Weathering - GEOLOGY (engineering geology- kannur university )
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Transcript of Geology
Earth’s StructureEarth’s Structure
Name the zones of the earthCrust, mantle, core
Now do it again with more detailCrust, lithosphere, asthenosphere, mantle, outer core, inner core
Fig. 10.2, p. 212
Mantle
Core
Crust
Low-velocity zone
Solid
Outer core(liquid)
Innercore(solid)
35 km (21 mi.) avg., 1,200˚C
2,900km(1,800 mi.)3,700˚C
5,200 km (3,100 mi.), 4,300˚C
10 to 65km
100 km
200 km
100 km (60 mi.)200 km (120 mi.)
Crust
Lithosphere
Asthenosphere(depth unknown)
What is in each zoneWhat is in each zone
Core – mostly iron and a little nickel, inner solid and outer is liquid
Mantle – mostly iron, silicon, oxygen, and magnesium, mostly rigid except near surface which is plastic (asthenosphere)
Crust – mostly oxygen, silicon, aluminum, and iron (by weight)
Convection belowConvection below
Heat from the formation of the earth combined with energy from radioactive decay gives way to convection currents of rock (very slow) or mantle plumes in which hot rock rises
Plate tectonicsPlate tectonics
The lithosphere is broken into many large plates which move due to convection currents within the asthenosphere
Remember continental drift (Pangaea)
Fig. 10.5b, p. 214
EURASIAN PLATE
CHINASUBPLATE PHILIPINE
PLATE
INDIAN-AUSTRLIAN PLATE
PACIFICPLATE
JUAN DEFUCA PLATE
COCOSPLATE
CARIBBEAN PLATE
NORTHAMERICAN
PLATE
SOUTHAMERICAN
PLATE
EURASIAN PLATE
ANATOLIAN PLATE
ARABIAN PLATE
AFRICAN PLATE
AFRICAN PLATE
CarlsbergRidge
Southwest IndianOcean Ridge
ANTARCTIC PLATE
Transformfault
East PacificRise
Transformfault
Mid-IndianOceanRidge
Southeast IndianOcean Ridge
Mid-AtlanticOceanRidge
ReykjanesRidge
Transformfault
Divergent ( ) andtransform fault ( )boundaries
Convergentplate boundaries
Plate motionat convergentplate boundaries
Plate motionat divergentplate boundaries
Plate boundariesPlate boundaries Divergent – plates move apart, form mid ocean ridges
Convergent – plates slam together, form largest mountains in the world
Subduction is a type of convergent where one plate dives beneath another and usually creates trenches and volcanoes nearby
Transverse – slide sideways past each other (San Andreas Fault)
Fig. 10.6b, p. 215
Lithosphere
Trench Volcanic island arc
Asthenosphere
Risingmagma
Subductionzone
Trench and volcanic island arc at a convergentplate boundary
Fig. 10.6c, p. 215
Fracture zone
Transformfault
Lithosphere
Asthenosphere
Transform fault connecting two divergent plate boundaries
Fig. 10.3, p. 213
Oceanic crust(lithosphere)
Abyssalhills Abyssal
floorOceanic
ridgeTrench
Volcanoes
Folded mountain belt
Craton
Mantle (lithosphere)
Mantle (asthenosphere)
Ab
ys
sa
l p
lain
Continental crust(lithosphere)
Mantle(lithosphere)
Continentalrise
Continentalslope
Continentalshelf
Abyssal plain
Abyssalfloor
Erosion and WeatheringErosion and Weathering These are the external processes Erosion is the moving of rock material from one
place to another (deposition)
Weathering is the breaking down of rock by natural forces
Ice wedging, rain, wind, gravityChemical weathering, carbonic acid
Fig. 10.7, p. 216
Dunes Lagoon
SpitsStream
Glacier
Lake
Tidalflat
Barrierislands
Shallow marineenvironment
Volcanicisland
Coral reef
Abyssal plain
Deep-sea fan
Continental shelf
Continental slope
Continental rise
DeltaDunes
Beach
Shallow marineenvironment
Rocks and mineralsRocks and minerals
Mineral – an element or inorganic compound that occurs naturally, is solid, and has a regular crystalline internal structure
Rock – type of music meant to be played loud, also any material that makes up a large, natural, continuous part of the earth’s crust
Types of rockTypes of rock
IgneousGranite, pumice, basalt
SedimentaryShale, sandstone, limestone (coral reef)
MetamorphicSlate, marble, quartzite
