Radiogenic Osmium in Ganga river sediments of India.

Ganga river Sediments are the major source of radiogenic Osmium.
by
Dr. Nitish Priyadarshi

The Ganga sediments are characterized by high Re/Os (rhenium-osmium) ratios and are extremely radiogenic as evident from their 187 Os/ 188 Os isotopic ratios. Samples from the tributaries Alaknanda, Bhagirathi, Gandak and Ghaghra show pronounced 187 Os/ 188 Os. High Os concentrations combined with sediments flux makes the Ganga an important source for soluble Os isotopic evolution in oceans.

Interest in rhenium-osmium systematics in rivers has risen sharply in recent years due to the revelation of changes associated with sea water Os isotopic compositions during the past 70 Ma. Radiogenic 187 Os is produced from the β- decay of 187 Re. Osmium isotopic composition in sea water is derived from the weathering of basaltic and peridotitic oceanic crust, hydrothermal solutions, additions from cosmic dust and continental weathering products.

Os isotopes in the oceans convey the then prevalent continental weathering processes. The Osmium isotopic composition of the present day sea water is markedly higher since the past 70 Ma. This enhancement in radiogenic Os in sea water is largely attributed to the Himalayan tectonics with its accompanying increased silicate weathering and in particular, chemical weathering of the extremely radiogenic black shales in the lesser Himalayan region.

Marine black shales have been proposed as a source of very radiogenic Os because of their large enrichments in Re and because they can even at trace amounts weather very fast due to oxidative processes. If true, this then has the possibility of tracking exposure and weathering of organic carbon in the form of black shales in the past, e.g. uplift of the Himalayas or the Andes.

According to the article published in Geochim. Cosmochim. Acta in year 1999, Indus and Brahmaputra are less radiogenic than the Ganges, presumably due to the erosion of ophiolitic assemblages exposed along the Indus-Tsangpo suture zone.

The tributaries in the upstream, Alaknanada and Bhagirathi flow through predominantly silicates (shales, phyllites, quartzites, crystalines) and show high Re/ Os ratios of 24.9 and 19.8 respectively. Re is preferentially incorporated into the silicate minerals relative to Os.

Rivers draining the Canadian Shield have radiogenic values at low concentrations (24 to 35 fmol/kg). They are more radiogenic than the Zaire draining the Congo shield (1.4) or the Tapajos draining the Amazon shield (1.33) in the tropics.

Recently osmium concentrations and isotopic compositions in groundwater samples from the Bengal plain have been reported. Groundwaters have Os concentrations (16.9–191.5 pg/kg), about 5–10 times higher than those published for most rivers or seawater. 187Os/188Os varies widely (from 0.96 to 2.79) and is related to the isotopic signatures of the sediments constituting local aquifers.

Table-1 Osmium in Ganga River and its tributaries (in ppt).

Bhagirathi- 32.8
Alaknanda- 21.1
Yamuna- 64.3
Chambal-33.8
Gandak-55.7
Ganga- 37.7 to 51.7

Reference:

Chakrapani, G.J. et.al 2002. Osmium isotopic compositions in Ganga river sediments. Current science, Vol.83, no. 10.

High levels of black carbon likely to impact Tibetan Plateau's temperature.

The Dark Side of Black Carbon

by

Dr. Nitish Priyadarshi

Image Credit: NASA

As interest in Earth's changing climate heats up, a tiny dark particle is stepping into the limelight: black carbon. Commonly known as soot, black carbon enters the air when fossil fuels and biofuels, such as coal, wood, and diesel are burned. Black carbon is found worldwide, but its presence and impact are particularly strong in Asia. Black carbon, a short-lived particle, is in perpetual motion across the globe. The Tibetan Plateau's high levels of black carbon likely impact the region's temperature, clouds and monsoon season.

