MOVEMENT OF THE OCEANS

The water of the oceans and seas are in constant motion. They move horizontally as well as vertically. The movement of the ocean water includes three types-

Waves

The up and down movements on the surface of ocean waters are known as waves. The formation of waves is caused due to the force of the blowing wind. Formation of waves depends on the factors like the speed of wind, duration and the size of the area over which the wind blows.

The upper part of a wave is called crest and the lower part is called trough. The vertical distance between the crest and trough is called wave height and the horizontal distance between two crests or two troughs is called wave length. The height of the wave depends on the speed of the wind.

Waves have great force and become a powerful agent of erosion and deposition along the coastlines. When waves pound the shores, they create landforms like beaches.

Natural calamities like earthquakes, volcanic eruptions and underwater landslides also create huge waves which often cause widespread destruction. Such waves are very large and are called tidal waves or tsunamis. ‘Tsunami’ is a Japanese word that means harbor waves, as the harbors get destroyed whenever there is a tsunami. Tsunami is a specific type of wave which is not caused by wind, but by geological factors.

The Most Destructive Tsunamis occurred:

The tsunami of 2004 Indian Ocean was an undersea earthquake that occurred on Sunday, December 26, 2004, with an epicenter off the west coast of Sumatra, Indonesia was the most destructive and disastrous tsunamis of the world.

The tsunami of Japan that occured on 11th March 2011 was one of the most recent tsunamis.

Ocean Currents

An ocean current can be defined as a horizontal movement of ocean water in a particular direction. They are like rivers in the ocean. A slow moving ocean current is called a drift. Generally, the ocean currents circulate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. The main causes behind the origin of currents include wind, rotational movement of the earth, and difference in temperature. They are of two types:

Warm Ocean Current: They carry warm water from the equatorial region to the polar region. Some of the warm currents of the world are Gulf Stream Current, North Equatorial Current, South Equatorial Current, Kuro Siwo Current.

Cold Ocean Currents: They carry cold water from the polar region towards the equatorial region. Some of the cold currents of the world are Peru Current, Labrador Current, Falkland Current, Benguela Current.

Tides

Tides are the periodic and rhythmic rise and fall of the ocean water level, which occur at regular intervals twice a day. This vertical movement takes place on account of the gravitational pull of the Moon and to some extent the Sun on the Earth’s surface. The rise in the level of water is called high tide and the fall in the level of water is called low tide.

During the full moon and the new moon, the earth, moon, and sun are in the same straight line. The moon and the sun exert their combined gravitational pull in the same direction, resulting in extra high tides called spring tides. In the first and third quarters of the moon, the sun and the moon are at right angles with respect to the earth. They nullify each other’s gravitational pull, which results in very low tides called neap tides. Each day there are two high tides and two low tides. The time between one high and one low tide is a little over 6 hours and the entire tidal cycle repeats itself two times each day. The regularity of the tides is regulated by the corresponding position of the moon orbiting the Earth and the rotation of the Earth on its own axis.