Fig. 10.8, p. 217
Igneous RockGranite, pumice,
basalt
Metamorphic RockSlate, marble,
quartzite
Magma(molten rock)
Cooling
Heat, pressure
Melting
Heat,pressure,
stress
Sedimentary RockSlate, sandstone,
limestoneDepositionTransportation
Erosion
Weathering
EXTERNAL PROCESSES
INTERNAL PROCESSES
EarthquakeEarthquake Fault – break in the lithosphere Focus – where the earthquake took place Epicenter – location above focus at surface Richter scale – used to measure magnitude, less than 3
is not felt, logarithmic scale, so each increase of 1 is a factor of 10
Minor < 5, damaging 5-6, destructive 6-7, major 7-8, great over 8
Aftershock – reduced shaking after original movement
Volcano – it can happen here!Volcano – it can happen here! Volcano - Wherever magma reaches the surface
through a vent or fissure (also released are gases carbon dioxide, water vapor, hydrogen sulfide, ash, and other ejecta
Mt. St. Helens – worst US volcano disaster
Ring of fire – other than a song by Social D, this is the edge of the pacific plate where most volcanoes are located
SoilSoil
Produced slowly (200-1000 years typically) by weathering of rock, deposition of sediments, and decomposition of organic matter
Soil horizons – separate zones within soil Soil profile – cross-section view of soil
HorizonsHorizons O horizon – surface litter A horizon – top soil, made up of inorganic
particles (clay, silt, sand) and humus (organic particles from decomposed organisms)
Dark topsoil is richer in nutrientsReleases water and nutrients slowlyProvides aeration to rootsHealthy soil contains many nematodes and bacteria, fungi, etc.
Fig. 10.12, p. 220
Oak tree
Fern
O horizonLeaf litter
A horizonTopsoil
B horizonSubsoil
C horizonParent
material
Root system
Mature soil
Red earthmite Springtail
Bacteria
Fungus
Actinomycetes
Nematode
Mite
Pseudoscorpion
Young soil
Regolith
Bedrock
Immature soil
RockfragmentsMoss and
lichen
Organic debrisBuilds upGrasses and
small shrubsMole
Dog violet
Honeyfungus
Millipede
Earthworm
Lords andladiesWord
sorrel
Poor topsoilPoor topsoil Grey, yellow and red are not the colors of healthy
topsoil Generally means that soil is lacking nutrients
Best soil is called loam with equal parts sand, silt, clay and humus
Leaching – dissolving and carrying nutrients (or pollutants) through soil into lower layers
B – horizon and C - horizonB – horizon and C - horizon
B – Subsoil mostly broken down rock with little organic matter
C- parent material broken down rock on top of the bedrock
SoilsSoils
Texture – relative amount of different sized particles present (sand, silt, clay)
Porosity – volume of pore space in the soil Permeability – the ability of water to flow through
the soil
SoilsSoils
Clay – high porosity, low permeability Sand – high permeability, low porosity
Acidity is another factor Where rain is low, calcium and other alkaline
compounds may build up (sulfur can be added – turns to sulfuric acid by bacteria)
Fig. 10.15b, p. 223
Acidiclight-coloredhumus
Iron andaluminumcompoundsmixed withclay
Forest litterleaf mold
Humus-mineralmixture
Light, grayish-brown, silt loam
Dark brownFirm clay
Acid litterand humus
Humus andiron andaluminumcompounds
Light-coloredand acidic
Tropical Rain Forest Soil(humid, tropical climate)
Deciduous Forest Soil(humid, mild climate)
Coniferous Forest Soil(humid, cold climate)
Fig. 10.15a, p. 223
Weak humus-mineral mixture
Mosaicof closelypackedpebbles,boulders
Dry, brown toreddish-brownwith variableaccumulationsof clay, calciumcarbonate, andsoluble salts
Desert Soil(hot, dry climate)
Grassland Soil(semiarid climate)
Alkaline,dark,and richin humus
Clay,calciumcompounds
Soil erosionSoil erosion
Causes – mainly water and wind Human induced causes – farming, logging,
mining, construction, overgrazing by livestock, off-road vehicles, burning, and more (go us!)