Black soot deposited on Tibetan glaciers has contributed significantly to the retreat of the world's largest non-polar ice masses, according to new research by scientists from NASA and the Chinese Academy of Sciences. Soot absorbs incoming solar radiation and can speed glacial melting when deposited on snow in sufficient quantities.
Temperatures on the Tibetan Plateau -- sometimes called Earth's "third pole" -- have warmed by 0.3°C (0.5°F) per decade over the past 30 years, about twice the rate of observed global temperature increases. New field research and ongoing quantitative modeling suggests that soot's warming influence on Tibetan glaciers could rival that of greenhouse gases.

Since melt water from Tibetan glaciers replenishes many of Asia's major rivers -- including the Indus, Ganges, Yellow, and Brahmaputra -- such losses could have a profound impact on the billion people who rely on the rivers for fresh water. Areas going to most affected in India would be Uttrakhand, Uttar Pradesh, Bihar, Jharkhand, West Bengal and Assam. While rain and snow would still help replenish Asian rivers in the absence of glaciers, the change could hamper efforts to manage seasonal water resources by altering when fresh water supplies are available in areas already prone to water shortages.
Researchers led by Baiqing Xu of the Chinese Academy drilled and analyzed five ice cores from various locations across the Tibetan Plateau, looking for black carbon (a key component of soot) as well as organic carbon. The cores support the hypothesis that black soot amounts in the Himalayan glaciers correlate with black carbon emissions in Europe and South Asia.
Black carbon or BC is formed through the incomplete combustion of fossil fuel, biofuel, and biomass, and is emitted in both anthropogenic and naturally occurring soot. Black carbon warms the planet by absorbing heat in the atmosphere and by reducing albedo, the ability to reflect sunlight, when deposited on snow and ice. Black carbon stays in the atmosphere for only several days to weeks, whereas CO2 has an atmospheric lifetime of more than 100 years. The term black carbon is also used in soil sciences and geology, referring either to deposited atmospheric BC or to directly incorporated BC from vegetation fires. Especially for the tropics, BC in soils significantly contributes to fertility as it is able to adsorb important plant nutrients .

Black carbon is a potent climate forcing agent, estimated to be the second largest contributor to global warming after carbon dioxide (CO2). Because black carbon remains in the atmosphere only for a few weeks, reducing black carbon emissions may be the fastest means of slowing climate change in the near-term.

Black carbon emissions from northern Eurasia, North America, and Asia have the greatest absolute impact on Arctic warming.

In some regions, such as the Himalayas, the impact of black carbon on melting snowpack and glaciers may be equal to that of CO2.Warmer air resulting from the presence of black carbon in South and East Asia over the Himalayas contributes to a warming of approximately 0.6°C. An “analysis of temperature trends on the Tibetan side of the Himalayas reveals warming in excess of 1°C.

Black carbon sources vary by region. For example, the majority of soot emissions in South Asia are due to biofuel cooking, whereas in East Asia, coal combustion for residential and industrial uses plays a larger role.

Black carbon can be controlled in developing countries through the implementation of cleaner fuels, new cooking technologies, and changing crop management practices.

Reference:

http://www.sciencedaily.com/releases/2009/12/091214173658.htm
http://fixtheclimate.com/component-1/the-solutions-new-research/black-carbon/
http://www.nasa.gov/multimedia/imagegallery/image_feature_1546.html
http://en.wikipedia.org/wiki/Black_carbon

Sedimentation by Himalayan Rivers may cause Earthquakes and Land subsidence in Eastern India.

It's not a question of whether the big one is coming, only of when.
by.

Dr. Nitish Priyadarshi

Image of the Ganges River delta and the Bay of Bengal acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS). This image shows the massive amount of sediments delivered to the Bay of Bengal by the Ganges River, sediments that are derived from erosion of the Himalayan mountain range to the north.

Sediments deposited in Bay of Bengal

Sediment loads in Kosi River in Bihar.

