Easterly Tilt Of The Deccan Plateau - Update

I first wrote about this topic in 2011 in response to a question by a reader. I thought I would update my post with some new maps and explanations. Why is there such a pronounced pattern of easterly flow of the rivers in the Indian Peninsula.  I keep getting asked this question.  It was time for an update on this interesting topic on geology and landscapes. 

The region south of the Tapi river covering the Deccan basalts and the southern Indian peninsula exhibits an easterly drainage with the rivers flowing into the Bay of Bengal. The map below shows the Indian peninsular region with easterly drainage. The Deccan Plateau is mostly but not entirely covered by the Deccan basalts. South of this region is the Karnataka Plateau with a Precambrian geology. Along the east coast there are Permian-Triassic and Cretaceous basins.

Source: Hetu C. Sheth: Deccan Beyond the Plume Hypothesis

The question posed to me was - What is the relationship between the Deccan volcanics and the easterly tilt of the Indian plateau (i.e. the plateau covering the Deccan volcanics and the southern Indian peninsular region)?

The easier more intuitive answer would have been that the western ghats provide the topography and Deccan volcanism created a lava pile that is thicker to the west and which thins to the east, thus generating an east sloping surface. Rivers follow the slope to the Bay of Bengal. 

There are some geologic age inconsistency in this answer and this also does also not fully explain why the region south of the Deccan Volcanics too has an easterly drainage. Clearly, something more is going on. 

To understand the evolution of the Peninsular drainage patterns let us look back to the time when the Peninsula didn't exist. In early Mesozoic, India was part of Gondwanaland and was joined to Antarctica and Australia to the east, and Africa to the west. The triangular shape of south India with characteristic eastern and western coastlines had not formed yet. 

How can we find out the direction rivers were flowing back then? Geologists look to clues in the sedimentary basins of that age. The composition of sand in sandstone is matched to the most likely source terrain. And current directions can be inferred from studying ripples preserved on the surface of ancient sand. 

The paleo geographic maps below shows Gondwanaland and the location of the Pranhita Godavari basin in the Mesozoic. 

 

Source: Sankar Kumar Nahak and Coworkers 2024.

West North West flowing rivers originating in the highlands of the future Antarctica and in the Eastern Ghats were funneling sediment to the basin. Much of the interior of the region that would become the southern Peninsular India was a peneplain. There wasn't much topography towards the west for an easterly drainage network to develop. 

India broke away from Antarctica beginning about 140 million years ago. A distinct eastern continental margin formed. Several NE- SW oriented basins developed along the edge of the Indian continent. Since by this time an expanding Indian Ocean lay to the east, the orientation of a natural drainage system would have been from the west towards the east. 

We can say with some confidence that by 90 to 80 million years ago, east flowing rivers originating in the interior of the Indian continent were depositing sediment along the eastern Indian margin. See this map of sediment distribution along the Indian east coast. 

 Source: K.S. Krishna and Coworkers 2016.

It shows the thickness of  Mid- Late Cretaceous sediment, ranging in age from about 100 million years ago to 65 million years ago. The sediment lobes coincide with the mouths of the Godavari, Krishna rivers and other southern rivers, indicating that the paleo Godavari and the paleo Krishna system had begun building deltas from that time. Since there were no Western Ghats then, these rivers may have been shorter, with their source somewhere in the Archean and Proterozoic terrain of Peninsular India. 

Further to the south, geologists find a similar story with the ancient Cauvery. The Cauvery basin formed when Sri Lanka detached from the Indian continent. Its delta and marine deposits too contains sediment from the Late Cretaceous. 

The easterly drainage pattern of Peninsular India developed before Deccan Volcanism and the formation of the Western Ghats. 

India broke away from Madagascar about 88 million years ago  and subsequently from the Seychelles about 66-64 million year ago. The latter separation coincided with Deccan Volcanism and the eventual formation of the western Indian continental margin. Block faulting that accompanies continental breakup would have created a north south oriented high area, which would eventually evolve into the present day Western Ghats. The thinning of the lava pile to the east also would have created an easterly slope. Rivers originating in the western highland now would flow across the length of the Peninsula. 

New streams would have incised the fresh volcanic surface as lava buried the older etched landscape. But the regional  pattern of easterly flow persisted.

Some geologists maintain that there has been some fairly recent Cenozoic age (past 15-20 million years) uplift of the Western Ghats which has accentuated relief and produced the youthful looking topography of scarps, waterfalls, and deep canyons. These earth movements would have certainly given new energy to the drainage system, but there is some geologic evidence to suggest that the streams originating in the western ghat region are antecedent to the uplift of the ranges. 

For example, in the Mahabaleshwar area easterly drainage cuts across the axis of a north south oriented gentle anticlinal structure, implying that the drainage predates the uplift and warping of lava flows. Evidence from sedimentation patterns of the eastern river deltas also show that the easterly drainage originated much earlier than the formation of the Western Ghats. 

What then created that initial slope to the east that imprinted the drainage network that continues today? 

One reason is that the eastern margin formed first. Basin formation along the eastern edge of the continent would have created a relief difference between the western interior and the eastern depressions, resulting in stream networks flowing eastwards.  Secondly, the new oceanic crust made of lava that formed when India and Antarctica separated in the Late Jurassic and Early Cretaceous would have cooled by Late Cretaceous times. Becoming colder and denser it has been sinking and dragging the Peninsular region with it. 

Earlier eastern basin formation and a tug from the floor of the Bay of Bengal may have been enough to impress an east flowing drainage. Later, the east sloping lava surface and the rise of the Western Ghats reinforced this distinction between the west and the east perpetuating the direction of river flow initiated since Cretaceous times. 

Plastic In Sediment, Antarctica Ice Core, Alfred Wallace

A few interesting readings:

1) Sedimentation Shifted - How rivers move sediment along their course to the sea is an important aspect of sedimentology research. Grain size, shape, and density, all affect how currents move sediment, and where and in what proportions sand, silt, and mud particles come to be deposited. Now there is a new kid on the block: plastic. Catherine Russell has written a fascinating article diving deep into experimental work on how plastic impacts sediment transport. The work she describes has important implications for our understanding of plastic pollution in rivers, and the role plastic particles plays in enhancing erosion rates and sediment redistribution in riverbeds. 

