Waves and tides

Correct answer: A. They affect water level, erosion, deposition and human activities

The governing concept is the interaction of marine processes with coastal environments. Tides periodically raise and lower sea level, influence the timing of navigation, expose or cover intertidal habitats and affect the movement of water in estuaries. Waves transfer energy to the shore, causing erosion of cliffs and beaches, transporting sediment and building depositional features such as beaches and bars. Together, tides and waves influence ports, fishing, tourism, coastal settlements and hazard planning. Option A correctly includes both physical and human effects. B, C and D are too narrow or false: these processes are not limited to clouds, do not instantly create mountains, and are not merely responsible for changing sea colour.

Correct answer: A. Wave direction can also change

The governing concept is wind-generated wave formation. Wind transfers energy and momentum to the ocean surface through friction and pressure variations. Therefore, a sustained change in wind direction can alter the direction in which new waves travel, especially when the wind has enough speed and duration over a sufficient fetch. Existing waves may continue briefly because they possess momentum, and swell can travel away from the area where it was generated, so the change is not necessarily instantaneous or exact. Option A is correct because wave direction can respond to the changed wind forcing. B is too absolute, while C confuses waves with tides and D has no physical basis.

Correct answer: A. Because bottom friction becomes effective sooner

The governing concept is shallow-water wave transformation. As a wave moves from deep water toward a shallow coast, the lower part of its orbital motion begins to interact with the seabed. Bottom friction reduces the wave’s forward speed and changes its shape. The wavelength becomes shorter, while the wave height and steepness increase; once the wave becomes too steep to remain stable, the crest topples and the wave breaks. This process is called shoaling and breaking. Option A is correct because seabed friction becomes important sooner in shallow water. The Moon, salinity and wind may influence coastal conditions, but options B, C and D do not explain the immediate mechanical reason for breaking.

Correct answer: A. When wave energy falls and the waves can no longer carry all their sediment

Waves can transport sediment while they have enough energy. When their energy and carrying capacity decrease, some of that sediment settles on the shore or seabed. Thus option A describes the conditions for deposition. Without sediment, there is nothing to deposit, and ordinary waves do not turn sediment into gas.

Correct answer: A. Alignment gives spring tides; a right-angle position gives neap tides

The correct answer is A. Near new and full moons, the Sun, Moon, and Earth are approximately aligned, so the Sun’s and Moon’s tidal effects reinforce one another and the tidal range is greater; this is a spring tide. Near the first and third quarter moons, the Sun and Moon are approximately at right angles as viewed from Earth, and the tidal range is smaller; this is a neap tide.

Correct answer: A. Ordinary surface waves are mainly generated by wind, while tides are periodic sea-level changes caused chiefly by the Moon’s and Sun’s gravity

Ordinary surface waves are mainly driven by wind, which transfers energy to the sea surface. Tides are periodic rises and falls in sea level caused chiefly by the gravitational effects of the Moon and Sun. These are different processes, so option A is correct. Earthquakes can generate tsunamis, but that does not mean they cause all waves or tides.

Correct answer: A. The waves may not grow very large

Fetch is the uninterrupted distance over water across which the wind blows. A short fetch gives wind waves less distance to grow, even when the wind is strong. The waves may therefore remain relatively small. Option A is correct; tides do not stop because of a short fetch.

Correct answer: B. Because wind transfers energy to the water for longer

Wind transfers energy to the sea surface. If it continues to blow, that transfer can continue and waves can grow in height, provided there is enough fetch and the wind is otherwise suitable. Wave height also depends on wind speed and fetch, so duration is not the only factor. Therefore, option B is correct.

Correct answer: C. Because water particles mainly move in orbital paths while the wave energy travels forward

In a surface wave, water particles mainly move in orbital paths rather than travelling forward with the wave. The wave’s energy and disturbance move forward, while particles generally return close to their starting positions over a wave cycle. This is why wave motion is not the same as a steady current. Therefore, option C is correct.

Correct answer: D. As the water becomes shallower, the wave slows and steepens until its crest topples forward

As a wave enters shallow water, interaction with the seabed slows the wave and shortens its wavelength. The wave becomes steeper, and its crest eventually topples forward, producing a breaking wave. Therefore, option D gives the correct sequence.

