Friday, February 14, 2014

Geology of Dasam Falls in Ranchi district of Jharkhand State, India.

 The Dassam Fall is a natural cascade across the Kanchi River.
by
Dr. Nitish Priyadarshi
Geologist






A waterfall is a place where water flows over a vertical drop in the course of a stream or river. Waterfalls are also called cascades. Waterfalls are commonly formed when a river is young. At these times the channel is often narrow and deep. When the river courses over resistant bedrock, erosion happens slowly, while downstream the erosion occurs more rapidly. As the watercourse increases its velocity at the edge of the waterfall, it plucks material from the riverbed. Whirlpools created in the turbulence as well as sand and stones carried by the watercourse increase the erosion capacity. This causes the waterfall to carve deeper into the bed and to recede upstream. Often over time, the waterfall will recede back to form a canyon or gorge downstream as it recedes upstream, and it will carve deeper into the ridge above it.

The process of erosion, the wearing away of earth, plays an important part in the formation of waterfalls. Waterfalls themselves also contribute to erosion.

Often, waterfalls form as streams flow from soft rock to hard rock. This happens both laterally (as a stream flows across the earth) and vertically (as the stream drops in a waterfall). In both cases, the soft rock erodes, leaving a hard ledge over which the stream falls.

Erosion is just one process that can form waterfalls. A waterfall may form across a fault, or crack in the Earth’s surface. An earthquake, landslide, glacier, or volcano may also disrupt stream beds and help create waterfalls. 

Running water always erodes rock, but some rocks are more resistant than others. So a waterfall occurs when geological forces have produced either a sudden change in rock types or a steepening of a gradient where a stream is flowing. With a break in elevation, a stream or river becomes a waterfall.

The Dassam Falls  (also known as Dassam Ghagh) is a waterfall located near Taimara village in Bundu police station of Ranchi district in the Indian state of Jharkhand. Scenery around the falls is very much beautiful. Tourists visiting the Dasham falls get fascinated after viewing the scenery and glory of the place. Tourists from all over India come to visit this beautiful place, which must form an integral part of your Jharkhand itinerary. Natural beauty of the place attracts visitors throughout the year. Tourists can enjoy bathing in the stream, but they are advised to be cautious while taking a dip in the stream.
Dassam means ten. Since ages and till today, whenever the waterfall is seen, ten streams of water can be seen falling. Hence, the name is given. The Dassam Falls is a natural cascade across the Kanchi River, a tributary of the Subarnarekha River. The water falls from a height of 44 metres (144 ft). The sound of water echoes all around the place. Dassam Falls at one of the edges of the Ranchi plateau is one of the many scarp falls in the region.

The Dassam Falls is an example of a nick point caused by rejuvenation. Knick point, also called a nick point or simply nick, represents breaks in slopes in the longitudinal profile of a river caused by rejuvenation. The break in channel gradient allows water to fall vertically giving rise to a waterfall.

Geology of Chota Nagpur Plateau:

The Chota Nagpur Plateau is a plateau in eastern India, which covers much of Jharkhand state as well as adjacent parts of Odisha, West Bengal, Bihar and Chhattisgarh. The Indo-Gangetic plain lies to the north and east of the plateau, and the basin of the Mahanadi River lies to the south. The Chotanagpur Plateau (22°-25° 30'N and 83°47'-87° 50'E) covering an area of 87,239 sq. km includes Ranchi, Hazaribagh, Singhbhum, Dhanbad, Palamau, Santhal Parganas (Jharkhand) and Purulia dis­tricts (West Bengal). It is composed of Archaean granite and gneiss rocks with patches of Dharwar rocks (phyllite, mica-schists).
The Chota Nagpur Plateau of Jharkhand state is a continental plateau - an extensive area of land thrust above the general land. The plateau has been formed by continental uplift from forces acting deep inside the earth. The Gondwana substrates attest to the plateau's ancient origin. It is part of the Deccan Plate, which broke free from the southern continent during the Cretaceous to embark on a 50-million-year journey that was violently interrupted by the northern Eurasian continent. The northeastern part of the Deccan Plateau, where this ecoregion sits, was the first area of contact with Eurasia.

Chotanagpur consists of a series of plateaus standing at different levels of elevation; the highest general elevation of about 1100 m in the mid-west­ern portion known as the Pat lands. From here the land descends in all directions in a series of steps particularly towards the east until it merges gradu­ally with the Lower Ganga Plain. The sharp break in slope are marked by steep scarps where the rivers like Barakar, Damodar, Subamarekha north and south Koels have carved out deep gorges and water­falls. The most characteristic features of relief are revealed in the Hazaribag and Ranchi plateaus standing at same general elevation (600 m) but separated by the Damodar trough (Permo-Triassic trough fault).

Water falls of Ranchi plateau.

It is the largest part of the Chota Nagpur Plateau. The elevation of the plateau land in this part is about 700 metres (2,300 ft) above mean sea level. The general topography is undulating. The Ranchi plateau gradually slopes down towards south-east into the hilly and undulating region of Singhbhum (earlier Singhbhum district or what is now Kolhan division. The plateau is highly dissected. Damodar River originates here and flows through a rift valley. To the north it is separated from the Hazaribagh plateau by the Damodar trough.To the west is a group of plateaux called pat.

