Rocks/ WeatheringAS Level Physical Geography

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DefinitionsAccretion: the process by which a substance grows by the collection and clustering of different partsGeomorphology: 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 oxygenMagnetic Field: Area around and affected by a magnet or charged particles

THE BEGINNING OF IT ALLIntroduction

Formation of EarthCollisions of objects in the galaxy forming protoplanetsSoon the planets arrange into the 8 planetsAsteroid belt between Mars and Jupiter (messed up planet)

Formation of EarthEarth is formedProcess of differentiationHeavy elements (NIFE) sink to the coreLighter elements (Silicates float to surface)

Formation of EarthAnother object collided with earthSome of earths materials knocked outAccreted and formed moon

Formation of earthEarth cools down at 3.8 4 billion years agoWater vapor condensesTorrential rainOcean was formed then

Start of Life3.8 Billion years agoProkaryote first appearsStart photosynthesizingOxygen producedThe reactivity of oxygen caused Oxygen holocaust 2.5 Billion killed off a lot of single cell organisms1.7 Billion years ago - Eukaryote

GEOLOGICAL EPOCHSGEOLOGICAL EPOCHS

A Profile OF EARTHINTRODUCTIONhttps://www.youtube.com/watch?v=zw-z_iTnIdc&feature=iv&src_vid=PT7qhBUffvY&annotation_id=annotation_3093859399

Our Solar System

About Earth3rd Planet from the Sun150 million kilometers from the sunDiameter: 12,756 km365.256 Days to orbit the sun24.9345 hours to rotate once

Earth and LifeThe only planet to harbor lifeRapid Spin + NIFE (Nickel, Iron) core = large magnetic fieldAtmosphereBoth of the above shielded earth from radiation/ meteors

The Atmosphere

The Hydrosphere

The Lithosphere

Definition of Rocks and MineralsA mineral is an inorganic, naturally occurring solid that has a definite chemical composition and an atomic structureInorganic: Not living, not composed of biological Definite chemical composition: Unique elemental make-up Feldspar, Sulfur, QuartzColor, Hardness, Luster(metallic/non-metallic), streak(color in particles), cleavage/fractureBuilding blocks of rocks

Plate TectonicPart 1

Earths InteriorScientists can determine earths inner core through seismology/ nebular theorySeismo = Greek for shock

Seismic movement4 categories of seismic wavesMost waves are between: 3 15 km/s2 types travelled along the surface in rolling swellPrimary(compression)/ Secondary(shear) waves penetrates the earths interiorPrimary travels through rocks/ waterSecondary cannot travel through rockSpeed of waves reduce when in contact with hotter matterThese differences in seismology allow scientists to identify the different properties of rocks underground

Earths Interior

Mechanical layer of the earthThe topmost = crustUnder the crust the coolest top layer of the mantle Elements are different from the crustLITHOSPHERE 10 200 KM 10 is unusual, usually close to the hotspotDeeper 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 dont confuse with the atmospheric Mesosphere) still act like solidOUTER 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

Chemical StructureThe Denser element sunk to the center during the formation of earthThe core is almost entirely made up of heavy metal

Earth is shaped from the inside outTransfer of heat (hotspot, convection current) or more specifically energy determines the landscape of the earthCauses plate tectonicVolcanic eruptionEarthquakeSeafloor spreadingOrogeny (Mountain building)

Inner CoreA very hot, very dense center of the planetRadius about 1218 km1.7% of earths massInner core is solidFrozen with high pressureNIFE (Nickel, Iron)

Outer Core30.8% of the earths mass2200 km thickLiquid-likeComposition: NiFeConductive/ hot site of violent convectionElectrical current caused by churning of metals here forms magnetic fieldsStill NIFE however may contain Oxygen/ SulfurBullen discontinuity borders the core and the mantle the hottest

MantleThe most solid bulk of the earths interior (semi-molten)84% of the earths volumeAt 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 lavaMaterials: Silicate (oxygen+Silicon), Calcium, Sodium, Aluminum, Iron, Magnesium oxideMantle is more viscous near plate boundary and magma plume

