|
A new study combining the latest archaeological evidence withstate-of-the-art geoscience technologies provides evidence thatclimate change was a key ingredient in the collapse of the greatIndus or Harappan Civilization almost 4000 years ago. The studyalso resolves a long-standing debate over the source and fate ofthe Sarasvati, the sacred river of Hindu mythology. Once extending more than 1 million square kilometers across theplains of the Indus River from the Arabian Sea to the Ganges, overwhat is now Pakistan, northwest India and eastern Afghanistan, theIndus civilization was the largest-but least known-of the firstgreat urban cultures that also included Egypt and Mesopotamia. Like their contemporaries, the Harappans, named for one of theirlargest cities, lived next to rivers owing their livelihoods to thefertility of annually watered lands. "We reconstructed the dynamic landscape of the plain where theIndus civilization developed 5200 years ago, built its cities, andslowly disintegrated between 3900 and 3000 years ago," said LiviuGiosan, a geologist with Woods Hole Oceanographic Institution(WHOI) and lead author of the study published the week of May 28 inthe Proceedings of the National Academy of Sciences. "Until now, speculations abounded about the links between thismysterious ancient culture and its life-giving mighty rivers." Today, numerous remains of the Harappan settlements are located ina vast desert region far from any flowing river. In contrast toEgypt and Mesopotamia, which have long been part of the Westernclassical canon, this amazingly complex culture in South Asia witha population that at its peak may have reached 10 percent of theworld's inhabitants, was completely forgotten until 1920's. Since then, a flurry of archaeological research in Pakistan andIndia has uncovered a sophisticated urban culture with myriadinternal trade routes and well-established sea links withMesopotamia, standards for building construction, sanitationsystems, arts and crafts, and a yet-to-be deciphered writingsystem. "We considered that it is high time for a team of interdisciplinaryscientists to contribute to the debate about the enigmatic fate ofthese people," added Giosan. The research was conducted between 2003 and 2008 in Pakistan, fromthe coast of the Arabian Sea into the fertile irrigated valleys ofPunjab and the northern Thar Desert. The international teamincluded scientists from the U.S., U.K., Pakistan, India, andRomania with specialties in geology, geomorphology, archaeology,and mathematics. By combining satellite photos and topographic data collected by theShuttle Radar Topography Mission (SRTM), the researchers preparedand analyzed digital maps of landforms constructed by the Indus andneighboring rivers, which were then probed in the field bydrilling, coring, and even manually-dug trenches. Collected samples were used to determine the sediments' origins,whether brought in and shaped by rivers or wind, and their age, inorder to develop a chronology of landscape changes. "Once we had this new information on the geological history, wecould re-examine what we know about settlements, what crops peoplewere planting and when, and how both agriculture and settlementpatterns changed," said co-author Dorian Fuller, an archaeologistwith University College London. "This brought new insights into the process of eastward populationshift, the change towards many more small farming communities, andthe decline of cities during late Harappan times." The new study suggests that the decline in monsoon rains led toweakened river dynamics, and played a critical role both in thedevelopment and the collapse of the Harappan culture, which reliedon river floods to fuel their agricultural surpluses. From the new research, a compelling picture of 10,000 years ofchanging landscapes emerges. Before the plain was massivelysettled, the wild and forceful Indus and its tributaries flowingfrom the Himalaya cut valleys into their own deposits and left high"interfluvial" stretches of land between them. In the east,reliable monsoon rains sustained perennial rivers that crisscrossedthe desert leaving behind their sedimentary deposits across a broadregion. Among the most striking features the researchers identified is amounded plain, 10 to 20 meters high, over 100 kilometers wide, andrunning almost 1000 kilometers along the Indus, they call the"Indus mega-ridge," built by the river as it purged itself ofsediment along its lower course. "At this scale, nothing similar has ever been described in thegeomorphological literature," said Giosan. "The mega-ridge is asurprising indicator of the stability of Indus plain landscape overthe last four millennia. Remains of Harappan settlements still lieat the surface of the ridge, rather than being buried underground." Mapped on top of the vast Indo-Gangetic Plain, the archaeologicaland geological data shows instead that settlements bloomed alongthe Indus from the coast to the hills fronting the Himalayas, asweakened monsoons and reduced run-off from the mountains tamed thewild Indus and its Himalayan tributaries enough to enableagriculture along their banks. "The Harappans were an enterprising people taking advantage of awindow of opportunity - a kind of "Goldilocks civilization," saidGiosan. "As monsoon drying subdued devastating floods, the land nearby therivers - still fed with water and rich silt - was just right foragriculture. This lasted for almost 2,000 years, but continuedaridification closed this favorable window in the end." In another major finding, the researchers believe they have settleda long controversy about the fate of a mythical river, theSarasvati. The Vedas, ancient Indian scriptures composed in Sanskrit over 3000years ago, describe the region west of the Ganges as "the land ofseven rivers." Easily recognizable are the Indus and its currenttributaries, but the Sarasvati, portrayed as "surpassing in majestyand might all other waters" and "pure in her course from mountainsto the ocean," was lost. Based on scriptural descriptions, it was believed that theSarasvati was fed by perennial glaciers in the Himalayas. Today,the Ghaggar, an intermittent river that flows only during strongmonsoons and dissipates into the desert along the dried course ofHakra valley, is thought to best approximate the location of themythic Sarasvati, but its Himalayan origin and whether it wasactive during Vedic times remain controversial. Archaeological evidence supports the Ghaggar-Hakra as the locationof intensive settlement during Harappan times. The geologicalevidence-sediments, topography- shows that rivers were indeedsizable and highly active in this region, but most likely due tostrong monsoons. There is no evidence of wide incised valleys like along the Indusand its tributaries and there is no cut-through, incisedconnections to either of the two nearby Himalayan-fed rivers ofSutlej and Yamuna. The new research argues that these crucial differences prove thatthe Sarasvati (Ghaggar-Hakra) was not Himalayan-fed, but aperennial monsoon-supported watercourse, and that aridificationreduced it to short seasonal flows. By 3900 years ago, their rivers drying, the Harappans had an escaperoute to the east toward the Ganges basin, where monsoon rainsremained reliable. "We can envision that this eastern shift involved a change to morelocalized forms of economy: smaller communities supported by localrain-fed farming and dwindling streams," said Fuller. "This mayhave produced smaller surpluses, and would not have supported largecities, but would have been reliable." Such a system was not favorable for the Indus civilization, whichhad been built on bumper crop surpluses along the Indus and theGhaggar-Hakra rivers in the earlier wetter era. This dispersal ofpopulation meant that there was no longer a concentration ofworkforce to support urbanism. "Thus cities collapsed, but smaller agricultural communities weresustainable and flourished. Many of the urban arts, such aswriting, faded away, but agriculture continued and actuallydiversified," said Fuller. "An amazing amount of archaeological work has been accumulatingover the last decades, but it's never been linked properly to theevolution of the fluvial landscape. We now see landscape dynamicsas the crucial link between climate change and people," saidGiosan. "Today the Indus system feeds the largest irrigation scheme in theworld, immobilizing the river in channels and behind dams. If themonsoon were to increase in a warming world, as some predict,catastrophic floods such as the humanitarian disaster of 2010,would turn the current irrigation system, designed for a tamerriver, obsolete.". We are high quality suppliers, our products such as China Hydraulic Pumps And Motors , Hydraulic Adapter Fittings for oversee buyer. To know more, please visits Sauer Pumps.
Related Articles -
China Hydraulic Pumps And Motors, Hydraulic Adapter Fittings,
|
