Geography Chap 4,5 (Goh Cheng Leong + NCERT)

Chap 5
Landforms made by running water

chapter=4:
Background of Ground water:
--Porus rocks:
        > Allows water to be stored in gap.
        >Grain size =High
        >Example= Clay(large particle) but it’s impermeable.
--Permiable rock:
        >Allows water to flow through it.
        >Grain size= Small.
        >Example= Granite ==many cracks/ faults in it allows water to flow.
                              >>But small grain size doesn’t allow water to enter crystal
Conclusion:
Water table= fluctuates very fastly in a region with Permeable+ non porus rocks.

Development of River system:
--Drainage tributary = Oblique + Right angle.
     >Oblique= When underlying rocks= Homogenous. = Dendritic drainage.
     >Right angle=Out crops of roct—at right angle to main stream. =Trelised drainage.

Mechanism of Humid erosion:
--Soil creep = soil moves down the slope @ Gravity
                   >Water does lubrication= speed ups.
--Land slide=under cutting may result into it.

Processes of River Action:
--River loads (3 type):
     >Materials in solution= ex- minerals.
     >Materials in Suspension= ex- Clay, sand, mud etc
     >The traction load= ex- pabbles, stone, rocks etc
--Suspension = 4 X solution.
--Factors(@river)=Velocity+ volume + Load geometry(Shape,size etc).

River erosion and transportation:
--Erosion + Transportation= simultaneously.
--Corrosion(Abrasion) = mech grinding(Sideway@ banks + bottom)
--Reason= Traction load
     >Type:
        >>Lateral corrosion= V-valley into U-valley.
        >>Vertical corrosion= depth ↑
--Corrosion(Solution)=Chemical/ solvent
    >ex- Limeston rock dissolves in Water
--Hydrolic action:
     >by river water itself= splash of water eroding bank.
     >Forms= cracks and crevices.
--Attrition:
     >wear and tear of transported material.
     >gets rounded à lighter moves farther.

The course of River:

The upper/Mountain Course:
--usually at Source/watershed.
--vertical erosion= down cutting is so rapid that lateral cutting can’t take place.   
--formation= V-shaped valley, Gorges, Canyons.
  >V-shaped valley:
    >>Forms = vertical cutting> lateral cutting.
  >Gorges=resistive rocks==narrow valley==steep sides. Ex= Indus gorge, Kashmir.
  >Canyons=Arid region= little rainfall to widen ==cuts deep. Ex=Great canyon.

-- -- River Capture (image ↓):

      >it produces sudden change in river volume.
      >though takes a long time in river behading.
      >Ex- Yamuna flew in West making Saraswati== now east ----Chambal took the pirated water.
-- --Rapids, cataracts and waterfalls:
       >Region= mostly mounatneous = abrupt change in gradient.
       >Rapids (image ↓):

         >>alternate= soft and hard rock.
         >>with time soft erode= leaving outcrop of hard rock.
         >>Water jumps, as shown in above image ↑.
    
      >Cataract:
         >>greater dimension of “Rapids”.

      >Water fall:
        1)resistant rock=lying transverse.=Ex- Niagra fall
        2)Fault line scarp = Ex- Victoria Fall on Zambeji river (Zambia)
        3)Edge of plateau= Ex-River congo.
        4)Glaciation =produces “Hanging calley”= Ex- Yosemite Fall, California.

The Middle or Valley Course:
--Lateral corrosion > Vertical corrosion.
--V-shaped to----- U-shaped.
--Volume ↑ = confluence of many tributaries.==Load↑.
--increased load= primary work “Transportation with some deposition”.
--Inter-locking pattern= due to soil creep + land slide + deposition etc (image ↓):

-- --Meander:
      >some times forms ox bow lakes .
-- --River cliff and slip- off slopes:
      > river if meanders>>> due to inertia strikes bank >>> erodes= vertical “river cliff” >>> deposits on other side = due to centrifugal circulation set by impact on cliff side.
(Image ↓):

-- --Inter locking spurs:
      >Meander in “middle course” unlike in plain causes “Interlocking counter”……in plain it expands.
(Image ↓):

The lower or Plain course:
--Vertical corrosion virtually ceased.
--Lateral still occurs.
--Thus widening of river plain.
--Coarse material are dropped>>>>finer are carried.
--Large sheet of material are deposited in path of river forming “Braided pattern (Image ↓)”:

--major forms:
-- -- Flood plain:
      >Tethy sea-------is now filled with “Deposition by himalyan rivers”.
      >therefore this reason is now famously called= Gana Plain.
      >other ex= Yangtze , Mississippi, Po(across N. Itly from alps) , Hwan ho(Sorrow of China).

-- --Ox-bow lakes:
      >cutting out from “Meandering river” (Image ↓):

-- --Delta:
      >extension of flood plain into sea.
      >Aluvial deposit into sea.
      >ganga delta = sundarban
      >Condition of Delta formation:
        >> 1)more load capacity of river.
        >> 2)Tide less coast  .
        >> 3)Shallow coast.
        >> 4)no inland lake in the depositing river to filter the load.
        >> 5)no perpendicular river to main river----wash away deposits.

River rejuvenation:
(Being young again)
--if sea level falls or deposition ↑ = hydrostatic potential of water ↑
--more cutting = young behavior .
--Rejuvenation impact:
   > upper coarse = deep gorges
   >Middle or Lower= existing meanders are vertically eroded>>> Vertical corrosion replaces lateral corrosion.
--When opposite of renovation= rise of sea level ↑= deposition increases.

Artificial rejuvenation:
-Dredging