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AS Level Physical Geography - Rocks and Weathering

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AS Level Physical Geography - Rocks and Weathering

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The earth's surface is an ever-changing entity. With the forces of weather and climate and tectonic variability, the rocks and minerals that make up the earth are always changing in size, shape and forms - a fascinating, ancient, never-ending process.

The earth's surface is an ever-changing entity. With the forces of weather and climate and tectonic variability, the rocks and minerals that make up the earth are always changing in size, shape and forms - a fascinating, ancient, never-ending process.

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AS Level Physical Geography - Rocks and Weathering

  1. 1. Rocks/ Weathering AS Level Physical Geography
  2. 2. Definitions • Accretion: the process by which a substance grows by the collection and clustering of different parts • Geomorphology: The study of origin and evolution of topographic and bathymetric features created by physical, chemical and biological processes at or near the earth surface. • Silicates: Most common group of minerals – include silicon and oxygen • Magnetic Field: Area around and affected by a magnet or charged particles
  3. 3. THE BEGINNING OF IT ALL Introduction
  4. 4. Formation of Earth • Collisions of objects in the galaxy – forming protoplanets • Soon the planets arrange into the 8 planets • Asteroid belt between Mars and Jupiter (messed up planet)
  5. 5. Formation of Earth • Earth is formed • Process of differentiation • Heavy elements (NIFE) sink to the core • Lighter elements (Silicates float to surface)
  6. 6. Formation of Earth • Another object collided with earth • Some of earth’s materials knocked out • Accreted and formed moon
  7. 7. Formation of earth • Earth cools down at 3.8 – 4 billion years ago • Water vapor condenses • Torrential rain • Ocean was formed then
  8. 8. Start of Life • 3.8 Billion years ago • Prokaryote first appears • Start photosynthesizing • Oxygen produced • The reactivity of oxygen caused Oxygen holocaust – 2.5 Billion – killed off a lot of single cell organisms • 1.7 Billion years ago - Eukaryote
  9. 9. GEOLOGICALEPOCHS GEOLOGICALEPOCHS
  10. 10. A PROFILE OF EARTH INTRODUCTION https://www.youtube.com/watch?v=zw- z_iTnIdc&feature=iv&src_vid=PT7qhBUffvY&annotation_id=annota tion_3093859399
  11. 11. Our Solar System
  12. 12. About Earth • 3rd Planet from the Sun • 150 million kilometers from the sun • Diameter: 12,756 km • 365.256 Days to orbit the sun • 24.9345 hours to rotate once
  13. 13. Earth – and Life • The only planet to harbor life • Rapid Spin + NIFE (Nickel, Iron) core = large magnetic field • Atmosphere • Both of the above shielded earth from radiation/ meteors
  14. 14. The Atmosphere
  15. 15. The Hydrosphere
  16. 16. The Lithosphere
  17. 17. Definition of Rocks and Minerals • A mineral is an inorganic, naturally occurring solid that has a definite chemical composition and an atomic structure • Inorganic: Not living, not composed of biological • Definite chemical composition: Unique elemental make-up • Feldspar, Sulfur, Quartz • Color, Hardness, Luster(metallic/non-metallic), streak(color in particles), cleavage/fracture • Building blocks of rocks
  18. 18. PLATE TECTONIC Part 1
  19. 19. Earth’s Interior • Scientists can determine earth’s inner core through seismology/ nebular theory • Seismo = Greek for shock
  20. 20. Seismic movement • 4 categories of seismic waves • Most waves are between: 3 – 15 km/s • 2 types travelled along the surface in rolling swell • Primary(compression)/ Secondary(shear) waves – penetrates the earth’s interior • Primary travels through rocks/ water • Secondary cannot travel through rock • Speed of waves reduce when in contact with hotter matter • These differences in seismology allow scientists to identify the different properties of rocks underground
  21. 21. Earth’s Interior
  22. 22. Mechanical layer of the earth • The topmost = crust • Under the crust – the coolest top layer of the mantle – Elements are different from the crust • LITHOSPHERE 10 – 200 KM – 10 is unusual, usually close to the hotspot • Deeper you go… ASTHENOSPHER (Still act like solid – jelly, puddy layer, the temperature semi - melted the rock – the plates move on top of this [660 km deep]) • Next layer of the mantle (MESOSPHERE – don’t confuse with the atmospheric Mesosphere) – still act like solid • OUTER CORE – The high temperature comes into effect here – the temperature overrides the pressure – the pressure can not affect the metal too much – liquid-like (5100 KM) • INNER CORE – Solid due to pressure – 1218 km
