chapter 14 notes power point

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Geology:

Processes, Hazard, and Soils

Chapter 10



What is the earth’s structure?

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)

Fig. 10.26,400 km (3,900 mi.), 4,300˚C



Features of crust and mantle

Lithosphere: rigid, brittle

Asthenosphere: plastic, deformed by heat/pressure Fig. 10.2

Oceanic crust(lithosphere)

Abyssalhills Abyssalfloor

Oceanicridge

TrenchVolcanoes

Folded mountain beltCraton

Mantle (lithosphere)

Mantle (asthenosphere)

A b y s s

a l p l a i n

Continental crust(lithosphere)

Mantle(lithosphere)

Continentalrise

Continentalslope

Continentalshelf Abyssal plain

Abyssalfloor

Fig. 10.3



Why do the plates move?

Tectonic plate

Collision betweentwo continents

Oceanic tectonicplate

Spreadingcenter Oceanic tectonicplate Ocean trench

Plate movement Plate movement

Continentalcrust

Subductionzone

Oceaniccrust

Oceaniccrust

Continentalcrust

Mantle

Innercore

Hot outercore

Two plates movetowards each other.One is subductedback into the mantleon falling convectioncurrent.

Mantleconvectioncell

Hot materialrisingthroughthe mantle

Material coolsas it reachesthe outermantle

Cold densematerial fallsback throughmantle



Lithosphere

AsthenosphereOceanic ridge at a divergentplate boundary

Lithosphere

Trench Volcanic island arc

Asthenosphere

Risingmagma

Subductionzone

Trench and volcanic island arc ata convergent plate boundary

Fracture zone

Transformfault

Lithosphere

AsthenosphereTransform fault connecting twodivergent plate boundariesFig. 10.6,

Tectonic plates (60 mi.)LithosphereAsthenosphere

Three types of boundariesDivergent boundary

Oceanic ridges

Convergent boundarySubduction zoneVolcanic islands

Transform fault

earthquakes

Earth’s internal processes



EURASIAN PLATE

CHINASUBPLATE PHILIPPINE

PLATE

INDIAN-AUSTRLIAN PLATE

PACIFICPLATE

JUAN DEFUCA PLATE

COCOSPLATE

CARIBBEANPLATE

NORTHAMERICAN

PLATE

SOUTHAMERICAN

PLATE

EURASIANPLATE

ANATOLIANPLATE

ARABIANPLATE

AFRICANPLATE

SOMALIANSUBPLATE

CarlsbergRidge

Southwest IndianOcean Ridge

ANTARCTIC PLATE

Transformfault

East PacificRise

Transformfault

Mid-Indian

OceanRidge

Southeast Indian

Ocean Ridge

Mid-Atlantic

OceanRidge

ReykjanesRidge

Transformfault

Divergent ( ) andtransform fault ( )boundaries

Convergentplate boundaries

Plate motionat convergentplate boundaries

Plate motionat divergentplate boundaries



Natural hazards of the earth’s

processes:Earthquakes

Primary effects:ShakingDisplacement

Secondary effects:Rock slidesTsunamisflooding

Liquefaction ofrecent sedimentscauses buildingsof sink

Landslides mayoccur onhilly ground

Shockwaves

Epicenter

Focus

Two adjoining platesmove laterally alongthe fault line Earth movements

Cause flooding inLow-lying areas




processes:Earthquakes

Faults

Severity /Richter scaleInsignificant (<4.0)Minor (4.0-4.9)Damaging (5.0-5.9)Destructive (6.0-6.9)Major (7.0-7.9)Great (>8.0)

