Lithosphere and Geomorphology

8/2/2019 Lithosphere and Geomorphology

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Lithosphere and geomorphology


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Lithosphere

The Earth consist of the crust,the mantle and the core.Lithosphere is created by theEarths crust and solid mantle.

It lies upon the plastic mantlerock - astenosphere.Lithosphere is studied bygeology. It is the sciencewhich study the origin,structure, composition and

history of the Earth.


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Lithosphere-crust:

The crust is the outer layerwhich is thin and rigid. It floatson the semi-molten rockmantle. It can be divided intotwo main types continentalcrust and oceanic crust.

Continental crust (150 250 km thick) graniticcrust because it consist ofSiAl(silica & aluminum)-,covers the land surface, the

base of land mass, it is thickerand lighter than oceanic crust Oceanic crust basaltic crust

because it consist of SiMg(silica & magnesium), graniticlayer missing cover the floor of

worlds ocean


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In the core of the Earth is radioactive decayfrom which the convection currents escapetowards the surface. They tear the crust apartand dividing it into huge fragmentstectonicplates (crustal plates) moving away fromeach other(divergence) or being pushedtogether (convergence).

Crustal plates are pushed across the Earthssurface at 50mm/y.

Continental drift process- continents constantlychanged position and size.

Major tectonic plate: Eurasian, North American,South American, African, Pacific, Nazca,IndoAustalian, Antarctic, Phillipine


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Map of tectonic plate


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Crustal plates can converge, diverge or collide.We know 3 maintypes of plate boundaries according to the direction and movementof the plates.

Diverging(constructive)

forced apart and new crust is createdbetween (e.g. under the ocean magma reaching the sea floorproducing new oceanic crust) - Mid Atlantic Ridge (Europe ismoving away from North America)

Converging( destructive) one plate collides with another, slides

under the other (e.g. heavier oceanic plate slides below the lightercontinental plate- subduction zone ) Nazca plate sinks under theSouth America plate

Slipping2 plates move horizontally slip past one other TheIndian plate collide with the Eurasian plate to form the Himalayas

Plate boundariesRift valleys East African Rift ValleyMid- oceanic ridges Mid-Atlantic ridgeFold mountains Himalayas

Horizontal faults San Andreas in USA


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Tectonic plate


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Diverging, converging and slipping boundaries


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East African Rift Valley and Mid-Atlantic Ridge


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Himalayas and San Andreas in USA


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Region where the Earth lithosphere forms, are typical for hugeseismic and volcanic activity, tectonic movements andendogenic processes which take place within the Earth.

Tectonic movements- mechanical movements of the crust causedby pressure, tension of gravitation, e.g. mountain folding


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Tectonic forces (movements) create many crustal failures: faults andfolds

faulting usually occurs during an earthquake

Fault - fracture in a rock which involves a movement along one side or both sides.

Shift - total movement

Throw- vertical displacements

Heave- horizontal displacements


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Normal fault - result of atension, strata are pulledapart, one side of it is throwndown - increase of land area(divergence)


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Reverse (thrust) fault- result of a compression,one side of the fault plainis thrust over the other(convergence) -overlapping of the strataand the surface area isdecreased, e.g. steepslopes are formed of

more resistant rocks,gentle slopes are foundon softer rocks that arethrown down (by erosion)


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Wrench (tear) fault -movement is horizontal but thefracture is vertical, nearbyplate boundaries (product of

an earthquake)


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Landforms produced by faults:

Horst= upland area bounded by lowground either side (fault scarps)a) uplift of a blockb) depression of surrounding lande.g.: Harz Mts., Black ForestExtensive horst produce plateau areas(block mountains). Further Earthmovements tilt the blocks = tilted blocks=they are divided by faults into subsided(wide deep basins) and elevated sections(mountains).

Rift valley (graben) = reverse of a horst,

its formed by tension, compression orparallel faults and accompanied by horsts oneither side, also can be formed nearby plateboundaries where the plates are pullingapart (e.g. East African Rift Valley).