2) Antarctica: 1.2-Million-Year-Old Ice- Scientists use gases trapped in old ice to measure ancient atmospheric composition and estimate past climatic conditions. A long running drilling program in Antarctica had so far recovered 800,000 year old ice. That record has been recently broken. Scientists have reached the very bedrock of the Antarctica continent. The oldest ice at the very bottom is 1.2 million years old. This is the longest continuous record of our climate that we have so far.  It hold much valuable information on climate fluctuations through the Pleistocene and Holocene. This article is a press release of the University of Bern. 

3) Beyond Evolution: Alfred Russel Wallace’s critique of the 19th century world- Alfred Russel Wallace is the co-discover of evolution through natural selection along with Charles Darwin. He was a brilliant naturalist and made foundational contributions to natural history. But he also was very sympathetic to the plight of local people suffering under colonialism and the environmental degradation the race to strip the land of resources was causing. Marshall A. summarizes nicely Wallace's observations on the impact of environmental damage, both in his native Wales and also during his travels in the far away Malay archipelago. 

Let me take this opportunity to share again this lovingly crafted documentary on the life and work of Alfred Wallace. It is made as a paper-puppet animation, produced by Flora Litchman and Sharon Shattuck and narrated by George Beccaloni of the  Natural History Museum London and Andrew Berry of Harvard University.

 

What a fine example of science outreach. 

Ganga Earthquake, Nile, Deep Sea Habitats

Some readings over the past few weeks:

1) An Earthquake Changed the Course of the Ganges. Could It Happen Again?  Sediment load carried by big rivers like the Ganga often choke up channels and force the river to cut another path. Sudden channel shifts can also occur due to tectonic movements. A recent survey of the Ganga about 100 km south of Dhaka, Bangladesh , identified an old channel of the Ganga. Exploring this area, researchers came across veins of sand cutting across the sediment layers. These veins or sand dikes were  injected into the surrounding sediment. They are a sign of major ground trembling triggered by a large earthquake. Ground motion may pressurize buried sand and inject it  upwards. Further studies showed that this event may have been a 7-8 magnitude earthquake that occurred 2500 years ago. Kevin Krajick writes about this discovery and the larger geologic context.

2)  Lessons from the Nile about rivers and society. The Nile river has sustained agriculture, human habitation, and royal dynasties for millennia. A Nature Geoscience editorial summarizes a collection of sedimentological and geomorphologic studies that track the evolution of the Nile through the Holocene. Phases of the river cutting a deep valley changed to phases of the river flooding laterally and building fertile floodplains. This geomorphological evolution driven by climate change and more recent dam building have influenced agriculture and social systems in the past as well as the present. 

3) Ocean Exploration: Meet The Deep. I highly recommend this site. National Ocean and Atmospheric Administration, U.S.A., has compiled some stunning photographs and videos of deep sea habitats and the diverse forms of life that inhabit this little understood world. Corals, sponges, brittle stars, molluscs, worm tubes- attached to the bottom, living around energy sources such as hydrothermal vents and cold seeps. It is an absolutely fascinating exploration of the biodiversity of the deep sea. 

Octocoral and Brittle Star: Source NOAA Ocean Exploration

As a bonus, these images make great wallpaper for your mobile phone!

Books: Speaking Rivers, The Ice Age

 Ordered and received!

Prof. Vipul Singh is with the Dept. of History, University of Delhi, and he writes in the acknowledgments section that environmental history as a formal subject of study in history departments had a late start in India. The focus of the book is the flat lands of Bihar with its annual floods and shifting river channels and how Mughal and later British land use policies transformed the people's relationship with the river system. Looks like a very meaty book with plenty of Notes, Maps and a long Reference section. Will be sharing interesting snippets as I read along.

 

As one blurb says... "Perfect to pop into your pocket for spare moments".  A fine introduction by Jamie Woodward. The recognition that the earth has passed through several glacial and interglacial phases is really a triumph of field geology. Thick sedimentary deposits in Europe and N. America were recognized as being left behind by advancing ice sheets. The stellar role played by geologists in the mid-late 1800's and their debates grounded within the prevailing schools of catastrophism versus uniformitarianism is highlighted. And there are good succinct sections on the many modern theoretical advances in climate science and the techniques that geologists and climate scientists bring to bear upon understanding the mode and tempo of climate change.

 

Happy Reading.

Books: Tree Story, Rivers of Power

A friend pointed out these two books.

1) Tree Story: The History of the World Written in Rings by Valerie Trouet.

Review: "Trouet, a leading tree-ring scientist, takes us out into the field, from remote African villages to radioactive Russian forests, offering readers an insider's look at tree-ring research, a discipline formally known as dendrochronology. Tracing her own professional journey while exploring dendrochronology's history and applications, Trouet describes the basics of how tell-tale tree cores are collected and dated with ring-by-ring precision, explaining the unexpected and momentous insights we've gained from the resulting samples"...



2) Rivers of Power: How a Natural Force Raised Kingdoms, Destroyed Civilizations, and Shapes Our World by Laurence C. Smith

.."From ancient Egypt to our growing contemporary metropolises, Rivers of Power reveals why rivers matter so profoundly to human civilization, and how they continue to be indispensable to our societies and wellbeing"...

Two other books on rivers that I would recommend are Unruly Waters by Sunil Amrith and The Water Kingdom by Philip Ball.

I also want to read The Unquiet River: A Biography of the Brahmaputra by Arupjyoti Saikia. Hoping to get to it soon.


Happy Reading!

Ganga Water: Future Availability

The Ganga river basin is being modified by the building of infrastructure to trap and divert water. There are many environmental repercussions resulting from this dam and canal construction. That is not the topic of this note.
 
Will there be enough water available for these different projects?

First, the Inland Waterways project will need water to be released from upstream dams to maintain a certain water depth in the navigable channel in the summer months. Second is the River Linking Plan, based on the rationale that there is excess water in the Gangetic system. The plan envisages transferring Ganga system water during the summer months to the southern Peninsular rivers. And third, the Uttarakhand dam building companies will try to keep as much water locked up behind dams for power generation in the summers.

