Importance of Water : Chapter Summary
Water continuously changes its form and circulates between the water bodies, air and land through a process called ‘water cycle’. The water in rivers, lakes and oceans heats up due to the sun’s heat, turn into steam or water vapour and move into the air. This is the process of evaporation.
When water vapour rises in the air, it cools down and turns into tiny droplets of water which collect together to form clouds. This process is called condensation. When the clouds become heavy with water droplets, and cannot hold any more water, it falls to the ground in form of rain. This process is called precipitation.
Water precipitates in the form of rain, sleet, dew, snow or hail. Water falls on both water bodies and land; water that falls on land either flows back into the oceans as runoff water or gets soaked up by the ground. The water soaked by the earth gets stored as groundwater. This is called infiltration.
Almost 3/4th of the earth’s surface is covered by water. However, about 97% of this water is in the oceans and seas and is saline. Saline water has large amounts of dissolved salts – most of which is sodium chloride and hence cannot be used for drinking and cooking.
Therefore, only the remaining 3% of the water is fresh water in rivers, ponds, springs and glaciers. Of this 3% fresh water, 2% is frozen in ice caps and glaciers and a little less than 0.7% is trapped in underground aquifers. This leaves only 0.3% of water in the surface-water sources, i.e. rivers, lakes and ponds, actually available for us to use.
Water is an extremely essential component for our survival. The extent of water scarcity across the world is increasing at an alarming rate. Growing population, urbanization and industrialization have led to the misuse and mismanagement of water.
Wastage of water means wastage of an extremely precious resource. In order to avoid the scarcity of water, we must conserve it.
Ocean Current : Chapter Summary
The water on the surface of the oceans is constantly flowing in one direction from one place to another. These flowing movements of water in oceans are called ocean currents.
Ocean currents are streams of water flowing constantly on the ocean’s surface in definite directions. They are caused by differences in the temperature and salinity of water, by wind, solar heating and gravity.
The winds majorly responsible for creating ocean currents are the Westerlies and the Trade winds. Owing to the earth's rotation, winds blow anti-clockwise in the northern hemisphere and clockwise in the southern hemisphere. This pattern of blowing winds is called the Coriolis effect.
Ocean currents also move in the same pattern as winds i.e. anit-clockwise in the northern hemisphere and clockwise in the southern hemisphere. The ocean currents can be warm or cold, depending on their origin. Warm ocean currents originate near the equator and move towards the poles or higher latitudes while cold currents originate near the poles or higher latitudes and move towards the tropics or lower latitude.
The ocean currents greatly influence the temperature of an area. In areas where warm and cold currents meet, the temperature falls, giving rise to foggy conditions. Whoever, mixing of warm and cold currents supports a rich marine life.
Ocean Movements : Chapter Summary
Oceans are large bodies of salty water covering almost 3/4th of the earth’s surface. The movements which occur in oceans are classified as waves, tides and currents. A wave is the constant rising and falling of water caused by winds blowing across the oceans. Tsunami is a series of huge, destructive waves, caused by underwater earthquakes, volcanic eruptions and underwater landslides.
The water of the oceans rises and falls rhythmically twice a day. This movement of oceans is called a tide. When ocean water rises to its highest level and covers much of the shore, it is a high tide while when the water falls to its lowest level and recedes from the shore, it is a low tide. Tides are caused due to the gravitational pull of the moon and the sun on the ocean water.
On full moon and new moon days when the sun, the moon and the earth are in the same line, exceptionally strong gravitational forces exerted by the sun and the moon cause high tides, called as spring tides.
A neap tide occurs when the moon is in its first or third quarter and is at right angles to the sun. The ocean waters get pulled in diagonally opposite directions by the gravitational pull of the sun and the moon, resulting in low tides called Neap tides.
High and low tides help us in navigation, fishing and generating electricity.
Indian Ocean Tsunami - A Case Study : Chapter Summary
The lithosphere is made up of a series of huge plates which are in constant motion. When two plates collide against each other, one of the plates may slide below the other causing an underwater earthquake. An underwater earthquake is the most common cause of a tsunami.
A tsunami is a series of huge waves caused by the shifting of large amounts of ocean water. Tsunamis are also caused by volcanic eruptions and underwater landslides.
The 2004 Indian Ocean tsunami, also called Asian Tsunami was the most devasting Tsunami in the history. The wave was the result of an earthquake with the epicentre close to Sumatra.
The 2004 tsunami killed almost 2,00,000 people, destroyed property and 1000s of miles of coastline, leaving millions of people homeless. The devastation was so much that it completely washed away some of the islands in the Indian Ocean. The Indira Point, in Andaman and Nicobar islands which marks the southern-most tip of India, was completely submerged.
Though it is difficult to predict an earthquake in advance, it is possible to give a three-hour notice of a potential tsunami. The three factors primarily responsible for the huge damage to life and property in the 2004 tsunami were lack of monitoring, lack of early warning systems and inadequate knowledge among the coastal dwellers.