Oceanic CrustFormed at points of sea floor spreading center (Mid Atlantic Ridge/ Pacific Rise)0.99% of earths mass200 million years oldDense 3.0 g/cm3Thinner 6 - 16 kmNew new lands are formed hereBasaltic Rock (Igneous) (SIMA) (MAFIC)Starts at mid ocean ridge ends at subduction zoneEdge can be stranded on land

Continental CrustFormed through arc volcanism and accretion0.347% of the earth mass4 billion years old Lighter 2.6 g/cm3Made up of crystalline rock with quartz and feldsparThicker average up to 30 70 km in thickness

Difference between Basaltic/ Igneous RockBasaltic extrusive igneous rock (Volcanic) Magma burst out through the earth surface and cools down quickly not much time for mineral crystalsGranitic Intrusive igneous rock (Plutonic) crystals form due to the slow cooling in the earth continent

Factors affecting the earths surfaceMovement of the platesEarthquake and seismic activitiesVolcanic activitiesFormation of fold mountainsChemical weatheringChanges in temperature leading to wetheringErosion by windHydrology

The Plate Tectonic Theory Key PrinciplesOuter layer of earth divided into Lithosphere and AsthenosphereAsthenosphere has a convection current and an almost adiabatic heat gradientThe lighter lithosphere is divided into different plates riding on the more viscous and dense asthenosphere1 tectonic plate = lithospheric mantle with crustal materials on topPoints where 2 plates meet = plate boundaries

The Continental Drift TheoryFirst introduced by Alfred WegenerA German meteorologistIn 1911, he found the that similar organisms could be found in different continents across the Atlantic

The Continental Drift TheoryThe continents seemed to fit like jigsaws the eastern coast of South America and the Western coast of AfricaSome other scientists supported him with fossils ideas as well as evidences of fold mountainsHowever, Wegener couldnt come up with a mechanism to support the movement of plate

Mohorovicic DiscontinuityIf the earth was made of uniform mass (which it isnt) 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 accelerateHe realized the wave mustve been travelling through a denser layer of the earth it refracted to the direction it was going accelerationThe boundary between mantle/ crust is now called the Mohorovicic discontinuity

The Plate Tectonic TheorySince the 1950s further exploration of the theory supported Wegeners claimEarly 1960s Hess and Dietz discovery of the Mid Atlantic Ridge and Sea Floor SpreadingDiscovery of paleomagnetism

Evidences supporting the theory

1. The Fitting of the continentsThe 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

2. Biological Fossil EvidencedVarious fossils found across the earths continents e.g. discovery of the Mesosaurus fossil in both South America and India discovery of plant fossil like Glossopteris in the southern continents.

3. Geological EvidenceGlacial depositions that seems connected between Antarctica and brazil.Fold Mountains e.g. The Swiss AlpLater The Appalachian mountain range was also used as an evidence for the connection between the Eurasian and the North American Plate

4. The Mid Atlantic RidgeA distinct land form discovered in 1948 found at divergent plate boundary - showing that two plates are actually coming apart

5. Seismic evidence/ ActivitySeismic, volcanic and geothermal activity found in connected network of linesThis includes the Mohorovicic Discontinuity

6. PaleomagnetismMagnetic 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.

Mantle ConvectionThe theory first put forth by Arthur Holmes in the 1930sThe differences between temperature beneath the lithosphere creates a convection current which moves the plateThere are many theories regarding how plates moveDebates are still going on regarding this

The Hotspot TheoryThe Hotspot theory states that the activities in the core causes semi molten parts of the mantle to riseThe creates a plume of magma rising .As the viscous rocks reach the plate the magma might break through causing riftsThe magma flowing outward as they reach the plate may create dragging forcesHowever, the greatest hotspot of the world Hawaii is not a plate boundary

The Dragging TheoryHis states that the colder edges of the plates are colder and denserThey therefore sink at points of subductionHis sinking causes a dragging process

Plate boundary type1: Divergent2 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 lithosphereThe arc becomes a crack in the lithosphereMagma rises up filling in the gaps between the platesThe magma rises up due to lower density of the asthenosphere.This also pushes the plates apart

Sea-floor spreadingAt Divergent plates boundaryThe crack appears at the ocean floorHeat from asthenosphere makes material hot and less dense these rises forming an elevated ocean floorCrack widens magma bubbles up and spill overThe sea water cools down the magma turns into igneous rock (basaltic) becomes a new earth crust