Over and above the water requirements of these projects, environmental regulations will require a  certain amount of water flow to be maintained throughout the year in the river. This will be detrimental to the river linking and power generation projects.

Each of these massive waterworks will be competing for a limited amount of Ganga water during the same time of the year. This allocation problem will lead to water disputes, both, among the managers of these projects, and across different States. As a result, these projects are unlikely to operate optimally.

I haven't come across an official water budget analysis projected 100 years into the future, that takes into account water availability and the impact that these three projects will have on each other.

Environment Links: River Issues In India

Sharing a few interesting and informative articles I came across in the past few weeks on rivers.

Endangered Himalayan Rivers: This one is from 2012. A large number of dams are planned on the Alaknanda and Bhagirathi rivers in the state of Uttarakhand.  Parineeta Dandekar writes about the weaknesses and bias in the Environment Impact Assessment process.

Rally For Rivers Plan. Will It Help?: The Rally For Rivers campaign by the Isha Foundation is calling on creating a 1 km wide tree plantation along the river banks. This, they claim, will help rejuvenate India's dying rivers. Veena Srinivasan, Sharad Lele, Jagdish Krishnaswamy and Priyanka Jamwal with the Ashoka Trust for Research in Ecology and the Environment, Bengaluru examine their claims in detail and find them wanting.

Caution Warranted For River Linking Project: The gargantuan river linking project envisages a series of dams and canal systems to transfer water from Himalayan rain and snow fed river basins to the drier Peninsular rivers in the south. Is it worth it?

Reuter's Erroneous Reporting On The Ken-Betwa River Linking Project: Two rivers in Madhya Pradesh and Uttar Pradesh are to be linked. SANDRP clarifies that the permissions process has yet to be completed. The two states don't even have a water sharing agreement! Reuter's screwed up.

Environment Ministry Panel Reject's Uttar Pradesh's Religious Smart City Plan: I'm including this to give an example of the utter indifference to ecology and environment shown by "planners and developers". The plan is for a smart city to be built inside the Hastinapur wildlife sanctuary, along the banks of the Ganga, which would have destroyed dolphin habitat and river ecology along a 7 km stretch. How does one even come up with such ideas? Fortunately, the usually pliant Environment Ministry has balked at approving this outrageous plan.

Sedimentation Patterns Bay Of Bengal: How Old Is The River Ganga

...In our legends it is said that the goddess Ganga's descent from the heavens would have split the earth had Lord Shiva not tamed here torrent by tying it into his ash-smeared locks. To hear this story is to see the river in a certain way: as a heavenly braid, for instance, an immense rope of water, unfurling through a wide and thirsty plain. That there is a further twist to the tale becomes apparent only in the final stages of the river's journey - and this part of the story always comes as a surprise, because it is never told and thus never imagined. It is this : there is a point at which the braid comes undone; where Lord Shiva's matted hair is washed apart into a vast knotted tangle. Once past that point the river throws off its bindings and separates into hundreds, maybe thousands of tangled strands....

Amitav Ghosh- The Hungry Tide

A study by K.S Krishna and colleagues published recently in Current Science shows very elegantly using sesimic reflection profiles and sediment isopach maps how the Bay of Bengal has been filling up with sediment since Late Cretaceous times.

The Bay of Bengal (BoB) originated with the rifting of India from Antarctica by early Cretaceous, thus forming the Indian east coast margin. The depression over time evolved into an ocean basin with new oceanic lithosphere forming in the Bay of Bengal at sea floor spreading centres. Its conjugate oceanic crust is probably beneath the Enderby Basin at the margin of East Antarctica. In this depression, an enormous volume of sediment has been deposited from mid-late Cretaceous to recent times. The age ranges of sediment packages, their distribution, geometry and thickness tell us about the changing source regions of these sediments and the influence of the rising Himalayas and the monsoons on sedimentation history.

Scientists involved in this study used seismic  reflection profiles to construct a seismic stratigraphy of the sediment pile in the BoB. The ages ranges of the sesimic sequence were then calibrated using biostratigraphy erected from two deep sediment cores from the vicinity of the seismic lines. Thus, a Cretaceous to recent subdivision of the mega sequence into distinct depositional episodes separated by unconformities could be recognized. The seismic profiles also revealed the geometry and thicknesses of the sedimentary sequences and the topography of the basement.

Several coast perpendicular grabens (linear depressions) were clearly outlined. These are continuations of ancient Archaean and Proterozoic sutures zones and rifts now occupied by the major rivers of Peninsular India, the Cauvery, Krishna, Godavari and the Mahanadi. Sedimentary packages until the late Oligocene are thicker near the east coast and thin out into the deeper shelf areas. From early Miocene onwards the sediment packages are thicker near the Ganges Brahmaputra delta and in the deeper shelf areas to the east and north and thin towards the shallower coastal shelf. This implies a changes in direction of sediment delivery systems, with the Indian craton being the major source in the earlier phase, to the Himalayas and the Indo Burman ranges being the major source in the younger phase.

This is brought out beautifully by sediment isopach maps constructed for several time slices. Isopach maps show the thickness of sediments for a particular time slice. In this case four time slices were used: 1) Basement to Late Cretaceous 2) Late Cretaceous to Oligocene 3) Oligocene top to Late Miocene 4) Late Pleisocene to recent.

The results are shown below and they clearly show changing sediment sources and distribution pathways.

From Cretaceous to the Oligocene, thick sediment wedges coincide with the Peninsular river grabens indicating that sediments derived by erosion of the Indian craton was the major source to the BoB.

 Source: K.S Krishna et al. 2016

From late Oligocene throughout much of the Miocene the sediments are thickest in the Ganges Brahmaputra delta region and thin out southwestwards towards the east coast shelf area.

 Source: K.S Krishna et al. 2016

This indicates that river systems eroding the rising Himalayas were now the major suppliers of sediment to the BoB. Sediment thickness from late Miocene to mid Pleistocene also show enhanced sedimentation from the north and this pattern coincides with an increase in the Asian monsoon. From Pleistocene to recent times, there has been more sediment from the Godavari Krishna system to the Bob, while a strong sediment delivery system from the Ganges-Brahmaputra continues.

