Waves and tides

The governing concept is hydraulic sorting by changing wave energy. As waves approach shallow water and break, part of their energy is dissipated through turbulence, turbulence, and friction. This energy is not distributed equally among all grains: larger or denser particles require stronger flows to move, whereas fine particles can be suspended or carried more easily. Repeated swash and backwash therefore separate grains according to size, density, and settling behaviour, often leaving relatively coarse material in higher-energy zones and finer sediment in calmer areas. Option A is correct; the other choices deny wave energy or confuse tides and lunar motion.

The structure of a coast affects how waves behave when they reach land. Headlands, bays, shallow slopes, reefs, beaches, and the hardness of rocks can reflect, refract, absorb, or concentrate wave energy. As a result, one part of a coast may experience strong erosion while another part receives transported sediment and develops deposition. Coastal form therefore changes both the distribution of wave energy and the visible landforms produced by it.

Option A is correct because it includes changes in wave-energy distribution and in erosion and deposition. Coastal structure cannot remove the Moon’s gravity, turn tides into wind, or freeze the whole sea. Those choices confuse different processes. The local shape and material of the coast must be considered when explaining the work of waves.

The governing concept is differential coastal erosion and deposition. Wave energy is not distributed uniformly along a coast: headlands, bays, beaches, nearshore depth, slope, rock resistance, and the direction of wave approach can all alter the force and sediment movement at a particular site. High-energy zones commonly remove material, while sheltered or lower-energy zones allow transported sediment to settle. A sediment-rich location may therefore experience deposition even while another nearby section is being eroded. Option B includes the essential controls and best explains the contrast. The other choices deny wave action or propose a uniform change, neither of which accounts for local differences.

The governing concept is that coastal change reflects an interaction between wave energy and the resistance of the material being attacked. High-energy waves can increase hydraulic pressure, abrasion, and sediment transport, while strong, resistant rock generally erodes more slowly than weak, jointed, or unconsolidated material under comparable conditions. Local shoreline orientation, exposure, and sediment supply may also be examined, but the first two factors in option A are the most directly relevant choices provided. Moon colour, cloud number, forest height, mountain age, river names, and city size do not explain rapid wave erosion in this context. Hence A is correct.

The governing concept is sediment budget and the spatial variability of wave action. Energetic waves have enough force to detach and transport material, but they do not produce the same result at every point along a coast. Headlands, coves, changing water depth, shoreline orientation, obstacles, and differences in current speed can focus energy in one place and reduce it in another. Material may be eroded from an exposed section, carried alongshore, and deposited where transport capacity falls or a sheltered pocket exists. Therefore option A correctly describes a mixed result. The other options claim impossible changes to the sea, tides, or lunar influence.

The governing concept is tidal navigation. A high tide changes available water depth, while a strong tidal current can push a vessel sideways, alter its speed over ground, and make steering or berthing more difficult. Their combined occurrence therefore requires mariners to consult tide tables and local current information, choose a suitable window, adjust speed, maintain a safe course, and allow sufficient clearance near channels or harbour entrances. Option A states the essential precaution: regulate vessel speed and timing according to tidal conditions. Sea colour and moonlight are not reliable controls, and removing all sediment is neither practical nor a navigation procedure.

The governing concept is the interaction between erosional force and material resistance. High wave energy can still exert hydraulic pressure, abrasion, and impact on a rocky coast, so very hard rock does not make erosion automatically impossible. However, its strength, low porosity, and resistance to fracturing can reduce the rate compared with weak, highly jointed, or unconsolidated material exposed to similar waves. The actual rate also depends on rock structure, wave frequency, weathering, and sediment tools. Option B is therefore the balanced conclusion. A is absolute and false, C wrongly excludes waves, and D ignores the principal driving force.

A large tidal range means that the difference between high tide and low tide is substantial, so the volume of water entering and leaving the coastal basin can be considerable. In a narrow bay or inlet, the restricted cross-section forces the tidal flow through a limited passage. This can increase current speed, especially near the entrance or during changing tide, while the water level inside the bay still rises and falls markedly. The exact response depends on the bay's length, depth and resonance, but strong tidal currents and noticeable water-level changes are a physically reasonable combined effect. Option A therefore fits. The remaining options concern neither tidal dynamics nor coastal geometry.

