Physical Geography (UPSC) (Part-II)

Periyar Lake is favoured by the construction of the dam across the Mullaperiyar River. It is an artificial lake in the middle of the Periyar wildlife sanctuary.

• The Periyar’s source is high in the Western Ghats. Periyar is a river that starts on the Idukki district’s southeastern boundary.
• The river’s source is located in the Periyar Tiger Reserve’s remote forests.
• Chokkanamattii Mala, a hill on the southern edge of the Periyar Tiger Reserve, is said to be the river’s source, according to many accounts.
• The Periyar River rises in the Western Ghats’ Sivagiri Hills and runs through the Periyar National Park.
• It eventually drains into Vembanad Lake and then into the Arabian Sea.
• In the Indian state of Kerala, the Periyar is the longest river and the one with the greatest discharge capacity.
• It is one of the region’s few permanent rivers, and it supplies drinking water to numerous large cities.
• It runs through a zone of industrial and commercial activity and provides a substantial percentage of Kerala’s electrical power via the Idukki Dam.
• The river has been dubbed the “Lifeline of Kerala” for these reasons.
• Kochi city, which is located at the river’s mouth, gets its water from Aluva, an upstream location that is sufficiently free of marine intrusion.
• Along the banks of the river Periyar, 25% of Kerala’s industry is located.
• Muthirapuzha River, Mullayar River, Cheruthoni River, Perinjankutti River, and Edamala River are its primary tributaries.
• Muthayar, Perunthuraiar, Chinnar, Cheruthony, and Kattapanyayar are minor tributaries.

Earth is the only known planet that supports life due to its optimal distance from the Sun, moderate temperature, presence of water, life-supporting atmosphere, and ozone layer. About 71% of Earth’s surface is covered in water, giving it a blue-green appearance from space. The Moon is Earth’s only satellite.

Earth’s 23.5° axial tilt causes seasonal changes. It is the 5th largest planet in the solar system. Its equatorial radius is 6,378 km, polar radius is 6,356 km, and its perimeter is approximately 40,000 km. The exoplanet Kepler-452b is considered Earth’s closest cousin.

• Water in the atmosphere plays a crucial role in weather patterns and climate dynamics. It exists in three primary forms: water vapor, liquid droplets, and ice crystals.
• Water vapor is invisible but is a key component of the atmosphere, influencing temperature and weather conditions. As air rises, it cools, and water vapor may condense into liquid droplets, forming clouds.
• The amount of water vapor in the air determines humidity, impacting comfort levels and precipitation patterns.
• Water in the atmosphere also influences energy transfer. When water vapor condenses, it releases latent heat, which helps fuel storms and weather systems like cyclones. Additionally, water vapor can lead to phenomena like fog, mist, and precipitation (rain, snow, hail).
• Evaporation from oceans, lakes, and rivers, and transpiration from plants contribute to the atmospheric water supply. Understanding the dynamics of water in the atmosphere is vital for forecasting weather and understanding the global climate system.

Rainforests now cover less than 6% of Earth’s land surface. Scientists estimate that more than half of the world’s plant and animal species live in tropical rain forests and tropical rainforests produce 40% of Earth’s oxygen. A tropical rain forest has more kinds of trees than any other area in the world. Scientists have counted about 100 to 300 species. Seventy per cent of the plants in the rainforest are trees. About 1/4 of all the medicines we use come from the rainforest.

All tropical rain forests are similar. Many of the trees have straight trunks that don’t branch out. The majority of the trees have a smooth, thin bark because there is no need to protect them from water loss and freezing temperatures. It also makes it difficult for plant parasites to get a hold on the trunks. The bark of different species is so similar that it is difficult to identify a tree by its bark. Many trees can only be identified by their flowers

Each of the three largest rainforests–American, African, and Asian has a different group of animal and plant species. Each rain forest has many species of monkeys, all of which differ from the species of the other two rain forests. Also, different areas of the same rain forest have different species. Many kinds of trees that grow in the mountains of the Amazon rain forest do not grow in the lowlands.

• Rainfall is a form of precipitation where water droplets fall from clouds to the Earth’s surface. It occurs when moist air rises, cools, and condenses into water vapor, forming droplets that combine to create larger drops.
• When these drops become heavy enough, they fall due to gravity. Rainfall is essential for replenishing freshwater supplies, supporting agriculture, and maintaining ecosystems. It plays a critical role in the water cycle, helping to distribute moisture across the globe.
• The amount, intensity, and frequency of rainfall vary based on geographic location, climate, and seasonal variations.
• For example, tropical regions experience heavy, consistent rainfall, while arid regions receive minimal rainfall.
• Rainfall patterns are influenced by factors like temperature, humidity, atmospheric pressure, and wind patterns, affecting weather systems and climate change.

• Unlike the equatorial rain forests, Coniferous forests are of moderate density and are more uniform. The trees in coniferous forests grow straight and tall.
• Almost all conifers are evergreen. There is no annual replacement of newer leaves as in deciduous trees.
• The same leaf remains on the tree for as long as five years. Food is stored in the trunk, and the bark is thick to protect the trunk from excessive cold.
• Conifers are conical in shape. Their conical shape and sloping branches prevent snow accumulation. It also offers little grip to the winds.
• Transpiration can be quite rapid in the warm summer, so leaves are small, thick, leathery and needle-shaped to check excessive transpiration.
• The soils of the coniferous forests are poor. They are excessively leached and very acidic. Humus content is also low as the evergreen leaves barely fall and the rate of decomposition is slow. Under-growth is negligible because of the poor soil conditions.
• Absence of direct sunlight and the short duration of summer are other contributory factors.
• Coniferous forests are also found in regions with high elevation (Example: The forests just below the snowline in Himalayas).
• But on very steep slopes where soils are immature or non-existent, even the conifer cannot survive (Example: Southern slopes of Greater Himalayas).

Characteristics of volcanic mountains

• A magma chamber is a hollow space inside the earth surface. The molten rocks are called magma. It is present just below the vent of the volcano and is a source of lava.
• Magma chamber contains molten rocks and gases under high pressure. Conduit is a pipe-like structure through which magma comes out and it opens into the main vent. The depth of the magma chamber is usually 1km to 10 km.
• A vent is a hole in the earth's surface through which the lava comes out with great pressure. Generally vent is a weak point on the crust of the earth. There could be more than one vents of a volcanic mountain.
• Lava is the molten rock or magma that comes through a volcanic vent. It generally consists of silicates or silica rocks and is in liquid or semi-solid form. The temperature of lava is anywhere between 700°C to 1200°
• Lava cools and hardens after coming into contact with the air. This cooled lava forms a volcanic mountain-like shape.
• Craters are the circular depressions around the main vent. Craters are developed due to a large explosion in the volcano. These are formed when the magma chamber is present near the vent.
• The volcano becomes active due to the creation of high pressure in the magma chamber. Generally, the magma chamber contains a large amount of water which is continuously converting into steam because of the geothermal energy. When the pressure becomes so high, it comes out as an explosion causing a volcanic eruption.
• A pyroclastic flow is the flow of molten semi-liquid lava away from the volcanic mountain, downhill.