An Encyclopaedia of Indian Archaeology v1.c14.s9: 9.9 River Terraces
An Encyclopaedia of Indian Archaeology v1.c14.s9
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9.9 River Terraces
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River terraces have a special significance in prehistoric studies. They are topographic platforms, benches, flats or steps in the river valleys representing the former levels of valley floors or flood plains. The flood plains were suitable for human settlements at all times on account of the availability of water from the river and the presence of natural vegetation and games in the fertile tracts. The study of the terraces is therefore helpful in the relative dating of the prehistoric cultures, as often the terrace deposits contain Stone Age artefacts, vestiges of human occupations and shells and fossils of contemporary animal life. The latter throw considerable light on the palaeo-environment.
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Three types of terraces can be distinguished: (1) tectonic terraces formed due to the uplift or subsidence of a part of the river course; (2) eustatic terraces due to fluctuations of the sea level; and (3) climatic terraces formed due to glacial-interglacial or pluvial-interpluvial climatic conditions. No single process of terrace formation is exclusively effective in a particular region. For example in the Himalayan region the dominant action is tectonic, that of climatic change being subordinate; in the peninsular area however the terraces are formed mainly by climatic changes, while tectonic action is very mild. In coastal tracts like Saurashtra, although the marine and aeolian actions are evident in the shaping of the Quaternary landscape the effect of climatic variation and mild tectonic activity cannot be ruled out.
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Terraces can further be distinguished as (1) paired or unpaired; and (2) erosionai or aggradational. Most of the terraces are usually unpaired, i.e., the surfaces of the two banks of the river are not at the same level; this is generally due to lithology and layout of the initial drainage. In some river valleys the processes of erosion and deposition take place in a sequential order. Thus the river cuts its valley deeper due to steep gradient or increase in the flow of water due to climatic changes. The surfaces occurring on both banks will be the (oldest) rock-cut terraces with a thin veneer of river-flood sediments. The deeper valley may get filled with sediments, again due to amelioration of climate causing aggradation. During the subsequent rejuvenation the river will degrade its bed and will thus be formed an aggradational terrace below the older erosional terrace. These are of the cut-and-fill type which are common in peninsular rivers.
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While transversing the Siwalik hills all the Himalayan rivers have developed unpaired high-level terraces, which are due to the slow uplift in the building of the Himalayan mountains during the Quaternary. In the BEAS-BANGANGA valley such terraces occur at about 183, 125, 50, 30 and 10 m above the present river-bed, while in the Bilaspur area they lie at heights 350, 225, 75 and 15 m above the Sirsa river. The MARKANDA valley around Nahan has terraces at 50, 30, 18, 15 and 5 m. In all these river valleys Lower Palaeolithic tools [4.2] comprising choppers, heavy scrapers (chopper-chopping tools) worked on pebbles have been found. Cleavers have been obtained on the third terrace at the confluence of the BEAS and BANGANGA. On the basis of the geological stratigraphy these terraces could be dated from the late Middle Pleistocene to the Holocene.
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In the Kashmir basin the terraces (*karewas*) have been cut into the former lake-deposits. At places they have preserved animal fossils and plant remains which are helpful in dating them. No Stone Age artefacts have been found on these terraces. But at BURZAHOM, a Neolithic-cum-Megalithic site has been noticed on such a terrace. The sequence of terraces with which are associated Stone Age cultures (Sohan industries) noticed on the Sohan river in Potwar region in Pakistan, a tributary of the Indus, has been related to the Quaternary Glacial and Interglacial episodes of the Himalayas [4.2].
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In the peninsula terraces are formed due to climatic changes although the effect of a mild tectonic activity cannot be ruled out. These river terraces are of the cut-and-fill type.
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A well-developed rock-cut terrace of the late Pleistocene occurs on the GODAVARI river near PAITHAN at a height of 20 m above the present bed. The terrace is covered by gravel and sand and contains Middle Palaeolithic artefacts which could be dated to about 60000 years B.P. [4.2] on faunistic and stratigraphic considerations. A similar terrace with Middle Palaeolithic industries also occurs in the KRISHNA valley near Raichur in Karnataka [4.2].
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For sites and river valleys see respective entries in vol. II.—R.V. JOSHI