Soil erosionSoil erosion Types Sheet
Uniform loss of soil, usually when water crosses a flat field
RillFast flowing water cuts small rivulets in soil
GullyRivulets join to become larger, channel becomes wider and deeper, usually on steeper slopes or where water moves fast
Global soil lossGlobal soil loss This is a major problem world wide Have lost about 15% of land for agriculture to soil
erosionOvergrazingDeforestationUnsustainable farming
Also 40% of ag land is seriously degraded due to soil erosion, salinization, water logging and compaction
Fig. 10.19, p. 226
Areas of serious concern
Areas of some concern
Stable or nonvegetative areas
Global soil erosion
DesertificationDesertification Turning productive (fertile) soil into less
productive soil (10% loss or more)OvergrazingDeforestationSurface miningPoor irrigation techniquesPoor farming techniquesSoil compaction
SalinizationSalinization As water flows over the land, salts are leached out When water irrigates a field it is left to evaporate
typically This repeated process causes the dissolved salts to
accumulate and possibly severely reduce plant productivity
Fields must be repeatedly flushed with fresh water to remove salt build up
WaterloggingWaterlogging When fields are irrigated they allow water to sink
into the soil. Winds can dry the surface As more water is applied the root area of plants
is over saturated reducing yield
As clay is brought to subsoil levels it can act as a boundary for water infiltration
Fig. 10.22, p. 229
Evaporation
Evaporation TranspirationEvaporation
Waterlogging
Less permeableclay layer
Soil conservationSoil conservation
Conservation tillage – (no till farming) disturb the soil as little as possible
Reducing erosion also helps – save fuel, cut costs, hold water, avoid compaction, allow more crops to be grown, increase yields, reduce release of carbon dioxide
Soil conservationSoil conservation Terracing – making flat growing areas on
hillsides Contour farming – planting crops perpendicular
to the hill slope, not parallel Strip cropping – planting alternating rows of
crops to replace lost soil nutrients (legumes) Alley cropping – planting crops between rows of
trees
Soil conservationSoil conservation Gully reclamation – seeding with fast growing native
grasses, slows erosion or “reverses” itAlso building small dams traps sedimentsBuilding channels to divert water or slow water
Windbreaks – trees planted around open land to prevent erosion
Retains soil moisture (shade, less wind)Habitats for birds, bees, etc.
Land classification – identify marginal land that should not be farmed
Soil fertilitySoil fertility
Inorganic fertilizers – easily transported, stored, and applied
Do not add humus – less water and air holding ability, leads to compactionOnly supply about 3 of 20 needed nutrientsRequires large amount of energy for productionReleases nitrous oxide (N2O) during production, a green house gas
Soil fertilitySoil fertility Organic fertilizers – the odor is a problem Animal manure – difficult to collect and transfer
easily, hard to store Green manure – compost, aerates soil, improves
water retention, recycles nutrients Crop rotation – allows nutrients to return to soil,
otherwise same crop continually strips same nutrient, keeps yields high, reduces erosion