Samacheer Class 10 Social Science - India - Location, Relief and Drainage

The Himalayas are indeed called young fold mountains primarily because of their relatively recent geological formation and the process by which they were created. They were formed approximately 50 to 70 million years ago when the northward-moving Indian tectonic plate collided with the much larger Eurasian plate. This immense collision caused the sedimentary rocks accumulated in the ancient Tethys Sea, which lay between these two landmasses, to buckle, fold, and uplift, forming the towering mountain ranges we see today. The term "fold" refers to this process of crustal compression and bending. They are considered "young" because this mountain-building process, known as orogeny, is still ongoing, meaning the Himalayas are continuously rising at a measurable rate. This ongoing tectonic activity also explains their high peaks, deep gorges, rugged relief, and frequent seismic activity, all characteristic features of geologically young mountain systems.

The Himalayan rivers and Peninsular rivers exhibit several significant distinctions. Himalayan rivers, such as the Ganga, Indus, and Brahmaputra, originate from the Himalayan ranges and are perennial, meaning they flow throughout the year. This continuous flow is due to their dual sources: the melting of snow and glaciers in the Himalayas and the abundant monsoon rainfall. They have large basins, long courses, and have carved out deep gorges and V-shaped valleys through erosional activity. These rivers carry a substantial amount of silt and are known for forming extensive deltas at their mouths. In contrast, Peninsular rivers like the Godavari, Krishna, Kaveri, Narmada, and Tapi originate from the Peninsular plateau and are largely seasonal, depending primarily on monsoon rainfall for their water supply. They have shorter courses, smaller basins, and generally flow in shallower, well-adjusted valleys. Their flow fluctuates significantly between the wet and dry seasons, and they often form estuaries rather than large deltas, especially the west-flowing ones.

The Western Ghats and Eastern Ghats are two prominent mountain ranges that define the eastern and western edges of the Peninsular Plateau of India, exhibiting several key differences. The Western Ghats run parallel to the western coast, forming a continuous chain of mountains. They are higher in elevation, with an average height of about 900-1600 meters, and their highest peaks include Anai Mudi and Doda Betta. The Western Ghats cause orographic rainfall by obstructing monsoon winds, leading to a narrow coastal plain to their west. In contrast, the Eastern Ghats run parallel to the eastern coast but are highly discontinuous and irregular, dissected by rivers flowing into the Bay of Bengal. They are lower in elevation, with an average height of about 600 meters, and their highest peak is Mahendragiri. The Eastern Ghats do not receive as much orographic rainfall and have a broader coastal plain to their east. The Western Ghats are known for their steep western slopes and gentle eastern slopes, while the Eastern Ghats have a more varied topography due to river erosion.

The Western Coastal Plains and Eastern Coastal Plains are two distinct geographical features bordering the Peninsular Plateau of India, separated by the Western and Eastern Ghats respectively. The Western Coastal Plain is a narrow strip of land located between the Western Ghats and the Arabian Sea. It is relatively narrow, averaging about 10-25 km in width, and is highly dissected. It is characterized by numerous swift-flowing short rivers that form estuaries rather than deltas, and it receives heavy rainfall. This plain is further subdivided into the Konkan (north), Kanara (central), and Malabar Coast (south). In contrast, the Eastern Coastal Plain lies between the Eastern Ghats and the Bay of Bengal. It is much broader, ranging from 80-100 km in width, and is relatively flat. Major east-flowing rivers like the Mahanadi, Godavari, Krishna, and Kaveri form large, fertile deltas on this plain, making it agriculturally productive. It receives rainfall from both southwest and northeast monsoons and is subdivided into the Northern Circars (north) and the Coromandel Coast (south).

Most South Indian rivers are east-flowing primarily due to the fundamental geological characteristic of the Peninsular plateau, which has a general eastward slope. The ancient Peninsular block tilted gently towards the east during its formation, influencing the drainage pattern of the region. Consequently, major rivers such as the Godavari, Krishna, Kaveri, and Mahanadi originate in the Western Ghats or the central highlands but follow this eastward gradient, traversing the plateau before emptying into the Bay of Bengal. As they flow eastward, these rivers often form extensive and fertile deltas near their mouths, which are crucial for agriculture. The only notable exceptions are the Narmada and Tapi rivers, which flow westwards into the Arabian Sea, a phenomenon attributed to their flow through rift valleys that run in an east-west direction.

Indian Standard Time (IST) is the uniform time that is followed throughout the whole of India. India is a very large country stretching across about 30 degrees of longitude from east to west, so the local time of the easternmost point and the westernmost point differs by nearly two hours. If every region followed its own local time, it would cause great confusion in railways, transport, communication and daily life. To avoid this, a single standard time is fixed for the entire country. Indian Standard Time is based on the local time of the 82.5 degrees East longitude, which passes near Mirzapur in Uttar Pradesh, and it is five and a half hours ahead of Greenwich Mean Time. Its importance lies in giving the whole nation one common, uniform time.

If one were to travel from West Bengal to Gujarat along the beautiful coasts of India, the journey would involve traversing the entire eastern coastline, crossing the southern tip of the Indian peninsula, and then moving northwards along the western coastline. The states that would be passed through, in sequential order, are: West Bengal, Odisha, Andhra Pradesh, Tamil Nadu. After covering the eastern coast and reaching the southernmost point, the journey would then proceed along the western coast, passing through Kerala, Karnataka, Goa, Maharashtra, and finally reaching Gujarat. This extensive coastal journey would showcase the diverse geographical features, cultural landscapes, and economic activities characteristic of India's two major coastal plains, from the fertile deltas of the east to the rugged cliffs and backwaters of the west, encompassing a rich tapestry of India's maritime heritage and natural beauty.

