Movements of Ocean Water Class 11 Geography Chapter 13 CBSE Notes 2025-26

Ocean water is always moving because of many factors such as temperature, salinity, density, and the forces exerted by the Sun, Moon, and wind. These factors cause both horizontal and vertical movements in the oceans. Horizontal movements include ocean currents and waves, whereas vertical movements are mainly seen as tides. Water actually travels from one place to another mainly via currents, while waves mainly transfer energy. Tides, on the other hand, are the periodic rise and fall of sea levels due to the gravitational pull of the Moon and Sun.

Waves are the visible motions on the ocean surface, representing the movement of energy, not the water itself. The water molecules move in small circles as the wave passes. Most waves are generated when wind blows over the sea, transferring energy. The waves grow larger with stronger winds, and white caps often appear when they break. As waves approach shallow coastal waters, friction with the sea floor slows them down until they break near the beach.

The actual water movement beneath a wave is circular, so objects in the water are lifted up and forward then down and back as the wave passes. The strength and height of a wave depend on wind speed, duration, and the area over which the wind blows. Steep, high waves are often young and formed by local wind, while those with gentle slopes may have traveled from distant regions.

• Wave Crest and Trough: The crest is the wave’s highest point, the trough is the lowest.
• Wave Height: The vertical distance from trough bottom to crest top.
• Wave Amplitude: Half the wave’s height.
• Wave Period: Time between two successive crests or troughs passing a fixed point.
• Wavelength: Horizontal distance from one crest to the next.
• Wave Speed: How fast a wave moves through the water, usually measured in knots.
• Wave Frequency: Number of waves passing a given point every second.

Tides are the regular rise and fall of sea levels, usually happening once or twice daily. They are mainly caused by the gravitational pull of the Moon, with the Sun also playing a smaller role. The centrifugal force due to the Earth-Moon system's rotation also affects tidal bulges on opposite sides of the planet. This results in two high tides and two low tides each day in most places. Tidal movement is not only influenced by astronomy but also by the coastline’s shape and ocean floor features.

Meteorological effects such as winds and atmospheric pressure changes cause irregular sea level movements known as surges, which are not true tides. Tides are predictable because Earth, Sun, and Moon positions follow a regular pattern.

• Semi-diurnal Tide: Two high tides and two low tides each day, most common pattern, heights are similar.
• Diurnal Tide: One high tide and one low tide per day, heights are similar.
• Mixed Tide: Two high and two low tides of different heights each day, commonly seen along the Pacific and west coast of North America.

The tug-of-war between the Sun and Moon leads to two special types of tides:

• Spring Tides: Occur when the Sun, Moon, and Earth are aligned, producing the highest high tides and lowest low tides. Happens twice a month at the full and new moon.
• Neap Tides: Occur when the Sun and Moon are at right angles to the Earth, resulting in lower high tides and higher low tides. Occur about a week after spring tides.
• Largest tides also occur when the Moon is closest to Earth (perigee) or when Earth is closest to the Sun (perihelion).

The time between high and low water, when the level falls, is called "ebb." When the water rises from low to high, it is "flow" or "flood."

Tides play a significant role in human activities, especially navigation and fishing. They allow ships to enter or exit shallow harbours and help remove sediments and pollutants from river estuaries. In some places, the power of tides is used to generate electricity. For example, a tidal power project is ongoing at Durgaduani, Sunderbans, West Bengal, India.

Famous high tides are found in regions like Canada’s Bay of Fundy, which experiences up to 15-16 meters of tidal difference every day.

Ocean currents are large-scale, regular movements of water, like rivers flowing through the ocean. These movements are set in motion by primary forces (like solar heating, winds, gravity, and the Coriolis effect) and modified by secondary forces (like coastline shape and ocean floor relief). Solar energy heats ocean water, causing it to expand, which creates gradients and sets water in motion.

Wind is a major driver, pushing along the surface water. Gravity pulls water down slopes, and the Coriolis effect causes water to turn to the right in the northern hemisphere and left in the southern hemisphere, forming circular systems called gyres. Density differences (due to temperature and salinity) play a role in vertical movement: denser cold, salty water sinks while lighter warm water rises, setting up large-scale circulation.

• Surface Currents: Occupy roughly the upper 400 metres and make up about 10% of the ocean water. Driven mostly by wind.
• Deep Currents: Occur below the surface, making up 90% of ocean water and moving because of differences in density and gravity, with water sinking in cold, high-latitude areas.

Currents are also classified by temperature:

• Warm Currents: Flow from the equator towards the poles, usually along the east coasts of continents in low and middle latitudes.
• Cold Currents: Flow from polar and temperate regions towards the tropics, often along the west coasts of continents.

Major ocean currents align closely with the major wind belts on Earth. In middle latitudes, circulation is mainly anticyclonic (clockwise in the northern hemisphere, counterclockwise in the southern). In higher latitudes, where cyclonic wind patterns prevail, the currents follow a similar direction. In regions affected by monsoons, current direction changes with the seasons.

The general circulation of ocean water helps transport heat across the globe. Cold currents cool the tropics and warm currents heat polar areas. This balancing act helps regulate climate and temperature in coastal regions.

Current movement is described by its "drift," which is the speed (measured in knots). Surface currents are usually the fastest, moving at up to 5 knots, while deep currents are much slower. The strength of a current refers to how fast it moves; typically, surface currents are stronger and diminish with depth.

Ocean currents strongly influence climate and human life. For example, warm currents on the west coasts of Europe keep winters milder, while cold currents along subtropical west coasts lead to dry, foggy conditions. The mixing of warm and cold currents promotes the growth of plankton, vital for fish populations, making such areas top global fishing zones.

• Waves transfer energy but not matter; currents actually transport water across the oceans.
• Tides are regular and predictable, while surges are irregular and linked to weather conditions.
• Spring tides occur during full and new moons; neap tides appear during quarter moons.
• Ocean currents influence regional climate, navigation, fishing, and even power generation.

Class 11 Geography Chapter 13 Notes – Movements of Ocean Water: Quick Revision Points

These Class 11 Geography Chapter 13 notes on Movements of Ocean Water provide a structured summary of all key concepts like waves, tides, and currents. Find important definitions, processes, and reasons behind oceanic movements in easy language for fast last-minute recaps. Understand the factors influencing ocean water motion and their real-world significance.

Use these revision notes to boost memory retention before exams and grasp the practical applications of tides and currents in navigation, climate, and fishing. These concise, student-friendly points ensure nothing is missed from the NCERT Geography Fundamentals Chapter 13.