Fundamental Of Physical Geography Chapter 14 Movements Of Ocean Water

The disadvantages are: 
i. Tides are sometimes harmful for ships and boats.

ii. Tides check the formation of the deltas.

iii. Marshes are formed due to accumulation of tidal water.

iv. Tides also hinder fishing.

Mixed tide. 

i. Tides having variations in height are known as mixed tides.

ii. These tides generally occur along the west coast of North America and on many islands of the Pacific Ocean.

The three things that affects the size of the waves are:

i. Wind,
ii. Origin,
iii. Area.

It is the number of waves passing a given point during a one second time interval.

Ocean currents can be classified based on temperature: as cold currents and warm currents:

(i) cold currents bring cold water into warm water areas. These currents are usually found on the west coast of the continents in the low and middle latitudes (true in both hemispheres) and on the east coast in the higher latitudes in the Northern Hemisphere;

(ii) warm currents bring warm water into cold water areas and are usually observed on the east coast of continents in the low and middle latitudes (true in both hemispheres). In the northern hemisphere they are found on the west coasts of continents in high latitudes.

The ocean currents is classified based on their depth as surface currents and deep water currents:

(i) surface currents constitute about 10 percent of all the water in the ocean, these waters are the upper 400 m of the ocean;

(ii) deep water currents make up the other 90 per cent of the ocean water. These waters move around the ocean basins due to variations in the density and gravity. Deep waters sink into the deep ocean basins at high latitudes, where the temperatures are cold enough to cause the density to increase.

The time between the low tide and high tide, when the tide is rising, is called the flow or flood.

Every wave has a wave length, velocity, height and wave period. The distance between two successive crests or two successive troughs is called wave length. The time taken by a wave length to pass a fixed point is known as the wave period. The vertical distances between a trough and crest is the wave height.

Fig : 14.4 : Motion of Waves

Characteristics of ocean currents:

1. Permanent winds or prevailing winds, 2. Variation in temperature, 3. The rotation of the earth, 4. Variation in salinity, 5. The direction of land masses.

The prevailing winds such as trade winds (westerlies) exert one way drag on sea surfaces over vast expanses of oceans. This drag produces a system of drift system.

Difference in density can also set currents in motion and these are described as thermocline currents.

1. Warm currents :
(a) Florida Currents
(b) Gulf Stream and North Atlantic drift,

2. Cold currents :
(a) Canary current,
(b) Labrador Current.

The climate of the coasts become warm or cold according to the currents passing through the coasts. United Kingdom and Labrador (U.K. N.America) are in the same latitude but remains unfrozen due to warm Gulf Stream and Labrador is frozen for nine months due to cold Labrador currents. Norway Coasts are unfrozen throughout the year due to North Atlantic Drift. Thus the currents affect the climate of the coastal areas.

The importance:
i. Tide helps the navigators and fishermen plan their activities. Tidal flows are of great importance in navigation.

ii. Tidal heights are very important, especially harbours near rivers and within estuaries having shallow ‘bars’ at the entrance, which prevent ships and boats from entering into the harbour.

iii. Tides are also helpful in desilting the sediments and in removing polluted water from river estuaries.

iv. Tides are used to generate electrical power (in Canada, France, Russia, and China). A 3 MW tidal power project at Durgaduani in Sunderbans of West Bengal is under way.

This current is responsible for mild climate throughout the North West Europe. Even in winters Norwegian parts along the Atlantic are ice-free most of the time. From the Grand Bank the Gulf Stream Current flows eastward across the Atlantic. On reaching the British Isles it divides into two branches, the northern branch and southern branch and flows between Spain and Azores.

1. due to the gravitational pull of the moon and of the sun on the earth.

2. due to gravitational pull waters of the oceans are attracted towards moon. Water being liquid rises higher than the solid crust of the earth. This is known as the high tide. When the level of the water falls, it is known as low tide.

3. due to the rotation of the earth tides occur twice a day at a place.