The Indian landmass, a floating continent started to collide with the Asian landmass some 20 million years ago (m y). After its separation from South Africa and Madagascar the floating continent must have been like a Noah’s Arc carrying all its fauna and flora on its body. The great collision between the two landmasses led to the formation of the youngest and tallest mountain ranges, the Himalayas.

Once the Himalayas started to rise a southward drainage developed. The Himalayas subsequently controlled the climate of the newly formed continent, and there started the season of monsoon as well. The river system thus developed because of rains and melting snow started to drain south into the fore-deep. The newly formed rivers were like sheets of water flowing towards the fore-deep carrying whatever came in their way. Once the rivers reached the plains their gradients became lesser, their hydraulics changed and they started to dump their load. During monsoons these rivers carried a sediment load which was many times more than their normal load. All the material they carried was dumped enroute their final destination, the Sea.

The sediments are carried from their point of origin to the local stream network commonly by mass weathering processes, typically soil creep, and eventually become part of the stream load. Very fine fragments move quickly along the network as suspended load, but the downstream progress of larger fragments is usually very slow. Thus, the weathering process does not end in the source area but continues to operate during the long process of stream transport.

Sedimentation rates generally cannot be expressed in absolute data because periods of rapid sedimentation alternate with periods of slower deposition, non-sedimentation, or erosion. Nevertheless, it is important to gain some understanding of the average values of net sedimentation in various depositional environments in order to better comprehend the geological and chemical processes that take place on the surface of the earth. An understanding of net sedimentation rates has become increasingly valuable with onset of intensive water pollution studies, because sedimentation is one of the most important processes in the removal of pollutants from natural waters.

Presently sedimentation loads are being considered as one of the possible cause of earthquakes. It works on the theory that deposition of sediments alters the loading of the earth’s crust and tectonic stresses in its interior. Such stresses could reactivate preexisting faults.
Combination of the biological, chemical, geological, and geographical factors that influence sedimentation rates are almost infinite, are different for each depositional environment, and have continuously fluctuated throughout the past.
The most extensive vertical deposition of sediments by Himalayan rivers flowing through Uttar Pradesh, Bihar, Jharkhand, and Bengal States of India, occurs during floods (July to October).

Coleman (1969) investigated channel deposition and erosion patterns of the braided Brahmaputra River in India during flooding and found that as the current velocity decreased, rapid sedimentation occurred, and as much as 3 m. of sediment was deposited along the channel bottom. When a meandering river floods its banks, its velocity is rapidly checked, and sediment deposition occurs adjacent to the banks. The rate of floodplain deposition usually ranges from several mm to several cm/year (Kukal, 1971).
Each year these rivers were flooded leaving behind a fresh layer of sediments. The Indo-Gangetic plains are a product of such floods. Study carried out by Rajiv Sinha, of Geoscience group, IIT Kanpur has brought to light amazing quantity of sediment load carried by the Ganga River in its present hydrodynamic regime. Gangetic Rivers erode bulk of the sediments from upstream areas in the Himalayas and deposit part of it in the alluvial plains and a significant part in the Bay of Bengal. His study reveals that the Ganga river annually erodes around 749 million tonnes of sediments, mostly from the Himalayas, brings about 729 million tonnes at Farrakka and finally dumps 95 million tonnes in the Bay of Bengal. Thus the floodplain of the Ganga gets an annual increment of about 65 million tonnes of sediments.

The quantity of sediments eroded by the river depends upon the gradient, distance from the source area and also the geology and geomorphology of the terrain. Thus Ganga at Haridwar and Yamuna at Allahabad are characterized by low sediment yield of 150-350t/km2/yr, while the eastern tributaries like Kosi and Gandaki carry a much higher sediment load of 1500-2000t/km2/year.