Mid Ocean RidgesThe elevated ocean floors form large mountain ranges e.g. Mid Atlantic Ridges or the East Pacific Rise or the Southeast Indian RidgeSlow spreading ridges = tall narrow cliffs/ mountains because of smaller magma chamber = discontinuous eruptionsFast spreading ridge = large magma chamber = sheets of lava = gentler slopesAs the oceanic crust moves away it becomes thickerThe end of the plate sees a collision

Rift ValleyOccur when two plates move apartTwo plates moving apart creates cracksThe land in between the cracks begin to sinkLeaving a valleyOften found at Transform faults or triple junctions

Plate boundary type2: ConvergentTwo plates converge/ collideMay be oceanic vs. Continental, oceanic vs. oceanic or continental vs. continentalProduce different landforms

Subduction ZoneElements:Subduction ComplexAccretionary Prism/ wedgeOcean trenchFore-arc basinSedimentary arcVolcanic ArcVolcanic islandBack-arc basin

Fold MountainsWhen 2 plates collideOceanic + continental the heavier/ denser oceanic sinks into the asthenosphere.One plate subducts beneath anotherThis forces the continental plate to buckle and fold inlandThe land rises into a mountain range e.g. The AndesIn areas such as these fore arc basins may accrete to form a rising mountainFront island arcs may also be of causesSubduction zone means volcanic arc may be formed

Fold MountainsContinental crust + Continental crustBoth are equally dense they collideSediments on both basins are folded and buckled forming a huge mountain rangeGenerally oceanic lithosphere is lost between themThese may cause some insignificant volcanic activities

Ocean TrenchesA deeper part of the ocean where subduction takes placeWhere one plate is subducted right beneath the other there is an area where the ocean floor deepensThis point can be quite hot proximity to the asthenosphereTrench outer rise marking the point where the plate is subductedOuter slope gentleInner slope - steepE.g. Mariana trench

Island ArcsWhere oceanic lithospheres collideThe denser one will sink beneathDestroyed at asthenosphereThe water on the subducting sphere cause meltingThis melted material riseCreating a bulge then breaking throughSolidifies into an islandThe island arc runs along a boundaryThere may be volcanic featureIsland arcs can also be formed at Hotspot points

Plate boundary type3: TransformWhen two plates move alongside each otherThere is no spreading or destroying of plates hereMay be caused by diverging/ converging of nearby boundariesRift valleys may be formedFaults will be formedMay offset nearby landformsSan Andreas fault best example

EarthquakeEarthquakes may occur when there is a release of pressure at plate boundaries

Earthquakes at Divergent boundaryshallow earthquake at sea floor spreading regions there isnt much friction or pressure however

Earthquakes at Convergent plate boundaryDeep earthquake at the benioff zone (Wadati-benioff zone points angling at 30 45 degrees)Major earthquakes when plates sliding under another plate frictions are causedE.g. 2004 Tsunami caused by Indo-Australian plate subducting beneath the Eurasian plate

Transform plate boundaryRelease of pressure One plate may stop when friction is too greatWhen this friction is overcame a release of pressureThe 1906, 1989 earthquake in San Francisco

TsunamiOccurs near subducting plate marginsA bulge in the ocean floor caused by the accumulation of magma beneath the overlying plateOR the general bulging caused by the dipping of the subducting plateThis makes the ocean floor riseWater is pushed up some 15 mCausing huge Tsunami waves

Vulcanicity/ VolcanologyAll the processes by which solid, liquid or gaseous materials are forced into the earths crust or are ejected into the earth surface

Causes of Volcanic eruptionRelease of pressure at local pointsDue to folding, faulting, other movementsSemi-molten magma becomes moltenReduction in density causes magma to riseForces its way through weaknesses in the crust

Extrusive vs. IntrusiveExtrusive RocksMagma reaches the surface and cools quickly Not much crystal formede.g. Basalt The Oceanic plates

Extrusive vs. IntrusiveMagma doesnt reach the surfaceInjected into the earths crustCools, hardens slowly under the surfaceExposed by removal of overlying rocksLarge crystals