  23. 23. Chemical Structure • The Denser element sunk to the center during the formation of earth • The core is almost entirely made up of heavy metal
  24. 24. Earth is shaped from the inside out • Transfer of heat (hotspot, convection current) or more specifically energy – determines the landscape of the earth • Causes plate tectonic • Volcanic eruption • Earthquake • Seafloor spreading • Orogeny (Mountain building)
  25. 25. Inner Core • A very hot, very dense center of the planet • Radius about 1218 km • 1.7% of earth’s mass • Inner core is solid • Frozen with high pressure • NIFE (Nickel, Iron)
  26. 26. Outer Core • 30.8% of the earth’s mass • 2200 km thick • Liquid-like • Composition: NiFe • Conductive/ hot – site of violent convection • Electrical current caused by churning of metals here forms magnetic fields • Still NIFE – however may contain Oxygen/ Sulfur • Bullen discontinuity borders the core and the mantle – the hottest
  27. 27. Mantle • The most solid bulk of the earth’s interior (semi- molten) • 84% of the earth’s volume • At 4.5 billion years ago, iron and nickel separate from other minerals to form the core while other molten materials formed the mantle. • Mantle solidifies into molten state during outgassing where water erupts with lava • Materials: Silicate (oxygen+Silicon), Calcium, Sodium, Aluminum, Iron, Magnesium oxide • Mantle is more viscous near plate boundary and magma plume
  28. 28. Oceanic Crust • Formed at points of sea floor spreading center (Mid Atlantic Ridge/ Pacific Rise) • 0.99% of earth’s mass • 200 million years old • Dense – 3.0 g/cm3 • Thinner – 6 - 16 km • New – new lands are formed here • Basaltic Rock (Igneous) (SIMA) (MAFIC) • Starts at mid ocean ridge – ends at subduction zone • Edge can be stranded on land
  29. 29. Continental Crust • Formed through arc volcanism and accretion • 0.347% of the earth mass • 4 billion years old • Lighter – 2.6 g/cm3 • Made up of crystalline rock – with quartz and feldspar • Thicker – average up to 30 – 70 km in thickness
  30. 30. Difference between Basaltic/ Igneous Rock • Basaltic – extrusive igneous rock (Volcanic) – Magma burst out through the earth surface and cools down quickly – not much time for mineral crystals • Granitic – Intrusive igneous rock (Plutonic) – crystals form due to the slow cooling in the earth continent
  31. 31. Factors affecting the earth’s surface • Movement of the plates • Earthquake and seismic activities • Volcanic activities • Formation of fold mountains • Chemical weathering • Changes in temperature leading to wethering • Erosion by wind • Hydrology
  32. 32. The Plate Tectonic Theory – Key Principles • Outer layer of earth divided into Lithosphere and Asthenosphere • Asthenosphere has a convection current and an almost adiabatic heat gradient • The lighter lithosphere is divided into different plates – riding on the more viscous and dense asthenosphere • 1 tectonic plate = lithospheric mantle with crustal materials on top • Points where 2 plates meet = plate boundaries
  33. 33. The Continental Drift Theory • First introduced by Alfred Wegener • A German meteorologist • In 1911, he found the that similar organisms could be found in different continents across the Atlantic
  34. 34. The Continental Drift Theory • The continents seemed to fit like jigsaws – the eastern coast of South America and the Western coast of Africa • Some other scientists supported him with fossils ideas as well as evidences of fold mountains • However, Wegener couldn’t come up with a mechanism to support the movement of plate
  35. 35. Mohorovicic Discontinuity • If the earth was made of uniform mass (which it isn’t) – the materials would get denser to the center – the time taken for a wave to get to a distance should be proportional to the distance (same velocity) • 1909 earthquake – Andrija Mohorovicic – at 200 km from the earthquake – the wave began to accelerate • He realized the wave must’ve been travelling through a denser layer of the earth – it refracted to the direction it was going – acceleration • The boundary between mantle/ crust is now called the Mohorovicic discontinuity
  36. 36. The Plate Tectonic Theory • Since the 1950s – further exploration of the theory supported Wegener’s claim • Early 1960s – Hess and Dietz – discovery of the Mid Atlantic Ridge and Sea Floor Spreading • Discovery of paleomagnetism
  37. 37. Evidences supporting the theory
  38. 38. 1. The Fitting of the continents The Shapes of the continents fit together very well – this was first noted by Francis Bacon in the 16th century. The most visible fitting is between South America and Africa
  39. 39. 2. Biological Fossil Evidenced Various fossils found across the earth’s continents e.g. discovery of the Mesosaurus fossil in both South America and India – discovery of plant fossil like Glossopteris in the southern continents.
