Counter-intuitive influence of Himalayan river morphodynamics on Indus Civilisation urban settlements

In truth nothing new . As a friend of mine pointed me in short : 

'' ...they confirm the date of 8000 BP for the shift of the Sutlej. ''

Counter-intuitive influence of Himalayan river morphodynamics on Indus Civilisation urban settlements

Ajit Singh, Kristina J. Thomsen, Rajiv Sinha, Jan-Pieter Buylaert, Andrew Carter, Darren F. Mark, Philippa J. Mason, Alexander L. Densmore, Andrew S. Murray, Mayank Jain, Debajyoti Paul & Sanjeev Gupta

 Abstract  

Urbanism in the Bronze-age Indus Civilisation (~4.6–3.9 thousand years before the present, ka) has been linked to water resources provided by large Himalayan river systems, although the largest concentrations of urban-scale Indus settlements are located far from extant Himalayan rivers. Here we analyse the sedimentary architecture, chronology and provenance of a major palaeochannel associated with many of these settlements. We show that the palaeochannel is a former course of the Sutlej River, the third largest of the present-day Himalayan rivers. Using optically stimulated luminescence dating of sand grains, we demonstrate that flow of the Sutlej in this course terminated considerably earlier than Indus occupation, with diversion to its present course complete shortly after ~8 ka. Indus urban settlements thus developed along an abandoned river valley rather than an active Himalayan river. Confinement of the Sutlej to its present incised course after ~8 ka likely reduced its propensity to re-route frequently thus enabling long-term stability for Indus settlements sited along the relict palaeochannel.

From the paper : 

This finding resolves a question that has been debated for well over a hundred years. Our analysis shows that the Ghaggar–Hakra palaeochannel is a former course of the Himalayan Sutlej River that formed and occupied an incised valley from at least ~23 ka (Fig. 10a). Initial abandonment of this incised valley by the Sutlej River commenced after ~15 ka, with complete avulsion to its present course shortly after ~8 ka. This involved a lateral shift of the Sutlej River by up to 150 km, with the avulsion node located close to the Sutlej exit at the Himalayan front (Fig. 10). While we cannot identify the root cause of this avulsion, its timing after ~8 ka corresponds with the onset of a long phase of decline in the strength of the Indian Summer Monsoon (ISM)77, 78 that may indicate a possible climatic control on river reorganisation. However, it is important to point out that avulsion is an autogenic mechanism and need not mark a response to an external event.

Our study sheds new light on the role of river dynamics on early urbanisation. We find that the locus for the abundant Indus Civilisation urban settlements along the Ghaggar–Hakra palaeochannel was the relict, underfilled topography of a recently abandoned valley of the Himalayan Sutlej River rather than an active Himalayan river. We suggest that this abandoned incised valley was an ideal site for urban development because of its relative stability compared to Himalayan river channel belts that regularly experience devastating floods and lateral channel migration.

and : 

 A significant unresolved issue is that not all urban settlements in the region are necessarily co-located with the Ghaggar–Hakra palaeochannel84. The largest Indus site in the region, Rakhigarhi, widely considered to be of the scale of an Indus city14, 16, 85, is situated at least 50 km from the Ghaggar–Hakra palaeochannel. Although its location has been linked to another abandoned river system, the Drishadvati85, in situ data are necessary to determine the existence and timing of such river activity before drawing inferences on how such sites were sustained.

In conclusion, our results firmly rule out the existence of a Himalayan-fed river that nourished Indus Civilisation settlements along the Ghaggar–Hakra palaeochannel. Instead, the relict Sutlej valley acted to focus monsoon-fed seasonal river flow as evidenced by very fine-grained sediments in the upper part of the valley-fill record. This and the potential to pond flood waters in the topographic depression38 formed by the valley likely offered favourable conditions that led Indus populations to preferentially settle along the incised palaeovalley. We find that river dynamics controlled the distribution of Indus sites in the region, but in the opposite sense to that usually assumed: it was the departure of the river, rather than its arrival, that triggered the growth of Indus urban settlements here. We posit that a stable abandoned valley, still able to serve as a water source but without the risk of devastating floods, is a viable alternative model for how rivers can nucleate the development of ancient urban settlements. 

Yog .

See also : 

The Chronology of Puranic Kings and Rigvedic Rishis in Comparison with the Phases of the Sindhu–Sarasvati Civilization

Tracing the Vedic Saraswati River in the Great Rann of Kachchh

Large-Scale, Multi-Temporal Remote Sensing of Palaeo-River Networks: A Case Study from Northwest India and its Implications for the Indus Civilisation

Holocene landscape dynamics in the Ghaggar-Hakra palaeochannel region at the northern edge of the Thar Desert, northwest India