Geological action of river or Fluvial processes The geological action of river is divided chiefly into three parts as Erosion, Transportation and Deposition. Erosion: River erosion is mainly due to mechanical breaking down of rock fragment. The chemical action of rivers is minimal. A wide variety of processes are involved in river erosion as follows; a. Hydraulic action: It is the process of mechanical loosening or removal of the material by the action of the water alone. The effectiveness of hydraulic action of a river is depends on gradient, velocity of the stream, width, depth and shape of the channel and discharge. b. Abrasion: The process of wearing-away of bed rock surfaces by mechanical processes such as rubbing, cutting, scratching, grinding and polishing etc. is known as abrasion. c. Attrition: The process of mechanical wearing and tearing of the transported rock fragments into smaller fragments due to mutual impact and collision. d. Cavitation: Highly turbulent rivers in rocky channels erode their beds by hydraulic plucking, in which pieces of bed rocks are lifted out by strong eddies spiraling up around vertical axes. This sucking out of the rock pieces produces cavities or depressions within the rock. This type of process is called cavitation. e. Corrosion: The chemical processes of rock erosion by river water are known as corrosion or solution. Important erosional features: a. Potholes: These are cylindrical or bowl-like depressions in the rocky beds of streams, which are excavated in the floors of the streams by extensive, localized abrasion. These are commonly found in softer bedrocks. b. Water fall: These are defined as magnificent jumps made by stream or river water at certain specific parts of their course where there is a sudden and considerable drop in the gradient of the channel. c. River valleys: The river channel carved out by the flow of running water is commonly known as a river valley. d. Gorges or canyons: During the river erosion, down cutting of its cannel gives rise to a deep narrow valley with vertical or steep walls. Such a valley is termed as a gorge or canyons. e. Escarpments: These are erosional land forms produces by rivers in regions composed of alternating beds of hard and soft rocks. During river erosion soft rocks erode much faster than hard rocks, leaving behind steep slopes on one side and a gentle slope on the other. The steep slope side is known as the escarpment. Hog’s back: This is a sharp ridge like structure with high angle sides on two sides formed by harder rocks in an inclined series of beds. Mesa and butte: In regions of horizontal strata in which isolated portions of land is capped by a hard, erosion- resistant bed, the erosional landforms produced will have an isolated flat-topped land area with seep sides, commonly known as mesa. Isolated masses without flat tops are called buttes. Transportation: A river is a most powerful agent of transportation. All the material being transported by a

1. Geological action of river

2. ABOUT STREAM
Streams alter the Earth's landscape through the
movement of water and sediment . Streams are powerful
erosive agents moving material from their bed and banks. In
mountainous regions, stream erosion often produces deep
channels and canyons. Streams also deposit vast amounts of
sediment on the terrestrial landscape and within lakes and
ocean basins.

3. TYPES OF STREAMS
 CONSEQUENT STREAM:- In any area these are the first stream to
have developed in accordance with the topography of the area.
 SUBSEQUENT STREAM:-These are the generally tributaries to the
consequent streams. The characters of the rocks over which they flow
controls their direction of flow
 OBSEQUENT STREAM:-These are tributaries to the subsequent
streams. In most cases their direction of flow may be opposite to the main
or consequent stream.
 INSEQUENT STREAM:-They may also be called irregular stream. These
are found to flow in canals that show no well defined relationship with
either the slope of the area or the character of the rocks.

5. DRAINAGE SYSTEM
A drainage system is the pattern formed by the streams, rivers,
and lakes in a particular drainage basin. They are governed by the
topography of the land whether a particular region is dominated by
hard or soft rocks, and the gradient of the land. Geomorphologists
and hydrologists often view streams as being part of drainage basins.
A drainage basin is the topographic region from which a stream
receives runoff, through flow, and groundwater flow. Drainage
basins are divided from each other by topographic barriers called a
watershed.

6. Types of drainage system
 DENDRETIC:
 PINNATE:
 TRLLIS
 RECTANGULAR
 PARALLEL:
 CENTRIPETAL:
 CENTRIFUGAL
 RADIAL:

11. The Work of Rivers
The erosional work of streams/rivers carves
and shapes the landscape through which
they flow.
Three functions of rivers
a. Erosion
b. Transportation
c. Deposition

12. How rivers erode
 HYDRAULIC ACTION The force of the
water weakens and breaks up the rocks
 ABRASION The material carried in the
river wears away the river bed
 ATTRITION As the pebbles carried by
the river crash into each other,they
become smaller and rounder
 SOLUTION The water in the river
dissolves the minerals in the rocks

13. How rivers transport
Rolling stones along the river
bed.( needs lots of energy)
Traction Suspension
Clay sized particles are carried
along by the river flow
Saltation
Sand sized particles
bounce along the riverbed
Solution
Some minerals are dissolved
by the riverwater
river flow

14. Source
of river
Upper
Course
Middle
Course
Lower
Course

18. FEATURES OF THE UPPER COURSE
EROSIONAL FEATURES:
V-SHAPED VALLEYS WITH
INTERLOCKING SPURS
POT HOLES ON RIVER BED
WATERFALLS AND RAPIDS

