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GEOMORPHIC PROCESSES ANDLANDFORMS
An Overview
• Many Physical and Chemical Processesoperate because the earth’s surfaceundergoes alterations.
• The processes are known as geomorphicprocesses
• These processes leave their distinctive imprintupon landforms and each geomorphic processdevelops its own characteristic assemblage oflandforms.
• Endogenic and exogenic forces have an impacton the alteration of the earth’s surface
• Diastrophism and volcanism are endogenicprocesses
• Weathering, mass wasting, Erosion andDeposition are Exogenic Processes
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WEATHERING
• The disintegration and decomposition of rockin situ i.e. in its original position.
• It is the first stage under denudation forces• It is different from erosion because it does not
involve any movement of material.
Weathering
Weathering Processes
• Mechanical/Physical Weathering• Chemical Weathering• Biological
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Mechanical / Physical Weathering
• The disintegration of rocks into smallerparticles by mechanical processes without anychange in chemical composition of the rock
• Usually occurs in areas with no vegetations i.e.deserts, high mountains and arctic regions
• Temperature change play a crucial role on thisprocess.
Physical weathering processes• No change in chemical composition--just
disintegration into smaller pieces.• Physical breakuppressure releasewater: freeze - thaw cycles crystallization of salt in cracks
• Thermal expansion and contraction All thisincreases the total surface area exposed toweathering processes.
Physical weathering processes
• Exfoliation:- Rock breaks apart in layers that are parallel to
the earth's surface; as rock is uncovered, itexpands (due to the lower confining pressure)resulting in exfoliation.
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Exfoliation:
Exfoliation:
Sheet Joints(Exfoliation)
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Frost Wedging/shattering
• Rock breakdown caused by expansion of ice incracks and joint
Shattered rocksare common incold and alpineenvironmentswhere repeatedfreeze thawcycles graduallypry rocks apart.
Thermalexpansion/insolation/exfoliation/onion
weathering• The disintegration of upper layers due to the
influence of insolation.• Prominent in desert areas.• Repeated swelling and shrinking of minerals
with different expansion rates will also shatterrocks.
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Thermal expansion
Chemical WeatheringTransformation/decomposition of onemineral into another
• Mineral breakdown– carbonate dissolves– primary minerals --> secondary minerals
(mostly clays)Net loss of elements retained in the soil.Water is the main operator:– DissolutionMany ionic and organic compounds dissolve in
water – Silica, K, Na, Mg, Ca, Cl, CO3, SO4
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• – Acid Reactions
• Water + carbon dioxide <---> carbonic acid
• Sulfur + Water <---> sulfuric acid
• H+ effective at breaking down minerals
• water + carbon dioxide + calcite dissolveinto calcium ion and bicarbonate ion
• Biological activity in soils generatessubstantial CO2
• Bicarbonate is the dominant ion insurface runoff.
Chemical Weathering Processes
• Oxidation– Oxygen dissolved in water promotes
oxidation of sulfides, ferrous oxides,native metals.
• Organic Activity– Plant material makes H+ ions
available
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• Hydration:
• Attachment of water molecules tocrystalline structure of a rock, causingexpansion and weakness.
• Hydrolysis:• Combination of hydrogen and oxygen
in water with rock to form newsubstances.
• Solution:Process by which rock is dissolved in water- Is strongly influenced by pH and temperature- When water becomes saturated, chemicals
may precipitate out forming evaporitedeposits.
- Calcium carbonate (calcite, limestone),sodium chloride (salt), and calcium sulfate(gypsum) are particularly vulnerable tosolution weathering.
Biological Weathering• The disintegration and decomposition of rocks
due to the influence of living organisms (Floraand Fauna)
• Can be both chemical and mechanical innature.
• roots split rocks apart.• roots produce acids that dissolve rocks (humic
Acid)• tree throw .• Burrowing animals
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Biological Weathering
Animals that burrow in the ground break upsoil and loosen rocks to be exposed to furtherweathering
Factors Affecting Weathering
• The nature of the rock• Climate• Plants and animals• Relief• Time
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KARST SCENERY• Word is German form of the Yugoslavian term
“Kras” means “bare stony ground”• Named after investigating a region near the
Adriatic Sea in Yugoslavia• In modern Geomorphology the term refers to any
landscape formed by dissolution of the underlyingbedrock
• Characterized by distinctive landforms which don’ttypically occur in any other circumstance
• e.g. North of Infrane-middle Atlas (Morocco),South of Dayete Ifrah, Jamaica, etc.
Karst Landforms
• Karst is a term used to describe landscapesthat are formed by chemical weatheringprocess controlled by groundwater activity.Karst landscapes are predominantly composedof limestone rock that contains > 70 percentcalcium carbonate.
