Sunday, August 23, 2009

Are Impact Craters Useful?

ECONOMIC DEPOSITS ARE ASSOCIATED WITH TERRESTRIAL IMPACT STRUCTURES.
BY
Dr. Nitish Priyadarshi
Terrestrial impact craters are important geological and geomorphological objects that are significant not only for scientific research but for industrial and commercial purposes. The structure may contain commercial minerals produced directly by thermodynamic transformation of target rocks (including primary forming ores) controlled by some morphological, structural or lithological factors and exposed in the crater (Masaitis, 1992). Iron and uranium ores, nonferrous metals, diamonds, coals, oil shales, hydrocarbons, mineral waters and other raw materials occur in impact craters.

Terrestrial impact craters are relatively new objects for multi disciplinary investigations. Their discovery and study represents one of the most interesting episodes in the history of geological science.

Economic deposits associated with terrestrial impact structures range from world-class to relatively localized occurrences. The more significant deposits are introduced under the classification : progenetic, syngenetic or epigenetic, with respect to the impact event.
Natural impact craters are the result of the hypervelocity impact of an asteroid or comet with a planetary surface. Impact is an extraordinary geological process involving vast amounts of energy, and extreme strain rates, causing immediate rises in temperature and pressure that produce fracturing, disruption and structural redistribution of target materials. Some economic deposits of natural resources occur within specific impact structures or arc, in someway, impact related. Masaitis (1992) noted approximately 35 known terrestrial impact structures that have some form of potentially economic natural resource deposits.

In a review of the economic potential of terrestrial impact structures, Grieve and Masaitis (1994) reported that there were 17 known impact structures that have produced some form of economic resources.

Impact cratering must be one of the most spectacular displays ever witnessed in the solar system. Although the ancient Indian astronomers, the ancient Vedic texts and the poets who have chronicled the history of India in the great Ramayan and Mahabharata, described heavenly events in the past in lines of great poetic beauty, the subject has not evoked much interest in modern generation of geoscientists. India has a hoary tradition of study of astronomical bodies, but these studies have come to be neglected, considered more as myths deserving no serious attention (Radhakrishna,2008.)

Earth is a part of the solar system and solar gaseous matter in the form of planetesimals floated and orbited in the region between planets. The largest of these planetesimals could be as large as 1000 km in diameter. These planetesimals, although part of the solar nebula, may not all have had similar chemical composition. It is possible some planetesimals formed in special zones of metal enrichment. One possibility of the special concentration of metals to a specific region on earth could be due to impact of such metal–rich asteroids hitting the earth especially during its early history (Radhakrishna, 2008). They had the same composition as the earth’s mantle but with additional attribute of having segregated metals such as iron, nickel, chromium and gold in the form of metal droplets. This is very likely in view of the abnormal conditions of enormous heat and pressure prevailing which permits segregation in asteroids. Such asteroids when they struck the earth gave rise to anomalous concentration of metals at points where they struck. If this view is considered feasible, the importance of the study of impact structures as a possible source of minerals and metals of economic importance will become evident. It is reported that a German Professor, Gerhard Schmidt from the University of Mainz has been investigating surface samples from impact sites for highly siderophile elements rich in elements like gold and PGE (Platinum Group Elements) and concluded that the metals have a Cosmochemical source (Times of India, 24 Sept. 2008, p.19).

The enrichment of heavy metals in the outer crust appears to be the result of extra-terrestrial impact especially in the earlier part of the history of the earth. Impact Structures are not just some special features; they are to be recognized as the result of normal processes operating on the earth and have to be studied in detail with all care to locate them. In the present age where satellite images and aerial photographs on different scales are available, such studies are specially warranted.

According to the currently accepted theory, the starting point of the Universe was the Big Bang which occurred some 12-15 billion years ago. By 4,600 m.y., the released energy had evolved into several galaxies, one of which was the solar system with the Sun at its centre and a group of planets revolving round it. Planet Earth was one such accumulation of planetary solar dust.