There are many waterfalls at the edges of Ranchi plateau where rivers coming from over the plateau surface form waterfalls when they descend through the precipitous escarpments of the plateau and enter the area of significantly lower height. The North Karo River has formed a 17 metres (56 ft) high Pheruaghaugh Falls at the southern margin of Ranchi plateau. Such falls are called scarp falls. Hundru Falls (75 m) on Subarnarekha River near Ranchi, Dassam Falls (44 m) on Kanchi River, east of Ranchi, Sadni Falls (60 m) on Sankh River (Ranchi plateau) are examples of scarp falls. Sometimes waterfalls of various dimensions are formed when tributary streams join the master stream from great height forming hanging valleys. At Rajrappa (10 m), the Bhera river coming over from the Ranchi plateau hangs above the Damodar River at its point of confluence with the latter. The Jonha Falls (25.9 m) is another example of this category of falls. In fact the Gunga River hangs over its master stream, Raru River (to the east of Ranchi city) and forms the said falls.

Formation of Waterfalls in Ranchi Plateau.

The waterfalls of Ranchi plateau including Dasam falls are due to disturbances in late geological age. The Ranchi plateau (or the whole of Peninsular India) believed to have undergone uplift as the side effects of the Himalayan orogeny particularly during the late Tertiary. As the streams descend they are marked by waterfalls.

The Chotanagpur Plateau is made up mainly of Precambrian rocks but has witnessed uplifts synchronously with Himalayan uplift in the Cenozoic.

Some times, waterfalls of varying dimensions are formed when the tributary streams join their master streams from great height forming hanging valleys. In other words, hanging valley falls are formed when the level of the junction of the tributary streams is much higher than the level of the main valley of the master stream. The Rajrappa falls ( 10 m.) at the junction of the Bhera river and the receiving Damodar river (located to the north of Ranchi city) is a typical example of hanging valley waterfalls as the Bhera river after coming from over the Ranchi Plateau hangs above the Damodar river as its confluence with the latter. The Gautamdhara or Johna falls ( 25.9 m.) is another example of this category of falls. In fact, the Gunga river hangs above its master stream, Raru river, ( to the east of Ranchi city) and forms the said falls.

Some falls of Ranchi plateau comes under knick point falls. The breaks in channel gradient caused by rejuvenation are called knick points or heads of rejuvenation. These breaks in channel gradient or knick points denote sudden drops of elevation in the longitudinal profile of the rivers and allow the water to fall down vertically giving birth to waterfalls of varying dimensions. Hundru falls ( 76.67 m) on Subarnarekha river ( near Ranchi city), Johna or Gautamdhara falls at the confluence of Raru and Gunga rivers (to the east of Ranchi). Dasam falls ( 39.62 m and 15. 24 m ) on Kanchi river (east of Ranchi) are the examples of knickpoint falls.


Geology of Dasam falls:
 

Surface rocks surrounding the area are highly smooth. This is due to abrasion. Abrasion is the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosion. This phenomenon is active there from millions of years.

Ptygmatic folding of quartzo-feldspathic veins are prominent on the Precambrian (granite-gneiss) rocks of the area.

The ptygmatic folding term is now used essentially for highly contorted quartzo-feldspathic veins found in areas of intense metamorphism and granitisation. Their origin has been a matter of controversy, two different theories have been put forward 1.the veins were originally intruded as flat sheets and the folding is due to deformation of the host rock. 2. Folding took place during the process of injection, which occurred under special circumstances.

It is possible to demonstrate experimentally that material being injected into a weaker host material will develop ptygmatic folding, if it encounters a more rigid mass. This is clearly what happens when ptygmatic veins are formed in granitised or migmatic materials.


 Fig. Ptygmatic folding in rocks of Dasam falls.


Fig. Quartzo-feldspathic intrusion.


Fig. Faulting in the rocks of Dasam Falls.


There are also many potholes in the rocks of  Dasam falls area. Potholes are the kettle-like depressions in the rocky bed of streams. The stream beds in Ranchi plateau are frequently dotted with potholes. Potholes are due to localized drilling action of rock fragments. Where there is an originally minor depression the water of the stream will undergo swirling and the dancing rock fragments will grind against the side and bottom of the depression which will undergo gradual enlargement in perimeter and depth.



  Fig. Potholes in the rocks of Dasam Falls.

Potholes develop particularly in coarse-grained rocks like sandstone or weathered granite
( as in Dasam Falls). In recently uplifted areas like Dasam falls the supply of the boulders or angular rock fragments encourages potholing. The original minor depression could result from local lithological weakness of the rock or joint intersection or the erosion of a local rock piece. The hollow begins to arrest rock fragments.
  
Reference:

Ahmad, E. 1985. Geomorphology. Kalyani Publishers, New Delhi.

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

Singh, S. 1994. Physical Geography. Prayag Pustak Bhawan, Allahabad, India.




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