Waves and tides

Correct answer: B. The Sun and Moon are at approximately right angles as viewed from Earth

The correct answer is B. At the first quarter, the Sun and Moon are approximately at right angles as viewed from Earth. Their tidal effects partly oppose one another, producing a smaller tidal range, known as a neap tide. Alignment near the new and full moons instead produces spring tides. Wind fetch affects wind-generated waves, and an undersea earthquake is not the regular cause of this tidal pattern.

Correct answer: A. A right-angle position is associated with a neap tide

When the Sun and Moon are approximately at right angles as seen from Earth, their tidal effects do not reinforce each other as strongly, so the tidal range is smaller. This is a neap tide. Spring tides occur near new and full moon, when the Sun, Earth, and Moon are approximately aligned. Therefore A is correct; tides still occur at right angles, and the Moon’s effect does not disappear.

Correct answer: C. Tsunami can form from a sudden disturbance of the sea floor

The governing concept is the origin or generating mechanism of a water wave. Ordinary wind waves are produced mainly when wind transfers energy to the sea surface, whereas a tsunami may be generated when an earthquake, submarine landslide, volcanic eruption, or another sudden event displaces a large volume of seawater. Therefore, the useful distinction is not colour, tide classification, or distance from the sea; it is the source of the disturbance. Option C is correct because a sudden sea-floor movement can push the overlying water and create long-wavelength waves that travel across an ocean. Option B is incorrect because a tsunami is not a type of neap tide, and options A and D have no scientific basis.

Correct answer: D. Tidal current or tidal range can increase

The governing concept is the interaction between tidal forcing and coastal geometry. Tides are caused primarily by the gravitational effects of the Moon and Sun, but the height and flow of tides at a particular coast are modified by the shape, depth, width, and orientation of bays and estuaries. A narrowing or funnel-shaped bay can concentrate incoming water, sometimes producing a stronger tidal current and a larger tidal range toward its head. Thus option D is correct. The effect is local and depends on resonance and the dimensions of the basin; it does not mean that every bay will show the same increase. Options A, B, and C are unrelated physical claims and do not describe the result of tidal concentration.

Correct answer: A. According to the timing and depth of the water level

The governing concept is tidal clearance for navigation. A large tidal range means that the sea level changes considerably between high tide and low tide. Since a ship requires a minimum depth beneath its keel, port authorities must relate arrival, departure, berthing, and channel passage to the predicted time and height of tide. At high tide, a channel may provide sufficient depth for a vessel with a large draught; at low tide, the same route may become unsafe or inaccessible. Therefore option A is correct. Sea colour, fish sounds, and coastal language do not determine navigational depth or the safe timing of ship movement. Actual planning also considers wind, waves, currents, channel width, and safety margins.

Correct answer: B. High water level and energetic waves can together cause more damage

The governing concept is compound coastal hazard. Tide level determines the starting elevation of seawater, while wave energy determines how strongly waves can run up the beach, overtop a barrier, erode sediment, and strike coastal structures. If a high tide or storm surge coincides with energetic waves, the waves begin from an already elevated water surface and can reach farther inland. Their combined effect may increase flooding, erosion, overtopping, and damage even when each factor is considered separately. Option B is correct because it expresses this interaction. The other options are unrelated: tides and waves do not change the Moon’s colour, do not eliminate rivers, and are directly connected with coastal processes.

Correct answer: A. Because there is no material to deposit

The governing concept is that deposition requires both suitable transport energy and available sediment. Low-energy waves may be unable to keep sand or gravel in motion, so they can encourage settling; however, settling cannot create a deposit if no particles are present in the first place. A beach, bar, or other coastal deposit therefore depends on a supply of sediment from rivers, cliff erosion, offshore material, or longshore transport, as well as conditions that reduce carrying capacity. Option A is correct because it identifies the missing necessary condition. Option B is too absolute: low energy commonly favours deposition rather than always causing erosion. Options C and D confuse tides or wave generation with sediment supply.

Correct answer: A. Because wind has a shorter distance over which to act on the sea surface

The governing concept is fetch, the uninterrupted distance across water over which wind transfers energy to the sea surface. Wave growth depends on wind speed, the duration of wind action, and fetch. When fetch is short, wind acts over a limited distance, so waves have less opportunity to gain energy, increase in height, and develop longer periods. They may remain relatively small even if the wind is strong, although local conditions and existing swell can modify the result. Option A is correct because it states the direct physical reason. Gravity does not end, the Moon does not normally block the wind, and waves can form in open water rather than only at the coast. Thus fetch is an important control on wave development.

Correct answer: A. It can raise energy potential through water-level difference

The governing concept is tidal energy generation from the periodic rise and fall of seawater. A large tidal range means a greater vertical difference between high tide and low tide. This difference can allow more water to be stored, released, or passed through turbines, increasing the usable energy potential when suitable coastal conditions and engineering are available. Therefore, option A is correct. Option B is impossible because tides do not remove seawater. Option C concerns atmospheric movement, not the main mechanism of tidal power, and option D is unrelated to Earth–Moon interactions. The exact output also depends on basin shape, flow, turbine design, and environmental limits, but a large range is a major favourable factor.