Such of the material which did not segregate as planets is believed to have floated in outer space and continued to orbit as planetary debris and is recognized as asteroids and comets. Individual asteroids could be as large as 1000 km in diameter. When forced out of their orbits, they collide with near by planets, the impact carving huge circular hollows. The pock-marked face of the Moon, disfigured by circular basins of various sizes, is evidence of this early history of bombardment which the planets went through. Greenstone belts on Earth were probably the result of bombardment similar to lunar maria. It is reasonable to assume that earth, too, went through a similar process of brutal battering which destroyed the originally formed crust. What we now see appears to be a secondary crust largely made up of material derived from extra-terrestrial sources subjected to further erosion and tectonic change.

The oldest components which we recognize on this secondary (?) crust today are largely igneous, made up of an unusual rock type called Komatiite and its variants, cherts, and graphite schists which, in all likelihood, represent material derived from outer space as remnants of the early phases of bombardment.

We should be thankful for the keen minds of the investigators who first recognized the significance of the circular depressions surrounded by rims that result from meteorite impact. We should remember also that these gifts from space were used by people in the early stage of human evolution. The fragments of iron meteorites, along with impact glasses and tektites, were used for making tools and for ceremonial purposes. In some cases, the impactites ( suevites and tagamites) are used as building materials. The Rathaus and Church of St. George’s in Nördlingen (Ries basin), together with the Rochechouart Castle (Rochechouart astrobleme, France) are magnificent examples of the application of Suevite for wall blocks and architectural detail. In many astroblemes the allogenic breccias, and the blocks of dense rocks in them, are utilized quarrying building stone and road materials. Pure silica which originated from shocked sandstone was mined for glass production in Meteor Crater, Arizona.

Moldavites are tektite glasses that are most probably the produce of ejecta from Ries basin. They are well known as the raw material for the manufacture of fashion decoration. Every women wearing accessories made from moldavites will no doubt give a positive answer to the question, ‘Are impact craters useful?”.

For the present, the assessment of the use of impact craters and their study has two related aspects in terms of their importance to modern society. On one hand, there is the possibility of direct industrial and economic use, while on the other hand, knowledge about the Earth and Space can be developed by using the data obtained during the investigation of impact craters.

Characteristics of natural resource deposits:

The location and origin of economic natural resource deposits in impact structures are controlled by several factors related to the impact processes and the specific nature of the target. The types of deposits are classified according to their time of formation relative to the impact event: progenetic, syngenetic, and epigenetic.

Progenetic economic deposits are those that originated prior to the impact event by purely terrestrial concentration mechanisms. The impact event caused spatial redistribution of these deposits and, in some cases, brought them to surface or near-surface position. From where they can be exploited.

Syngenetic deposits are those that originated during the impact event, or immediately afterwards, as a direst result of impact processes. They owe their to energy deposition from the impact event in the local environment, resulting in phase changes and melting.

Epigenetic deposits result from the formation of an enclosed topographic basin, with restricted sedimentation, or the long term flow of fluids into structural traps formed by the impact structure.

Impact Structures and their economic significance:

Gold in the Witwatersrand Basin, South Africa:
Vredefort crater :The multi-ringed Vredefort crater
Monochrome satellite view of the crater.
The world’s largest and oldest structure in the Vredefort Dome in South Africa at the centre of the Witwatersrand Basin. The structure is 2 million years old and is believed to have been caused by a huge asteroid which struck the Kapvaal craton, forming a crater 300 km in diameter, the largest impact structure so far known. Mineralization is confined to conglomerates and the world’s largest concentration of gold, over 50,000 tonnes extracted to date.
The asteroid that hit Vredefort is one of the largest to ever impact Earth (at least since the Hadean) estimated at over 10 km (6 miles) wide. The crater has a diameter of roughly 250 - 300 km (155 - 186 miles), larger than the 200 km (124 miles) Sudbury Basin, and the 170 km (106 miles) Chicxulub crater. This makes Vredefort the largest known impact structure on Earth (though the Wilkes Land crater in Antarctica, if confirmed to have been the result of an impact event, is even larger at 500 kilometers across). The age is estimated to be over 2 billion years (2,023 ± 4 million years), impacting during the Paleoproterozoic era. It is the second oldest known crater on the Earth, a little less than three hundred million years younger than the Suavjärvi crater in Russia.
It was originally thought that the dome in the center of the crater was formed by a volcanic explosion, but in the mid 1990s evidence revealed that it was the site of a huge bolide impact, with telltale shatter cones often discovered in the bed of the nearby Vaal River.
The Vredefort crater site is one of the few multi-ringed impact craters on Earth, though they are more common elsewhere in the solar system. Perhaps the best example of one is Valhalla crater on Jupiter’s moon Callisto, though Earth's Moon has a number as well. Geological processes, such as erosion and plate tectonics, have destroyed most multi-ring craters on Earth.
Vredefort structure is the eroded remnant of a very large complex impact structure. The Witwatersrand Basin is the world’s largest goldfield, having supplied some 40% of the gold ever mined in the world. Since gold was discovered there in 1886, it has produced 47,000 tonnes of gold. The annual Witwatersrand gold production for 2002 was approximately 350 tonnes, or approximately 13.5 % of the global gold supply, and current reserve estimates are around 20,000 tonnes of gold (Grieve,2005).

