Chapter 5. Water

• circulation of water is movement of water or its changing forms [liquid- solid – gas] between oceans, Atmosphere and land.
• Evaporation: process of change of vapour from water by help of sunlight [heat] is known as evaporation.
• Condensation: When vapour changes its form and converts into liquid. This process is called condensation.

Distribution of Water
• three-fourth of earth’s surface is covered by water.
• Oceanic water are salty and on other hand availability of fresh water is in limited amount therefore so many countries face water scarcity.

Table: Distribution of water
• following table gives distribution of water in percentage.
Oceans : 97.3
Saline Water Ice-caps : 02.0
Ground water : 0.68
Fresh water lakes : 0.009
Inland seas and salt lakes : 0.009
Fresh Water Atmosphere : 0.0019
Rivers : 0.0001
• Salinity is amount of salt in grams present in 1000 grams of water. average salinity of oceans is 35 parts per thousand.
• Dead sea in Israel has salinity of 340 grams per litre of water. Swimmers can float in it because of increased salt content which makes it dense.

Ocean Circulation
• movements that occur in oceans can be broadly categorised as: waves, tides & currents.

• Waves are alternatively rises and falls of surface water of ocean. During a storm, winds blowing at a very high speed forms huge waves. These can cause tremendous destruction.
• An earthquake, a volcanic eruption or underwater landslides can shift large amounts of ocean water.

Tsunami – Earth’s Pandemonium
• Tsunami or harbour wave struck havoc in Indian Ocean on 26 December 2004.
• wave was result of earthquake that had its epicentre close to western boundary of Sumatra.
• magnitude of earthquake was 9.0 on Richter scale.
• As Indian plate went under Burma plate, there was a sudden movement of sea floor, causing earthquake.
• Indira point in Andaman and Nicobar islands that marked southernmost point of India got completely submerged.

Ocean Currents
• They are streams of water flowing on surface of ocean in a particular direction.
• When these currents originate near equator they carry a large amount of warm water towards poles, known as warm currents.
• But when they are carrying cold water from poles to equator or tropics, that are known as cold currents.
• ocean current influences temperature conditions of area.
• Warm currents bring about warm temperature over land surface.
• areas where warm and cold currents meet provide best fishing grounds of world.

• rhythmic rise and fall of ocean water twice in a day is known as a tide.
• During full moon and new moon days, Sun, moon & earth are in same line and tides are highest. These tides are known as spring tides.
• But when moon is in its first and last quarter, ocean waters get drawn in diagonally opposite directions by gravitational pull of Sun and Moon resulting in low tides. These tides are known as neap tides.

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