This is the end of part 1 of the post, but I had an intriguing question..

How old is the river Ganga of the plains, flowing from the Himalayan front near Haridwar to the Bay of Bengal?  What does the data from the Bengal Basin tell us about paleo-rivers and how do geologists go about collecting and analyzing this data?

Is The Ganga River The Longest River In The Ganga Basin?

Seems like a strange question to ask? The Ganga is no doubt the most important north Indian river in terms of its cultural and religious significance but is it the longest?

A new study published in Current Science (open access) which measured the lengths of various river segments from headwaters to their confluence with the Ganga segment and further to the mouth, finds that it is not. The honor goes to the Tons-Yamuna segments:

The length and discharge data together suggest that there exists a river within the Ganga Basin which is longer than the Ganga River by at least 370 km (Table 3). This is the segment originating from the Banderpunch Mountains (i.e. Tons River). But, is this the main stem in the Ganga basin? It is well known that the main stem of a river sets the base level for its tributaries. Therefore, we measured incision by both the Ganga and the Yamuna rivers upstream of Allahabad up to 100 km. The results showed that the Yamuna River is more incised, thus setting the base level for the Ganga River (Figure 4). This analysis further strengthens the result of the present study that the river segment in the Ganga Basin from the Banderpunch Mountains (source point S8) is the main stem. The total length of the river comes to 2758 km up to its confluence with the Brahmaputra.

Not only is the Ton-Yamuna segment longer than the Alaknanda-Ganga segment up to Allahabad (confluence of Yamuna and Ganga) but the discharge of the Yamuna is significantly more than the Ganga at the confluence.  This is because of the contribution to the Yamuna of the large Chambal river draining the Pre-Cambrian heartland of India. Of interest too is that the Chambal discharges more water than the Yamuna at the confluence of these two rivers.

This kind of work is important because:

This finding has huge implications on the geomorphic study of the Ganga Basin rivers. It would mean that the HFR (the authors have named the newly calculated longest segment as the Himalayan Foreland River for scientific purposes only) sets the base level for the Ganga River. Since several relationships are worked out with the length of a river (e.g. basin area versus stream length, discharge versus stream length, grain size versus stream length, etc.), there is a need to re-evaluate these relationships for the Ganga Basin with this length. Further, changes in these relationships can affect the predictability of river response that can in turn influence any river-related planning in the Ganga Basin.

I have one additional  comment. The authors ask :

The results also raise an important question; in spite of greater length why has this segment not gained importance? This question remains unanswered and the only possible answer could be that rivers in the Ganga Basin attained their present set-up at a much later stage, e.g. the Yamuna River is suggested to have started flowing towards east only during Late Pleistocene.

What could they possibly mean by this? Are they talking  of cultural  significance of these rivers? We are now reasonably sure  that the Yamuna started flowing along its present course as early as 50,000 years ago (1 ,2) much before any of these north Indian rivers came to be deified.

Huh? Thousands Of Rivers Wiped Off Map Of China

The first national water census pointed out that thousands of rivers (28 thousand was the figure given) shown on previous maps are now missing from China' s state water maps. See this article.

Explanations:

Official- Climate change is to blame for the drying of some waterways. Plus some earlier mistakes by cartographers

Environmentalists: Ill conceived development and over use of underground water resources.

That last one is an important point. Much of the base flow of rivers, especially those which are not sourced from glaciers comes from groundwater discharging as springs. That means the water you see flowing in the river channel months after the rains are over is actually groundwater seeping out along river banks. Even rivers connected to glaciers may have a significant component of their flow provided for by groundwater discharge. A survey in the Nepal Himalayas revealed that groundwater contributes more than melting glaciers to the annual discharge of the rivers. 

Rivers may gain water from groundwater over long stretches. Such streams are called effluent (fig on left: source: USGS) . Rivers that lose water to groundwater are called influent.  Here is an excellent USGS  primer on the impacts of groundwater exploitation on surface water.

All the important monsoonal rivers in Peninsular India as well,  Narmada, Mahanadi, Cauvery, Krishna and Godavari depend on groundwater discharge to remain perennial. If the local water table plummets well  below the river bed due to over extraction of groundwater then discharge into the river will cease.

River management must include management of groundwater resources as well. The USGS article I linked to points out: " From a sustainability perspective, the key point is that pumping decisions today will affect surface-water availability; however, these effects may not be fully realized for many years".

A lesson not taken seriously in China and in India as well.

India Still Not Serious About Environmental Impact Assessment

Last year I compiled comments made by the then new Minister of Environment and Forest (MoEF) Ms. Jayanthi Natarajan. Here is the list from an article that appeared in The Hindu (emphasis mine):

....Jayanthi Natarajan has assured the corporate world that steps will be taken for promoting growth and “one window” fast clearances for big projects.

at the same time, said she would “do everything” to protect the environment. ...

She said that there will not be “any change” once clearance is given to a project....

Asked whether she could assure speedy clearances for such projects, Ms. Natarajan said she will do so but environment should be protected at “all cost” in all its “dimensions.”  

Dismissing the perception that Prime Minister Manmohan Singh appointed her as a result of a compromise to appease corporate India, Ms. Natarajan said, “My actions will show that there can be no compromise on either issue that I will always act for the best welfare of the country.

That these supreme examples of fence sitting and contradictions is not just a list to chuckle at but reflects how the MoEF actually takes on the task of Environmental Impact Assessment (EIA) of developmental projects is painfully brought out by Parineeta Dandekar in an InfoChangeIndia article on the ongoing efforts to dam the Chenab river in Himachal Pradesh and Jammu and Kashmir.

From the article: 

While other rivers like the Sutlej, Beas and Ravi, as well as smaller streams and tributaries in Himachal have been almost completely dammed, the Chenab is the last comparatively free-flowing healthy river in the state.

As things stand now, if all projects are implemented, less than 10% of the river will be seen flowing at all. Dams are being constructed bumper-to-bumper in a very tight sequence, where water from one hydro project meets not the river but the reservoir of the next hydro project in line. This conversion of a living river into a series of puddles, alternating with dry stretches and bypassed by tunnels, will have a profound impact on the ecology, biodiversity, hydrology, sociology and water availability of the region.