The key concept is the difference between wind waves and tsunami waves. A strong undersea earthquake can suddenly lift or lower part of the seabed, displacing a large column of seawater. The disturbance then travels outward as a long-wavelength wave; as it reaches shallow coastal water, its speed decreases and its height can increase greatly, producing destructive inundation. Ordinary wind waves are generated mainly by frictional energy transferred from moving air to the sea surface and usually have much shorter wavelengths. Option A correctly identifies the earthquake-related source and explains why the wave should not be classified as a normal wind wave. The Moon mainly produces tides, not this sudden earthquake-triggered disturbance.

The governing concept is fetch-limited and duration-limited wave growth. High wind speed can transfer substantial energy to the sea surface, but waves need enough open-water distance and sufficient time to grow. If fetch is short, the waves quickly reach a boundary or coast and cannot remain under the wind long enough to reach their full potential. If the wind acts for only a short duration, energy input is also limited. Therefore the waves may become steep or locally energetic, but their height is likely to remain limited compared with fully developed waves under a long fetch and long duration. Option A is the balanced conclusion. High wind alone does not make a tsunami, and it does not end tides or remove the wind-wave relationship.

The governing concept is compound coastal risk. High tide starts with an elevated water level, so waves and storm surge operate from a higher base than they would at low tide. Storm waves also contain greater energy and can produce stronger wave attack, overtopping, erosion, and flooding. When these conditions coincide, the total coastal impact can be substantially greater than either condition alone, although the exact result depends on shoreline shape, storm direction, defences, and local bathymetry. Option A is therefore correct. The effects do not always cancel, and options C and D ignore well-established mechanisms of coastal flooding and erosion.

The governing concept is the influence of coastal geometry on tidal currents. A narrow bay provides a smaller cross-sectional passage for water entering during flood tide or leaving during ebb tide. If a substantial tidal volume must pass through that restricted opening or channel, continuity of flow generally requires a greater current speed, provided other conditions such as friction and depth do not dominate. Local shape can therefore amplify tidal currents and sometimes produce strong streams. Option B is correct. The current does not become zero merely because the bay is narrow; the sea does not permanently dry, and the Moon’s gravity is not removed. The question concerns concentration and speed of flow, not disappearance of the tidal force.

The governing concept is the balance between sediment supply and transporting energy. Deposition occurs when moving water loses enough energy that it can no longer keep sediment grains in motion or carry them farther. If wave energy remains very high, turbulence and strong currents may suspend, roll, or move available sediment along the shore or offshore instead of allowing it to settle. Thus the presence of material alone does not guarantee deposition; a lower-energy environment is also needed. Option C is correct. The Moon does not simply stop sediment, tides contain water, and ordinary coastal sediment does not always become gas. Deposition depends on both material availability and the energy conditions of the environment.

Astronomical forcing establishes the basic tidal cycle, but the observed tidal range at a particular place is also shaped by local geography. A narrowing or funnel-shaped bay can guide and concentrate tidal water, while its depth, coastline, seabed form, and resonance characteristics may amplify the difference between high and low water. Therefore option A correctly identifies the principle: coastal configuration modifies tidal behaviour. Option B is false because lunar gravity remains essential. Option C confuses tides with wind-generated waves, and option D has no logical connection with a larger tidal range. Local amplification does not mean that the bay creates tides independently of astronomical forces.

In a port with a large tidal range, the vertical position of the sea surface changes substantially during the tidal cycle. That change alters the water depth over channels, bars, harbour entrances, and berths. Ship planners must therefore compare the vessel’s draft with the available depth at the predicted time of high or suitable tide, while also allowing a safety margin for under-keel clearance, waves, and channel conditions. Option B is correct because tide timing and navigable depth directly affect safe entry, departure, and loading. Sea colour, coastal language, and fish sounds provide no reliable information about clearance or navigation.

The governing concept is compound coastal risk: different marine processes can operate at the same time and amplify one another. A high tide raises the starting water level, so waves can reach farther inland and attack beaches, dunes, seawalls, roads, and buildings with less remaining protective elevation. Energetic waves add strong uprush, backwash, erosion, and sometimes overtopping. Therefore, risk assessment must combine water level, wave height or energy, shoreline elevation, and exposure rather than studying either factor alone. Option C is correct. A is irrelevant, B is scientifically false, and D ignores the direct coastal action of tides and waves.