Gold in Australia:

Rich pockets of gold close to the surface have been worked at Bendigo, Ballarat and the Klondike. The super pit at Kalgoorlie in Western Australia is the world’s largest operation for gold. The pit is 3 km long and 1.5 km wide, has reached a depth of 290 m below surface and is proposed to be taken down to a depth of 600 m. the pit has produced 1600 tonnes of gold so far. Olympic Dam in South Australia is another large accumulation of metals containing resources of approximately 2500 tonnes of gold.

Gold in Kolar gold field, India.:

Heavy concentration of gold is confined to narrow zones of Kolar, India. The early prospectors spotted a peculiar mylonitic gneiss charged profusely with opalescent blebs of quartz.

Diamond:

The first indication of impact diamonds was the discovery in the 1960s of diamond with lonsdaleite, a high pressure (hexagonal) polymorph of carbon, in placer deposits, e.g. in the Ukraine, although their source was unknown (Cymbal and Polkanov,1975).

In the 1970s, diamond with lonsdaleite was discovered in the impact lithologies at the Popigai (100 km in diameter) impact structure in Siberia. This large structure is profusely charged with micro diamonds. Since then, impact diamonds have been discovered at a number of structures, e.g. Kara, Puchezh-Katunki, Reis, Sudbury, Ternovka, Zapadnaya, and others.

One of the more interesting features of Popigai is that diamonds are found in and around the crater environs. The pressure waves released by whatever phenomenon caused the crater are thought to have compressed the graphite within the gneiss formations and instantaneously transformed it into diamond. The blast that created the precious gems also threw them over 150 kilometers to the east, where they can be found loose in the soils and the rivers.

The diamonds not only inherit the tabular shape of the original graphite grains but they additionally preserve the original crystal's delicate striations

Impact diamonds originate as a result of phase transitions from graphite, or crystallization from coal, and occur when their precursor carbonaceous lithologies were subjected to shock pressures greater than 35 G Pa (Masaitis, 1998).

The diamonds from graphite in crystalline targets usually occur as paramorphs with inherited crystallographic features and as microcrystalline aggregates. At Popigai, these aggregates can reach 10 mm in size but most are 0.2-5 mm in size (Masaitis, 1998). The diamonds, generated from coal or other carbon in sediments, are generally porous and coloured. In the case of Popigai, the original source of carbon is Archaean gneisses with graphite.

The Reis structure in Germany is a diamond –producing mine and is believed to be the result of impact, with a pipe 24 km in a diameter. Canada is rich in diamonds in its northern territories. It is recently reported that a carbon-rich comet crashed over diamond fields of Canada 12,900 years ago and caused scattering of diamonds over a large area. Besides diamond, gold and silver too are reported to be present (Peizer Benny, CCNet,110, Science Daily, 3 July 2008, Tankersbay, Cincinatti Newsletter).
The oldest working for diamonds known in India is at Panna, Madhya Pradesh. The structure is a cup-shaped open pit with rings of breccia in which diamonds are distributed (Radhakrishna,2008)

Of more importance are the diamonds gravels exposed in the banks of the lower reaches of Krishna River in Andhra Pradesh. A cluster of Kimberlite pipes have been identified but these could not have provided all the diamonds. More likely, the source region lies within the Proterozoic Cuddapah Basin, itself of possible impact origin, as has been suggested based on geophysical evidence.