Extrusive Landforms

LavaThe types of Extrusive landforms depends on:Viscosity of the lavaGaseousness of the lava

Basaltic LavaUpward movement of mantle materialsAt ocean ridges (Mid Atlantic)Hotspot points (Hawaii)Rift Valley (Ethiopia)

Andesitic LavaResult of the Subduction processOccurs as island arcsVolcanic eruptionsE.g. Andes

Pyroclastic materialsMaterials ejected by Volcanoes in fragmentsTephraAshLapilli (small stones)BombsPyroclastic flow move down the side as cloudsHeavy rainfall

Basaltic vs. AndesiticLow viscosity, hotter (1200oC)Lower silica contentLonger time to cools, flow at longer distanceExtensive, gentle slope landformFrequent, gentle eruptionLava/ steam ejectedHigh viscosity, less hot (800oC)Higher silica contentShorter time to cool, flow at shorter distanceSteesides, local featureLess frequent eruption but violent due to gas build-upPyroclastic materials ejected

Different Types of VolcanoesFissure eruptions e.g. IcelandBasic/ Shield e.g. Mauna Loa Acid/ Dome e.g. KarymskyAsh VolcanoComposite Volcano e.g.. VesuviusCaldera e.g. Andes

Minor Extrusive landformsMud Volcanoes: Combination of hot mud/ waterSulfatara: Gas such as Sulphur released from cracksGeysers: Water vapors heats up and rises, pressure increases, steam exploding through at points of weaknessesFumeroles: Superheated water reaches the surface, reduction in pressure casues it to turn to steam

Nature of ExplosionsIcelandic: Lava flow gently from a fissureHawaiian: lava emitted gently from a ventStrombolian: Small but frequent eruptionVesuvian: More violent, less frequentKrakatoan: Explosions violent enough to remove original conePelean: Violent eruption with Pyroclastic flowPlinian: Large amount of materials and lava are ejected

HydromagmaticAny eruptive processes where magma and lava interacts with waterDeep marine eruptions pressure of water suppresses lava to undergo cooling: forms pillow lavaLava flows into the seaShallow marine eruptionCrater lake eruptionSubglacial e.g. VatnajokullMagma comes into contact with groundwater

Intrusive Landforms

Intrusive LandformsMost of the magma do not reach surfaceIntruded into the crust where it solidifiesWhen overlying rocks worn awayLandforms are revealed

Batholith

Dikes

Sill

The Pacific Ring of FireAn area of high volcanic and seismic activities found along plate boundaries of the Pacific islandsThese plates are generally subducting90% of volcanic activities appear here75% of the active volcanoes are hereCourse: Southern tip of South America along the coast of north America across the Bering strait through Japan into New Zealand

Rocks and WeatheringPart 2

The Rock CycleThe Rock Cycle is a model that describes the formation, breakdown and reformation of rocks into 3 main rock typesIgneousSedimentaryMetamorphic

Igneous RocksRocks that are formed from the cooling and solidifying of the lavaCan be intrusive or extrusiveExample: Granite

Sedimentary RocksRocks that are formed by sediments deposited by erosion.Example: Limestone Carboniferous and Dolomites - sandstone

Metamorphic RockRocks that are formed from igneous and sedimentary rocks under under high heat and pressure Example: Gneiss, Slate, Marbles, Quartsize

Physical WeatheringFreeze ThawExfoliationCrystallizationPressure Release

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

Features supporting freeze Thaw weatheringTemperature fluctuating around 0oC hence freezing is involved.Places: Alpine regions, periglacial climate, polar climate is less often (lack of freeze thaw cycle)Mountainous regionNorth facing slope in the Northern hemisphere, or a South facing slope in the Southern hemispherePrecipitation required

Features supporting freeze Thaw weatheringRocks may also be porous eg. SandstoneRock has to be EXPOSED not covered in vegetationHence, too much precipitation will not be good as it leads to more vegetation

ResultsFrost shattering: materials broken down into small angular fragments clastic states e.g. fragmented at foot of mountains/ slopesFrost wedging: Block disintegrationFrost spallingFrost susceptible soil result in capillary actions of water to move toward freezing front hence soil creep upward may form terracettes.

