Planetary Science Seminar

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Ancient Rivers and Ancient Civilizations: How Himalayan River Migrations Influenced Bronze-age Indus Civilization Urban Centres in NW India

Abstract: The migration of rivers is postulated to influence large-scale spatiotemporal settlement patterns in early urban societies. However, evidence for such links is often confounded by poor chronological constraints. The Bronze-age Indus Civilisation (~4.8 - 3.9 thousand years before the present, ka), contemporaneous with the earliest urban societies of Egypt and Mesopotamia, was really the most extensive of the earliest Old World urban cultures. Urbanisation in the Indus Civilisation has been linked to water resources provided by large Himalayan river systems, although the largest concentration of urban-scale Indus settlements are located far from extant Himalayan rivers. Palaeoriver channel traces observed near these sites have been proposed as evidence of former large Himalayan rivers that sustained such settlements. However, lack of in situ data has rendered such links as speculative. In this talk I will discuss the results of our project to analyse the chronology and provenance of a major palaeochannel associated with these settlements, that has been linked with the mythical 'Saraswati river'. We show that river morphodynamics exerts a hitherto unexpected influence on early urbanisation. We find that important Indus urban settlements such as Kalibangan in NW India developed adjacent to a large fluvial valley system entrenched into surrounding alluvial plains. We show using isotopic fingerprinting that the palaeochannel is a former course of the Sutlej River, the third largest of Himalayan rivers. But using optically stimulated luminescence dating of sand grains, we demonstrate that flow of the Sutlej in this course terminated considerably earlier than Indus occupation thus ruling out a role for Himalayan river flow in sustaining Indus urban centres in NW India. Indus urban settlements developed along a relict valley rather than an active Himalayan river. Confinement of the Sutlej to its present incised course through the mid- to late Holocene likely reduced its propensity to re-route frequently thus enabling long-term stability for Indus settlements sited along the relict palaeochannel. I will end the talk by discussing how these studies impact understanding of present day water resource (mis-) management in the agricultural breadbasket of India.