The Deccan Plateau is a large, roughly triangular tableland that covers most of the southern part of India, to the south of the northern plains. It is one of the oldest and most stable landmasses in the country. It is bordered by the Western Ghats on its west and the Eastern Ghats on its east, with the Satpura and Vindhya ranges to its north. The plateau slopes generally from west to east, which is why most of the big peninsular rivers, such as the Godavari, the Krishna and the Cauvery, flow eastward across it into the Bay of Bengal. The Deccan Plateau is rich in minerals such as iron ore, coal and manganese, and its black soil, formed from old lava, is very fertile and good for growing cotton. It is therefore important both for mining and for agriculture.

Most of the large rivers of peninsular India flow towards the east, but a few important rivers flow towards the west and empty into the Arabian Sea. The chief west-flowing rivers are the Narmada and the Tapti, or Tapi. The Narmada rises in the Amarkantak plateau in Madhya Pradesh and flows westward through a rift valley between the Vindhya and the Satpura ranges. The Tapti rises in the Satpura range and also flows west, more or less parallel to the Narmada. Unlike the eastern rivers, these rivers flow through narrow valleys and do not form large deltas; instead they form estuaries where they meet the sea. Other smaller west-flowing rivers include the Mahi and the Sabarmati, together with the many short, swift streams that flow down the Western Ghats along the western coast.

Lakshadweep is a group of small islands lying in the Arabian Sea, off the south-western coast of India, opposite the state of Kerala. The name 'Lakshadweep' means 'a hundred thousand islands', though the group actually consists of about thirty-six small islands, of which only a few are inhabited. The islands are coral islands, made up of coral reefs and atolls built up by tiny sea creatures, and they are low-lying and small in size. Kavaratti is the capital of this Union Territory. The people are mostly Malayalam-speaking and depend on fishing and the growing of coconuts for their livelihood. The islands have beautiful lagoons, clear blue waters and rich marine life, which make them attractive for tourism, but their low height makes them vulnerable to a rise in the level of the sea.

The Northern Mountains (the Himalaya) are divided into three main parallel ranges: the Greater Himalaya (Himadri) with the highest peaks and permanent snow; the Lesser Himalaya (Himachal) consisting of steep valleys and hill ranges; and the Outer Himalaya (Shivalik) of lower elevation with young sediments. Some classifications include the Trans-Himalayan ranges (e.g., Karakoram) to the north. Importance: they act as a climatic barrier protecting the subcontinent from cold Central Asian winds and helping retain monsoon rainfall; they are the source of major perennial rivers (Ganga, Brahmaputra and their tributaries) vital for irrigation and hydropower; they harbour rich biodiversity and forests; they are important strategic frontiers and attract tourism and pilgrimage.

The peninsular rivers of India are those that flow across the Deccan Plateau in the southern part of the country. Unlike the Himalayan rivers, they are mostly rain-fed and so are seasonal, carrying much less water in the dry season. Because the plateau slopes from west to east, most of the major peninsular rivers flow eastward into the Bay of Bengal. The chief east-flowing rivers are the Mahanadi, the Godavari, which is the largest of them and is sometimes called the 'Dakshin Ganga', the Krishna and the Cauvery, each of which forms a fertile delta where it meets the sea. The Narmada and the Tapti are the two main rivers that flow westward into the Arabian Sea. These rivers are very important for irrigation, drinking water, hydroelectric power and agriculture in the peninsular region.

The Ganga basin is one of the largest alluvial basins in the world, covering parts of northern and eastern India and Bangladesh. It originates in the Himalaya (confluence of Bhagirathi and Alaknanda) and flows southeast across the plains, receiving major tributaries like the Yamuna, Ghaghara, Gandak, Kosi (from the north/right) and the Son (from the south/left). The basin includes diverse landscapes from high mountains to fertile Gangetic plains with rich alluvium (Bhangar and Khadar). It supports dense population, intensive agriculture (rice, wheat, sugarcane), major cities, river transport, and extensive irrigation and hydropower systems. The basin is culturally significant and prone to seasonal floods that replenish soils but also cause damage.

Major plateau divisions: Deccan Plateau (including Karnataka Plateau, Maharashtra uplands), Central Highlands (Malwa plateau, Bundelkhand), Chota Nagpur Plateau (eastern plateau in Jharkhand/Odisha), Meghalaya Plateau (northeast), Gujarat Plains and Rann uplands (northwest peninsular fringe).

The peninsular rivers of India can be broadly categorised into two groups based on their direction of flow: East-flowing rivers and West-flowing rivers. The major East-flowing rivers, which drain into the Bay of Bengal, include the Mahanadi, Godavari, Krishna, Kaveri, Pennar, and Subarnarekha. These rivers are generally longer, have larger catchment areas, and flow across the Deccan Plateau, creating extensive and fertile deltas at their mouths. They are crucial for irrigation and agriculture in the eastern and southern parts of India. In contrast, the major West-flowing rivers, which drain into the Arabian Sea, include the Narmada, Tapi (Tapti), Mahi, Sabarmati, and Periyar. These rivers are typically shorter and swifter, often flowing through rift valleys or along the steep western slopes of the Western Ghats. Due to their relatively shorter courses and the hard rock terrain, they usually form estuaries instead of deltas. The Narmada and Tapi are notable for flowing westward through rift valleys, unlike most other major peninsular rivers.