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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