And the impunity with which even the most basic norms of a fair and transparent EIA process are being seemingly violated:

The MoEF sanctioned TORs for cumulative impact assessments of the Chenab in February 2012. Surprisingly, this critical task has been entrusted to the Directorate of Energy, Government of Himachal Pradesh. Can there be any agency with greater conflict of interest than the Directorate of Energy for this study? Can we expect this department to conduct the study in an unbiased manner? Even as the directorate put out a request for proposals for contractors to carry out the study, it did not mention that the consultant had to be an independent agency with a credible track record, as specifically instructed by the EAC.

The MoEF seems to have meekly accepted the Himachal Pradesh chief minister's demand for delinking environmental clearances from cumulative impact assessment studies, without any questions asked. Indeed, the EAC and MoEF have been according clearances and TORs to projects on the Chenab with great efficiency....

and this self defeating exercise:

In rare cases where consultants have showed courage and integrity by recommending that certain projects be dropped, their reports have been ridiculed and 'saviour' committees have been appointed to look into the reports again to make 'all ills go away', like the B K Chaturvedi Committee which is now looking at the WII study which recommended dropping 24 projects planned in the upper Ganga. The MoEF decided to dump the recommendation of the Teesta cumulative impact study when it stated that no projects should be built upstream of the Chungthang.

A case where political compulsions are going too far... and here is another study (press release) on the likely impact on ecology and social disruptions due to this frenzy of dam building activity in the Himalayas.

K.S Valdiya On The Glacial Saraswati In Current Science

In the latest issue of Current Science, geologist K.S. Valdiya has written a long response to a paper   by  Giosan et.al 2012 which concluded that the Yamuna and Sutlej rivers of northwest India stopped flowing into the Ghaggar river by early Holocene. There is a companion paper by Clift et al 2012 on this topic which Valdiya does not elaborate on.

The Ghaggar floodplains formed the agricultural heartland of the Harappan civilization. This finding by Giosan et al and Clift et al if true, meant that during the Harappan civilization the Ghaggar was not a glacial fed river but a monsoon fed river, but likely a perennial one due to a wetter climatic regime in the Ghaggar catchment areas of the Siwaliks. That in turn had implications for Harappan water use and agriculture methods. This question has also fed the controversy about the origin of the Aryans and the relationship between Aryans and the Harrappan civilization, since some say that a glacial Ghaggar was the Vedic Saraswati mentioned in the Rig Ved, an ancient collection of hymns in the Sanskrit language composed perhaps around 1500 B.C. or so.

K.S. Valdiya strongly disagrees with Giosan et al's findings that Holocene climate imparted a characteristic geomorphology to large glacial rivers of this region and that their finding suggests that there was no glacial river flowing on the plains of Haryana and Punjab during mid late Holocene. Goisan et al in due course may provide a detailed reply to Valdiya's arguments. I do have several comments on the way in which K.S. Valdiya has presented his evidence.

Fluvial History And The Fortunes Of The Harappan Civilization

 

In a recent issue of PNAS Liviu Giosan et.al. use a combination of high resolution topographic data, geomorphologic analysis and sediment dating to establish a chronology of the evolution of fluvial landforms of the Indus and its tributaries.

The Harappan civilization over a 600 year period from around 4500 B.P (before present) to about 3900 B.P flourished in this region and then went into decline with urban centers abandoned and populations moving eastwards towards the Himalayan foothills and the Gangetic plains. Goisan et.al's work - and there is also independent evidence for this -  shows that this 600 year period was a kind of a Goldilocks period. The region became arid, but not too arid.

Indus and its tributaries get water from two climatic regimes, the summer monsoons from the Arabian sea and winter rains from the northwesterly winter disturbances bringing moisture from the Mediterranian, Caspian and Black sea region. Most of the sediment load of these rivers is generated during the heavy erosion that takes place in the Himalayas during the summer monsoons. When rivers carry and deposit sediment along their course they are said to be in an aggradational mode i.e. the stream bed and the surrounding floodplains get raised as more and more sediment is deposited.

Over much of the earliest part of the Holocene, the Indus and its tributaries were aggradational. Then the monsoons weakened and the sediment load reduced. Winter rains falling as snow though kept river discharge active. Rivers without sediment or less sediment incise or cut into their own deposits. So, by mid Holocene all these rivers had developed a characterized profile of incised valleys and river terraces marking the original river bed and broad surrounding plains that because of  reduced rainfall were less prone to severe flooding.

Giosan et.al suggest that the Harappan people took advantage and adapted to these circumstances. There are Harappan and even pre-Harappan sites within these incised valleys of the Indus and its tributaries like the Beas and the Sutlej. This suggests that incision had occurred in the early Holocene and agriculture evolved to take advantage of manageable floods and a perennial water supply within the valleys and adjoining plains. 

After around 3900 B.P. the aridification intensified. The agricultural heartland of this civilization was along the  Ghaggar/Hakra river, located between the Sutlej and the Yamuna. This river was monsoonal fed and would have been perennial until then. As it slowly dried up, urban population centers could not be sustained and the Harappan civilization went into decline. There was a movement of people to the east towards the wetter Himalayan foothills.

This eastward civilizational shift is captured well in the figure to the left (Source Giosan et.al.). Red dots are Harappan sites. White dots are  Painted Grey Ware sites. Painted Grey Ware is a cultural phase that overlaps with the late Harappan.

This study also lends additional support that the Ghaggar river which has been identified as the mythical Saraswati river mentioned in the Rig Veda was not a glacial river in the Holocene. It has been proposed that the Sutlej and the Yamuna flowed into the Ghaggar and changed course around 4000 B.P to 3900 BP, triggering a water crisis. This study points out that the landforms of incised valleys typical of these glacial rivers are not present across the Ghaggar Hakra region. Sediment dates of river terraces along the Sutlej also indicate that the Sutlej had incised and was flowing along its present course by late Pleistocene.

Work by Clift et.al, using zircon dating to fingerprint sediment and Himalayan catchment areas of these rivers, which I reviewed in an earlier post  indicates that although the Sutlej and Yamuna likely did flow into the Ghaggar in the Pleistocene they changed course towards the Indus and the Ganges by late Pleistocene, thousands of years before civilization was established in this region. And there is some independent isotope studies on ancient water in buried channels along the Ghaggar that also suggests that there were no glacial rivers flowing into the Ghaggar during the Holocene.