Along the river's traverse, large tributaries enter the Ganga and significantly increase its flow and change its character. The Ganga is joined by the Ram Ganga, Yamuna, Ghaghara, Gomti, Gandak and Kosi tributaries. The rivers of the Ganga basin carry one of the largest sediment loads in the world. Today sediment loads in the Ganga are higher than in the past due to the complete deforestation of the Gangetic plains and the ongoing deforestation of the Himalayan foothills.

Sedimentation in plains of Ganga River and Bay of Bengal.

In the plains Kosi (major tributary of Ganga) River is building up a large delta of its own through which its channels have wandered for centuries. It is believed that the Kosi originally joined the Mahananda, a river coming from the Darjeeling Himalayas. It is known that the Kosi flowed by Purnea (Bihar) 200 years ago, but its present course is about 160 km to the west of that place, having swept over an area of 10,500 sq. km on which it has deposited huge quantities of sand and silt (Krishnan, 1982). It now joins the Ganga 32 km west of Manihari but formerly it used to join that river near Manihari itself. The Kosi is notorious for its frequent and disastrous floods and the vagaries of its channels. In high flood it is said to have a flow of nearly one million cusecs loaded with much gravel, sand and silt (Krishnan, 1982).

The Hooghly River (main channel of the Ganga in West Bengal) estuary is notorious for its sand banks and dangerous shoals of which the James and Mary Sands, 56 km below Calcutta (now Kolkata) and between the mouths of the Damodar and Rupnarain, are well known. New areas are being reclaimed by the sediments brought down by the Ganga. These are known as the Sundarbans.

Compared to the Peninsular rivers, the three main Himalayan river systems are mighty giants. The Indus carries to the sea an average of about a million tons of silt per day, the Ganges a little less and the Brahmaputra a little more (Krishnan, 1982). The Irrawaddy has been estimated to transport about two-third million tons of silt per day. The Himalayan rivers are fed both by rain and snow, by rain during June to September and by snow during the warmer half of the year. In their courses through the mountains they have good gradients and carry much coarse materials including pebbles and boulders, brought in by glaciers and also torn off from the beds and banks. They carry enormous quantities of fine sand and silt derived from the Himalayas as well as from higher peninsular up-lands.

The Ganga and the Brahmaputra have changed their courses in the plains frequently in historic and pre-historic times leaving behind huge sediments in the plains. Deposition of sediments in Bihar, Bengal, and in Bay of Bengal is going on from the geological past. Millions of tons of sediments are being deposited per day by the Himalayan rivers in the Eastern India thrusting pressure over the crust below.

Now it is widely accepted that huge sediment loads may cause mild to high tremors even in the non-seismic zone. This may be due to the great lateral thrust of sediment load contributing to stress imbalances or due to the reactivation of subterranean faults by the newly developed stresses or due to increased pore pressure in the adjoining rocks which lowers their shearing strength, resulting in earthquake occurrence.

An earthquake is generally caused by dislocation in the earth’s crust along pre-existing cracks or faults. The cause of earthquakes is probably the existence of such faults or cracks in the bottom of the depression hidden under alluvium. Moreover, there are well marked reversed faults at the junction of the outer and the inner Himalayas, and when dislocation occurs along these faults, earthquakes result.

An additional factor favoring dislocation along such surface or subterranean faults is the strain which exists between the Himalayas and the Bihar plains. This strain is due to the following facts. The section of the Himalaya north of the Bihar is the highest mountain region of the world. The higher a region, the more it is subjected to erosion. So, vast amount of sediments are being eroded from the Himalayas and carried down to the Bihar plains as in the case of Kosi river which contributes heavy sediment in Bihar plains. The silt yield of the Kosi is about 10 cubic yard /acre/yr, one of the highest in the world. As the mountains are eroded they are deloaded and have a tendency to rise. On the other hand, the plains get loaded by the sediments and have a tendency to subside. These opposed tendencies of movements between the Himalayas and the Bihar plains cause strain in the hinge-zone, i.e. in the southern part of the mountains. Here fault already exists. Dislocation may occur along these faults as a result of the strain and devastating earthquakes may result.