Hydrocarbons:

Hydrocarbons occur at a number of impact structures. In North America, approximately 50% of the known impact structures in hydrocarbon-bearing sedimentary basins have commercial oil and/or gas fields.

The Ames structure is located in Oklahoma, USA, and is a complex impact structure about 14 km in diameter, with a central uplift, an annular trough, and slightly uplifted rim. It is buried by up to 3 km of Ordovician to Recent sediments (Carpenter and Carlson, 1992) making an exploration difficult. However, some rocks recovered from the central uplift were reported to shows quartz grains with shock-diagnostic planar formation features, indicating an impact origin for the structure. The feature has morphological characteristics, such as a central uplift surrounded by a circular depression and an outer ring, which are typical of those of complex impact craters. The central uplift is about 5 km in diameter and is collapsed or eroded in center.

Its origin has been variously attributed to meteorite impact, volcanic activity, dissolution collapse and other causes. Geological arguments for an impact origin have been based on geomorphology, rock textures, mineral deformation, and stratigraphic relations( Nick, 1994).

The first oil and gas discoveries were made in 1990 from an approximately 500 m thick section of Lower Ordovician Arbuckle dolomite in the rim. Due to impact –induced fracturing and Karsting, the Arbuckle dolomite in the rim of Ames has considerable economic potential (Grieve, 2005)

Other impact structures also produce hydrocarbons. For example, the 25 km diameter Steen River structure, Canada, produces oil from two wells on the northern rim. The large diameter (180 km) Chicxulub in Mexico is known for its oil and gas accumulation. The Chicxulub crater is an ancient impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named — as well as the rough translation of the Mayan name, "the tail of the devil."The crater is more than 180 kilometers (110 mi) in diameter, making the feature one of the largest confirmed impact structures in the world; the impacting bolide that formed the crater was at least 10 km (6 mi) in diameter. The crater was discovered by Glen Penfield, a geophysicist who had been working in the Yucatán while looking for oil during the late 1970s. Evidence for the impact origin of the crater includes shocked quartz, a gravity anomaly, and tektites in surrounding areas.
The age of the rocks and isotope analysis show that this impact structure dates from the end of the Cretaceous Period, roughly 65 million years ago. . Recent evidence suggests that the impactor may have been a piece of a much larger asteroid that broke up in a collision in distant space more than 160 million years ago.
A major impact structure along the Indian Seychelles plate margin- ‘the Shiva crater’- one half of which has been identified off the west coast of India has been recognized, the giant oil field of Mumbai lies within this structure. Concentration of hydrocarbons is ascribed to impact fracturing and breciation of host rock, making it porous.
The Shiva crater is a sea floor structure located beneath the Indian Ocean, west of Mumbai, India. It was named by the paleontologist Sankar Chatterjee after Shiva, the Hindu god of destruction and renewal.
Its age is estimated to around 65 million years ago, at about the same time as a number of other impact craters and the Cretaceous-Tertiary extinction event (K-T boundary). Although the site has shifted since its formation because of sea floor spreading, the formation is approximately 600 kilometers long by 400 km wide. It is estimated that a crater of that size would have been made by an asteroid or comet approximately 40 km in diameter. The Shiva complex adds weight to the theory that the K-T extinction was caused by a massive asteroid fragmenting and hitting the Earth in several locations, known as the "Multiple impact theory."
At the time of the K-T extinction, India was located over the Réunion hotspot of the Indian Ocean. Hot material rising from the mantle flooded portions of India with a vast amount of lava, creating a plateau known as the Deccan Traps. It has been hypothesized that either the crater or the Deccan Traps associated with the area are the reason for the high level of oil and natural gas reserves in the region.
Structures in the Gulf of Mexico are known to be producers of vast amounts of oil and gas in brecciated rocks at the Cretaceous- Tertiary boundary.

A report from NASA (Nature, v.454,2008, p. 589 and 609-610) states that the US-Europe cosmic spacecraft CASSINI has spotted large lakes containing liquid hydrocarbons and ethane on Titan, the largest moon of Planet Saturn. This open up the possibility of identifying extra-terrestrial object being possible source of hydrocarbons.