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folding occurs when layers of rock aredistorted but not fractured Fold - distorted layers of rock Simple fold - anticline + syncline Recumbent fold - crumpled several times Asymmetric fold Over fold


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Earthquakes seismic activity

- tremors or ground movements caused by shock waves => occurnormally at plate boundaries. Plate movement causes stress to buildup within the crustal rocks until the rocks break along the line of afault or cracks in the Earths crust.

Actual movement = few cms but the sudden release of seismic(earthquake) energy can be enormous

focus - the point at which the rocks break within the crust. Thismay be some distance below the surface and the seismic energyemitted from the focus travels in all directions as seismic waves.

epicentre.- the point on the Earths surface above the focus

More powerful earthquake is when: stress was built up for a long time focus is near the surface


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Each year - thousands of earthquakes => few are centred nearpopulated areas and strong enough to cause loss of lives - primaryeffects (from the violent shaking of the ground during anearthquake), e.g. buildings may collapse killing people inside them,

shattered window glass may shower on to the streets below huge cracks may open in the ground roads may be damaged water pipes and (electricity) mains may be cut off

Primary effects can generate secondary effects, e.g. deaths because of food and water shortage fires _ gas or oil leaking from fractured pipes diseases _ lack of medical care and clean drinking water

tsunamis _ huge waves caused when earthquake occurs under thesea (1000 kph in open water, 65kph close to land + 15 m high).Created by displacing of the seabed (seafloor) => great damages tocoastal areas.

Geomorphological effects = land movements, tsunami, landslides,

avalanches.


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Volcanoes volcanic activity

Geothermal heatis released from the Earths core at the surface mainly through volcanoes.

Magma pours onto the surface as lavaacid & basic.

Acid lava volcano - mainly steep-sided, common along destructive plate boundaries, Magma -melting of basaltic oceanic crust and marine sediments, (e.g. volcanoes of Phillipines)

Basic lava volcano - common along constructiveplate boundaries, magma - basalt arisingdirectly from the mantle, e.g. Mauna Loa in Hawaii

Geothermal activityAreas with geothermal activity = crust is thin and magma is present at quite shallow depth-magma heats rocks above it (350C at a depth of less than 5 km). Percolating groundwater isheated and then driven upwards by convection through cracks in the crust. Superheated waterbegins to boil closer to the surface and then is emitted onto the surface - fumerole (superheated water turned to steam because of the sudden drop in pressure) mudpool (bubbling pool of mud liquefied soil where steam condenses near surface) hot spring (superheated water + cold groundwater = hot spring at the surface) geyser (regular eruption of hot water and steam, e.g. geysers in New Zealand)


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Endogenic processes

processes within the Earth

Platforms - shields and tables - basic building elements of all the continents - The older the platform, the smaller the relief!

Mobile orogenic zones- fold (range) mountains from Paleozoic, Mesozoic and Tertiary ages

Land massShields - cores of the land mass, e.g. old Scandinavian, Canadian, African, Australian shield created by oldigneous (granite) and metamorphic (marble) rocks

Tables - parts of platforms where older fold parentn rock was covered by younger (sedimentary) rocks - plains(East-European)

Orogenic zones = determined by faults, originated in platform rims or in between them -mountain foldingactivity

Ocean

Oceanic floor - continental shelf, continental slope, abyssal plain, seamounts, mid-oceanic ridges,volcanicislands and trenches

Oceanic platformsthe biggest part of oceans floor, they are called basins, e.g. Brazil, Argentine south-westpart of Atlantic ocean

Oceanic mobile zones - midoceanic ridges, long and narrow mountain ranges, somewhere occurring above thesea level as islands (Pacific Ocean), their length is about 45 000 km e.g. Mid-Atlantic Ridge


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Rocks

In the upper part of lithosphere we can find all the chemical elements. There are mostly silicate

minerals which are combination of oxide, silicon and some other metals mica

rocks - composition of minerals or organic remainsigneous rockssedimentary rocksmetamorphic rocks

Metamorphic rocks - is formed by pressure and extreme heat applied to existing rocks withinthe earths crust causing them to change their mineral structure and texture. E.g marble, gneiss


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Igneous rock-created by crystallization of

silicate minerals, water and various gases

consist of magma or lava.