Correct answer: A. It can alter the distribution of wave energy and the areas of erosion and deposition.

The governing concept is that coastal geometry controls how incoming wave energy is focused, refracted, reflected, or dispersed. Headlands may concentrate wave energy, especially near their exposed sides, so erosion can be strong there. Bays often receive relatively less energy because waves refract around projecting land, allowing sand and other sediment to accumulate. Rock resistance, beach slope, water depth, and the orientation of the shoreline also modify the result. Thus option A is correct. Option B confuses coastal form with lunar gravity; option C incorrectly mixes tides and wind; option D has no normal geomorphological basis. Coastal structure changes the distribution of wave work, not the fundamental causes of tides.

Correct answer: B. Wave energy and sediment condition vary by location

The governing concept is spatial variation in coastal processes. Wave energy is not distributed uniformly: exposed headlands, steep shores, shallow-water refraction, currents, and differences in shoreline orientation can make some locations more erosive. Where wave energy falls, or where sediment supply is adequate and transport slows, deposition becomes more likely, especially in sheltered bays. Therefore option B is the best explanation. Option A is false because waves are a major coastal agent. Option C is unnecessary and scientifically wrong; tides may continue while erosion and deposition occur. Option D contradicts the existence of a coast and ocean processes. The pattern reflects changing energy, sediment supply, and local coastal form.

Correct answer: A. The Moon’s position and motion keep changing

The governing concept is the Moon’s changing position relative to Earth and the Sun. Earth rotates beneath the tidal bulges, but the Moon also moves eastward in its orbit each day. Consequently, a location must rotate a little farther before it aligns with the Moon again, so successive high or low tides generally occur about 50 minutes later on average, although local coastlines and basins modify the exact interval. Thus option A is correct. Sea colour, fish numbers, and language do not control the astronomical timing of tides. Local winds, pressure, depth, and coastal shape can alter observed height and timing, but the regular daily shift is chiefly linked to lunar motion.

Correct answer: A. Sediment movement and ship planning

The governing concept is that a tidal current is the horizontal movement of seawater produced by the rising and falling tide. A strong current can transport, sort, or redistribute sediment, thereby influencing channels, shoals, mudflats, and coastal deposits. It also affects navigation because ships may gain or lose speed, drift from a planned track, or need to schedule passage with the current. Hence option A correctly combines a physical coastal effect with a practical human activity. Tidal currents do not change the colour of the Moon, the size of the Sun, mountain height, forest age, cloud weight, or a river’s name. These alternatives are unrelated to tidal flow.

Correct answer: A. A spring tide is not related to a season; it has a large tidal range when the Sun, Moon and Earth are nearly aligned

The governing concept is tidal alignment, not the annual season. Near a new moon or full moon, the Sun, Moon, and Earth are approximately aligned. Their gravitational effects reinforce one another, producing higher high tides and lower low tides; consequently, the tidal range is relatively large. This event can occur in every month and is called a spring tide because the water appears to spring or rise strongly, not because of springtime. Thus option A is correct. Wind may generate or strengthen surface waves but is not the main cause of spring tides. A tsunami is a different phenomenon, usually generated by sudden seafloor displacement, and option B wrongly assigns the event to warmer seasonal water.

Correct answer: A. Spring tide can increase tidal range

The governing concept is the relationship between tidal range and extractable tidal energy. Around a full moon, the Sun, Earth, and Moon are approximately aligned, so solar and lunar gravitational effects reinforce each other. This produces a spring tide, with higher high water and lower low water than during a neap tide. The greater water-level difference can increase the energy available to a barrage, lagoon, or other tidal system, subject to local geography and engineering design. Therefore option A is correct. Option B describes the opposite condition: neap tides usually have a smaller range. Sea colour and complete wind stoppage neither cause the lunar tidal maximum nor explain energy potential.

Correct answer: A. Nature of coastal rock and wave energy

The governing concept is differential coastal erosion. Rock type determines resistance: hard, well-cemented rock generally withstands wave attack better than weak, fractured, or unconsolidated material. Wave energy determines how much force reaches the shore; storm conditions, exposure, depth, and refraction can increase that force. Examining both factors helps explain why one section retreats quickly while a nearby section remains stable or forms a different landform. Therefore option A is correct. Moon colour and cloud number do not describe the relevant local controls. Forest height, mountain age, river names, and city size may be geographical information, but they do not directly measure the immediate wave erosion mechanism in this question.

Correct answer: A. Waves can become higher and more energetic

Wave development depends mainly on wind speed, the duration for which the wind acts, and fetch, which is the uninterrupted distance across water over which the wind blows. Strong wind transfers energy to the sea surface; a long duration allows that energy to accumulate, while a long fetch provides a broad path for continued wave growth. Therefore, waves may become higher, longer, and more energetic, although the exact result is also affected by water depth and existing sea conditions. Option A is correct. Options B, C, and D are unrelated or absolute: wind does not always destroy waves, tides do not lose gravity, and a windy sea does not permanently dry up.