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

Features affectingWide ranging Diurnal temperature variation between day and night achieved in the arid regions.The lack of precipitation = less vegetation cover = maximum insolationHigh insolation so lack of cloud coverLack of cloud cover --- maximum out-radiation at night colder night temperatureGriggs(1936) proved an idea that some moisture will be needed for rocks to expandRocks compositionsExposure of rock face

ResultsDivides rocks into sub-planar slabsAs the outer layer peels away, the pressure is released causing the underlying rock to expand and fracture parallel to the surface. pressure releaseDisintegration blocks/ screes can be found

Salt Crystallization

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.Water with salt evaporates away leaving crystals. These expand under high temperature.

Feature affectingRock may contain saltRocks may be porous/ permeableSurface texture speed of breakdown increase over time with coarse materialsArid climate the evaporation of water will leave salt close to the surfaceCoastal area sea waterSalt from snowflake in Alpine regions

ResultsMost effective salts: Sodium sulphate, Magnesium Sulphate, Calcium ChlorideProduces the highest rate of break downWhen combined with freeze-thaw

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)

PRESSURE RELEASERocks are usually formed under the surface under high pressure.The unloading of such pressureCause cracks/ joints to form at right angle to the unloading surfaceHence at pseudo bedding planes there are cracks and joints right angled to the surfaceAt cliff faces the cracks are vertical along the cliff face.

Chemical WeatheringOxidationCarbonationHydrationHydrolysis

Carbonation

Rainfall slightly acidic to the pH of 5.6 combines with CO2 to form Carbonic acidCarbonic acid reacts with Calcium Carbonate in rocks (Carboniferous limestone for example/ Chalk) to form Calcium bicarbonateH2CO3 + CaCO3 = Ca(HCO3)2

Features neededRocks with CarbonatePrecipitation is required rain waterLow vegetation cover, exposed rocks surfacesCracks and joints that allow water to flow throughPorosity but lack of permeability allow rocks to be retained in jointsCooler climate rainwater can hold more CO2 than usualpH of water varies and different rocks react differently to acidity.

Oxidation

Oxidation occurs with metal mostly Iron (Fe) and Oxide mineralsThese rocks have distinctive blue black colorsAddition of oxygen and water cause the rocks to turn orange from Ferrous to Ferric AKA rustingMakes it easier to crumble

Features supportingHigh oxygen area hence usually happens in rain forest e.g. the AmazonHigh amount of rainfall wet rocks/ soil (usually in areas of high runoff, precipitation and humidity)Rocks should contain oxides or hydroxideCONTRAST: Reduction of ferric iron to ferrous in marshy area may produce rocks with blue colors

Hydration

When minerals absorb water, expand/change and hence change the rocks compositionMechanical stresses also derive from exerting pressure from expansion

E.g. Anhydrite GypsumE.g. Shales - Mudstone

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)

Features supportingDepends heavily on the amount of hydrogen in the atmosphereHence, the amount of air in the waterThe presence of organic acid (humic acid)The activities of organismsTO produce H+

ResultsFormation of clayE.g. Feldspar --- Kaolin (China Clay)

Biological Weathering

Plants/ AnimalsRoots of the trees growing can exert pressure on the rocks creating cracks leads to physical disintegrationChemical 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.Animals burrowing cause lost of underlying support leads to mass movementAnimals burrowing lead to loosening of soil and rock particles

Property of LimestonePermeable can hold a lot of waterSoluble in rain water/ groundwaterConsist of Calcium CarbonateHarder in strengthSurface is dry: high permeabilityCarboniferous limestone harder and less permeable/porous with more resistant to water landforms tend to shape more

Carboniferous limestoneMassively jointed: Have distinct pattern of joints and bedding planes allow water to percolate through and dissolve the rockDissolving of rocks: Carbonation-solution of base-rich rockReversible process limestone can be re-deposited as speleotherms

System affecting Carboniferous LimestoneCarboniferous LimestoneCarbonationFreeze-thaw weatheringGlacial erosionWater erosionMass movementsPrecipitation/ GroundwaterCalcium bicarbonate in waterDeposits as SpeleothemsCarbonation