  40. 40. 3. Geological Evidence Glacial depositions that seems connected between Antarctica and brazil. Fold Mountains – e.g. The Swiss Alp Later – The Appalachian mountain range was also used as an evidence for the connection between the Eurasian and the North American Plate
  41. 41. 4. The Mid Atlantic Ridge A distinct land form discovered in 1948 – found at divergent plate boundary - showing that two plates are actually coming apart
  42. 42. 5. Seismic evidence/ Activity Seismic, volcanic and geothermal activity found in connected network of lines This includes the Mohorovicic Discontinuity
  43. 43. 6. Paleomagnetism Magnetic anomaly existing in bands of rocks across the mid Atlantic ridge – also symmetrical to between the 2 sides of the ridge: Best explanation is when the plate diverges, the magma rises, as it cools and harden, it obtains the current magnetic field of the earth which keeps on changing - hence the anomaly.
  44. 44. Mantle Convection • The theory first put forth by Arthur Holmes in the 1930s • The differences between temperature beneath the lithosphere creates a convection current which moves the plate • There are many theories regarding how plates move • Debates are still going on regarding this
  45. 45. The Hotspot Theory • The Hotspot theory states that the activities in the core causes semi molten parts of the mantle to rise • The creates a plume of magma rising . • As the viscous rocks reach the plate – the magma might break through – causing rifts • The magma flowing outward as they reach the plate may create dragging forces • However, the greatest hotspot of the world – Hawaii – is not a plate boundary
  46. 46. The Dragging Theory • His states that the colder edges of the plates are colder and denser • They therefore sink at points of subduction • His sinking causes a dragging process
  47. 47. Plate boundary type1: Divergent • 2 Plates moving apart – could be due to rising of hot matters starting from the core (hotspot theory) • Also called Constructive plate margin (constructs new land) • Magma creates a lump/ an arch in the lithosphere • The arc becomes a crack in the lithosphere • Magma rises up – filling in the gaps between the plates • The magma rises up due to lower density of the asthenosphere. • This also pushes the plates apart
  48. 48. Sea-floor spreading • At Divergent plates boundary • The crack appears at the ocean floor • Heat from asthenosphere makes material hot and less dense – these rises forming an elevated ocean floor • Crack widens – magma bubbles up and spill over • The sea water cools down the magma – turns into igneous rock (basaltic) – becomes a new earth crust
  49. 49. Mid Ocean Ridges • The elevated ocean floors form large mountain ranges e.g. Mid Atlantic Ridges or the East Pacific Rise or the Southeast Indian Ridge • Slow spreading ridges = tall narrow cliffs/ mountains – because of smaller magma chamber = discontinuous eruptions • Fast spreading ridge = large magma chamber = sheets of lava = gentler slopes • As the oceanic crust moves away – it becomes thicker • The end of the plate sees a collision
  50. 50. Rift Valley • Occur when two plates move apart • Two plates moving apart – creates cracks • The land in between the cracks begin to sink • Leaving a valley • Often found at Transform faults or triple junctions
  51. 51. Plate boundary type2: Convergent • Two plates converge/ collide • May be oceanic vs. Continental, oceanic vs. oceanic or continental vs. continental • Produce different landforms
  52. 52. Subduction Zone • Elements: 1. Subduction Complex 2. Accretionary Prism/ wedge 3. Ocean trench 4. Fore-arc basin 5. Sedimentary arc 6. Volcanic Arc 7. Volcanic island 8. Back-arc basin
  53. 53. Fold Mountains • When 2 plates collide • Oceanic + continental – the heavier/ denser oceanic sinks into the asthenosphere. • One plate subducts beneath another • This forces the continental plate to buckle and fold inland • The land rises into a mountain range e.g. The Andes • In areas such as these – fore arc basins may accrete to form a rising mountain • Front island arcs may also be of causes • Subduction zone – means volcanic arc may be formed
  54. 54. Fold Mountains • Continental crust + Continental crust • Both are equally dense – they collide • Sediments on both basins are folded and buckled – forming a huge mountain range • Generally – oceanic lithosphere is lost between them • These may cause some insignificant volcanic activities
  55. 55. Ocean Trenches • A deeper part of the ocean where subduction takes place • Where one plate is subducted right beneath the other – there is an area where the ocean floor deepens • This point – can be quite hot – proximity to the asthenosphere • Trench outer rise – marking the point where the plate is subducted • Outer slope – gentle • Inner slope - steep • E.g. Mariana trench
  56. 56. Island Arcs • Where oceanic lithospheres collide • The denser one will sink beneath • Destroyed at asthenosphere • The water on the subducting sphere – cause melting • This melted material rise • Creating a bulge then breaking through • Solidifies into an island • The island arc runs along a boundary • There may be volcanic feature • Island arcs can also be formed at Hotspot points