Correct answer: A. Because the Sun, Moon, and Earth are approximately aligned, producing a larger tidal range

Spring tides occur near the new and full moons, when the Sun, Moon, and Earth are approximately aligned. The combined tidal effects produce a larger tidal range: high tides are higher and low tides are lower than at neap tides. Thus, option A is correct. “Spring” refers to the increased tidal range, not the season.

Correct answer: B. Because the tidal effects of the Sun and Moon partly oppose one another when they are at right angles

The correct answer is B. Near the first and third quarter moons, the Sun and Moon are approximately at right angles as viewed from Earth. Their tidal effects partly oppose one another rather than reinforcing one another, so the tidal range—the difference between high tide and low tide—is smaller. The Moon’s gravity does not disappear.

Correct answer: C. Spring tide

The difference between high-tide and low-tide levels is called the tidal range. Spring tides have the greatest tidal range because, near the new and full moons, the Sun, Moon, and Earth are nearly aligned and the solar and lunar tidal effects combine. This produces higher high tides and lower low tides than usual. Therefore, a very large difference most likely indicates a spring tide, so option C is correct. Neap tides have a smaller range. A tsunami is a separate disturbance, often caused by sudden displacement of the seafloor.

Correct answer: D. It may be a neap tide

Correct answer: D, it may be a neap tide. The difference between the water level at high tide and low tide is called the tidal range. A relatively small range occurs during neap tides, when the Sun and Moon pull in directions that partly oppose one another as viewed from Earth. Their tidal effects therefore do not reinforce each other fully. A is wrong because spring tides have the greatest tidal range, not the smallest; they occur when solar and lunar effects align more closely. B is wrong because a tsunami is a long wave caused by a major disturbance such as an undersea earthquake, not simply a small tidal range. C is wrong because wind waves are separate from the periodic rise and fall of tides. Cue: spring tide means springing higher range; neap tide means weaker, smaller range.

Correct answer: A. Because the Moon is closer to Earth

Tides are governed mainly by the differential gravitational pull, or tidal force, exerted by celestial bodies on different parts of Earth. Although the Sun is much more massive, the Moon is far closer to Earth, and tidal force decreases very rapidly with distance, approximately with the inverse cube of distance. Consequently, the Moon produces the stronger direct tidal influence, so option A is correct. The Sun does possess substantial gravity and also contributes to tides, especially during spring tides. The ocean is not made of the Moon, and wind is not the basic cause of astronomical tides.

Correct answer: C. Sediment can move along the coast

The governing coastal-process concept is longshore drift, also called littoral drift. When waves approach a beach obliquely, their uprush carries sand and pebbles up the shore at an angle. The backwash generally returns more directly down the beach under gravity, producing a net zigzag movement parallel to the coastline. Thus sediment can be transported along the coast, making option C correct. Oblique wave approach does not normally vaporise sediment or sever its connection with the sea. The material also remains within the coastal system; it cannot move to the Moon. The exact direction depends on the angle from which the waves arrive.

Correct answer: D. Because they can have greater height and energy

The governing concept is wave energy and coastal hazard. Strong, persistent winds over a sufficiently long fetch transfer energy to the sea, allowing storm waves to become higher, steeper and more powerful than ordinary waves. When these waves reach the coast, they can cause rapid erosion, dune or beach damage, flooding and destruction of coastal structures, so option D is correct. Storm waves do not necessarily have low energy, and they do not always stop tides. They also cannot make seawater fresh. The danger may become still greater when storm surge and high tide occur together, although the question specifically asks about the wave's height and energy.

Correct answer: A. Change in water level and available depth

The governing concept is the effect of tidal range on navigation. As the tide rises, the water level and therefore the depth over a harbour bar, channel or shallow entrance can increase. This extra depth may allow ships with a larger draught to enter or leave safely; at low tide, the same route may become too shallow. Hence option A is correct. Port authorities use tide tables and predicted heights to schedule movement, though actual safety also depends on channel shape, sediment, weather and currents. Sea colour, coastal language and fish sounds do not determine the navigable depth of a port.

