Ocean Waves & Movements of Ocean Water | UPSC

Ocean Waves & Movements of Ocean Water

Ocean water is never still. There are different types of movements of ocean water that occur under the influence of various physical characteristics such as temperature, salinity, density, etc. The movements of ocean water are also affected by external forces like the sun, moon, and winds.

The motion of ocean water can be classified in two directions –

• HORIZONTAL
• VERTICAL

Horizontal movements of the ocean waters can be classified into two –

• WAVES
• CURRENTS

Vertical movements of the ocean waters can be classified into two –

• TIDES
• UPWELLING

Ocean Waves

A wave is a rhythmic movement that carries energy through matter or space. Ocean waves refer to the undulatory motion of the water surface.

• Waves are oscillatory movements that result in the rise and fall of the water surface.
• Waves are a kind of horizontal movement of ocean water.
• It is actually the energy, not the water as such, which moves across the ocean surface.
• This energy for the waves is provided by the wind.
• In a wave, the movement of each water particle is in a circular manner.
• A wave has two major parts: the raised part is called the crest while the low point is called the trough.
  

Parts of a Wave

Wave Crest and Trough

The highest point of a wave is called the crest. It is the topmost portion of the wave where the water surface reaches its peak. The lowest point of a wave is called the trough. It is the depression between two consecutive crests.

Wave Height

Wave height is the perpendicular distance from the bottom of a trough to the top of a crest of a wave. It measures the total vertical distance between the lowest and highest points of a wave.

Wave Amplitude

Wave amplitude is one-half of the wave height. It is the distance measured from the still-water level to either the crest or the trough of the wave.

Wave Period

Wave period is the time interval between two successive wave crests or troughs as they pass a fixed point. It represents the time taken for one complete wave to pass a given position.

Wavelength

Wavelength is the horizontal distance between two successive crests. It can also be measured between two consecutive troughs. Longer wavelengths are generally produced by stronger and more sustained winds.

Wave Speed

Wave speed is the rate at which the wave moves through the water. It indicates how fast the wave energy is travelling across the ocean. It is measured in knots.

Frequency

Frequency is the number of complete waves (or oscillations) that occur over a given period of time. It is usually measured in cycles per second.

Most of the waves present on the ocean’s surface are wind-generated waves.

Friction from the wind moving over the water causes the water to move along with the wind. If the wind speed is high enough, the water begins to pile up and a wave is formed.

As wind velocity increases: Wavelength, Wave period, and Height all increase.

Water molecules move in an orbital motion as the wave passes. Particles of water move around in circles. The farther below the surface, the smaller the circle.

• The diameter of the orbit increases with increasing wave size.
• The diameter of the orbit decreases with depth below the water surface.

As a wave approaches the shore and enters shallow water, the wave slows down. As the wave slows, its crest and trough come closer together. The top of the wave is not slowed by friction and moves faster than the bottom. This causes the wave to become steeper and eventually break.

Wave Types

Ocean waves can be classified into different types based on their generating force and restoring force.

• Capillary Waves (Ripples) – Very small waves caused by wind and restored by surface tension. They have very short periods.
• Gravity Waves – The most common ocean waves, including wind waves and swells. Gravity acts as the restoring force. Their periods range from 1 to 30 seconds.
• Swell – Wind-generated waves that have moved out of their storm area. They have more regular and uniform crests and longer periods.
• Tsunamis – Long-period waves generated by sudden displacements of the ocean floor, such as earthquakes, volcanic eruptions, or landslides.
• Tidal Waves – Extremely long-period waves caused by the gravitational pull of the Moon and the Sun on the Earth.
• Internal Waves – Waves that form at the boundary between water layers of different densities rather than at the ocean surface.

Wave Cut Action

When waves reach the coastline, they exert a strong erosive force on the coastal rocks and landforms. This process is known as wave cut action.

• The continuous pounding of waves against coastal rocks gradually wears them away over time.
• Wave cut action is responsible for the creation of several coastal landforms such as wave-cut platforms, sea cliffs, sea caves, arches, and sea stacks.
• It is one of the most important agents of coastal erosion and plays a major role in shaping the coastlines of the world.
• The intensity of wave cut action depends on factors like wave height, wave energy, rock hardness, and the angle at which waves approach the coast.

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