In this article we will discuss about the classification of waterfalls: 1. Waterfalls Due to Structural and Lithological Variations 2. Waterfalls Due to Upliftment 3. Hanging Valley Falls 4. Glacial Hanging Valley Falls 5. Waterfalls Due to River Capture 6. Coastal Hanging Valley Falls 7. Knickpoint Falls.
1. Waterfalls due to Structural and Lithological Variations:
The waterfalls originated due to variations in the structural and lithological characteristics of terrestrial rocks are called normal waterfalls. Various hierarchical orders of water falls (e.g., catracts, rapids and cascades) depend on the relative resistance and disposition of the beds of different rocks.
The cliffs formed due to the presence of hard and soft rocks in the courses of the rivers form large waterfalls which are called cataracts. Alternate bands of hard and soft rocks give birth to a series of small step-like falls which are called cascades.
The disposition of rock beds gives birth to waterfalls of varying dimensions in the following manner:
(i) When the rock beds dip upstream:
When the alternate bands of hard and soft rocks dip upstream in the longitudinal course of the river and if the caprock is resistant the underlying soft rocks are eroded more rapidly due to cliffing and thus the resistant rock beds form precipitous wall-like scarps which allow the river water to fall downstream vertically and ultimately a stupendous waterfall is formed.
Such waterfall recedes at faster rate due to cliffing and tumbling down of hanging head walls of the falls (fig. 18.2). Such falls, called as caprock falls, disappear when the river attains its graded profile of equilibrium.
(ii) When the rock beds dip downstream:
Rapids are formed when the alternate bands of hard and soft rocks dip downstream and the caprock is resistant to erosion. Such falls are called caprock rapids (fig. 18.3).
(iii) When the rock beds are horizontal:
Very massive and stupendous waterfalls are formed when the rock beds are arranged in horizontal manner and the caprock is quite resistant such as quartzitic sandstones, dolomitic limestones, granite-gneisses and the underlying rocks are soft and vulnerable to quick fluvial erosion such as shale, volcanic ash and unconsolidated geomaterials, because soft rocks are eroded more than the overlying resistant caprocks and thus resistant rocks form wall-like scarps which allow river water to fall down vertically.
Niagra Falls come under this category of waterfalls. The caprock of this waterfall is dolomitic limestones which are succeeded below by the successive beds of shales, limestones, sandstones, sandstones intercalated with shales, sandstones, and shales (Fig. 18.4).
The height of the fall is now 52m and the water discharge is 17,000 cumecs (cubic metres per second). The fall is supposed to have been formed about 10,000 years ago. It is receding at the rate of 3 to 4 feet per year. It is estimated that the Niagra fall has registered a total recession of about 7 miles (11.2 km) till now, Kaieteur falls (British Guiana) also fall under this category of caprock falls. The caprock is of resistant conglomerates. The Potaro river has cut deep through conglomerates and thus has formed 225.5 m high waterfall.
The waterfalls of the Rewa (Madhya Pradesh) and Rohtas (Bihar) plateaux also come under this category as the caprocks are sandstones and quartzitic sandstones underlian by weaker shales of Vindhyan formations. Chachai falls (127m, on Bihar river), Kevti falls (98m, on Mahana river), Odda falls (145m, on Odda river), Kuaridah falls (180m, on Ausane river), Rakimkund falls (168m, on Gayahat river) etc. are typical examples of caprock waterfalls.
(iv) When the rock beds are vertical:
When alternate resistant and soft rocks are arranged in vertical manner, soft rocks are eroded away rapidly but the resistant rock beds are less eroded and hence form precipitous scarps in the course of the river which give birth to waterfalls of steep slope. The intrusive dykes also form waterfalls because of their less (fig. 18.5) erosion than the surrounding rocks. Such waterfalls are called vertical barrier falls.
Great fall of the Yellowstone River of the Yellowstone National Park (USA) is a typical example of vertical barrier fall. Several such waterfalls have been formed in the ‘Patlands’ of Ranchi and Palmau (Jharkhand) but their heights range between 3m and 30m only. These waterfalls have been formed because of structural and lithological controls and differential erosion.
(v) Plateau waterfalls:
The rivers coming from over the plateau surface form waterfalls when they descend through the precipitous escarpments of the plateau and enter the region of significantly lower height. The Congo River has formed 275 m high Livingstone Falls while descending through the African Plateau.
Similarly, the Orange River has formed 140 m high Aughrabies Falls at the margin of the plateau. Nearly all of the significant northward draining streams and their tributaries have formed waterfalls at the northern margin of the Rewa plateau (M.P.) e.g. Chachai Falls (127 m) on Bihar river, Kevti Falls (98 m) on Mahana river, Odda Falls (145m) on Odda river etc. Karo River has formed 17m high Pheruaghaugh Falls at the southern margin of the Ranchi plteau.