The entire area has undergone downwarping due to Himalayan upheaval resulting in the formation of transverse faults and dislocations in the basement rocks, along pre-existing faults or cracks aided with occasional earthquakes. The foothills of the Himalayas, the Indo-Gangetic plains and the sedimentary basins of Vindhyans are all quake-prone areas of the Bihar state.

Several faults have been identified in the region and some have shown evidence of movement during the Holocene epoch. The West Patna Fault runs in a NE-SW direction from near Arrah in the south to the Nepalese border near Madhubani in the north. Running almost parallel to it is the East Patna Fault which extends from the south-east of Patna in the south to the Nepalese border to the east of Madhubani. Another fault, this one also lying parallel to the previous two, is the Munger-Saharsa Ridge Fault which runs from Biharsharif to near Morang in eastern Nepal. Apart from these there are east-west running tear faults in the region that control the courses of the main rivers.
The Gandak fan is bounded by the courses of the Ghagra and Rapti in the west, the Ganga in the south and the Rohini in the north. The courses of all these streams are along faults (Mohindra and Prakash, 1994).

The Gangetic plains, of which the Kosi megafan forms a part, is bound by E-W faults, which on analogy with the main boundary thrust may be thrust faults. The Kosi megafan is bound on the west by a NE trending prominent sinistral fault causing an offset of some 20 km of the Siwaliks juxtaposed against the Gangetic alluvium. There are several NW trending faults on the eastern fringes of the Kosi megafan (Mahadevan, 2002).

Bengal basin, having an area of 89000 square kilometers and sedimentary fill of 10-15 km, is the northernmost of the east coast basins of India . Indian Shield and Shillong massif form the western and northern limits of Bengal Basin. Eastwards the Basin extends into Bangladesh and is bounded by Arakan Yoma geanticlinal uplift. Southwards Basin plunges into Bay of Bengal beneath the continental shelf. Tectonically the basin can be divided into four structural elements i.e. basin margin fault zone, shelf, hinge zone/slope break and basin deep.

The tectonic history of Bengal Basin indicates that the drainage pattern in the Bengal basin as a whole had been and is greatly controlled by the tectonic features of the basin. Considerable evidence has been recorded of significant tectonic movements within and along the boundary of the basin in late Tertiary and the Quaternary times. Auden (1949) postulated that the western margin of the Bengal basin is faulted and the major tectonic movements have taken place along this zone in the Pleistocene.

Rocks at the depth in crust are subjected to the load pressure of the overlying column of rocks and sediments. This pressure is related to the thickness and mean density of the overlying material or sediments. Several million years under stress, most rocks will exhibit the kind of ductile behaviour familiar to all geologists. The rocks under higher stresses, however, will fracture and generate earthquakes (Park, 1983).

The San Francisco earthquake of 1906 was a major earthquake that struck San Francisco, CA and the coast of Northern California at 5:12 A.M. on Wednesday, April 18, 1906. The 1906 San Francisco earthquake was caused by a rupture on the San Andreas Fault, a continental transform fault that forms part of the boundary between the Pacific Plate and the North American Plate. This fault runs the length of California from the Salton Sea in the south to Cape Mendocino to the north, a distance of about 800 miles (1,300 km). The earthquake ruptured the northern third of the fault for a distance of 296 miles (477 km). The maximum observed surface displacement was about 20 feet (6 m); however, geodetic measurements show displacements of up to 28 feet (8.5 m).
It was interpreted that earthquake was caused due to large seasonal sediment loads in coastal bays that overlie faults as a result of the erosion.

Sedimentation also cause land subsidence. Subsidence may result from the accumulation of large volumes of sediment at the earth's surface in what is known as a sediment basin. An obvious setting in which this occurs is at river deltas. Each day, the Mississippi River deposits up to 1.8 million metric tons of sediment at its mouth near New Orleans. The weight of this sediment contributes to a gradual subsidence of the land on which New Orleans resides. Basins between mountains also can subside due to the weight of accumulating sediments.