The other case is represented in the Red Wing Creek astrobleme (North Dakota, USA). Here the authigenic breccia of the central uplift is covered by a clay layer, which forms a structural trap. Oil has migrated from the original Mississippi deposits into this trap and has been exploited. It is possible that the oil-bearing structures Viewfield, Eagle Butte and some others situated in that basin have the same impact nature.

Nickel, Copper and Platinum group elements in Sudbury Basin Canada:
Sudbury Basin is the oval structure, next to the much younger lake-filled Wanapitei crater
Fig. of Geological map of Sudbury Basin
This is another large basin believed to have been caused by impact of an extraterrestrial object more than 12 km in diameter, and its known for its nickel, copper and significant concentration of Platinum Group Elements. The basin is elliptical, 11 km long and 5 km wide. The structure dips inward. Mineralization is in Komatiites, rifted continental basalts and other ultramafic rocks.
It was created as the result of a 10 km meteorite impact that occurred 1.85 billion years ago in the Paleoproterozoic era. Debris was scattered over an area of 1.6 million square kilometers and travelled over 800 kilometers away — rock fragments ejected by the impact have been found as far as Minnesota. Its present size is believed to be a smaller portion of a 250 km round crater that the bolide originally created. Subsequent geological processes have deformed the crater into the current smaller oval shape. Sudbury Basin would then be the second largest crater on Earth, after the 300 km Vredefort crater in South Africa, and larger than the 170 km Chicxulub crater in Yucatán, Mexico.

Copper-Nickel were first noted at Sudbury in 1856. It was not until they were ‘rediscovered’ during the building of the trans-Canada railway in 1883 that they received attention, with the first production occurring in 1886 (Naldrett, 2003). By 2000, the Sudbury mining camp had produced 9.7 million tonnes of Cu, 70 thousand tonnes of Co, 116 tonnes of Au, 319 tonnes of Pt, 335 tonnes of Pd, 37.6 tonnes of Rh, 23.3 tonnes of Ru, 11.5 tonnes of Ir, 3.7 tonnes of Ag, 3 thousand tonnes of Se and 256 tonnes of Te (Lesher and Thurston 2002).

At Sudbury the nickel-copper deposits are associated with an elliptical basin that is about 65 kilometres long and 27 kilometres wide, containing layers of norite and diorites up to 3 kilometres thick, called the "Sudbury Igneous Complex".

Lead-zinc in Mississippi valley:

These are generally carbonate-hosted and strata bound. Major deposits are found in Canada (Pine Point) and in the Upper Mississippi valley of the United States. Ore occurs at shallow depths, not greater than 600 m. The well-known Rampur-Agucha deposits at Rajasthan, India, probably belongs to this category.

Century (Lawn Hill) Zn-Pb Deposit, Queensland, Australia:

A 19.5-km-wide impact structure has been described in close association with a major Zn-Pb deposit of world class rank (Australian Jour. Earth Sciences, v.55, 2008, pp. 587-603). The exact relationship of the impact structure to the generation of metals has yet to be determined.

Uranium:

The famous Carswell structure (side figure) in Saskatchewan, Canada, known for its uranium deposit, is ascribed to an impact structure eroded below the floor of the original crater.
The Athabasca Basin is the largest and richest uranium producing basin in the world. The basin is located just to the south of Lake Athabasca. The basin covers about 100,000 square kilometres in Saskatchewan and a small portion of Alberta. The surface of the basin consists of main sandstone sediment varying from 100 to 1000 metres in depth. The uranium is mostly found at the base of this sandstone, at the point where it meets the basement.
Uranium was discovered in the region in the 1940s. The first mine in the area was the Rabbit Lake Mine, which was discovered in 1968 by Gulf Mineral Resources and opened in 1975. The most important current mine is Cameco's McArthur River mine, the world's largest high-grade uranium mine.

Cumulative uranium production from the basin is approximately 1.5 billion pounds of uranium oxide, with a value of close to US $ 1.5 billion.

Reference:

Carpenter, B.N. and Carlson, R., 1992. The Ames impact crater. Oklahoma Geological Survey, 52, 208-223.