According to the presence of SiO2, rocks are

divided into:

- acid, e.g. granite,

- neutral, e.g. andesite,

- basic, e.g. basalt,


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Sedimentary rocks -is formed by deposition of

rock particles that have been eroded.

Mechanical and chemical disruption of rocks is

called weathering.

- Mechanical weathering =

disintegration of rocks by the influence of

different temperatures, frost or organisms

activity.

- Chemical weathering = rocks are

decomposited by air and water (by chemical

processes) and changed into rocks of different

nature compared to the previous ones. e.g

sandstone, limestone, dolomite


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Metamorphic rocks - is formed by pressure and extreme heat applied to

existing rocks within the earths crust causing them to change their mineral

structure and texture. E.g marble, gneiss


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Geomorphology

- is science about the Earths relief. It studies the formation, evolution and character of relief andits forms.

-it is a landmark between solid lithosphere + pedosphere and liquid hydrosphere + gaseousatmosphere

Relief (Georelief) - complex of shapes of the Earths surface, it is created by geomorphologicalprocesses many forms of georelief e.g. slopes, valley, mountains, basins, lowlands, plateaux,plains, etc. Relief also influences other parts of the Earth e.g. flora, fauna, climate, constructionof buildings, agriculture, etc

Many forms of it can be a disaster for people. e.g. landslides, avalanches, earthquakes,volcanoes, soil erosion, etc.

The most basic feature of the relief isaltitude. Also there are many others:descend (slope) line a line perpendicular to countours (contour lines)aspect orientation to points of the compass (cardinal points) e.g. southern aspect receivesmore insolationcrest line line joining places of a crest, places of the highest altitude upon a crest

valley line line joining places of a valley, places of the lowest altitude within a valley

Vertical segmentation of relief- vertical difference (meters) between the highest and thesmallest point of certain area.

Horizontal segmentation of relief- the number of valley lines

Hierarchy of relief formsSmaller areas are parts of larger ones - riverbed - flat - valley - mountain range continent


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Weathering - decomposition and disintegration of rocks in situ (in the same place)

- breaking down of rock into smaller components at or near the Earths surface

3 types of weathering:Mechanical (physical) weathering Chemical weathering

Biological weathering

Chemical weathering =decomposition of a rock, rocks are broken down by chemicalreactions e.g. kaoliniteCarbonation:Rainwater absorbs carbon dioxide (CO2) as it falls through the air and soaksthrough the soil. This makes is acidic. It will attack rocks composed of calcium carbonate (CaCO3)e.g limestoneOxidation:Metals and metallic minerals (Fe) in rocks combine with oxygen (O2) from the air toform another substance. Rocks which contained of iron are especially weathered by this process.Hydrolysis:Some rock minerals combine with rainwater and break down into other chemicalforms. This process of hydrolysis is important in producing sand and clay when water (H2O)

combines granite.

Mechanical (physical) weathering- disintegration of a rock, rocks break up due to stresse.g. screeFreeze-thaw (ice crystal growth or frost shattering) water expands by 1/10 when it freezes(below 0C) ice crystals in a rock grow and then a rock is splitted as a result of the pressure

Biological weathering (biotic forces)- mechanical + chemical weathering e.g plants roots,

animals, etc.


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Slope processes

Slope - any part of the solid land surface.

Slope - an inclined surface or hillslope - an angle of inclination or slope angle

Surfaces can be:sub-aerial (exposed)sub-marine (underwater)aggradational (depositional)degradational (erosional)transportational or any mixture of these.

Geography (geomorphology) studies the hillslope = area between the watershedand the base

Slope form = the shape of the slope in cross-section

Slope processes = activities acting on the slopes

Slope evolution = development of slopes with time

Endogenic processes occur within the Earth (tectonic forces)


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Exogenic processes operate at/near the Earths surface

(weathering/erosion, mass movements) large-scale movement of theEarths surface without a moving agent(river, glacier) e.g. rockfall,landslide, mudflow, avalanche

The simplest model of slope form:waning slope (concave)scree slopecliffwaxing slope (convex)

Slopes - an open system -active processes that shape passivematerials:

Inputs:energy (insolation)

mass (water and sediment)

Outputs:energy (re-radiated heat)mass (water regolith)