  57. 57. Plate boundary type3: Transform • When two plates move alongside each other • There is no spreading or destroying of plates here • May be caused by diverging/ converging of nearby boundaries • Rift valleys may be formed • Faults will be formed • May offset nearby landforms • San Andreas fault – best example
  58. 58. Earthquake • Earthquakes may occur when there is a release of pressure at plate boundaries
  59. 59. Earthquakes at Divergent boundary • shallow earthquake at sea floor spreading regions – there isn’t much friction or pressure however
  60. 60. Earthquakes at Convergent plate boundary • Deep earthquake at the benioff zone (Wadati- benioff zone – points angling at 30 – 45 degrees) • Major earthquakes when plates sliding under another plate – frictions are caused • E.g. 2004 Tsunami – caused by Indo-Australian plate subducting beneath the Eurasian plate
  61. 61. Transform plate boundary • Release of pressure • One plate may stop when friction is too great • When this friction is overcame – a release of pressure • The 1906, 1989 earthquake in San Francisco
  62. 62. Tsunami • Occurs near subducting plate margins • A bulge in the ocean floor caused by the accumulation of magma beneath the overlying plate • OR… the general bulging caused by the dipping of the subducting plate • This makes the ocean floor rise • Water is pushed up some 15 m • Causing huge Tsunami waves
  63. 63. Vulcanicity/ Volcanology • All the processes by which solid, liquid or gaseous materials are forced into the earth’s crust or are ejected into the earth surface
  64. 64. Causes of Volcanic eruption • Release of pressure at local points • Due to folding, faulting, other movements • Semi-molten magma becomes molten • Reduction in density causes magma to rise • Forces its way through weaknesses in the crust
  65. 65. Extrusive vs. Intrusive • Extrusive Rocks • Magma reaches the surface and cools quickly • Not much crystal formed • e.g. Basalt • The Oceanic plates
  66. 66. Extrusive vs. Intrusive • Magma doesn’t reach the surface • Injected into the earth’s crust • Cools, hardens slowly under the surface • Exposed by removal of overlying rocks • Large crystals
  67. 67. Extrusive Landforms
  68. 68. Lava • The types of Extrusive landforms depends on: • Viscosity of the lava • Gaseousness of the lava
  69. 69. Basaltic Lava • Upward movement of mantle materials • At ocean ridges (Mid Atlantic) • Hotspot points (Hawaii) • Rift Valley (Ethiopia)
  70. 70. Andesitic Lava • Result of the Subduction process • Occurs as island arcs • Volcanic eruptions • E.g. Andes
  71. 71. Pyroclastic materials • Materials ejected by Volcanoes in fragments 1. Tephra 2. Ash 3. Lapilli (small stones) 4. Bombs • Pyroclastic flow move down the side as clouds • Heavy rainfall
  72. 72. Basaltic vs. Andesitic • Low viscosity, hotter (1200oC) • Lower silica content • Longer time to cools, flow at longer distance • Extensive, gentle slope landform • Frequent, gentle eruption • Lava/ steam ejected • High viscosity, less hot (800oC) • Higher silica content • Shorter time to cool, flow at shorter distance • Steesides, local feature • Less frequent eruption but violent due to gas build-up • Pyroclastic materials ejected
  73. 73. Different Types of Volcanoes • Fissure eruptions e.g. Iceland • Basic/ Shield e.g. Mauna Loa • Acid/ Dome e.g. Karymsky • Ash Volcano • Composite Volcano e.g.. Vesuvius • Caldera e.g. Andes
  74. 74. Minor Extrusive landforms • Mud Volcanoes: Combination of hot mud/ water • Sulfatara: Gas such as Sulphur released from cracks • Geysers: Water vapors heats up and rises, pressure increases, steam exploding through at points of weaknesses • Fumeroles: Superheated water reaches the surface, reduction in pressure casues it to turn to steam
  75. 75. Nature of Explosions 1. Icelandic: Lava flow gently from a fissure 2. Hawaiian: lava emitted gently from a vent 3. Strombolian: Small but frequent eruption 4. Vesuvian: More violent, less frequent 5. Krakatoan: Explosions violent enough to remove original cone 6. Pelean: Violent eruption with Pyroclastic flow 7. Plinian: Large amount of materials and lava are ejected
  76. 76. Hydromagmatic • Any eruptive processes where magma and lava interacts with water • Deep marine eruptions – pressure of water suppresses lava to undergo cooling: forms pillow lava • Lava flows into the sea • Shallow marine eruption • Crater lake eruption • Subglacial e.g. Vatnajokull • Magma comes into contact with groundwater
  77. 77. Intrusive Landforms
  78. 78. Intrusive Landforms • Most of the magma do not reach surface • Intruded into the crust – where it solidifies • When overlying rocks worn away • Landforms are revealed
  79. 79. Batholith
  80. 80. Dikes
  81. 81. Sill
  82. 82. The Pacific Ring of Fire • An area of high volcanic and seismic activities found along plate boundaries of the Pacific islands • These plates are generally subducting • 90% of volcanic activities appear here • 75% of the active volcanoes are here • Course: Southern tip of South America – along the coast of north America – across the Bering strait – through Japan – into New Zealand