Such falls are called as scarp falls. Hundru falls (75 m) on Subaranrekha river (near Ranchi), Dasam falls (39.62 m) on Kanchi river (east of Ranchi), Sadni falls (60m) on Sankh river (Ranchi plateau) etc. are the examples of scarp falls or knick line falls. The Tons River while descending through the Rewa plateau and draining northward to meet the Ganga makes a vertical falls of 70m known as Purwa falls. Similarly, its tributary the Bihar River makes a stupendous Chachai falls of 127 m height.
Yenna falls (180m) on Mahabaleshwar plateau, Gokak falls (54 m) in Belgaun district (Karnataka), Gersoppa falls (253m) on the Sharavati (in North Kanara), Sivasamudram (90m) on the Cauvery river etc. are also examples of scarp falls.
(vi) Step falls:
The arrangement of alternate bands of horizontal beds of hard and soft rocks in the course of the rivers produces a series of low water falls due to differential erosion. These falls are in fact rapids. Bhagawati falls on the Krishna River in the Raichur district of Karnataka (India) is an example of step (cascade) falls.
2. Waterfalls Due to Upliftment:
Waterfalls of varying dimensions are formed due to upliftment of local nature in the courses of the rivers. These waterfalls are obliterated when the rivers regrade their longitudinal profiles. A series of waterfalls on the rivers along the junction of Palamau upland and the northern flat plain (Palamau district, Jharkhand) are said to have been formed due to origin of escarpment caused by the upliftment of southern Palamau during Tertiary period. Patam falls (45.72 m) and Datam falls (30.45 m) on the Patam River (in Bhandaria Anchal, Palamau, and Bihar) are typical examples of such categories.
Gersoppa falls (253m) or Jog falls is also believed to have been formed due to upliftment. The waterfalls on the eastern margin of the Ranchi plateau (e.g. Hundru falls on the Subarnarekha river, Dasam falls on the Kanchi river, Jonha or Gautamdhara falls on the Gunga river etc.) are also quoted as the examples of waterfalls resulting from upliftment.
3. Hanging Valley Falls:
Sometimes, waterfalls of varying dimensions arc formed when the tributary streams join their master streams from great height forming hanging valleys (fig. 18.6). 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 Rajroppa falls (10m) at the junction of the Bhera nadi and the receiving Damodar river (located to the north of Ranchi city) is a typical example of hanging valley waterfalls as the Bhera nadi after coming from over the Ranchi plateau hangs above the Damodar river at its confluence with the latter. The Gautamdhara or Jonha falls (25.9m) 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.
4. Glacial Hanging Valley Falls:
The fluvially originated river valleys are largely modified by glaciers during ice ages. The glaciers flowing through the main valleys deepen them more due to erosion than the tributary valleys. Thus, the tributary valleys hang over the main valleys and discordant levels are formed.
These valleys are again occupied by the rivers after the ice age is over and glaciers are ablated. Consequently, the tributary streams hang over the main rivers at their junctions and waterfalls are formed (fig. 18.6). Such glacial hanging valley waterfalls are found in Norway, Sweden, Finland, Canada etc.
5. Waterfalls Due to River Capture:
Sometimes, waterfalls are formed when the streams flowing over higher but flat lands are captured by the streams of relatively lower height. Thus, the captured streams drain into the captor streams by making waterfalls. Such falls are abundantly found in the Himalayas.
6. Coastal Hanging Valley Falls:
The rivers while descending through sea cliffs or cliffed coast form vertical waterfalls before debouching into the sea (fig. 18.7). Such waterfalls are also called coastal hanging valley falls as the river hangs through the vertical cliffed coast.
7. Knickpoint Falls:
The breaks in channel gradient caused by rejuvenation (either due to upliftment or fall in sea level) are called knick points or heads of rejuvenation. These breaks in channel gradient or knickpoints 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 the Subarnarekha river (near Ranchi city), Jonha or Gautamdhara falls at the confluence of the Raru and the Gunga rivers (to the east of Ranchi), Dasam falls (39.62 m and 15.24 m) on the Kanchi river (east of Ranchi), Burhaghaugh falls (148 m) on the Burha river, a tributary of the North Koel (Palamau upland, Jharkhand), Dhunwadhar falls on the Narmada river (near Jabal pur, M .P.), major fall s of Rewa plateau (e.g. Chachai falls-127 m on the Bihar nadi, Kevti falls-98 m on the Mahana nadi, Tons or Purwa falls-75m on the Tons river, Odda falls -145 m on the odda nadi etc.) etc. are the examples of knick point waterfalls.