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Mass movements

- large-scale movement of the Earths surface without a movingagent(river, glacier, ocean wave), type of exogenic processes

Mass movement:very slow soil creepfast avalanchedry rock fallfluid (wet) mud flow

Mass movement on the slope is determined by:1. gravity- it can move the material down slope - slide component- it holds the particle to the slope - stick component2. slope angle the downslope movement is proportional to the weight of

the particle and to the slope angle3. pore pressure water fills the spaces between the particles, lubricatesthem and pushes them apart under pressure, very important in movementof wet material on low-angle slopes


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Types of mass movement

Surface wash takes place when soils infiltration capacity has been exceeded,in particular when the ground is frozen orheavily saturated, on the other hand, it might take place also in semi-arid and arid regions where particles size preventpercolation

Sheetwash unchannelled flow of water over a soil surface, is capable of transporting material dislodged by rainsplacsh.On most slopes it breaks into areas of high velocity and areas of lower velocity.

Throughflow takes place when water moves down through the soil. It is chennelled into natural pipes in the soil, it givesthe sufficient energy to transport material of considerable volume.

Heave/creep small scale movement occurring mostly in winter.

Talus creep slow movement of fragments on a scree slope

Rainsplash erosion erosive effect of raindrops on hillslope

Falls - on steep slopes (>70) weathered rocks are detached and fall due to gravity-short fall - produces a straight scree-long fall - produces a concave scree

Slides - when the whole mass of material moves along a slip plane-rockslideschist, mica-landslidea) downslope force > the resistance (friction and cohesion)

b) material moves downslope after a shear failure

Slumps - rotational slides on softer rocks (claystone) along a curved plane.

Flows - continuous, fluent movements of fine, deeply weathered clay, saturated with water=> highly fluid, no cohesion

Avalanches - rapid movements of snow and ice, rock and soil (debris avalanche) down a slope, very common in mountainareas.-dry avalanche = newly fallen snow falls off older snow mainly in winter-wet avalanche = partially melted snow (triggered by skiing) in spring


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Glaciation

is formation of glaciers in certain areasMany landforms are results of glacial erosion and deposition.

2 main phases:

cold periods glacial ice advanced southwardswarm periods interglacial ice retreated northwards

Accumulation of ice when a mass of ice is formed in a valleyformation of a glacier

It can flow slowly downhill because of influence of gravity. E.glargest glaciers in the Himalayas, Rocky mountains and the AlpsContinuous mass of ice covering a large land surface ice sheet.


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Glacier as a system Inputs:

Precipitation, meltwater, sunlight, frost shaterring sediments

Processes:Storage of glacier ice

Output:

Meltwater, ice, rock debris, water(gas)

A glacier moves into warmer areas where the ice is melt 2 parts:Zone of accumulation(inputs>outputs) glacier is growing,snowfall>melting

Zone of abalation (outputs>inputs)- glacier is shrinking andretreating, melting>accumulation


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Glacial erosion and transport

Cold polar glaciers - move very slowly

Warm, temperate glaciers move faster because meltwater helps to reduce the frictional force

Glaciers can transport large amounts of rock debris moraine- can be brought:on the surface of the glacierwithin the glacieralong the glacier

Corrie semi-circular, steep-side basin cut into the side of a mountain or at the head of avalley.

Corrie lake(tarn)- glacier that has come into valley and interglacial period it melted onlywater remained glacial lakes

Pyramid peak 3-4 corries cutting back on each other

U-shaped valley created by a glacier moving downslopes

Hanging valley tributary glaciers flow into the main larger one. After malting these glaciersleave the valley hanging above them


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Landforms

Drumlins egg-shaped hills, formed under the glacuier by ice thathas moulded boulder clayu into this distinctive shape

Eskers long ridges of deposited material, formed by depositionfrom meltwater streams which flow under the ice.

Erratics boulders transported over a long distance and deposited

by glaciers.

Kames small mounds of debris within ice, after thawing thatdropped on the ground

Kettle holes detached blocks of ice, after melting water5 is in ahollow and could be lost by evaporation an infiltration

Outwash plains as meltwater streams flow away from theglacier, they begin to sort out material and deposit their load.

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Lithosphere and Geomorphology