Wherever sediments accumulate, we can be certain that in some other locality, a source has been relatively elevated with respect to the place where the strata are being deposited.

A delta is a subsidence-prone area because it receives a huge volume of sediments, which can be compressed due to post depositional consolidation, and the load of which can result in detectable isostatic sinking of the earth's crust.

In the year 2008 lots of reports were there regarding development of big cracks on the surface overnight in many parts of Uttar Pradesh state of India. This may be the side effects of land subsidence.

Two prehistoric seismic events dated to have occurred: (i) during 1700 to 5300 years BP and (ii) earlier than 25,000 years BP. From last several years Ganga Basin has not been affected with any major tremors or earthquakes, except of 1833, 1934 and 1988 earthquakes which rocked North Bihar and Nepal. Seeing the load of sediments, possibilities of major earthquakes cannot be ruled out in Eastern India including Bihar, neighbouring Uttar Pradesh and Jharkhand, and Bengal Basin. Most affected areas may be Munger, Dharbanga, Purnia, Bhagalpur, Saharsa, Supaul, Katihar, Patna in Bihar State, Sahibganj, Godda, Pakur etc. of Jharkhand State. It's not a question of whether the big one is coming, only of when.

Reference:

Auden, J.B., 1949. Proc. Ind. Nat. Instt. Sciences.,15.

Coleman, J. M., 1969. Brahmaptura River: Channel processes and sedimentation. Sed. Geol.,3, pp. 129-239.

Dasgupta, S., Pande, P., Ganguly, D., Iqbal, Z, Sanyal, K, Venkatraman, N.V., Dasgupta, S., Sural, B., Harendranath, L., Mazumdar, K., Sanyal, S., Roy, K., Das, L.K., Misra, P.S., Gupta, H. 2000. "Seismotectonic Atlas of India and its Environs", Geological Survey of India.


Krishnan, M.S. 1982. Geology of India and Burma. CBS publishers and distributors, India.

Kukal, Z., 1971. Geology of Recent Sediments. New York: Academic Press (in Czechoslavakia: Prague, Czechoslovak Academy Sci.), 490p.

Mahadevan, T. M. 2002. Geology of Bihar and Jharkhand. Geological society of India, Bangalore.

Mathur, S.M., "Physical Geology of India", National Book Trust of India, 1998.


Mohindra, R. and Prakash, B. 1994. Geomorphology and neotectonic activity of the Gandak mega-fan and adjoining areas, middle Gengetic Plains. Jour. Geol. Soc. India, v.43, pp. 149-157.

Park, R.G., 1983. Foundations of Structural geology. Blackie & Son Ltd. Glasgow.

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Glacier melting in Himalayas may bring devastating floods in north Bihar plains of India.

Bihar have recorded the highest number of floods during the last 30 years.

by

Dr. Nitish Priyadarshi

Retreating Glaciers Bhutan Himalaya. They are very beautiful and has a clear sign of slowly melting due to global warming. Easily visible are the ends of most of these glacial valleys’ surfaces turning to water to form lakes, a trend which has been noticed only in the last few decades.

Receding of Gangotri Glacier. Source : NASA Earth Observatory

The melting snow is causing floods in the plains of north Bihar state of India.. But higher temperature is also causing more rain and snowfall in the glacial resources. The flood in coming years will be severe because the glaciers are melting and at the same time the rainfall has increased many folds.

Flood hazard has long been recognized as one of the most recurring , wide spread and disastrous natural hazards in the densely populated regions of South Asia. In many parts of the Indian subcontinent, flooding reaches catastrophic proportions during the summer monsoon season. For centuries, monsoon floods in the Ganga and the Brahmaputra Basins have brought countless disasters to the inhabitants who have historically occupied the banks of these rivers. Some scientists have attributed the demise of the Harappan (Indus) civilization to a series of large floods on the Indus River. Catastrophes of out standing proportions have occurred in the past and there appears to be no end to the multicentury-old scourge of floods and associated problems.

