comparatively continuous horizontal flows produced by factors such as winds, density differences, temperature, salinity and Earth’s rotation. Therefore option A gives the complete basis. Temperature, depth and coastline length may influence particular processes, but they cannot adequately define all three. Salinity and colour are incomplete indicators, while language and population are human characteristics, not oceanic controls.

The governing concept is the neap tide. At the first-quarter and third-quarter phases of the Moon, the Sun, Earth and Moon are approximately at right angles. The solar and lunar tidal forces then act in different directions rather than reinforcing one another. Their combined tidal effect is weaker, so the difference between high tide and low tide, called the tidal range, becomes relatively small. At the third quarter this condition produces a neap tide, making option B correct. Strong alignment occurs near the new moon and full moon and produces a spring tide with a larger range. Wind can raise waves locally but does not explain the regular lunar phase relationship, and an undersea earthquake is associated with tsunami generation, not ordinary neap tides.

The governing idea is compound coastal hazard. A spring tide occurs when the Sun, Earth and Moon are nearly aligned, so the tidal range and the expected water level are relatively large. Storm waves, in contrast, are generated by strong winds and carry unusually high wave energy; a storm surge may also raise the water surface above the predicted tide. If these processes occur together, waves can run farther inland and attack beaches, dunes, seawalls and low-lying settlements with greater force. Therefore option A is the most suitable analysis. A spring tide does not stop storm waves, because tides and wind-generated waves have different causes. Storm waves cannot remove gravity, and both phenomena clearly have important coastal effects.

The governing concept is wave energy and selective sediment transport. As waves enter shallow water, friction with the seabed slows the lower part of the wave, the wave steepens, and it eventually breaks. Breaking releases energy and produces turbulence, swash and backwash. These flows can lift, roll or drag particles, but grains do not respond identically: smaller or lighter grains are transported more easily, whereas larger or denser pebbles require stronger flow. Repeated uprush and return flow can therefore separate material by size, weight or mobility, making sorting more rapid in suitable coastal conditions. Option A is correct. Breaking waves do not lack energy, do not erase tides, and cannot pull the Moon; those choices confuse unrelated processes.

Fetch is the uninterrupted distance over water across which wind transfers energy to the sea surface. Wave growth depends on fetch as well as wind speed and the length of time the wind blows. With a short fetch, the wind acts over only a limited distance, so waves have less opportunity to gain energy, increase in height and develop longer wavelengths. They may remain relatively small even if the wind is strong, although local conditions also matter. Therefore option A is correct. Gravity does not disappear; it helps restore the disturbed water surface. The Moon does not normally stop wind, and waves are not formed only at coasts: wind-generated waves commonly develop over open water before reaching the shore.

The governing concept is tidal-range energy. A tidal energy installation uses the predictable movement of seawater between higher and lower levels, often through a barrage, lagoon or tidal-stream system. A larger tidal range provides a greater difference in hydraulic head, allowing more water and potentially more gravitational energy to pass through turbines during filling or emptying. In simplified terms, greater usable height difference can increase the energy available, although actual output also depends on basin shape, flow rate, turbine efficiency, environmental limits and construction feasibility. Option A is therefore correct. A large tidal range does not dry the sea, stop wind or make the Moon disappear; those distractors confuse energy extraction with impossible changes in the ocean or astronomical system.

The governing concept is the interaction between wave energy and coastal morphology. Headlands, bays, reefs, beaches, rock type and the nearshore slope can refract, reflect, focus or dissipate incoming wave energy. Wave refraction commonly concentrates energy around exposed headlands, increasing erosion there, while energy may be reduced inside sheltered bays, encouraging deposition. A steep or resistant coast also responds differently from a gentle sandy shore. Thus option A correctly states that coastal structure changes the distribution of wave energy and consequently the balance between erosion and deposition. Coastal shape cannot eliminate the Moon’s gravity, convert tides into wind, or permanently freeze seawater. Those options confuse unrelated gravitational, atmospheric and thermal processes with the geomorphic effect of waves.

The governing concept is spatial variation in coastal sediment budgets. Wave energy is rarely uniform along an irregular coast: headlands may focus waves and experience strong erosion, while bays or protected stretches may receive weaker waves and become depositional environments. Longshore currents can also transport sand from one section to another, so erosion at a sediment source and deposition at a nearby sink may occur simultaneously. Differences in beach slope, rock resistance, wave approach angle and shelter further modify the local balance. Thus option A provides the best explanation. Waves do perform geomorphic work, and neither the complete disappearance of tides nor the absence of seawater is consistent with a coast showing active erosion and deposition. The processes are local and connected rather than contradictory.

The governing concept is tidal range, which is the difference in height between high tide and the following low tide. A spring tide occurs near the new moon and full moon, when the Sun, Moon, and Earth are approximately aligned. Their gravitational effects reinforce one another, producing higher high tides and lower low tides, so the tidal range is unusually large. The name “spring” refers historically to the idea of the water springing up, not to the spring season. Option A gives the correct correction. It is not restricted to the rainy season, is not generated mainly by wind, and is not a tsunami; a tsunami results from sudden displacement of seawater, usually during an undersea earthquake or similar disturbance.

The Moon is much closer to Earth, so its tidal effect is greater. Tides result from differences in gravitational pull across Earth, and this tidal effect depends very strongly on distance. The Sun also exerts a substantial tidal effect and can strengthen or weaken the lunar effect depending on the alignment. Thus A is correct; the Sun does have gravity and does not stop tides.

A narrow bay can confine the incoming or outgoing tidal flow, which may increase the speed of the tidal current. In some funnel-shaped bays, the tidal range may also increase toward the head of the bay. The exact effect depends on the bay’s shape, depth, and friction, so this is a possible—not universal—result. Therefore B is correct.

High tide raises the baseline sea level, so large waves can reach farther inland or overtop coastal barriers more easily. Their energy can contribute to flooding, erosion, and damage. The actual risk depends on wave height and direction, coastal shape, storm conditions, and protection measures; it is increased, not guaranteed. Therefore C is correct.

Deposition occurs when sediment is available and the water loses enough energy to carry it. As a current or wave weakens, its ability to keep particles moving or suspended decreases, and particles settle. Option D gives both conditions. High energy generally transports or erodes material, while no sediment cannot form a deposit.

Repeated wave impact, water pressure in cracks, and abrasion by carried sand or pebbles can remove rock from the coast. Weak or fractured rock may be eroded more quickly, causing cracks to widen or the shoreline to retreat. The rate depends on the rock and local wave conditions. Therefore A is correct.