One tide occurs on the earth surface facing moon and the other tide occurs at the opposite side of the earth.

Fig. 14.6 Currents of the Indian Ocean (Winter)

In the west, South Equatorial Current has two branches. One branch passes through Africa and Madagascar. It is called Mozambique Current. Another branch flows east of Madagascar parallel to the Mozambique Current. It is called Madagascar Current. These two branches meet each other south of Madagascar and form Agulhas Current. It later meets the South Pacific Current which flows from west to east. A branch of it flows along the western coast of Australia from south to north and meets the South Equatorial Current. The current along Western Australia is known as West Australian Current. Ocean Currents in North Indian Ocean :

Summer: In summer, the prevailing winds blow from sea towards land and are known as South-West Monsoon. Under its influence a branch of South Equatorial current turns towards Africa in the west. The current turns towards east from the Gulf of Aden, and takes a round of the Bay of Bengal washing the western and the eastern coasts of India.

Winter : The direction of monsoon winds in winter is just the reverse of that in summer. It is north-east in winter. Hence the an ocean current starting from the strait of Malacca flows along the coast in the Bay of Bengal. After crossing Sri Lanka its flows along the coasts of western India from south to north. It takes a round of Gulf of Aden in the west and begins to flow towards south where its direction is from west to east. Hence, it called South Indian Current.

Fig. 14.7 Currents of the Indian Ocean (Summer)

1. Effect on climate: The climates of coasts becomes warm or cool according as the current washing the coast is warm or cool.

2. Temperature : Oceanic currents also affect the temperature.

3. Rainfall: The currents of the oceans are helpful to bring the rain. If the currents were not present then rainfall would not materialize in the adjoining areas.

4. Effects on the marine ocean : Ocean currents sweep a large refuge off the coast which is the food for planktons.

5. Effect on Trade : The absence of ocean currents will adversely affect the trade and transport.

Following are the causes of currents:

1. North Equatorial Current : It is a warm current. It flows south of the equator from east to west.

2. South Equatorial Current: It is also a warm current. It flows south of equator from east to west.

3. Kuroshivo Current : It is a warm current. It flows along the coast of Japan.

4. New South Wales Current : It is also called East Australian Current. It is a warm current. It flows south along the east coast of Australia.

5. Antarctic Drift: It is a cold current. It flows round the globe from west to east near the Antarctic Ocean.

6. Humbolt Current: It is also known as Peruvian Current. It is a cold current. It flows from south to north along the west coast of South America. It is a branch of Atlantic Drift.

7. California Current: It is a cold current. It flows along the coast of California and Mexico.

8. Kuril Current: It is a cold current. From Bering Strait, it flows south along the coast of Kuril Islands.

1. Semi-Diurnal Tides: The most common tidal pattern featuring two high tides and two low tides each day.

2. Diurnal Tides : There is only one high tide and one low tide during each day. Successive high tides and low tides are approximately of the same height.

3. Mixed Tides : Tides having variation in heights are known as mixed tides.

On the basis of height, tides can be classified as under :

1. Spring Tides : Tides of certain periods of time are unusually lower or higher than normal height. When sun, moon and the earth are in a straight line the tidal range will be high. These are called spring tides.

2. Neap Tides : When the moon is at first and last quarter, the sun and the moon make a right angle to the earth. The attraction of the sun and the moon tends to balance each other. As a result tides with lowest amplitude occur which are termed as neap tides.

•  ripples
• Seas
• swells

Spring  Tide

(a) Warm currents : (i) Florida Currents (ii) Gulf Stream and North Atlantic drift,

(b) Cold currents : (i) Canary current, (ii) Labrador Current.

The climate of the coasts become warm or cold according to the currents passing through the coasts. United Kingdom and Labrador (U.K. N.America) are in the same latitude but remains unfrozen due to warm Gulf Stream and Labrador is frozen for nine months due to cold Labrador currents. Norway Coasts are unfrozen throughout the year due to North Atlantic Drift. Thus the currents affect the climate of the coastal areas.