  83. 83. ROCKS AND WEATHERING Part 2
  84. 84. The Rock Cycle • The Rock Cycle is a model that describes the formation, breakdown and reformation of rocks into 3 main rock types • Igneous • Sedimentary • Metamorphic
  85. 85. Igneous Rocks • Rocks that are formed from the cooling and solidifying of the lava • Can be intrusive or extrusive • Example: Granite
  86. 86. Sedimentary Rocks • Rocks that are formed by sediments deposited by erosion. • Example: Limestone – Carboniferous and Dolomites - sandstone
  87. 87. Metamorphic Rock • Rocks that are formed from igneous and sedimentary rocks under under high heat and pressure • Example: Gneiss, Slate, Marbles, Quartsize
  88. 88. Physical Weathering • Freeze Thaw • Exfoliation • Crystallization • Pressure Release
  89. 89. Freeze Thaw Freeze Thaw weathering is when rain water (precipitation- can be snowmelt) enters the joints/ cracks on a rock surface. As the temperature drops, the water freezes causing it to expand by 9- 10%. This increases the pressure exerted to about 14 kg/cm2. This exceeds the resistance of most rocks. When the temperature increases, the water melts again. By now the crack has widen and deepen [Frost shattering], the water enters deeper into the rock. More rainwater fills in the gap. The process repeats itself
  90. 90. Features supporting freeze Thaw weathering • Temperature fluctuating around 0oC – hence freezing is involved. • Places: Alpine regions, periglacial climate, polar climate is less often (lack of freeze thaw cycle) • Mountainous region • North facing slope in the Northern hemisphere, or a South facing slope in the Southern hemisphere • Precipitation required
  91. 91. Features supporting freeze Thaw weathering • Rocks may also be porous – eg. Sandstone • Rock has to be EXPOSED – not covered in vegetation • Hence, too much precipitation will not be good – as it leads to more vegetation
  92. 92. Results • Frost shattering: materials broken down into small angular fragments – clastic states e.g. fragmented – at foot of mountains/ slopes • Frost wedging: Block disintegration • Frost spalling • Frost susceptible soil – result in capillary actions of water to move toward freezing front – hence soil creep upward – may form terracettes.
  93. 93. Exfoliation Direct heating ray from insolation of the sun heats up the rock. Rocks are poor conductor of heat – hence only the outer layer begins to expand. At night, the temperate becomes lower, causing the rock to contract – once again, this mainly affects the outer layer. This cycle of expansion and contraction combines with the fact that different minerals in the rocks expand at different rates lead to the rocks having lower stability. Finally, the outer layer of the rock peels off like an onion skin. This also leads into pressure release…
  94. 94. Features affecting • Wide ranging Diurnal temperature variation between day and night – achieved in the arid regions. • The lack of precipitation = less vegetation cover = maximum insolation • High insolation so lack of cloud cover • Lack of cloud cover --- maximum out-radiation at night – colder night temperature • Griggs(1936) proved an idea that some moisture will be needed for rocks to expand • Rocks compositions • Exposure of rock face
  95. 95. Results • Divides rocks into sub-planar slabs • As the outer layer peels away, the pressure is released – causing the underlying rock to expand and fracture parallel to the surface. – pressure release • Disintegration blocks/ screes can be found
  96. 96. Salt Crystallization 1. Temperature rises (26-28oC) – causing Sodium sulphate and Sodium carbonate to expand by 3 times. Once again the pressure forces the joints to widen– or destabilize the rock. 2. Water with salt evaporates away – leaving crystals. These expand under high temperature.
  97. 97. Feature affecting • Rock may contain salt • Rocks may be porous/ permeable • Surface texture – speed of breakdown increase over time with coarse materials • Arid climate – the evaporation of water will leave salt close to the surface • Coastal area – sea water • Salt from snowflake in Alpine regions
  98. 98. Results • Most effective salts: Sodium sulphate, Magnesium Sulphate, Calcium Chloride • Produces the highest rate of break down • When combined with freeze-thaw
  99. 99. Pressure Release When overlying rocks are removed, the underlying rocks experience release in pressure that cause it to expand – fracturing parallel to the surface. The removal of overlying rocks can be the result of exfoliation, erosions or rock falls (if we are talking about a cliff face)
  100. 100. PRESSURE RELEASE • Rocks are usually formed under the surface – under high pressure. • The unloading of such pressure • Cause cracks/ joints to form at right angle to the unloading surface • Hence at pseudo bedding planes – there are cracks and joints right angled to the surface • At cliff faces – the cracks are vertical along the cliff face.