Sometime back I got involved in a debate with indologist Michel Danino on my blog. I had pointed out that glacier rivers like Sutlej and the Yamuna have developed a characteristic morphology of a relatively narrow belt of incised valley and terraces. As has been suggested, if such large perennial rivers were flowing across the plains of Punjab in the upper reaches near the Siwaliks and joining the Ghaggar they would have prevented the formation of the alluvial fans systems that have developed in the upper reaches of the interfluve areas around Ghaggar.

Michel though was convinced that the Sutlej had flowed into the Ghaggar until in fact medieval times. I bring this debate up because Michel, who is not a geologist, ultimately came to this conclusion based on his reading of the geological literature. And here, I think, that Indian geologists working on this problem have a lot to answer to.

That the Sutlej or Yamuna may have flowed into the Ghaggar in the past is a perfectly reasonable geological hypothesis. But until these recent studies by Clift et.al and Giosan et. al. there was no convincing evidence for it. Earlier, geological evidence of a glacial Ghaggar/Saraswati has been based primarily on the satellite mapping of dried up channels near the Ghaggar river which indicated that in the past the Ghaggar was a bigger river. But, these channels were never shown to be connected to the present day glacially connected Sutlej and Yamuna basins. They could just as well be interpreted as belonging to a monsoon fed river originating in the lower Himalayan ranges. Nor was there any firm sediment provenance that could identify a specific Himalayan source for these channels or a sediment chronology to establish the long term fluvial history of this region.

Paleobotanical and sedimentological criteria had always indicated that increasing aridification and reduction in monsoon strength better explained the drying of the Ghaggar around 3900 B.P.  Despite all this, the Sutlej or the Yamuna changing course at around 3900 B.P  became the favored explanation for the drying of the Ghaggar. This scenario of a once large Ghaggar neatly fitted the description in the Rig Veda of a mighty Saraswati, a holy river that just like the Ganges was thought to have its source in the high glacial Himalayas. I suspect that the glacial river theory had more emotional appeal and gained acceptance among some geologists.

The strong assertions by geologists that the diversion of glacial rivers from the Ghaggar coincided with the decline of the Harappan civilization was used by archaeologists like Prof. B.B. Lal to place the composers of the Rig Veda on the plains of the Punjab before the Ghaggar dried up, apparently bolstering the theory that the Harappan people and the Vedic people were one and the same. A geological narrative constructed without rigorous evidence has been promoted to support a theory of cultural evolution in northwest India.

Unfortunately, this glacial past of the Saraswati timed to the demise of the Harappan civilization is now enshrined in textbooks written by senior geologists like K.S. Valdiya. They should now be revised or at the very least these geologists  need to admit that their theory has been seriously challenged. If geologists working on this problem still want to stick to the theory of a glacial Saraswati, they will need to come up with a more convincing data driven rebuttal to the work of Clift et.al. and Giosan et. al.

Giosan, L., Clift, P., Macklin, M., Fuller, D., Constantinescu, S., Durcan, J., Stevens, T., Duller, G., Tabrez, A., Gangal, K., Adhikari, R., Alizai, A., Filip, F., VanLaningham, S., & Syvitski, J. (2012). PNAS Plus: Fluvial landscapes of the Harappan civilization Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1112743109

Additional Posts: K.S.Valdiya on the glacial Saraswati in Current Science

Yamuna And Sutlej Stopped Flowing Into Ghaggar / Sarasvati By Early Holocene

The Yamuna stopped flowing into the Ghaggar / Sarasvati and shifted course eastwards into the Ganga as early as around fifty thousand years ago. The Beas and the Sutlej stopped flowing into the Ghaggar / Sarasvati and joined the Indus before ten thousand years ago, several thousand years before the beginnings of the Harappan civilization.

That is the conclusion reached in a paper in Geology  (behind paywall) by Peter Clift and colleagues using U-Pb (Uranium - Lead) dating of zircon crystals from ancient channels and alluvium of the Ghaggar / Hakra river.

I had earlier suggested that the Ghaggar likely never had any glacial connection. That statement now needs to be modified to read that there is a strong possibility that the Yamuna flowed into the Ghaggar in the Pleistocene and the Sutlej until the early Holocene.

Detailed mapping of the region between the Indus and the Yamuna where the present day Ghaggar / Hakra flows  has revealed the presence of many dried up channels suggesting that a much larger Ghaggar river existed in the past. The Harappan urban civilization declined and was abandoned by around 2000 B.C to 1800 B.C. One of the main reasons given is a prolonged drying of the region which made agriculture unsustainable. Monsoonal strength over this region has fluctuated for the last ten's of thousands of years and evidence from many different sources indicates that this region began experiencing aridity by mid Holocene and this arid phase moved eastwards over time slowing making urban centers and agriculture unsustainable. The larger dried up channels point to this climate change.

Another explanation of many of these dried up channels is the hypothesis that large glacially fed rivers like the Yamuna and Sutlej once flowed into the Ghaggar. They shifted course away from the Ghaggar  in the late Holocene, dramatically reducing water supply to the Harappan urban centers and contributing along with climate change to their decline and eventual collapse.

How does one figure out whether ancient channels represent glacially fed rivers and match them to known rivers? Clift and colleagues use a conceptually simple yet technologically challenging geochemical technique to make this match between ancient channels, present day rivers and their source in the Himalayas.

The Himalayan mountains are made up of several geological terrains of different ages. The Karakorum and Kohistan terrain (Trans -Himalayas) are younger than 300 million years old, the Tethyan Himalayas are 300 -750 million years old, the Greater Himalayas are 750 - 1250 million years old and the Lesser Himalayas are 1500 -2300 million years old. The ages of these terrains have been well characterized over the decades using a number of different radioactive clocks.

