CBSE Notes Class 7 Geography Chapter 5 – Water
CBSE Notes Class 7 Geography Chapter 5 – Water
Water cycle
The water cycle, also known as the hydrological cycle, is the continuous movement and exchange of water between the Earth's surface, atmosphere, and hydrosphere (including oceans, lakes, rivers, and groundwater). It is a fundamental process that ensures the availability of freshwater and regulates Earth's climate. Here are the key steps of the water cycle:
Evaporation: The water cycle begins with evaporation, where heat energy from the sun causes water to change from liquid to vapor. This occurs primarily from the Earth's surface, including oceans, lakes, rivers, and moist soil. The water vapor rises into the atmosphere.
Condensation: As the water vapor rises higher into the atmosphere, it cools down, and condensation occurs. Water vapor transforms back into tiny liquid water droplets or ice crystals, forming clouds.
Precipitation: When the water droplets in clouds grow larger and become too heavy to remain suspended in the air, precipitation occurs. Precipitation can take various forms, such as rain, snow, sleet, or hail, depending on the atmospheric conditions.
Runoff: Once precipitation reaches the Earth's surface, it can either infiltrate into the ground (becoming groundwater) or flow over the surface as runoff. Runoff collects in rivers, streams, and eventually makes its way to lakes, oceans, or other bodies of water.
Infiltration: Some precipitation seeps into the ground through a process called infiltration. It percolates through soil layers and fills spaces in rocks, becoming groundwater. This groundwater may eventually flow into rivers, lakes, or oceans, or it can be stored in underground aquifers.
Transpiration: Transpiration is the process by which plants release water vapor through their leaves into the atmosphere. It complements evaporation by adding moisture to the air. Transpiration is a significant contributor to the water vapor content in the atmosphere.
Distribution of Water Bodies
Water bodies, such as oceans, seas, lakes, rivers, and glaciers, are distributed across the Earth's surface in various forms. Here's an overview of the distribution of these water bodies:
Oceans and Seas: Oceans cover about 71% of the Earth's surface and are the largest water bodies. There are five major oceans: the Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern Ocean, and Arctic Ocean. Oceans are interconnected and play a crucial role in regulating climate, absorbing heat, and storing vast amounts of water. They also support diverse marine ecosystems.
Lakes: Lakes are inland bodies of water that are generally surrounded by land. They can vary in size from small ponds to large, expansive water bodies. Lakes can be found in various locations worldwide, ranging from high-altitude mountain lakes to vast freshwater lakes in continental regions. They are important sources of freshwater, provide habitats for aquatic life, and often serve as recreational areas.
Rivers: Rivers are flowing bodies of water that usually originate from mountainous regions or highlands and flow towards lower elevations. They play a significant role in the water cycle, transporting water from land to the oceans. Rivers provide freshwater for drinking, irrigation, and various human activities. They also support diverse ecosystems along their course.
Glaciers: Glaciers are large masses of ice formed from compacted snow over many years. They are found primarily in polar regions, mountainous areas, and high-altitude regions. Glaciers play a crucial role in the hydrological cycle, storing and releasing freshwater as they melt. They contribute to the formation of rivers, affect climate patterns, and shape landscapes through erosion and deposition.
Wetlands: Wetlands are transitional areas where land and water interact. They can include marshes, swamps, bogs, and estuaries. Wetlands are ecologically rich and provide vital habitats for a wide range of plant and animal species. They also help regulate water flow, filter pollutants, and provide other important ecosystem services.
The distribution of water bodies is influenced by factors such as climate, topography, geology, and human activities. These water bodies, in their various forms, contribute to the Earth's ecosystems, support biodiversity, and play essential roles in the global water cycle.
Ocean Circulation
The movements that occur in oceans can be broadly categorised as waves, tides and currents.
Waves
Waves are alterations that move through a medium, moving energy from one spot to another without actually moving the medium. I'll concentrate on the idea of waves in connection to water, though waves can occur in a variety of circumstances, such as electromagnetic waves and sound waves.
Oceans, seas, lakes, and rivers all have water surfaces that are covered in oscillations called waves. They can also be sparked by other variables including seismic activity or gravitational pressures from celestial bodies, although their primary cause is the interaction of wind with the water's surface. Here are some important characteristics of water waves.
Tides
A tide is the name given to the twice daily, periodic rise and fall of ocean water. When the water level on the shore reaches its maximum point, it is high tide. When the waterfall reaches its lowest point and moves away from the shore, it is low tide.
The sun and moon's powerful gravitational pulls on the surface of the planet are what generate the tides. The sun, moon, and earth are all in line on full and new moon days, when the tides are at their highest. Spring tides are what we call these tides.
However, the ocean waters are drawn diagonally opposite ways by the gravitational pull of the sun and moon during the first and last quarters of the moon.
Ocean Currents
Ocean currents have significant impacts on climate, weather patterns, marine ecosystems, and global oceanic circulation. They transport heat from the equator towards the poles, influencing regional and global climate variations. Additionally, ocean currents affect marine life by distributing nutrients, providing habitats for various species, and affecting migration patterns
Ocean currents are continuous, directed movements of seawater within the ocean. They play a crucial role in the global circulation of the Earth's oceans, redistributing heat, nutrients, and dissolved gases, and influencing climate patterns
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