  101. 101. Chemical Weathering • Oxidation • Carbonation • Hydration • Hydrolysis
  102. 102. Carbonation Rainfall – slightly acidic to the pH of 5.6 – combines with CO2 to form Carbonic acid Carbonic acid reacts with Calcium Carbonate in rocks (Carboniferous limestone for example/ Chalk) to form Calcium bicarbonate H2CO3 + CaCO3 = Ca(HCO3)2
  103. 103. Features needed • Rocks with Carbonate • Precipitation is required – rain water • Low vegetation cover, exposed rocks surfaces • Cracks and joints that allow water to flow through • Porosity but lack of permeability allow rocks to be retained in joints • Cooler climate – rainwater can hold more CO2 than usual • pH of water varies – and different rocks react differently to acidity.
  104. 104. Oxidation - Oxidation occurs with metal – mostly Iron (Fe) and Oxide minerals - These rocks have distinctive blue black colors - Addition of oxygen and water cause the rocks to turn orange – from Ferrous to Ferric – AKA rusting - Makes it easier to crumble
  105. 105. Features supporting • High oxygen area – hence usually happens in rain forest e.g. the Amazon • High amount of rainfall – wet rocks/ soil (usually in areas of high runoff, precipitation and humidity) • Rocks should contain oxides or hydroxide • CONTRAST: Reduction of ferric iron to ferrous in marshy area may produce rocks with blue colors
  106. 106. Hydration When minerals absorb water, expand/change and hence change the rock’s composition Mechanical stresses also derive from exerting pressure from expansion E.g. Anhydrite – Gypsum E.g. Shales - Mudstone
  107. 107. Hydrolysis Hydrogen in rocks reacts with minerals in clay causing the breaking down of rocks into rocks – therefore water combines with the mineral H+ combines with OH- Occurs mostly on Orthoclase feldspar – Granite (Feldspar + mica+ Quartz)
  108. 108. Features supporting • Depends heavily on the amount of hydrogen in the atmosphere • Hence, the amount of air in the water • The presence of organic acid (humic acid) • The activities of organisms • TO produce H+
  109. 109. Results • Formation of clay • E.g. Feldspar --- Kaolin (China Clay)
  110. 110. Biological Weathering
  111. 111. Plants/ Animals 1. Roots of the trees growing – can exert pressure on the rocks – creating cracks – leads to physical disintegration 2. Chemical Weathering: Lichens and algae – can cause microbial erosion. Fungi may release organic acid that change the compositions of the rock. This creates holes in the rock which cause rocks to further break down. 3. Animals burrowing – cause lost of underlying support – leads to mass movement 4. Animals burrowing – lead to loosening of soil and rock particles
  112. 112. Property of Limestone • Permeable – can hold a lot of water • Soluble in rain water/ groundwater • Consist of Calcium Carbonate • Harder in strength • Surface is dry: high permeability • Carboniferous limestone – harder and less permeable/porous – with more resistant to water – landforms tend to shape more
  113. 113. Carboniferous limestone • Massively jointed: Have distinct pattern of joints and bedding planes – allow water to percolate through and dissolve the rock • Dissolving of rocks: Carbonation-solution of base-rich rock • Reversible process – limestone can be re- deposited as speleotherms
  114. 114. System affecting Carboniferous Limestone Carboniferous Limestone Carbonation Freeze-thaw weathering Glacial erosion Water erosion Mass movements Precipitation/ Groundwater Calcium bicarbonate in water Deposits as Speleothems Carbonation
  115. 115. The Water • If water has high amount of Carbon dioxide = more likely to weather limestone • Water that is likely to weather – Aggressive • If it reaches a saturation point – can’t dissolve much limestone • Non-aggressive due to over-saturation • At which point limestone is likely to precipitate
  116. 116. The Water • Colder water – can hold more Carbon dioxide – hence Karst sceneries are found in temperate areas • Warmer water – will cause deposition of limestone • Turbulence of flow • Meeting up with other streams – changing chemical compositions • The landform created by this process is called Karst topography
  117. 117. Limestone Scenery • Clint and grikes developed (Grikes are enlarged joints) GrikesClint
  118. 118. Limestone Scenery • Clint and grikes developed (Grikes are enlarged joints) – Clint are the large rocks separated by grikes • Processes: Carbonation-solution/ Freeze thaw/ ice action Grikes Clint
  119. 119. Limestone Scenery • Karren/ lapies: Small-scale solution grooves (2-3 cm deep) – runoff/solution of limestone • Swallow holes/ sinkholes: Caused by solution of limestone, enlargement of grikes systems, collapsed cavern • Dolines: Large depressions – solution/ Collapse of limestone – may be covered by glacial deposits • Uvalaas – 30 m in diameter
  120. 120. Formation of Dry Valley • A collapsed cavern • Climatic changes = less precipitation • A valley that used to have a stream (limestone is impermeable) – over a period of time the limestone becomes permeable and allow infiltration • Limestones became temporarily impermeable due to periglacial climate – permafrost.