Correct answer: B. Noticeable and regular tidal range

The governing concept is the conversion of periodic tidal movement into usable energy. A tidal-energy system needs a dependable change in water level or current so that turbines can operate repeatedly. A noticeable and regular tidal range provides a greater and more predictable head or flow, making option B the most favourable condition. A very small range generally offers little usable energy, while permanent drying would remove the water movement that the system requires. Complete absence of waves is not the defining requirement because tidal power depends primarily on tidal rise, fall or current, not ordinary wind-generated waves. Practical projects also require suitable coastal shape, environmental assessment and infrastructure.

Correct answer: C. Due to Earth's rotation and tidal bulges

The governing concept is the semi-diurnal tidal pattern. The Moon's gravity produces a tidal bulge on the side of Earth facing the Moon, while the Earth-Moon system also produces a second, opposite bulge on the far side. As Earth rotates, a coastal location passes through these two bulges and the two intervening lower-water regions. It therefore commonly experiences about two high tides and two low tides in one lunar day, roughly 24 hours 50 minutes, with about 12 hours 25 minutes between successive high tides. Local coastlines and basins can alter this pattern, but option C gives the basic explanation.

Correct answer: C. When waves strike coast with greater energy

The governing concept is wave erosion and energy transfer. When waves carry greater energy, their impact and turbulence at the shoreline are stronger. They can exert greater hydraulic pressure in cracks, remove loose particles, transport beach sediment and undercut cliffs, so option C is correct. Wave energy is influenced by factors such as wind speed, duration, fetch, wave height and the shape of the seabed near the shore. Very low-energy waves generally deposit or gently rearrange material rather than causing maximum erosion. If there is no water or the waves never reach the coast, wave erosion cannot operate at that location.

Correct answer: A. When energy decreases and sediment starts settling

The governing concept is the balance between wave energy and sediment movement. Powerful waves have enough competence to keep sand, pebbles, and other particles moving, so they commonly erode the shore or transport material along it. When wave energy decreases, because of greater water depth, sheltered coastal conditions, a gentler slope, or reduced wind, the water loses competence and its transporting capacity falls. Sediment then settles by gravity, producing deposition such as beaches, bars, or spits. Therefore option A is correct. Option B is impossible because waves do not convert sediment into gas; option C removes the material needed for deposition; and option D is irrelevant because deposition occurs in water.

Correct answer: B. Waves form by wind and tides by Moon-Sun gravity

The governing distinction is the primary force that generates each type of ocean movement. Ordinary surface waves are usually produced when wind transfers energy to the sea surface; their size also depends on wind speed, duration, and the distance over which the wind blows. Tides are regular, long-period rises and falls in sea level caused mainly by the gravitational attraction of the Moon and, to a lesser extent, the Sun, together with Earth’s motion. Thus option B gives the correct cause-based contrast. Option A reverses the causes. Earthquakes can generate tsunamis, but not all ordinary waves or tides, so C is too broad. Rivers do not produce global tides, making D incorrect.

Correct answer: C. Because it can form from sudden sea-floor disturbance

The governing concept is the difference between wind-generated surface waves and tsunami waves produced by rapid displacement of a large volume of water. A tsunami can result from an undersea earthquake that suddenly lifts or lowers the seabed; submarine landslides and, more rarely, volcanic activity or impacts can also displace water. In deep ocean water its height may be small, but its wavelength is very long, and it can grow dangerous as it enters shallow coastal water. Option C is correct because it identifies sudden sea-floor disturbance. Option A is meaningless, B confuses tsunami with a tide, and D wrongly attributes the event to light wind.

Correct answer: D. Range increases at new-full moon and decreases at quarters

The governing concept is the changing alignment of the Sun, Earth, and Moon. During the new moon and full moon, the Sun, Earth, and Moon are approximately aligned, so the solar and lunar gravitational effects reinforce one another. This produces spring tides, characterized by a greater tidal range: higher high tides and lower low tides than average. Around the first- and third-quarter phases, the Sun and Moon pull at roughly right angles relative to Earth. Their effects partially counteract each other, producing neap tides with a smaller range. Therefore option D is correct. Options A and B deny the established relationship, while C describes an unrelated visual feature.