Limestone Pavement
• Exposed areas oflimestone
• Rugged and barelandscape with flatareas of rock surface
• Gradual widening ofjoints and fractures(bedding)
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Features of limestone pavements• Clint: section of a limestone pavement
separated from adjacent sections by grikesGrike: vertical crack that develops along a jointin limestone
• Karren: small hollow that forms on the surfaceof a limestone clint
Sinkholes
• Collapsed/depressed limestone features thatdevelop in karst landscapes.
• The ground water slowly dissolves thelimestone rock below the surface until iteventually becomes unstable and collapsescreating local depressional features.
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•Groundwaterdissolves solublerock, creatingfractures and caves.
•Dissolving continuesto form larger cavesand fractures.
Disappearing Streams• Streams that flow on the surface and then
seemingly “disappear” below ground.• Disappearing streams disappear into a
sinkhole or other karst solution features (caves)• They may also disappear into factures or faults
in the bedrock near the stream.• Disappearing streams are also referred to as
losing streams, sinks, or sieves.
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Springs
• Karst springs are locations where groundwateremerges from the limestone and flows acrossthe surface forming a stream or containedpool.
Karst Topography
Karst Towers• Landscape is mottled with a maze of steep,
isolated limestone hills• Limestone beds are thick and highly jointed • E.g. Puerto Rico, western Cuba, southern
China, and northern Vietnam
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Caverns
• Limestone caverns and caves are large sub-surface voids where the rocks has beendissolved by carbonation.
• In sections where the ground water table hasdropped, pressure release promotesprecipitation of minerals creating a variety ofspeleothems
• Calcium carbonate precipitatesout of the saturated carbonatesolution and accumulates asdeposits.
• Stalactites are deposits thatgrow from the ceilingdownward
• Stalagmites are deposits thatgrow from the ground up.
• If the stalactite andstalagmites join they form acontinuous column.
• Mammoth Cave in Kentuckyand Carlsbad Caverns in NewMexico are good examples ofcave system
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Abîme• A vertical shaft in
karst that may bevery deep andusually opens intoa network ofsubterraneanpassages
Cenote,
• A deepsinkhole,resultingfrom collapseof limestonebedrock thatexposesgroundwaterunderneath
Polje• (karst polje, karst
field), a large flatspecificallykarstic plain. Thename "polje"derives fromSouth Slaviclanguages
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Polje Model
Karst fenster
• ("karst window"), afeature where aspring emergesbriefly, with thewater discharge thenabruptlydisappearing into anearby sinkhole
MASS WASTING
• The downslope movement of rock, regolith,and soil under the direct influence of gravity.
• Gravity is the controlling force
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Important triggering factors
• Saturation• Oversteepening• Removal of vegetation• Ground vibrations
Saturation of the material with water
• Destroys particle cohesion• Water adds weight
Oversteepened slopes• Unconsolidated granular particles assume a
stable slope called the angle of repose• Stable slope angle is different for various
materials• Oversteepened slopes are unstable• Undercutting by streams• Undercutting by human interference• Addition of material to top of slope
– Natural—deposition– Human-caused--construction
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Removal of anchoring vegetation
• Wildfires• Drought• Development, logging• Ground vibrations
– from earthquakes
Types of mass wasting processes
• Defined by– The material involved– The movement of the material
Types of mass wasting processes
• Defined by the material involved– Debris– Mud– Earth– Rock
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Types of mass wasting processes
• Defined by the movement of the material Thecharacter of the movement– Fall– Slide– Flow
Types of mass wasting processes
• Defined by the movement of the material Therate of the movement– Fast– Slow
Forms of mass wasting
– Slump– Rockslide– Debris flow– Earth flow– Creep– Solifluction/sludging
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Forms of mass wasting(Consolidated)
• Slump– Rapid movement
along a curvedsurface
– Occur alongoversteepened slope
• Rockslide– Rapid– Blocks of bedrock move
down a slope.– The rapid movement of
large blocks of detachedbedrock sliding more orless as a unit
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Rockslide impact in Mabatini –SinaiMwanza Tz in 2014
Rock Avalanche
• The rapid* massmovement of brokenrock material, oftenriding on a cushionof trapped air.Usually triggered b yan earthquake
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Creep
• The downhillmovement of soiland other debris,typically at rates ofabout 1 to 10mm/year
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Soil Creep
Earthflow• A fluid
movement ofrelatively fine‐grained material,e.g. soil,weathered shale,and clay.
Earth Flow Video
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Debris Flow• A fluid mass
movement ofrock fragmentssupported by amuddy matrix.May move atspeeds of upto 100 km/hr
Mudflow• A flowing mass of
material (mostlyfiner than sand,along with somerock debris)containing a largeamount of water. Itmay travel largedistances and highspeeds, and carryparticles as large as ahouse
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Mudflow in Salton Sea in southernCalifornia US. 2013
Mudflow
Effects of Mass wasting: A case ofBulambuli Landslide Monday,
29/8/2011