  121. 121. Equifinality • The idea that different processes can lead to the dame landforms : E.g. The formation of the Dry valley/ Granitic tor
  122. 122. Karst Topography • A system of well-developed landforms features on dry limestone – no surface drainage. • Includes: Cave or underground tunnels – carbonation-solution/ erosion of water • Speleotherms: Cave deposits formed by solutions containing Calcium carbonate
  123. 123. Karst Topography 1. Tufa: Precipitation of CaCO3 near streams/ Springs/ around algae/ Mosses – Tufa dams, Mounds/ waterfall curtains. 1. Stalactites: From the tope – dripping water slow – causing precipitation of Calcium carbonate 2. Stalagmites: From the bottom – dripping water is fast – accumulation of calcium bicarbonate 3. When top/ bottom combines - pillar
  124. 124. Granitic Tor • Tors: Isolated granite rocks layered on top of a mountain/ batholith • There are 2 theories as to how Granite Tors form
  125. 125. Theory 1 – Linton 1955 • That Tors can be formed during the warm, humid Tertiary era (Triassic, Jurassic, Cretaceous) • Chemical weathering – caused the breakdown of rocks other than granite which is more resistant • Strongest weathering at close joints/ bedding planes • Where joints are further away – the granite is left standing • Residues of weathering (growan) removed during periglacial period • Denudation
  126. 126. Theory 2 – Palmer and Neilson 1962 • Mention frost shattering from Freeze-thaw to be the main process near joints/ bedding planes • Evidences: The features are not round/ kaolin not present – chemical weathering usually produced these • Removal of growan by solifluctions
  127. 127. SLOPE PROCESSES Part 3
  128. 128. Slope • A slope is inclined hill or surface/ an angle of inclination • Sub-aerial: Slopes that are exposed to the atmosphere/ the elements • Submarine: Slopes that are underwater • Aggradation slopes: Inclination of earth surface that are formed/caused by depositions of materials • Degradation slopes: Inclination of earth surface caused/ formed by erosions/ weathering
  129. 129. The Slope as a system • The slope is affected by various natural factors • Climate/ Weather – differential insolation/weathering of rocks • Geology – different rocks have different resistance to different types of weathering • Hydrology – the presence of a river can increase erosion or deposition • Vegetation growth – increase biological weathering/ increase weight on the slope • Human activities
  130. 130. Slope as an open system Slope’s shape/ stability Climate INSOLATION Vegetation RegolithGeology Gradient Ground water flows from other aquifer Mass movement from other slopes Seismic activities Human activities
  131. 131. Slope System Control 1. Climate 2. Geology 3. Soil 4. Aspect 5. Vegetation
  132. 132. Climate • The climate affects: Process of weathering/ presence of stream runoff/ amount of insolation – hence the amount of vegetation present • E.g. in arid climate – jagged slopes created by physical weathering – screes at the bottom – exfoliation domes • In wet/humid climate – rounded slope created by chemical weathering – organic weathering favors soil – deep regolith- vegetation cover
  133. 133. Geological Structure • Rock types – resistance/ susceptibility to weathering • E.g. Limestone produces flat surface – due to erosions along the bedding planes • Heterogeneous rock types – can lead to differential weathering – destabilize a slope
  134. 134. Geological Structure • Permeability/ porosity of rocks – allow water to pass through • Existence of joint/ bedding planes – affect the rate of weathering – water entering may destabilize the slope • Risk of mass movements
  135. 135. Geological Structure • Plate movements • At subduction zones – fold mountains – how steep depends on the angle of dip • Rift valleys – steep sides • Transform faults – see steep sides.