For this study the U-Pb clock contained within zircon crystals was selected. Zircon (zirconium silicate) is a hard mineral which occurs in granites and metamorphic rocks which make up large portions of these terrains. It can survive physical attrition during long transport by streams. It is also chemically quite stable and there is less chance of chemical weathering leaching out U or Pb from the crystal. Another advantage is that there are two clocks inside zircon. One through the decay of U-235 to lead-207 and another through the decay of U-238 to lead-206. So there is an inbuilt crosscheck on your results.

Why not just use the types of minerals to fingerprint the source rocks? That method does work is certain contexts but geological terrains of different ages can contain similar suite of minerals making discrimination based on a unique signal difficult.

Below is a map of the study area.

Source: Clift et.al. 2012

Black dots represent trenches. Stars represent drill sites and white squares represent samples from modern rivers. Dotted lines are proposed courses of ancient Yamuna and Sutlej. U-Pb dates were calculated from zircons sampled from the Indus, Ghaggar,  Beas, Sutlej and the Yamuna. The idea is that the headwaters of each of these rivers would be eroding sediment predominantly from different geological  terrains and therefore if enough zircon crystals were analyzed it would be possible to identify a geological age signal that is unique to each river. For that though large number of crystals need to be dated for a statistically robust result.

For this study more than hundred grains per sample were analyzed using a scary sounding instrument- the Laser Ablation Inductively Coupled Plasma Mass Spectrometer.  It was found that individual rivers do cluster at different ages i.e. they contain a population of grains within a distinct age range and could be discriminated from each other. For example the Beas showed a major population of zircon grains of age 300 -750 million years ago implying that its headwaters drained mostly the Tethyan Himalayas. Similarly the  the Yamuna sample contained a major population which clustered around 1875 million years. The Sutlej has two populations clusters, one at 750 -1000 million years ago and another at around 1830 million years or so.

The next step was to find out whether ancient sediments from dried up channels associated with the Ghaggar river contained zircon populations with age clusters that could be matched to modern rivers. If they did, then that would mean that that particular river was flowing in that channel in the past. And carbon-14  or Optical Stimulated Luminesence (OSL) dating of the sediment could tell when. So there are two kinds of dating techniques used here. The U-Pb technique dates the geological age of the rocks in the Himalayan headwaters of the rivers. The carbon-14 and OSL techniques date the timing of deposition of sediments in the various channels.

Channel and overbank sediments close to Harappan archaeological sites along the northern edge of the Thar desert were sampled. The sediments were dated using a combination of 14C which dates organic matter and OSL, a technique that is used to calculate the time since the sediment was last exposed to sunlight.

Analysis showed that ancient sediments did contain populations of zircons of distinct age ranges that could be matched to the Yamuna, Sutlej and the Beas implying that these rivers were flowing through these channels sometime in the past. Constrained by carbon-14 and OSL dates of the sediment, the patterns indicate that the Yamuna signal was lost around fifty thousand years ago implying a change of course of the Yamuna eastwards towards the Ganga at that time. The Beas and Sutlej signal was lost prior to ten thousand years ago, these two rivers migrating north-northwestwards and joining the Indus.

All this sampling is in Cholistan, the portion of the Ghaggar/Hakra in Pakistan. Some studies has mentioned ancient channels interpreted as the Sutlej joining the Ghaggar in Haryana in India, upstream of these sites. These channels were not sampled in this study. However, the site at Fort Abbas samples the main Ghaggar channel. Any signal of the Yamuna or Sutlej  joining upstream would have shown up here. The results indicate no signal from these rivers in the oldest sediments which are five thousand seven hundred years old or so.

If possible, these analysis could be extended in the future to sample more extensively the dried up large channels upstream in India too for a more expansive analysis. Over the last year some more studies (preliminary results presented at last year's AGU meeting) have shown an earlier episode of the Ghaggar drying up in the latest Pleistocene that coincides with a regional climate shift towards drier conditions. Did tectonically driven avulsion coincide with this climate change?

On the other hand, a paper in the GSA Bulletin by Sinha et. al. 2009. suggest a younger Yamuna, meaning that the Yamuna has been flowing in its present course for only the last 2-3 thousand years and may have been flowing westwards towards the Ghaggar before that. This study was based on detrital grains provenance studies and OSL dating of the Yamuna and Chambal sediments. I found the provenance analysis itself to be sound but the young Yamuna interpretation questionable, due to lack of sampling upstream of the cratonic rivers confluence and just one OSL date from the present day Yamuna channel.

So,  there are still answers to be found regarding the interplay of tectonics, climate and the Pleistocene and Holocene geography of these rivers.

Having said that, this is one of the more convincing studies of Ghaggar sediment and water provenance that I have come across so far.  Many earlier studies have suggested a much later river avulsion scenario wherein the Yamuna and the Sutlej change course as late as 2000 B.C. My impression was that these studies lacked the kind of hard evidence needed to pinpoint the dates of the deposition and the origin of the sediments. They relied mainly on the size of the channels without demonstrating physical continuity with the large glacial rivers,  or the presence of certain metamorphic grains and pebbles. Both these parameters are open to multiple interpretations and are not convincing of a high Himalayan source by themselves.

This study by Clift and colleagues along with some earlier isotope dating and provenance work on Indus and Ghaggar sediments by some of the authors and independent work on oxygen isotopes of ancient Ghaggar /Hakra channel water are strong results in favor of the Yamuna and Sutlej leaving the Ghaggar river thousands of years before the beginnings of the Harappan civilization.

The results also imply that these two rivers most likely stopped flowing into the Ghaggar thousands of years before the presence of Aryans in this region.

This is a touchy topic and it deals with whether the Aryans migrated into northwest India from central Asia around 1500 B.C. or so, bringing with them cultural habits and religious ideas that evolved into the Vedic Culture, or whether the Aryans were indigenous to this part since times immemorial. The Ghaggar has been equated with the river Sarasvati mentioned in the Rig-Veda by supporters of the indigenous Aryan theory.

It is described as a mighty river flowing from the high Himalayas. This in turn has been interpreted to mean that the Sarasvati would have been flowing out of glaciers for it to be mighty, and therefore the Aryans must have been present in northwest India before 2500 - 3000 B.C., because there is evidence that since then the Ghaggar became a smaller river.  This argument is then taken further to claim that the Aryans built the Harappan civilization. In this scenario the glacial rivers change course only after 2500 - 2000 B.C or so and the resulting water crisis forces the "Vedic" Harappans to disperse eastwards towards the Gangetic basin.

