GEOLOGICAL WORK BY RIVER Flashcards
THREE WELL- DEFINED PHASES:
- EROSION
- TRANSPORT
- DEPOSITION
- carrying away of particles (rocks/ soils/ sediments) by means of mechanical disintegration or
chemical decomposition of rocks - Stream and rivers are the most powerful sub aerial agents of erosion. Others are wind and ice.
EROSION
- Prolonged erosion by river and the associated streams produces many interesting and
important surface features along their channels directly, and - In the drainage basin in an indirect manner some of these features develop, with the
passage of time to major geomorphological landforms.
FEATURE OF STREAM EROSION
FEATURE OF STREAM EROSION
- POTHOLES
- VALLEYS AND RIVERS
- WATERFALLS
These are various shaped depressions of different dimensions that are developed in the river bed by excessive localized erosion by the stream.
- The formation process for a pothole may be initiated by a simple plucking out of a
protruding or outstanding rock projection at the river bed by hydraulic action.
POTHOLES
- Low land surrounded on sides by inclined hill slopes and mountain.
- Every major river is associated with a valley of its own.
VALLEYS AND RIVERS
- Magnificent jumps made by stream or river water
- Many falls are easily attributed to unequal erosion of the channel rocks within a short
distance due to the inherent nature of the rocks.
WATERFALLS
✓ Every river receives enormous amount of material during its flow from head to mouth
✓ During transportation, heavier and larger materials move slowly while finer and lighter
material move
SEDIMENT TRANSPORT BY RIVERS
THE TRANSPORT SYSTEM
- BED LOAD
- SUSPENDED LOAD
- DISSOLVED LOAD
This fraction of the river loads comprises the heavier particles of sand, pebbles, gravels
and cobbles and other type of materials which are moved along the other side of the
roads.
BED LOAD
It is made up of fine sand, silt and clay sediments that are light enough to be transported
in the stream water in a state of suspension.
SUSPENDED LOAD
material is transported in a solution condition
DISSOLVED LOAD
- The process of dropping down of its loads by any moving natural agent is technically called deposition
- Wind rivers, glaciers and marine water are important natural agent that make typical deposits.
DEPOSITION BY RIVERS
DEPOSITION BY RIVERS
- ALLUVIAL FANS AND CONES
- NATURAL LEVEES
- DELTAS
- CHANNEL DEPOSITS
If the deposit is spread over a small area but has a relatively steep slope,
On the other hand, if the deposit is spread over a large area and has a gentle slope, it is called
an alluvial fan
ALLUVIAL FANS AND CONES
- These are essentially riverbank deposits made by a river along its bank during floods
- Sometimes helpful in preventing further flooding
NATURAL LEVEES
Defined as alluvial deposits of roughly triangular shape that are deposited by major river at
their mouth where they enter a sea.
DELTAS
- Many streams are forced by some natural causes to deposit some of their loads along the river bed. These are so-called channel deposits.
- They are of great economical use being the source of sands and gravel quite suitable for use as construction materials.
CHANNEL DEPOSITS
Air in motion is called Wind. Wind acts as an agent of erosion, as a carrier for transporting particles and grains that is eroded from one place, and also for depositing huge quantities of such wind-blown material at different places.
WIND
DIFFERENT WORKS OF WIND
- WIND EROSION
- DEFLATION
- ABRASION
- ATTRITION
- It is a process by which soil particles are detached and displaced by the erosive forces of the wind.
- Wind performs the work of erosion by at least three different methods: Deflation, abrasion,
and attrition.
WIND EROSION
Wind posses not much erosive power over rocks the ground covered with vegetation. But when moving with sufficient velocity over dry and loose sand it can remove or swept away
huge quantity of the loose material from the surface
DEFLATION
Wind becomes a powerful agent for rubbing and abrading the rock surface when naturally loaded with sand and dust particles This type of erosion involves rubbing, grinding, and polishing the rock surface.
ABRASION
The sand particles and other particles lifted by the wind from different places are carried away
to considerable distances. The wear and tear of load particles suffered by them due to mutual
impacts during the transportation process is termed as attrition.
ATTRITION
- The wind is an active agent of sediment transport in nature. Materials of fine particle size such as Clay, silt and sand occurring on surface of the earth are transported in huge volumes from one place to another in different regions of the world.
- The transporting power of wind depends on its velocity as also on the size, shape and density of the particles.
SEDIMENTATION TRANSPORT BY WIND
METHODS OF TRANSPORTING SEDIMENTS
- SUSPENSION
- SALTATION
The light-density clay and silt particles may be lifted by the wind from the ground and are carried high up to the upper layer of the wind where they move along with the wind.
SUSPENSION
The heavier and coarse sediments such as sand grains, pebbles, and gravel are lifted up
periodically during high-velocity wind only for a short distance. They may be dropped off and picked up again and again during the transport process.
SALTATION
Sediments and particles once picked up by the wind from any source on the surface are
carried forward for varying distances depending on the carrying capacity of the wind. Wherever and whenever the velocity of wind suffers a check from one reason or another a part or whole of the wind load is deposited at that place. These wind made deposits may ultimately take the shape of landform that is commonly referred as aeolian deposits.
DEPOSITION BY WIND
These are variously shaped deposits of sand-grade particles accumulated by the wind. A
typical sand dune is defined as a broad conical heap. A dune is normally developed when a
sand-laden wind comes across some.
DUNES
- The term Loess is used for wind-blown deposits of silt and clay-grade particles.
- Loess is an unconsolidated, unstratified, and porous accumulation of particles.
LOESS