  136. 136. Soil/ Regolith • Regolith: Superficial, unconsolidated materials found at the earth’s surface (Soil, scree, weathered bedrocks, organic materials, deposited materials) • Regolith – unconsolidated – large amount of them destabilize the slope • Composition: Clay holds more water – may be more susceptible • Deepness of soil
  137. 137. Aspects • Influences insolation • Insolated areas – more vegetation • Insolated areas – more human settlements • Both contributes to more weight • Insolated areas – Freeze thaw weathering/ solifluctions
  138. 138. Vegetation Cover – Destabilizing factors • Increased weight to the slopes • Increases chemical weathering – oxygen in the air/ humic acid for chelation • Biological weathering – if the vegetation is not abundant and if the slope is not of soil • Stops small landslide – causing soil to absorb water and increase in weight • Prevents small landslide but may induce large ones in long term
  139. 139. Vegetation Cover – Stabilizing factors • The Vegetation increases interception of water – stores water = less surface runoff = less possibilities for mass movements (flows) • The roots hold the soil together – stabilizing the slopes • May block insolation – reduces freeze thaw cycles/ exfoliation
  140. 140. MASS MOVEMENT
  141. 141. Mass Movement • Any large scale movements of the earth surface not caused or accompanied by moving agents such as water, wind, glacier and ocean wave.
  142. 142. Classifying Mass movement - 1 • Classifying by speed of movement • Slow movement: Soil/Talus creep (heave), Solifluction • Fast movement: Landslide, mudslide, rock slide, earthflow, mudflow, rock falls, avalanches
  143. 143. Classifying Mass Movement - 2 • By wetness • Wet movement: Solifluction, Mudflow, mudslide, Earthflow, avalanche • Dry movement: Soil/ Talus creep (heave), landslide, rockslide, rock fall
  144. 144. The Triangular graph
  145. 145. How do Mass Movement happen • A slope is stabilized by a dynamic equilibrium between shear strength and shear stress • Shear strength: The internal resistance of the slope • Shear stress: The forces acting on the materials on the slope that would cause them to move downslope
  146. 146. How do Mass Movement happen • Mass movement occurs when the shear stress exceeds the shear strength • Or • When the shear strength falls below shear stress due to internal destabilizing
  147. 147. How do Mass Movement happen • Shear strength: Affected by geological structure of the slope, type of soil and regolith, vegetation cover, water content • Shear stress: Affected by the gradient (gravitational pull), surface water, the weight of the forces acting on the slope, faults in the slope, the way the slope is being ‘hit’
  148. 148. Factors affecting Shear Stress
  149. 149. The Weight acting on the slopes • Heavier loading – increases the stress • Vegetation cover… • Soil/regolith • Water content • Human activities… houses… settlement
  150. 150. Lateral supports • Steepening of slope – by undercutting – causing overhang to fall • Increases the gradient • Rivers erosion… • Glacial erosions… • Wave-cut platforms… • Faulting (steepens an area) • Rockfalls/ slides remove lateral supports
  151. 151. Underlying supports removed • Losing supports below can cause slopes to fail – places emphasize on the weight acting on it • Wave undercutting… • River actions… at waterfall… • Underlying sediments removed • Human activities…
  152. 152. Lateral pressure • Water in cracks – freeze thaw • Swelling of cracks • Hydration of clays • Releases of pressure
  153. 153. Transient stress • Earthquake • Volcanic activities • Movement of trees in the wind
  154. 154. Factors affecting Shear Strength
  155. 155. Weathering • Granular disintegrations – cause slopes to destabilize (Freeze thaw) • Hydration of clay • Solution of materials – make the slope less compact
  156. 156. Pore Pressure • Water exerts differentiating pressure on the slopes • Saturated materials – becomes softer – more unconsolidated after a whiles
  157. 157. Changes in rock structure • In shales – fissures/ cracks – reduce the compact nature of a slope • Clays are remould • Sands are remould
  158. 158. Organic effects • Burrowing of animals • Roots of plants
  159. 159. TYPES OF MASS MOVEMENTS
  160. 160. Soil Creep • Slow movement of soil • Result of heaving (soil particles moving up at right angle from the surface due to freeze-thaw cycle or expansion caused by water) • After heaving the oil falls back but is now moved slightly downslope • More common in winter time
  161. 161. Solifluction • Soil placed in the state of permafrost • Warm weather thaws the layer of soil above – leaves the underlying layer frozen as a waterlogged zone • Thaw soil moves downhill along the permafrost layer
  162. 162. Rainsplash Erosion
  163. 163. Rainsplash Erosion
  164. 164. Falls
  165. 165. Mudflow
  166. 166. Earthflow
  167. 167. Landslides
  168. 168. Landslides
  169. 169. Rockslides
  170. 170. Mudslides
  171. 171. Avalanche
  172. 172. Avalanche
  173. 173. Sources and Websites • http://www.ucmp.berkeley.edu/history/wegener.h tml • http://education.nationalgeographic.org/encyclop edia/ • http://www.limestone- pavements.org.uk/geology.html • http://www4.uwsp.edu/geo/faculty/lemke/geomor phology/lectures/06_weathering.html

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