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.
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.
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.
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.