The WaterIf water has high amount of Carbon dioxide = more likely to weather limestoneWater that is likely to weather AggressiveIf it reaches a saturation point cant dissolve much limestoneNon-aggressive due to over-saturationAt which point limestone is likely to precipitate

The WaterColder water can hold more Carbon dioxide hence Karst sceneries are found in temperate areasWarmer water will cause deposition of limestoneTurbulence of flowMeeting up with other streams changing chemical compositionsThe landform created by this process is called Karst topography

Limestone SceneryClint and grikes developed (Grikes are enlarged joints)

GrikesClint

Limestone SceneryClint and grikes developed (Grikes are enlarged joints) Clint are the large rocks separated by grikesProcesses: Carbonation-solution/ Freeze thaw/ ice action

GrikesClint

Limestone SceneryKarren/ lapies: Small-scale solution grooves (2-3 cm deep) runoff/solution of limestoneSwallow holes/ sinkholes: Caused by solution of limestone, enlargement of grikes systems, collapsed cavernDolines: Large depressions solution/ Collapse of limestone may be covered by glacial depositsUvalaas 30 m in diameter

Formation of Dry ValleyA collapsed cavernClimatic changes = less precipitationA valley that used to have a stream (limestone is impermeable) over a period of time the limestone becomes permeable and allow infiltrationLimestones became temporarily impermeable due to periglacial climate permafrost.

EquifinalityThe idea that different processes can lead to the dame landforms : E.g. The formation of the Dry valley/ Granitic tor

Karst TopographyA system of well-developed landforms features on dry limestone no surface drainage.Includes: Cave or underground tunnels carbonation-solution/ erosion of waterSpeleotherms: Cave deposits formed by solutions containing Calcium carbonate

Karst TopographyTufa: Precipitation of CaCO3 near streams/Springs/ around algae/Mosses Tufa dams,Mounds/ waterfall curtains.Stalactites: From the tope dripping water slow causing precipitation of Calcium carbonateStalagmites: From the bottom dripping water is fast accumulation of calcium bicarbonateWhen top/ bottom combines - pillar

Granitic TorTors: Isolated granite rocks layered on top of a mountain/ batholith There are 2 theories as to how Granite Tors form

Theory 1 Linton 1955That 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 resistantStrongest weathering at close joints/ bedding planesWhere joints are further away the granite is left standingResidues of weathering (growan) removed during periglacial period Denudation

Theory 2 Palmer and Neilson 1962 Mention frost shattering from Freeze-thaw to be the main process near joints/ bedding planesEvidences: The features are not round/ kaolin not present chemical weathering usually produced theseRemoval of growan by solifluctions

Slope ProcessesPart 3

SlopeA slope is inclined hill or surface/ an angle of inclinationSub-aerial: Slopes that are exposed to the atmosphere/ the elementsSubmarine: Slopes that are underwaterAggradation slopes: Inclination of earth surface that are formed/caused by depositions of materialsDegradation slopes: Inclination of earth surface caused/ formed by erosions/ weathering

The Slope as a systemThe slope is affected by various natural factorsClimate/ Weather differential insolation/weathering of rocksGeology different rocks have different resistance to different types of weatheringHydrology the presence of a river can increase erosion or depositionVegetation growth increase biological weathering/ increase weight on the slopeHuman activities

Slope as an open systemSlopes shape/ stabilityClimateINSOLATIONVegetationRegolithGeologyGradientGround water flows from other aquiferMass movement from other slopesSeismic activitiesHuman activities

Slope System ControlClimateGeologySoilAspectVegetation

ClimateThe climate affects: Process of weathering/ presence of stream runoff/ amount of insolation hence the amount of vegetation presentE.g. in arid climate jagged slopes created by physical weathering screes at the bottom exfoliation domesIn wet/humid climate rounded slope created by chemical weathering organic weathering favors soil deep regolith- vegetation cover

Geological StructureRock types resistance/ susceptibility to weatheringE.g. Limestone produces flat surface due to erosions along the bedding planesHeterogeneous rock types can lead to differential weathering destabilize a slope

Geological StructurePermeability/ porosity of rocks allow water to pass throughExistence of joint/ bedding planes affect the rate of weathering water entering may destabilize the slopeRisk of mass movements

Geological StructurePlate movementsAt subduction zones fold mountains how steep depends on the angle of dipRift valleys steep sidesTransform faults see steep sides.