Cymbal, S.N. and Polkanov, Yu. A. 1975. Mineralogy of titanium-zirconium placers of Ukraine. Nauk Press, Kiev [in Russian]

Grieve, R.A.F. and Masaitis, V.L., 1994. the economic potential of terrestrial impact craters. International Geology Review, 36, 105-151.

Grieve, R.A.F., 2005. Economic natural resource deposits at terrestrial impact structures. Mineral deposits and Earth evolution. Geological Society, London, Special publications, 248,1-29.

Lesher, C.M. and Thurston, P.C. (eds.) 2002. A special issue devoted to mineral deposits of the Sudbury Basin. Economic Geology, 97. 1373-1606.

Masaitis, V.L. 1992. Impact craters: Are they useful?. Meteoritics, 27, 21-27.

Masaitis, V.L., 1998. Popigai crater. Origin and distribution of diamond-bearing impactites. Meteorities and Planetary Science,33, 349-359.

Naldrett, A.J.,2003. From impact to riches: Evolution of geological understanding as seen at Sudbury Canada. GSA Today, 13, 4-9.

Nick, K. E., 1994. Lithologic and stratigraphic evidence for the impact origin of a buried Ordovician age crater and reservoir near Ames, Major County, Oklahoma: American Association of Petroleum Geologists 1994 Annual Convention Official Program, p. 224.

Radhakrishna, B.P. 2008. Heavenly Bounty, some thoughts on impact metallogeny. Jr. of Geol. Soc. of India. v.72, no.6. 705-712.
http://en.wikipedia.org/wiki/Vredefort_crater
http://en.wikipedia.org/wiki/Sudbury_Basin
http://www.ccrs.nrcan.gc.ca/radar/spaceborne/radarsat1/action/canada/sudbury_e.php
http://en.wikipedia.org/wiki/Popigai_crater
http://en.wikipedia.org/wiki/Chicxulub_crater

Thursday, August 13, 2009

Satellites Unlock Secret to Northern India's Vanishing Water.

Reviewed and Submitted by
Dr. Nitish Priyadarshi
As animated here, groundwater storage varied in northwestern India between 2002 and 2008, relative to the mean for the period. These deviations from the mean are expressed as the height of an equivalent layer of water, ranging from -12 cm (deep red) to 12 cm (dark blue). Credit: NASA/Trent Schindler and Matt Rodell.

The map, showing groundwater withdrawals as a percentage of groundwater recharge, is based on state-level estimates of annual withdrawals and recharge reported by India's Ministry of Water Resources. The three states included in this study are labeled. Credit: NASA/Matt Rodell