I have stressed that this attempt to link a hypothesis of a mighty Sarasvati to the presence of Aryans is misguided and one that has caused harm to the public understanding of the topic and to what constitutes good science. Many geologists and archaeologists accepted the validity of a glacial Sarasvati without critically weighing the evidence. Taking their cue, in web forums and books, supporters of a glacial Sarasvati have popularized the hypothesis of a late river avulsion and often presented it as irrefutable evidence favoring the indigenous Aryan theory.

I have commented on this earlier in Pragati and on my blog (here and here ) and suggested that evidence at that time did not support a late avulsion and further that this issue of the timing of Aryan presence in this region doesn't really depend on  glacial rivers flowing into the Ghaggar. Rivers can be mythologized and worshiped whether they are big or small. The Aryans could just as well have considered holy a Siwalik fed river and exaggerated its size in their hymns.

Linguistics, cultural evidence, archaeology and perhaps in the future higher resolution genetic data are better placed to answer the question of Aryan origins. Unfortunately, during this saga of the search for the glacial Sarasvati some very questionable geological scenarios have been put forth as being definitive. Perhaps the time has come for supporters of that theory to at the very least start being more cautious when promoting the late river avulsion theory.

Meanwhile, whether there were glacial rivers connecting the Ghaggar during Harappan times is not just an interesting geological question but has implications in understanding  Harappan water use and agriculture patterns. Head over to Dorian Fuller's (one of the authors of this study) blog The Archaeobotanist for some comments.

Clift, P., Carter, A., Giosan, L., Durcan, J., Duller, G., Macklin, M., Alizai, A., Tabrez, A., Danish, M., VanLaningham, S., & Fuller, D. (2012). U-Pb zircon dating evidence for a Pleistocene Sarasvati River and capture of the Yamuna River Geology DOI: 10.1130/G32840.1

Also see additional posts on this topic - 1) New Geomorphological Work on Ghaggar
2) K.S. Valdiya on the glacial Saraswati in Current Science

 

Geological Update On River Ghaggar / Saraswati

The river Ghaggar which flows through the Indian states of Haryana, Punjab and Rajasthan and onwards into Pakistan had dried up in the latest Pleistocene. Therefore it may not have been the main water source for the later mid-Holocene Harappan settlements in that region and also likely was not the river Saraswati described in Rig-Ved.

That's the gist from three separate studies  (pages 23, 24, 103) on the Ghaggar river basin presented at a meeting of the American Geophysical Union and summarized in Science.

The finding that the river Ghaggar likely dried up or had a drastically reduced flow in the latest Pleistocene is not that surprising from the perspective of the broader climatic regime existing from Late Pleistocene to Holocene. However, it is a surprising finding if you consider another theory of Ghaggar water flow - the glacially fed Ghaggar -  which I will come to later.

First, the climate change perspective.

After the Last Glacial Maximum, monsoonal strength over the Indian subcontinent has fluctuated over a millennial scale resulting in dry and wet phases lasting a few thousand years each.

A late Pleistocene arid phase affecting north west India is well documented by various studies on sediments and landscapes in Rajasthan, Gujarat and western Maharashtra. See this paper by Mishra and Rajguru and references therein. The studies by Gupta et al and Maemoku et al which suggest that between 15,000 years and 10,000 years ago the Ghaggar basin shows signs of drying up, likely reflect this phase of aridity.

This late Pleistocene arid phase was followed by an early Holocene wet phase reflecting a stronger Indian monsoon. Then by mid Holocene another episode of aridity set in which coincided with the ultimate demise of the Harappan civilization.

I don't want to comment here on the implications of these studies regarding water dependency of the Harappan civilization or the Vedic Saraswati problem.

Instead I want to point out that these new geological findings by Gupta et al and Maemoku et al do hint at an answer to another interesting geological question.. whether the Ghaggar was a glacially fed river in the past.

It has been hypothesized that the Sutlej and the Yamuna, both glacially fed rivers, flowed into the Ghaggar during the Holocene and by late Holocene around 2500 B.C to 1800 B.C avulsed or shifted course to their present positions. So along with climate change, rivers changing courses is another explanation given for the reduced water flow of the Ghaggar by late Holocene.

I think the time frame over which this problem has been thought out has a bearing on the choice between the climate change and river avulsion theories. If you only consider the Holocene and one episode of a river drying up (a larger Ghaggar drying up by 1800 B.C) then a Late Holocene river avulsion event  seems as plausible an explanation as a climate change one.

But if more studies confirm Gupta's and Moemuko's finding that the Ghaggar had indeed dried up in the late Pleistocene then that would weaken the theory that the Yamuna and Sutlej flowed into the Ghaggar until the late Holocene.

A glacially fed Ghaggar would likely not have dried up even during the late Pleistocene arid phase. Summer melting of the large Himalayan glaciers built up through the Last Glacial Maximum would have maintained enough water flow in the Ghaggar throughout the year.

The simplest explanation of these alternating phases of river drying and rejuvenation through the late Pleistocene into the Holocene is that the Sutlej and the Yamuna never flowed into the Ghaggar. The Ghaggar was not glacially fed, but by streams originating in the lower and sub Himalayas, and its fortunes always depended on the strength of the Indian monsoons.

One scenario of rivers shifting courses that does fit this extended late Pleistocene-Holocene time frame depends on the Sutlej and / or the Yamuna getting diverted away from the Ghaggar much earlier, around 14,000 years ago or so. The drying of the Ghaggar brought out by these two studies then reflect a combination of river avulsion and climate change.

Either way, these new findings make it cumbersome to support the theory of a glacially fed Ghaggar river.

Tip: Varnam

[Update 2012): New geochemical and geomorphological studies strongly suggest that Yamuna and Sutlej stopped flowing in to the Ghaggar /Saraswati thousands of years before the Harappan civilization. See these posts for more on this topic - 


1) New Geochemical and Sedimentological Work On Ghaggar
2) New Geomorphological Work on Ghaggar
3) K.S. Valdiya on the glacial Saraswati in Current Science