The governing concept is that deposition requires both transportable material and a sufficiently low-energy setting. When wave energy decreases, the water may lose the ability to carry sediment, which favours settling. However, settling cannot create new material: if sand, silt, or gravel is scarce in the coastal system, only a small amount can accumulate. Thus low energy is a necessary or favourable condition in this case, but it is not sufficient by itself. Option D correctly identifies the limiting factor. A is wrong because reduced energy does not always cause erosion, B overstates the role of tides, and C incorrectly disconnects waves from coastal processes.

The governing distinction is between wave-driven longshore drift and tide-driven tidal currents. When waves approach the shoreline obliquely, swash carries sediment up the beach at an angle while backwash returns more directly downslope. Repetition produces a net movement parallel to the coast, called longshore drift. A tidal current, in contrast, is the periodic horizontal movement of seawater associated with rising and falling tides; it may flow landward during flood tide and seaward during ebb tide. Option A states both definitions correctly. B reverses them, C invents an eclipse condition, and D wrongly treats two different processes as identical.

The governing chain is wind direction, wave approach angle, sediment transport, and coastline response. A change in wind direction can alter the direction from which waves reach the shore. If the waves become more oblique, the balance between swash and backwash may change and longshore drift can strengthen, weaken, or reverse. That redistribution of sand and gravel may produce accretion in one sector and erosion in another, changing beaches, spits, bars, or the shoreline position. Therefore C is the valid indirect effect. A, B, and D are unrelated or physically impossible consequences of changing wave angle.

The governing concept is neap tide, which occurs near the first- and third-quarter Moon phases. At third quarter, the Sun and Moon are approximately at right angles relative to Earth. Their tidal-generating forces do not reinforce one another as strongly as they do at new or full moon, so the difference between high and low tide is smaller. A smaller tidal range commonly corresponds to weaker associated tidal currents, although local coastline and basin shape can modify the exact strength. Option C gives the appropriate analysis. A describes spring tide, B is an unsupported tsunami claim, and D is impossible.

The governing principle is spatial variation in coastal processes. Wave energy is not distributed uniformly along every shoreline because headlands, bays, reefs, beach slope, water depth, structures, and wave direction alter the local flow of energy. Sediment supply and sediment size also differ from place to place. Where wave attack and sediment removal dominate, erosion may occur; where wave energy falls or transported material accumulates, deposition may occur. Consequently, opposite landform changes can take place along the same coast. Option A correctly combines the controlling factors, while B, C, and D deny or misrepresent normal coastal processes.

The governing concept is the gravitational origin of tides. A spring tide is not named after the spring season; the word refers to the unusually large tidal range, meaning the difference between high-tide and low-tide levels. Near the new moon and full moon, the Sun, Moon, and Earth are approximately aligned, so the gravitational effects of the Sun and Moon reinforce one another. This produces higher high tides and lower low tides than average. Therefore, option A correctly separates season from astronomical alignment. Option B wrongly restricts the event to rainy months, while C confuses tides with wind-generated waves and D confuses an ordinary tidal phenomenon with a tsunami.

The governing concept is wave work on a coast. Fetch is the uninterrupted distance over which wind transfers energy to the sea; a long fetch can therefore produce energetic waves. When such waves meet weak or jointed rock, hydraulic action, abrasion, and impact may remove material, producing erosion. The moving water can then carry the loosened particles along the shore or offshore. Where wave energy falls, some of that sediment may be deposited. Thus erosion, transport, and local deposition can occur in the same coastal system, making option B correct. A confuses waves with tides, whereas C and D describe impossible consequences unrelated to coastal process.

The governing concept is astronomical control of tides. The Moon is the principal tide-generating body because of its close proximity, while the Sun also contributes through gravity. As their relative positions change during the lunar cycle, their gravitational effects may reinforce or partly offset one another. Near new moon and full moon, alignment produces spring tides with a larger range; near the first and third quarters, the right-angle arrangement produces neap tides with a smaller range. The stated relationship between celestial position and tidal range therefore supports option A. Wind can generate waves and modify coastal water conditions, but it is not the primary periodic control of tidal range; rivers do not control global tides.

The governing concept is the control of littoral sediment transport by wave approach. When tidal range remains unchanged, it is less likely to explain a sudden change in the direction of sediment movement. Waves arriving obliquely to the shoreline create a swash that moves sediment up the beach at an angle, while backwash tends to return more directly downslope. Repeated action can produce longshore drift, and a change in wave angle can reverse or redirect that transport. Therefore option D is the most relevant first check. Sea colour and fish numbers are not primary mechanical controls, and the Moon’s apparent size does not change in the way suggested or directly explain a local sediment-direction shift.