The map shows groundwater changes in India during 2002-08, with losses in red and gains in blue, based on GRACE satellite observations. The estimated rate of depletion of groundwater in northwestern India is 4.0 centimeters of water per year, equivalent to a water table decline of 33 centimeters per year. Increases in groundwater in southern India are due to recent above-average rainfall, whereas rain in northwestern India was close to normal during the study period. Credit: I. Velicogna/UC Irvine
WASHINGTON -- Using NASA satellite data, scientists have found that groundwater levels in northern India have been declining by as much as one foot per year over the past decade. Researchers concluded the loss is almost entirely due to human activity. More than 26 cubic miles of groundwater disappeared from aquifers in areas of Haryana, Punjab, Rajasthan and the nation's capitol territory of Delhi, between 2002 and 2008. This is enough water to fill Lake Mead, the largest manmade reservoir in the United States, three times. A team of hydrologists led by Matt Rodell of NASA's Goddard Space Flight Center in Greenbelt, Md., found that northern India's underground water supply is being pumped and consumed by human activities, such as irrigating cropland, and is draining aquifers faster than natural processes can replenish them. The results of this research were published today in Nature. The finding is based on data from NASA's Gravity Recovery and Climate Experiment (GRACE), a pair of satellites that sense changes in Earth's gravity field and associated mass distribution, including water masses stored above or below Earth's surface. As the twin satellites orbit 300 miles above Earth's surface, their positions change relative to each other in response to variations in the pull of gravity. Changes in underground water masses affect gravity enough to provide a signal that can be measured by the GRACE spacecraft. After accounting for other mass variations, such changes in gravity are translated into an equivalent change in water. "Using GRACE satellite observations, we can observe and monitor water storage changes in critical areas of the world, from one month to the next, without leaving our desks," said study co-author Isabella Velicogna of NASA's Jet Propulsion Laboratory in Pasadena, Calif., and the University of California, Irvine. Groundwater comes from the natural percolation of precipitation and other surface waters down through Earth’s soil and rock, accumulating in cavities and layers of porous rock, gravel, sand or clay. Groundwater levels respond slowly to changes in weather and can take months or years to replenish once pumped for irrigation or other uses. Data provided by India's Ministry of Water Resources to the NASA-funded researchers suggested groundwater use across India was exceeding natural replenishment, but the regional rate of depletion was unknown. Rodell and colleagues analyzed six years of monthly GRACE data for northern India to produce a time series of water storage changes beneath the land surface. "We don't know the absolute volume of water in the northern Indian aquifers, but GRACE provides strong evidence that current rates of water extraction are not sustainable," said Rodell. "The region has become dependent on irrigation to maximize agricultural productivity. If measures are not taken to ensure sustainable groundwater usage, the consequences for the 114 million residents of the region may include a collapse of agricultural output and severe shortages of potable water." Researchers examined data and models of soil moisture, lake and reservoir storage, vegetation and glaciers in the nearby Himalayas in order to confirm that the apparent groundwater trend was real. The loss is particularly alarming because it occurred when there were no unusual trends in rainfall. In fact, rainfall was slightly above normal for the period. The only influence they couldn't rule out was human. "For the first time, we can observe water use on land with no additional ground-based data collection," said co-author James Famiglietti of the University of California, Irvine. "This is critical because in many developing countries, where hydrological data are both sparse and hard to access, space-based methods provide perhaps the only opportunity to assess changes in fresh water availability across large regions." GRACE is a partnership between NASA and the German Aerospace Center, DLR. The University of Texas Center for Space Research in Austin has overall GRACE mission responsibility. GRACE was launched in 2002.
Article source:

Saturday, August 8, 2009

Fire erupted in National Highway in Jharkhand State of India.

Coal supply and environment are going to be badly affected.
Explosions are being heard.
By.
Dr. Nitish Priyadarshi





Ramgarh district administration of Jharkhand state of India on Friday (August 7,2009) suspended the movement of vehicles on the 35 Km stretch of National Highway (NH) 33 between Ranchi (capital of Jharkhand) and Patna (capital of Bihar). The underground fire erupted violently on 750 metre –stretch on highway on Friday. Explosions are also being heard.
Supplies of coal from this area to other parts of the country are going to be badly affected due to this fire and closure of the most important road. Other than environmental it is also going to affect the supply of the food grains to other parts of drought affected area of the Jharkhand state.
For detail story please scroll down this blog.

Tuesday, August 4, 2009

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.

http://adsabs.harvard.edu/abs/2007AGUFM.B23B1269G
http://www.agu.org/pubs/crossref/2008/2007JF000909.shtml
http://www.indianexpress.com/news/silting-not-pollution-chocking-ganga/376907/
http://www.auburn.edu/~alleykd/envirolitigators/gangatext.htm
http://science.jrank.org/pages/6563/Subsidence-Geologic-subsidence.html
http://disc.sci.gsfc.nasa.gov/oceancolor/additional/science-focus/ocean-color/sedimentia.shtml
http://geology.geoscienceworld.org/cgi/content/abstract/28/12/1083
http://www3.interscience.wiley.com/journal/68501812/abstract?CRETRY=1&SRETRY=0
http://en.wikipedia.org/wiki/1906_San_Francisco_earthquake
http://www.onepetro.org/mslib/servlet/onepetropreview?id=00014598&soc=SPE&speAppNameCookie=ONEPETRO
http://www.indiaenvironmentportal.org.in/content/palaeoliquefaction-evidence-prehistoric-largegreat-earthquakes-north-bihar-india
http://timesofindia.indiatimes.com/NEWS/City/Patna/Bihar-vulnerable-to-quakes/articleshow/977183.cms