The Hydrosphere Chapter Notes | Footprints Class 7: Book Solutions, Notes & Worksheets PDF Download

The Hydrosphere

• The hydrosphere is the watery part of the Earth that plays a crucial role in making our planet unique.
• It, along with the atmosphere and lithosphere, supports life on Earth by providing necessary conditions.
• The hydrosphere includes various water bodies and groundwater, existing in both liquid and solid states.
• Water on Earth is sustained through the hydrological cycle, a continuous process of water movement among the sea, air, and land.
• The water cycle comprises four main stages: evaporation, condensation, precipitation, and collection.
• For instance, water from oceans evaporates into the atmosphere, condenses into clouds, falls back to the ground as precipitation, and eventually returns to the oceans.
• The amount of water entering the cycle through precipitation generally equals the amount lost through evaporation and transpiration.
• Water availability varies across different regions and seasons, influenced by natural factors and human activities like deforestation and water pollution.

Fresh and Saline Water

• Definition of Fresh Water:
  • Fresh water contains very low levels of dissolved salts, making it suitable for human consumption.
• Sources of Fresh Water:
  • Rivers are essential sources of fresh water, providing a significant portion of the world's fresh water supply.
• Definition of Saline Water:
  • Saline water contains high concentrations of dissolved salts such as chlorine, sodium, sulphur, calcium, potassium, and magnesium.
• Sources of Saline Water:
  • Oceans and seas are examples of large water bodies that contain saline water.
• Salinity of Water:
  • Salinity refers to the concentration of salt in water and varies from place to place.
  • Salinity is typically measured in parts per thousand.
  • The average salinity of sea water is around 35 parts per thousand, indicating that 1000 grams of sea water contain 35 grams of salt.

Temperature of Ocean Water

• Variability of Ocean Water Temperature

  Ocean water temperature changes based on location and external factors like the Sun, wind, tides, and waves. Different regions experience varying temperatures.

• Temperature Gradient with Latitude

  The surface water temperature fluctuates with latitude. Tropical regions, where the Sun's rays are more direct, have warmer waters. From the Equator towards the Poles, oceanic temperatures generally decrease.

• Influence of Ocean Currents

  Normally, temperature decreases steadily from the Equator to the Poles. However, ocean currents disrupt this pattern by moving large water masses across latitudes, impacting temperature distribution.

• Depth-Related Temperature Changes

  Ocean water temperature decreases as depth increases. The Sun warms surface waters more effectively than deeper layers, creating variations in temperature profiles within the ocean.

Movements of Ocean Water

• Overview:
  • Ocean water is in constant motion, either vertically or horizontally, driven by various factors.
• Causes of Movements:
  • Differences in temperature and density of ocean water
  • Variations in salinity
  • The influence of prevailing winds
• Waves:
  • A wave is the regular rising and falling of ocean water due to wind action on the water's surface.
  • Characteristics of Waves:
    • A wave consists of a crest (upper part) and a trough (lower part).
    • The vertical distance between a crest and a trough is known as wave height.
    • The horizontal distance between two successive crests is called wavelength.
  • Wave Size:
    • The size of a wave is influenced by wind speed; stormy winds can lead to massive waves causing destruction.
• Tsunamis:
  • Tsunamis are massive tidal waves caused by the displacement of large volumes of water, often triggered by earthquakes, volcanic eruptions, or other disturbances.
  • Causes of Tsunamis:
    • Earthquakes
    • Volcanic eruptions
    • Underwater explosions
    • Landslides
    • Meteorite impacts
  • Impact of Tsunamis:
    • Due to the immense energy and water volume involved, tsunamis can result in widespread devastation along coastal areas.

Tides

• Sea water rises and falls in a rhythmic pattern known as tides, caused by gravitational forces from the Moon, Sun, and Earth.
• Tides' height varies daily based on the positions of the Moon, Sun, and Earth, leading to spring tides (during full and new moons) and neap tides (during first and last quarters of the lunar cycle).
• Importance of Tides:
  • Tides help clear mud and silt from river mouths, aiding in navigation.
  • Shipping benefits from tides, with ships using tides to enter and leave harbors.
  • Fishermen benefit from tides bringing fish closer to the coast during high tides.
  • Tides also serve as a source of renewable energy through tidal power stations in various countries.

Ocean Currents

• Ocean currents are continuous movements of water in specific directions, akin to rivers in the ocean.
• There are warm and cold ocean currents, influencing temperatures in different regions.
• Causes of Ocean Currents:
  • Ocean currents follow prevailing winds and are influenced by the rotation of the Earth and differences in water density.
  • Interactions with tides, other currents, and landmasses also impact ocean current directions.
• Effects of Ocean Currents:
  • Warm and cold currents affect local temperatures and rainfall patterns.
  • Convergence of warm and cold currents can lead to fog and impact navigation.
  • Areas where warm and cold currents meet, like the Grand Banks, are rich in marine life.
  • Sailing with ocean currents can enhance speed and save time and fuel for ships.

Importance of Hydrosphere

• The hydrosphere is crucial for supporting life on Earth within the biosphere.
• Water found in lakes and rivers serves essential purposes like domestic use and irrigation.
• It facilitates transportation and communication between different land masses.
• Various water bodies are rich sources of diverse marine life and marine products.
• Ocean waters provide salt and other valuable minerals.
• Oceans and water bodies play a significant role in influencing weather patterns and climate.
• Tidal energy can be harnessed from ocean water, while rivers contribute to hydroelectric power generation.
• Water is a precious resource that must be used wisely, with efforts to prevent pollution.
• Conservation of water is crucial to ensure its availability for the long term.