The interface between humans and hydrologic features across earth’s surface has helped shape human culture. From the earliest agricultural, complex societies established along some of the great rivers of the world to the bustling seaports of today, humans have gained from the myriad advantages of living in proximity to water. Fertile soil, ease of transportation, and availability of resources (both materials and energy) have allowed for the development of complex material and intellectual cultures. The relationship between water and humans also brings a great deal of risk. Flooding is one of these risks. The impact of floods on humans has been evident from ‘Genesis’ to tonight’s evening news.

Definition of floods:
Streams are linear water features that flow under the impetus of gravity. The amount of water contained in a stream is usually regulated by contributions of groundwater and surface runoff to the stream channel (Knighton,1998). Much of the time water in a stream flows within the confines of its channel. When inputs of water increase sufficiently, stream discharge leaves the stream channel and covers all or part of the adjacent flood plain (Jennings and Gruntfest, 2003). Since the flood plain surface is usually a virtually flat surface and near the elevation of the stream channel, water can easily spread over the flood plain once water exceeds the elevation of the stream’s banks.
Flooding is created by the delivery of larger than normal amounts of runoff into stream channel. Periods of above-average precipitation lead to floods.

In India floods are the most common feature since the dawn of civilization. At Mohen jo Daro flood control structures existed as early as 2700 to 3000 BC. These structures as well as storm water drainage works there show that heavy rains and consequent floods have been occurring in this country even in those prehistoric times. Floods have been occurring almost regularly each and every year in different parts of the country. In India, generally, floods occur during the southwest monsoon season. Heavy rainfall has been the main cause of floods in India for any river basin including plains of north Bihar which are some of the most susceptible areas in India. A recent review by Kale (1997) indicates that the plains of the north Bihar have recorded the highest number of floods during the last 30 years. The total area affected by floods has also increased during these years.

The Himalayan rivers are fed by the melting snows and glaciers of the great Himalayan range during spring and summer, and also from rains during monsoon. They carry significant flows during the dry weather due to snowmelt and minimum flows during winter.

Frequent overbank spilling of north Bihar Rivers is essentially an interplay of meteorological conditions in the region and hydrological and morphological characteristics of the rivers. The plains of north Bihar are characterized by monsoon rainfall and average annual rainfall ranges between 120 and 200 cm. The foothills above the plains experience even higher rainfall (greater than 200 cm.). Moreover, the distribution of rainfall, both in space and time, is extremely uneven which makes the individual floods unpredictable. Further, the mountain-fed rivers of the plains have mixed contributions from snowmelt runoff and monsoonal rainfall. Even during lean periods (summer), runoff contribution due to snowmelt is quite significant (Sinha and Jain, 1998). The monsoon follows the peak summer months and the cumulative effect of monsoon rainfall and snow melt runoff results in sudden increase in the river discharge with respect to lean discharge of most of the north Bihar rivers (almost 40-50 times). The shallow alluvial channels between the narrow banks and embankments cannot effectively carry this sudden jump in discharge consequently resulting in breaches and spilling of banks.

Recent trends are showing that Himalayan glaciers are melting due to impact of global warming. These melting may increase the flow intensity of river water followed by heavy precipitation, flowing through north Bihar plains. Major threat is from Ganga, Kosi and Gandak which are “mountain fed” rivers and are characterized by large catchment areas. Kosi and Gandak should be given more importance as they directly flow into north Bihar plains from the mountain.

