Nearly ten thousand years ago when mighty rivers started flowing down the Himalayan slopes, western Rajasthan was green and fertile. Great civilizations prospered in the cool amiable climate on riverbanks of northwestern India. The abundant waters of the rivers and copious rains provided ample sustenance for their farming and other activities. Some six thousand years later, Sarasvati, one of the rivers of great splendour in this region, for reasons long enigmatic, dwindled and dried up. Several other rivers shifted their courses, some of their tributaries were ‘pirated’ by neigbouring rivers or severed from their main courses.
The greenery of Rajasthan was lost, replaced by an arid desert where hot winds piled up dunes of sand. The flourishing civilizations vanished one by one. By geological standards, these are small-scale events; for earth, in its long 4.5 billion years history, had witnessed many such changes, some of them even accompanied by wiping out of several living species. But those that occurred in northwest India took place within the span of early human history affecting the livelihood of flourishing civilizations and driving them out to other regions.
The nemesis that overtook northwestern India’s plenty and prosperity along with the disappearance of the river Sarasvati, has been a subject engaging several minds over the last hundred and fifty years. However, convincing explanations about what caused all the changes were available only in the later half of the current century through data gathered by archaeologists, geologists, geophysicists, and climatologists using a variety of techniques. They have discussed and debated their views in symposia held from time to time, many of which have also appeared in several publications. Over the last thirty years, considerable volume of literature have grown on the subject and in this article some of the salient opinions expressed by various workers are presented.
Rivers constitute the lifeline for any country and some of the world’s great civilizations (Indus Valley, Mesopotamian, and Egyptian) have all prospered on banks of river systems. Hindus consider rivers as sacred and have personified them as deities and sung their praises in their religious literature, the Vedas (Rig, Yajur and Atharva), Manusmriti, Puranas and Mahabharata. These cite names of several rivers that existed during the Vedic period and which had their origin in the Himalayas. One such river Sarasvati, has been glorified in these texts and referred by various names like Markanda, Hakra, Suprabha, Kanchanakshi, Visala, Manorama etc.1,2, and Mahabharata has exalted Sarasvati River as covering the universe and having seven separate names2. Rig veda describes it as one of seven major rivers of Vedic times, the others being, Shatadru (Sutlej), Vipasa (Beas), Askini (Chenab), Parsoni or Airavati (Ravi), Vitasta (Jhelum) and Sindhu (Indus)1,3,4 (Figure 1). For full 2000 y (between 6000 and 4000 BC), Sarasvati had flowed as a great river before it was obliterated in a short span of geological time through a combination of destructive natural events.
Judged in the broader perspective of geological evolution, disappearance or disintegration of rivers, shifting of their courses, capture of one river by another (river piracy), steady decline of waters culminating in drying up of their beds, are all normal responses to tectonism (uplift, faulting, subsidence, tilting), earthquakes, adverse climate and other natural events. Such catastrophic events overtook Sarasvati river in quick succession, within a short geological span in the Quaternary period of the Cenozoic era (Figure 1) leading to its decline and disappearance. Similar changes to drainage of rivers have occurred during earlier geological periods also, much before human evolution. A few of the south Indian rivers like the east-flowing Pennar, Palar and Cauvery draining into the Bay of Bengal and west-flowing Swarna, Netravathi and Gurupur draining into the Arabian Sea are known to have changed their courses or got dismembered due to uplift of land. Today, their former courses or palaeochannels can be seen as dry beds5–8.
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