Correct answer: B. Because the wind has only a short distance over which to transfer energy

Fetch is the uninterrupted distance over which wind acts on the water surface. Even when wind speed is high, a short fetch restricts the distance and time available for transferring momentum and energy to the sea. Waves therefore may begin to grow rapidly but cannot develop the height and length that they could achieve over a long open-water track. Option B expresses this limitation accurately. The Moon does not function as a barrier to ordinary wind, tides do not automatically erase wind waves, and the question assumes a sea containing water. Thus A, C, and D are scientifically unsuitable distractors.

Correct answer: B. The gravitational effects of the Sun and Moon combine when they are nearly aligned

Spring tides occur near the new moon and full moon, when the Sun, Earth, and Moon are approximately aligned. The lunar and solar tidal forces then act along nearly the same line, reinforcing one another. This produces higher-than-usual high tides and lower-than-usual low tides, so the difference between high and low water, called tidal range, becomes large. The term spring refers to the increased range, not to the season of spring. Option B is correct. Wind direction can modify local water levels but does not cause the astronomical spring-tide cycle; salinity and river water are not the primary cause.

Correct answer: C. The Sun’s and Moon’s gravitational effects are nearly at right angles and partly counteract each other

Neap tides occur around the first-quarter and third-quarter phases of the Moon. At these times, the Sun and Moon are positioned approximately at right angles as viewed from Earth. Their tidal-generating forces do not reinforce one another along the same line; instead, their effects partly counteract the overall tidal bulges. Consequently, high tides are lower, low tides are higher, and the tidal range is smaller than during a spring tide. Option C gives the correct astronomical explanation. Seawater does not disappear, ordinary wind does not stop the tide, and the Moon does not suddenly move extremely far away during a neap-tide phase.

Correct answer: D. Spring tide

A very high high tide together with a very low low tide indicates a large tidal range. Near the new moon, the Sun, Earth, and Moon are approximately aligned, so the solar and lunar tidal-generating forces reinforce one another. This condition produces a spring tide, and a similar effect occurs near the full moon. Option D is therefore the correct identification. A neap tide occurs near the first and third quarters and has a smaller range. A wind wave is a surface oscillation produced mainly by wind, while a storm current is not the standard name for this lunar-phase tidal pattern. The decisive clues are new moon and unusually large range.

Correct answer: C. Because high water level and greater wave energy act together

The governing concept is the combined effect of tidal water level and wave action. High tide places the sea surface and the normal waterline at a higher elevation, so incoming waves can travel farther inland and reach places that may normally remain above water. If the waves are also large, they carry greater energy and exert stronger impact, pressure, and erosion on beaches, dunes, seawalls, and buildings. Thus, flooding and damage may increase even though the tide itself does not stop the waves. Option C is correct because it identifies both controlling factors. Option A is false because tides do not block waves, while B and D contradict basic ocean processes.

Correct answer: D. Decreasing wave energy and available sediment

Coastal deposition occurs when the transporting energy of water becomes too weak to keep available sediment moving. The material may be supplied by rivers, cliff erosion, longshore transport, or offshore sources. As waves enter shallow water, lose energy, or move into a sheltered bay, their carrying capacity decreases; sand, silt, or gravel can then settle. Option D is correct because it includes both essential conditions: a supply of sediment and declining wave energy. Option A describes energetic conditions that usually favour erosion or transport, and it also removes the necessary material. Option B has low energy but no sediment, so there is nothing to deposit. Option C does not describe deposition conditions and focuses on resistant bedrock.

Correct answer: A. Coastal erosion can become faster

The governing concept is marine erosion, especially the relationship between wave energy and the resistance of coastal material. Repeated energetic waves strike the shore, compress air in cracks, remove loose particles, and use abrasion to enlarge weaknesses in rock. A weak or highly fractured coast therefore loses material more readily than a strong, resistant coast. Continued undercutting can produce notches, sea cliffs, caves, or local collapse, although the exact landform depends on rock structure and wave conditions. Option A is correct because it states the likely process without claiming that every coast changes identically. The other options are unrelated: waves cannot freshen seawater instantly, stop tides, or remove the Moon's gravity.

Correct answer: B. The Sun and Moon being at right angles

The governing concept is the difference between spring tides and neap tides. At the first-quarter lunar phase, the Sun, Earth, and Moon are arranged approximately at a right angle as viewed in the orbital plane. Solar and lunar tidal forces then act in directions that partly offset one another in their effect on the tidal bulges. The result is a smaller difference between high tide and low tide, called a neap tidal range. Option B is correct because it identifies the right-angle geometry. Linear alignment occurs near the new moon and full moon and produces spring tides, which have a larger range. An undersea earthquake is associated with possible tsunamis, not the regular first-quarter tidal cycle, and fetch mainly affects wind waves.