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Landforms

Landforms

Section titled “Landforms”

2020-04-28 23:48:56

Mineral and Rocks

Section titled “Mineral and Rocks”
  • Have fixed atomic structure, definite chemical composition, 2 or more elements
  • Crystals appear when Magma cools,

Physical characterstics of minerals :

  • External crystal form ex cubes, hexagonal etc
  • Cleavage - tendency to break forming plane surfaces
  • Fracture - Crystals break irregularly not along cleavage
  • Lustre
  • Other characterstics are colour, streak (colour of ground powder), transparency, structure, hardness and specific gravity.

Metallic Mineral : contain metals ex Precious metals, Ferrous and Non Ferrous metals Non Metallic - ex Sulphur, Nitrates etc

Rocks

Section titled “Rocks”
  • Do not have definite compositin of minerals
  • Petrology is study of rocks

Igneous Rocks

Section titled “Igneous Rocks”
  • Formed by cooling and solidification of Magma and Lava aka primary rocks
  • If molten material is cooled slowly at great depths mineral grains will be very large
  • Sudden cooling will result in small and smooth grains, Intermediate condition will make medium sized grains
  • Examples of igneous rocks are granite, gabbro, pegmatite, basalt, volcanic breccia and tuff

Sedimentary Rocks

Section titled “Sedimentary Rocks”
  • Formed when Igneous, Sedimentary, Metamorphic rocks undergo denudation are later carried and deposited
  • Compaction results in their formation aka lithifaction

What are the different types of Sedimentary rocks?

  • Mechanically formed eg sandstone, conglomerate, limestone, shale, loess
  • Organically formed eg geyserite, chalk, limestone, coal etc
  • Chemically formed eg chert, limestone, halite, potash etc.

Metamorphic Rocks

Section titled “Metamorphic Rocks”
  • Changes form under action of Pressure, Volume, Temp
  • Techtonic process force rocks down which come into contact w/ molten magma, rocks above subject huge pressure -> recrystallisation, reorganisation.
  • Dynamic Metamorphism : change due to rushing and breaking but w/o chemical change
  • Thermal Metamorphism :
    • Contact metamorphism - occurs when rocks come into contact with hot magma and lava
    • Regional metamorphism occurs due deformation caused by tectonic shearing.
  • Rocks, grains or minerals get arranged in layers or lines during metamorphism this is called Foliation or Lineation
  • Alternating layer of light and dark shades in minerals are called Banding
  • MR Classified into foliated and Non foliated
  • Examples rocks are : Gneissoid, Granite, Syenite, Slate, Schist, Marble, Quartzite

Geomorphic Processes

Section titled “Geomorphic Processes”
  • Forces that bring change to surface.
  • Exogenic forces cause degradation and aggradation on surface ex Weathering, wasting, erosion and deposition.
  • Gradation : Wearing down of relief variation through erosion.

Endogenic Geomorphic Processes

Section titled “Endogenic Geomorphic Processes”
  • Energy from within ex Radioactivity, Rotation and Tidal Friction and Primordial heat
  1. Diastrophism : cause surface to move, elevate, build up earth’s crust . Various types of diastrophic processes are :
    • Orogenic : mountain building through severe folding and affects long and narrow belts of earth
    • Epeirogenic : uplift or warping of large parts of crust; continental building process.
    • Earthquakes
    • Plate techtonics
  2. [[1.1 Earth#Volcanoes|Volcanism]]

Exogenic Geomorphic Processes

Section titled “Exogenic Geomorphic Processes”
  • Energy source is atmosphere
  • ==All exogenic forces cause denudation== of material
  • Mechanical and chemical decomposition by weather and climate : Weathering
  • Weathering, Mass Wasting, Erosion and Deposition are examples

Types

Section titled “Types”
  • Weathering :
    Section titled “Weathering :”
    • Mechanical disintegration and Chemical decomposition
    • causes are geological, climatic, topographic, vegetative factors
      • Chemical : ex carbonation, hydration, oxidation etc
      • Physical/Mechanical : ex gravity, expansion due to temp, water pressure
      • Biological : changes caused due to growth/movement of organisms

    Exfoliation #card-reverse

    • Result of Weathering
    • Flaking of curved sheets of shells from rocks etc to form smooth and rounded surface
    • caused due to expansion and contraction
  • Mass Movement
    Section titled “Mass Movement”
    • Rock debris movt under direct influence of Gravity
    • Weathering not a prerequisite
    • No geomorphic processes participate viz glaciers, wind, waves, currents etc
    • Heave, flow and slide are types of movt

    Landslides

    • Rapid movt of rock in a slope without backward movt is called Slide
    • Slump is flow w/ backwards rotation of material, slide has no such phenomena

Erosion and Deposition

Section titled “Erosion and Deposition”
  • Weathering not a precondition
  • Deposition is consequence of erosion when agents lose their[[Soils#Soil Formation|Soil Formation]] is a consequence of it

[[kegy205.pdf]] - Minerals and Rocks [[kegy206.pdf]] - Geomorphic Processes

Running Water

Section titled “Running Water”

When rivers reach maturity in lower slopes, lateral erorsion causes flat low relief plain called peneplaing, the other formation is a Monadnock.

