LANDFORMS AND THEIR EVOLUTION(part1)

 LANDFORMS AND THEIR EVOLUTION

The earth surface does not have a regular shape in some places it is rugged while in other places it is undulating. Landforms are defined as specific features that appear on the surface of the earth. Some examples are mountains, plains, plateaus, valleys and hills. What is responsible for the formation of these landforms are the forces that work internally and externally on the Earth's surface.

Two forces are responsible for producing the major landforms and the unevenness of the earth surface. these are:

• Internal forces, otherwise known as tectonic forces or forces of diastrophism. These are forces acting underneath the surface to produce structural changes in the rocks.
• External forces, refer to forces acting on the surface of the earth to reshape it.
  Even where the land is level, some of these forces are also responsible for its being level. They act all the time.

Internal forces
Internal forces compress, tear, shatter, tilt, twist, fracture and dislocate the earth crust in many ways. This forces might be horizontal or vertical. Horizontal forces are either tensional forces when they pull apart, or compressional forces, when they pull towards each other. The forces disfigure the earth crust in many ways:

• Compressional forces give rise to folding or wrinkling of the rocks
• Both forces can in faulting or permanent fracturing of the rock in down warping or broad sagging or arching of the earth crust.
• Vertical forces sometimes push molten rocks called magma midway or all the way to the surface in a process called volcanicity or cause the earth crust to tremble in earthquakes.

External
Once the internal forces produce the landforms, external forces start to modify or reshape their surface immediately. We know more about these forces because we see them act on the surface. They are:

• Forces of erosion, which causes pieces of rocks to decay or weather and tear off from their parent rock.
• Forces of transportation, which carry these eroded material away to another location.
• Forces of deposition,which cause the materials to be deposited in the new location.

The forces of erosion and denudation together is known as denudation and those of deposition are generated by certain factors or agents. These include changes of temperature, running water, winds, ocean wave and glaciers. These factors are called agents of denudation and deposition.

RUNNING WATER

1.In humid regions rainfall is heavy so running water is dominant agent 2.there are two components of running water

 A. OVERLAND FLOW –SHEET EROSION     B. LINEAR FLOW –STREAM EROSION

Most of the erosional features are formed in upper course/youth ful stage of the river Depositional features are formed in the lower course /old stage of the river Steep the slo[e more the erosion/gentle the slope more the deposition Vertical erosion is more in the upper course lateral erosion is more in the lower course

 OVERLAND FLOW: 

it is also called as sheet erosion Depending on the irregularities of the surface the sheet erosion concentrate in to channels Due to sheer friction of the water narrow channels are formed They are called rills. Rills develop into gullies, gullies further deepen and converted into valleys In the erly stages downward cutting makes waterfalls, cascades in the middle stages streams cut their beds slower and lateral erosion of valley sides becomes severe. Later stages, the flat valley is formed with monadnocks. This type of plain is called peneplain.

 

Stages of the river

YOUTH

1.Less Streams 2. Less Integration 3. ‗V‘ shaped Valleys Are Common 4.Stream Divides Are Swampy Marshy Areas 5. Water Falls And Rapids Are Common

 

MATURE

1.More Streams 2. More Integration Of Streams 3.Deep ‗V‘ shaped Valleys4.Wider Flood Plains 5.Meanders Are Present 6.Rapids And Water Falls Disappear

 

OLD

1.Smaller Tributaries 2.Few In Number 3. Flood Plains Are Common 4. Natural Leaves And Oxbow Lakes Are Also Present 5. Most Of The Landscape Is Just Above Sea Level.

DIFFERENCE BETWEEN GORGE AND CANYON

GORGE                                             CANYON

1. steep sides                                          1. Step like sides

2. equal width of top and bottom              2.wider at the top and narrow at the bottom

 3.small in length                                     3. Longer in length

4.they are found in semi arid lands          4. Found in dry area   grand canyon bramhaputra gorge                ex  grand

POT HOLES:

 1. They are circular depressions 2.formed by abrasion 3.pebbles and boulders get collected in these holes and rotated and make depression wider and deep 4. They keep valley deepened 5.at the foot of the water falls they become plunge pools

PLUNGE POOLS

•  Found Foot Of The Water Falls
•  Formed Due To Soft Rocks
•  They Are Below The Level Of River Bed 

MEANDERS 

1. Lateral erosion is common in the lower course of the rivers

 2. Due to low kinetic energy water is changing its course 

3. Generally found in the flood plains

 4. When meanders are found in deep and hard rocky areas they are called incised or entrenched meanders

 5. Same meanders develop loops which later on converted

6.Some times they deepen the rocks and converted into canyons

RIVER TERRACES

Marking old valley floor They represent flood plain levels They may consist of stream deposits They are formed due to vertical erosion There may be number of formal flood plains

If they are at the same level they are called paired terraces If they are found at different levels    they are   called   nonpaired Unpaired terraces are found in the areas of slow upliftment areas Reasons for the formation of river terraces

1. receding water after a peak flow

2. change in hydrological regime due climatic change 

3.tectonic uplift of land

4. sea level changes  incase of rivers closer to the sea    alluvial fans.

1. Found near the foot of the hills

2. The river break into number of channels

3. Low gradient

4. Coarse load is deposited

5. Low gradient 

6. Cone shaped deposit 

7. Channels shift their position in the plain 

8. They are called distributaries 

9. Cones are gentle slope in humid areas and dry lands they have steep slope

Formed along the river banks 

1. Made of alluvial soils 

2. They are divided into two types khadar and banger

3. Khadar soils are found near the river and banger soils are found away from the river

4. They are very fertile 

DELTAS

 1.Found near by the mouth of the river 

2. Made of fine alluvial soils

3. They are in triangular shape

5. Similar to Greek letter Delta 

6. Divided by distributaries

 7. Deposited material is stratified on the basis of size. Coarse material is deposited first and then fine material