The Himalayas have the largest concentrations of glaciers outside the polar region. They feed numerous mountain lakes in Nepal and Bhutan as well as seven Asian rivers: the Ganges, Indus, Brahmaputra, Mekong, Thanlwin, Yangtze, and Yellow Rivers. Tributaries of the Kosi River encircle Mt Everest from all sides and are fed by the world's highest glaciers. The Gandak river basin is reported to contain 1025 glaciers and 338 lakes. These contribute substantially to the lean season flows of the river. The short-term result of glacial melting in the Himalayas has been flooding and landslides, which claim approximately 400 lives each year in Nepal. However, scientists fear that in future decades the water level in these rivers could decline sharply, leading to severe water shortages and threatening an agricultural region that feeds over one billion people.

As the climate warms, Himalayan glaciers are melting more rapidly with each passing year, and that means first floods and then droughts for people of north Bihar in India.

The WWF issued a new report documenting the rate of retreat of Himalayan glaciers. It shows that the world's highest glaciers are receding at an average rate of 10 to 15 meters (33 to 49 feet) per year, a rate that is accelerating as global warming increases.

In India, the Gangotri glacier, which supports one of India’s largest river basins, is receding at an average rate of 23 meters per year.

The melting snow is causing floods in the plains. But higher temperature is also causing more rain and snowfall in the glacial resources. The flood in coming years will be severe because the glaciers are melting and at the same time the rainfall has increased many folds.

A recent study by the Indian Space Research Organization, using satellite imaging to gauge the changes to 466 glaciers, has found more than a 20 percent reduction in size between 1962 and 2001, with bigger glaciers breaking into smaller pieces, each one retreating faster than its parent. A separate study found the Parbati glacier, one of the largest in the area, to be retreating by 52 meters a year during the 1990s. Another glacier that Dobhal has tracked, known as Dokriani, lost 20 percent of its size in three decades. Between 1991 and 1995, its snout inched back almost 17 meters each year.

Even the Himalayas have grown measurably warmer. A recent study found that mean air temperature in the northwestern Himalayan range had risen by 2.2 degrees Celsius (4 degrees Fahrenheit) in the last two decades, a rate considerably higher than the rate of increase over the last 100 years.

The loss of these glaciers would have a tremendous impact on the ecosystem of the region. With the retreat of glaciers in the Himalayas, a number of glacial lakes have been created. A growing concern is the potential for Glacial Lake Outburst Floods—researchers estimate 20 glacial lakes in Nepal and 24 in Bhutan pose hazards to human populations.

Indian glaciers are among the least studied in the world, lacking the decades of data that scientists need to deduce trends. Nevertheless, the nascent research offers a snapshot of the consequences of global warming for this country and raises vital questions about how India will respond to them.

Reading list:

Jennings, S., Gruntfest, E. 2003. Floods, from the handbook of weather, climate, and water: Atmospheric chemistry, hydrology, and societal impacts. Wiley.

Kale, V.S. 1997. Flood studies in India: A brief review, Jour. Geol. Soc. India, v.49, pp. 359-370.

Knighton, David, 1998. Fluvial Forms and Processes: A new perspective. Arnold, London.

Sinha, R., Jain, V. 1998. Flood hazards of north Bihar rivers, Indo-Gangetic plains. Ed. Vishwas S. Kale, Flood Studies in India. Geol. Soc. India, Memoir 41, pp. 27-52.

http://www.ens-newswire.com/ens/mar2005/2005-03-15-02.asp
http://www.indiadaily.com/editorial/1903.asp
http://www.nytimes.com/2007/07/16/world/asia/16iht-glacier.4.6680683.html
Sandeep Chamling Rai, Trishna Gurung, et alia. "An Overview of Glaciers, Glacier Retreat and Subsequent Impacts in Nepal, India and China" (pdf). WWF Nepal Program.
http://en.wikipedia.org/wiki/Retreat_of_glaciers_since_1850
http://en.wikipedia.org/wiki/File:Kali-gandaki.jpg
http://www.wayfaring.info/2009/06/10/extraordinary-images-of-earth/