  • Isolated hill of bedrock standing above the general level is called a Monadnock, aka inselberg.
    • alt text
  • Low-relief plain formed by protracted erosion is called Peneplain.
    • alt text

Characterstics of Various Stages of Rivers

Section titled “Characterstics of Various Stages of Rivers”
  • Youth
    • V shaped valleys, Waterfalls, Rapids, Interlocking spurs, Potholes,
    • Meanders can also exist but not widely present
    • Vertical erosion causes steep sides and narrow frills to form V Shaped valleys
  • Mature
    • Floodplains, deep V shaped valleys, strean divides become sharp
    • Swamps and Marshes of Y stage disappear
  • Old
    • Vast Floodplains, Ox bow lakes, Deltas, Natural Levees

Running Water Erosional Landforms

Section titled “Running Water Erosional Landforms”
  • Valleys
    • Start as rills -> gullies -> valleys
    • V-shaped, Gorge, Canyon are types
    • Deep valleys with steep to straight sides they are formed in hard rocks called gorges.
    • alt text
    • Gorge that have steep step like slope are canyons
      • wider at the top than at bottom and forms on sedimentary rocks
  • Potholes and Plungepools
    • Circular depressions formed in rocky beds of hill streams through stream erosion and abrasion of rocks are called Potholes.
    • alt text
  • Series of potholes is a plungepool, formed due to constant rotation of boulders and impact of water within a pothole
  • alt text
  • Incised/Entrenched Meanders
    • When meanders form in hard rocks they are called Incised or entrenched meanders
  • River Terraces
    • Formed due to vertical erosion by the stream into its own depositional floodplain
    • alt text
    • When river terraces occur on either side they are called Paired terraces

Running Water Depositional Landforms

Section titled “Running Water Depositional Landforms”
  • Alluvial Fans
    • formed at foot slope of low gradient when load becomes too heavy for streams to carry
    • cone shaped deposit
    • forms many distributaries
  • Deltas
    • Similar to Alluvial fans but form at mouths of river.
    • Well sorted with clear stratification - coarser material settles first finer ones carried to sea
  • Floodplains
    • formed when water spills over the banks and deposits silt and clay
    • When they are above the banks called inactive floodplain.
    • contain 2 types of deposit : flood and channel deposits.
    • Natural Levees.
      • Low linear and parallel ridges of coarse deposits along the banks of river are called
    • alt text
    • Point Bars aka Meander Bars found in concave side of ox bow lakes are sediments deposited inlinear fashion along banks contains mixed size of sediments
  • Meander
    • Formed due to lateral erosion of streams flowing over gentle slope common in flood and delta plains
    • alt text
    • not a landform but a type of channel pattern formed due to :
      • Lateral erosion in gentler slopes
      • unconsolidate alluvial deposits exerting lateral pressure
      • coriolis force acting

Groundwater

Section titled “Groundwater”

Groundwater Erosional Landforms

Section titled “Groundwater Erosional Landforms”
  • Karst topography
    • formed underground due to dissolution of sloluble rocks viz limestone, dolomite, gypsum etc
    • characterised by sinkholes and caves.
    • alt text
      • Small to medium sized round to sub rounded shallow depressions
      • formed on the surface of limestones
    • Sinkholes
      • openings circular at top and funnel shaped towards bottom
      • connected to a cave/roof of a void at the bottom
      • may collapse forming dolines
    • Uvalas
      • Closed Karst depressions
      • formed when sink holes and dolines join together because of slumping of materials along the margins or due to roof collapse.
  • Lapies or Karren or Ridges
    • Irregular, grooved, ridge like features in an open limestone field
    • formed due to solution activity along parallel and sub paralleljoints
    • eventually transform into limestone pavements
  • Caves
    • formed when water percolates and dissolves limestones
    • Cave w/ openings on both sides called tunnels

Groundwater Depositional Landforms

Section titled “Groundwater Depositional Landforms”
  • Stalacites hang like icicles in caves they drip to form Stalgamites at bottom.
  • Eventually both join to form pillars and columns

Glaciers

Section titled “Glaciers”
  • Piedmont glacier
    • valley glacier that spilled onto relatively flat plains
    • alt text

Glacier Erosional Landforms

Section titled “Glacier Erosional Landforms”
  • Cirques
    • bowl-shaped, deep, long and wide depressions that glaciers carve into mountains and valley sidewalls at high elevations.
    • Lakes can form at such places they are called cirque or tarn lakes.
  • Horns
    • formed when 3 or more radiating glaciers cut headward until their cirques meet.
  • Serrated/Saw Toothed Ridges
    • divide between cirques or head walls get narrow and turn into Serrated or saw tooth ridges aka Aretes.
    • alt text
  • Glacial Valleys/ Troughs
    • U Shaped w/ broad floors, smooth and steep sides
    • may contain Moraines
    • Fjords are Deep glacial troughs filled with sea water making up the shorelines.

Glacier Depositional Landorms

Section titled “Glacier Depositional Landorms”
  • Glacial tills - unassorted, coarse and fine debris dropped by melting galciers. Rock fragments are angular/sub angular
  • Moraines are Glacially formed accumulation of unconsolidated glacial debris (regolith and rock)
  • alt text
  • Outwash deposits are glacio fluvial deposits are stratified and assorted
  • Moraines
    • long ridges of deposits of glacial tills
    • Types of Moraines :
      • Lateral moraines : parallel to valleys they join to from horse shoe shaped ridge.
      • Ground Moraine : formed by retreating glacier leave irregular sheet of till
      • Medial Moraine in the centre.
    • Hanging Valleys are tributary valleys that hang above the main valley, commonly seen in U Shaped valleys.
  • Winding ridge of un-assorted depositions of rock, gravel, clay etc. running along a glacier in a till plain are called Eskers
  • alt text
  • Drumlin :
    • Inverted boat-shaped deposition in a till plain caused by deposition
    • has a stoss end and a tail
    • composed of gravel, sand

[[kegy207.pdf]] - Landforms and their evolution