NCERT Class 7 Geography Chapter 5: Air Completes Notes Part 2

Get unlimited access to the best preparation resource for IEO Class-7: fully solved questions with step-by-step explanation- practice your way to success.

Get the Video tutorial on this topic at:

Loading video

Water

Ocean Circulation

  • Waves:

    Loading video

    5 Secrets to Understand Waves and Currents - Oceanography

  • Tides:

    Loading video

    What Are Tides? What Causes Tides?

  • Currents

We talk about circulation of water we basically try to explain this by three fundamental concepts the waves, tides and currents. If you want to have detailed understanding these concepts of waves and currents and tide you refer above link.

Now let’s understand what are waves, what would happened if I have a ball and I throw it into a water that water would splash out and that splashing of the water would lead to formation of waves. There would be alternate rise and fall in the water that would occurs and this alternate rise and fall in the water is explained as waves. Now these waves could be huge or these could be gentle so if I say normal ocean waves those are gentle waves but what happens during tsunami, during tsunami or the earthquake that occurs below the surface of ocean you have strong waves or street waves that occurs and that hit the cost and those are again waves but they are huge waves and they come at a speed nearly 700 kms per hour or more.

What is the tsunami?

Recent Tsunami example is that happened in 2004 which hit the cost of Andaman and Nicobar Island. Epicenter was Sumatra and Indonesia island.

The prior indication to understand the concept of tsunami or to explain when tsunami is about to occur I could say so best indication is just before tsunami or immediately before tsunami there is rapid withdrawal of the water from the coast so all the water that is lying on to the coast would rapidly withdraw and then you would have huge waves would gush back into the coastline and that would devastate the coast.

Let’s understand tides, tide is a arithmetic rise and fall of the water level in the ocean surface and that occurs twice a day, technically we say tides are caused due to gravitational pull of sun and moon so there are two basic types

  1. Spring Tide: when you have sun, moon and Earth that lie into a parallel line you have the spring tide occurs and this spring tide usually occurs during the full moon and new moon that is Purnima and Amavasya.

Image of Spring Tide

Image of Spring Tide

Loading image
  1. Neap Tide: the first quarter and the fourth quarter of the moon cycle you would have the Neap Tide that occurs and the arrangement in the Neap tide to search that the moon, sun and earth are in a kind of perpendicular position and as a result Neap tide are not that strong as spring tide. Spring tides are considered as highest tides in contrast to which you have neap tides which are considered as low tides. High tide would bring lot of waves to coast. As a result you would have numerous fishes that would come in so fishing would increase during the period of high tides. Next you would arrive to the harbor easily because there would be sudden movement to the coast so they would be easy arrival to the harbor. But it would not be easy for the purpose of navigation. So navigators would face difficulties during period of high tide. These tides are also used to generate electricity.

Image of Neap Tide

Image of Neap Tide

Loading image
  • Currents

Image of Current

Image of Current

Loading image

Current are the streams of water that flow on to the glow and these streams could be either demarcated as cold stream or warm stream. So this streams with which originate from the polls to the equator, are definitely cold so those are which are originating from the polls would be cold and they are known as cold currents. However, those originating from the equatorial region are comparatively warm so all these which are marked in blue are the warm currents flow in. However, these which are flowing from the polar belts are comparatively cold. So a common example of cold current is Labrador current. However, a common example of warm current would be the gulf of stream that flows in. So this is how you have the formation that you can see here. So north equatorial and the south equatorial current formation of Gulf Stream would all be kind of warm currents. However you have the Cannery current, the Labrador current, the Alaskan current which are coming from the poles would be cold in nature and would be lead to cold currents. Again the region where you have merger of warm current and cold current would be the region which is based optimum for fishing. As a result you have huge fishing grounds which develop in the region where you have merger of cold currents and warm currents. Common example is Sea of Japan and the eastern parts of USA.