19. The River Avon has smoothed off parts
of this hard igneous rock. . .

20. Formation of a waterfall
Soft rock
Hard rock
Steep sides
( gorge )
Vertical erosion
Forms plunge pool
Undercutting
erodes the
softer rock
forming an overhang
The overhang
Eventually
collapses
The process
starts again
Eroded rock
Waterfall
Retreats upstream

21. PLUNGE
POOL
UNDERCUTTING
OF SOFT ROCK
OVERHANG
WATERFALL
RETREATS . .
UPSTREAM . .

23. MEANDERS
Flood plain
Meanders
© Used with the permission of the Geological Survey of Canada, Natural Resources Canada
Available at http://sts.gsc.nrcan.gc.ca – Terrain Science Division
Most erosion
on the outside
of the bend .. Fastest flow
Possible break
through point
Possible
ox-bow
lake

24. Fastest current slowest current
Outer bank
Is undercut
Slip off slope
( river beach )
Deposition of
Sand and shingle
Deepest part
of the river
Bank will
collapse
Small
river
cliff
River bend

25. Formation of an ox-bow lake
The meanders change shape
through time
At the bends the
river flows faster
at the outside
The bends migrate
Sideways leaving
deposits on the inside
Of the bend
The erosion makes the
Meanders more pronounced
Small river
cliff is formed
Most erosion
Most deposition
(Slip off slope)
Some bends get closer
and closer
The neck gets narrower
and narrower
Eventually during a period of
heavy river flow it cuts through
The river now follows the new route
The old meander
Is left as a small lake
(OX - BOW lake)
© Used with the permission of the
Geological Survey of Canada, Natural
Resources Canada
Available at
http://sts.gsc.nrcan.gc.ca –
Terrain Science Division

26. Want to see that again ?

27. NARROW MEANDER NECK
FUTURE
OX-BOW LAKE

28. Gentle valley sides
Flat floodplain
Layers of silt
Deposited during floods
Coarse material
Forms natural
levees
River is actually flowing above
The floodplain !!
Levees is often
artificially
strengthened

29. Characteristics Upper Course Middle Course Lower Course
Slope
Width
Depth
Straightness
Load
Main work
Valley width
Type of load
usually steep
narrow
shallow
winding
little
large/small
angular
erosion
transportation
quite steep
quite wide
quite deep
meandering
some
medium/small
rounded
Transportation
narrow
gentle
quite wide
wide
deep
big meanders
lots
small+
rounded
transportation
deposition
wide

32. Alluvial cone

33. Canyon
A long ,deep,narrow,very
Steep-sided valley cut
Primarily in bed rock in an
High local relief (mountain
Or high plateau terrain)

34. Delta: landform where the mouth of river flows into an ocean, sea, lake ,
estuary or another river

35. Estuary:

36. Reproduced with kind permission of Ordnance Survey © Crown Copyright NC/03/18990
tributaries
ox-bow
lake
meander
V shaped valley
Steep
Valley
sides
Flood
plain

37. Geological action of wind

38. Introduction:
The air currents in motion is called wind .
The wind is an important agent of erosion, transportation, deposition.
Its work particularly seen in arid regions.
Erosion: wind does erosion in three ways.
• Deflation: The process of removal of particles of dust and sand by strong
winds is called deflation. This process operates well in dry regions with
little or no rainfall i.e. desert area. (Lifting and removal of loose material.)
• Abrasion: The process of wearing and tearing of country rock
surfaces by wind borne particles is called wind abrasion. Sand
grains are used as tools for eroding rocks.
• Attrition: The wear and tearing suffered by load material due to
their mutual impacts during transportation process by wind is
called attrition.Collide against one another.

44. Deflation sometimes leads to the formation of depressions or hollows on the land
surface. At few places the depressions with its base touching the water table
at quite a depth are called as blowouts.

45. Ventifacts: These are polished and faceted rock fragments
produced by the abrasive action of windblown sand.

46. Saltation: Type of transportation which is carried out through a series of bounces
is called saltation.
Suspension: The finest materials derived from clay and slit move with the wind quickly and
remain in suspension in the air for quite some time and settle very slowly.
Surface creep: Type of transportation method carried out through rolling and
creeping is called surface creep. It is also known as traction.

47. Deposition
• When, the velocity of the wind is checked due
to some obstacles, a part or whole of the
drifting material carried by the wind will start
getting deposited and this type of deposits are
called aeolian deposits.
• Loess: It is a deposit of windblown silt and clay
particles.
• Dunes (Sand dunes): These are variously
shaped deposits of sand grade particles.

48. Barchans: These are asymmetrical, crescent shaped
(typically half moon shape) dunes in which the points
of the crescent are directed down wind side.

49. Longitudinal dunes: These are large symmetrical ridges of sand parallel to the wind direction.
Transverse dunes: These are elongated dunes form at right angles to the prevailing wind.
Parabolic dunes: These dunes are parabolic in shape and their horns pointing towards
the direction opposite to that of the blowing wind.

51. THANK U