Soil/ RegolithRegolith: Superficial, unconsolidated materials found at the earths surface (Soil, scree, weathered bedrocks, organic materials, deposited materials)Regolith unconsolidated large amount of them destabilize the slopeComposition: Clay holds more water may be more susceptibleDeepness of soil

AspectsInfluences insolationInsolated areas more vegetationInsolated areas more human settlementsBoth contributes to more weightInsolated areas Freeze thaw weathering/ solifluctions

Vegetation Cover Destabilizing factorsIncreased weight to the slopesIncreases chemical weathering oxygen in the air/ humic acid for chelationBiological weathering if the vegetation is not abundant and if the slope is not of soilStops small landslide causing soil to absorb water and increase in weightPrevents small landslide but may induce large ones in long term

Vegetation Cover Stabilizing factorsThe Vegetation increases interception of water stores water = less surface runoff = less possibilities for mass movements (flows)The roots hold the soil together stabilizing the slopesMay block insolation reduces freeze thaw cycles/ exfoliation

MASS MOVEMENT

Mass MovementAny large scale movements of the earth surface not caused or accompanied by moving agents such as water, wind, glacier and ocean wave.

Classifying Mass movement - 1Classifying by speed of movementSlow movement: Soil/Talus creep (heave), Solifluction Fast movement: Landslide, mudslide, rock slide, earthflow, mudflow, rock falls, avalanches

Classifying Mass Movement - 2By wetnessWet movement: Solifluction, Mudflow, mudslide, Earthflow, avalancheDry movement: Soil/ Talus creep (heave), landslide, rockslide, rock fall

The Triangular graph

How do Mass Movement happenA slope is stabilized by a dynamic equilibrium between shear strength and shear stressShear strength: The internal resistance of the slopeShear stress: The forces acting on the materials on the slope that would cause them to move downslope

How do Mass Movement happenMass movement occurs when the shear stress exceeds the shear strengthOrWhen the shear strength falls below shear stress due to internal destabilizing

How do Mass Movement happenShear strength: Affected by geological structure of the slope, type of soil and regolith, vegetation cover, water contentShear 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

Factors affecting Shear Stress

The Weight acting on the slopesHeavier loading increases the stressVegetation coverSoil/regolithWater contentHuman activities houses settlement

Lateral supportsSteepening of slope by undercutting causing overhang to fallIncreases the gradientRivers erosionGlacial erosionsWave-cut platformsFaulting (steepens an area)Rockfalls/ slides remove lateral supports

Underlying supports removedLosing supports below can cause slopes to fail places emphasize on the weight acting on itWave undercuttingRiver actions at waterfallUnderlying sediments removedHuman activities

Lateral pressureWater in cracks freeze thawSwelling of cracksHydration of claysReleases of pressure

Transient stressEarthquakeVolcanic activitiesMovement of trees in the wind

Factors affecting Shear Strength

WeatheringGranular disintegrations cause slopes to destabilize (Freeze thaw)Hydration of claySolution of materials make the slope less compact

Pore PressureWater exerts differentiating pressure on the slopesSaturated materials becomes softer more unconsolidated after a whiles

Changes in rock structureIn shales fissures/ cracks reduce the compact nature of a slopeClays are remouldSands are remould

Organic effectsBurrowing of animalsRoots of plants

TYPES OF MASS MOVEMENTS

Soil CreepSlow movement of soilResult 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 downslopeMore common in winter time

SolifluctionSoil placed in the state of permafrostWarm weather thaws the layer of soil above leaves the underlying layer frozen as a waterlogged zoneThaw soil moves downhill along the permafrost layer

Rainsplash Erosion

Rainsplash Erosion

Falls

Mudflow

Earthflow

Landslides

Landslides

Rockslides

Mudslides

Avalanche

Avalanche

Sources and Websiteshttp://www.ucmp.berkeley.edu/history/wegener.htmlhttp://education.nationalgeographic.org/encyclopedia/http://www.limestone-pavements.org.uk/geology.htmlhttp://www4.uwsp.edu/geo/faculty/lemke/geomorphology/lectures/06_weathering.html