Aftershocks

Liquefaction ofrecent sedimentscauses buildingsof sink

Landslides mayoccur onhilly ground

Shockwaves

Epicenter

Focus

Two adjoining platesmove laterally alongthe fault line Earth movements

Cause flooding inLow-lying areas




processes:VolcanoesActivity

EjectaLavaGases

ExplosiveFaults

QuietlyDivergent boundaries

extinctvolcanoes

magmareservoir

centralvent

magmaconduit

Solidlithosphere

Upwellingmagma Partially molten

asthenosphere



What processes occur on earth’s

surface?External processes are powered by solarenergy and gravity

Mechanical weatheringLoosens materialFrost wedging

Erosion (wind/rain) :Material worn away and carried elsewhere

Chemical weathering:

Reactions with carbon dioxide, oxygen, ormoisture



Minerals, Rocksand the Rock Cycle

MineralsElement, or inorganic compound found naturally

and is solid

RockAny material that makes up a large continuouspart of the earth’s crust,Can be a single mineral, or more than one

Igneous (granite, lava)Sedimentary (limestone, sandstone)Metamorphic (marble, slate)



The Rock Cycle

Fig. 10.8, p. 217

Igneous RocGranite,pumice,

basalt

Metamorphic RockSlate, marble,quartzite

Magma

(molten rock)

Heat, pressure,stress

Heat, pressure

Melting

edimentary RockShale,

Sandstonelimestone

Deposition

Transportation

Erosion

Weathering

Most of earth’s surface

1. Rocks2. Shells/skeletons3. Plant remains



External processes lead to

formation of soilMechanical weatheringLoosens material

Frost wedgingErosion:

Material worn away and carried elsewhere

Chemical weathering:Reactions with carbon dioxide, oxygen, ormoisture



Soils: Formation

O horizon:Leaf litter

A horizon:Topsoilhumus

B horizon:SubsoilMostly inorganic

C horizon:Parent

material Mature soil

Young soil

RegolithBedrock

Immaturesoil

Generally takes 200-1000 yrs to generate 1 inch of topsoil



Soil PropertiesInfiltrationMovement of

water downward

LeachingTransfer of

Dissolved soil components to lower layers

Soils vary in porosity/permeabilityDepending on their components

Water Water

High permeability Low permeability

Fig. 10.17



Soil StructureTexture determines porosityPorosity determines permeability for both water and airLoam: Soil with roughly equal components of each and humus

Texture Nutrient Infiltration Water-Holding Aeration Work-Capacity Capacity ability

Clay Good Poor Good Poor Poor

Silt Medium Medium Medium Medium Medium

Sand Poor Good Poor Good Good

Loam Medium Medium Medium Medium Medium



Soil Texture 100%clay

Increasingpercentage silt

Increasingpercentage clay

0

20

40

60

80

80

60

40

20

0100%sand 80 60 40 20 100%silt

Increasing percentage sand



Soil acidity or alkalinity:pH

Affects uptake of nutrients by plants

High pH,Common in dry areasTreatment

Addition of sulfur -> sulfuric acid

Low pHNeutralize with lime

Speeds up decomposition



Weak humus-mineral mixture

Mosaicof closelypacked

pebbles,boulders

Dry, brown toreddish-brown, withvariable accumulationsof clay, calciumcarbonate, andsoluble salts

Desert Soil(hot, dry climate) Grassland Soil(semiarid climate)

Alkaline,dark,and richin humus

Clay,calciumcompounds

Soilprofilesin biomes



Acidiclight-coloredhumus

Iron andaluminumcompoundsmixed withclay

Forest litterleaf mold

Humus-mineralmixtureLight, 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)

Soil profiles in biomes



Soils: ErosionWater/Wind

Usually slow

Sheet erosionUniform

Difficult to notice

Rill erosion: fast flowing rivulets

Gully erosion: wider/deeper channels

Fig. 10.18



Soils: ErosionHuman intervention

2 major effects:

Loss of soil fertilityLoss of water retentionRun-off pollutes water sources

Kills aquatic lifeClogs streams, rivers and lakes

Fig. 10.18



Soil Erosion: How serious?Soil is renewable unless used too fast.Poverty is issue

In the U.S. alone,Approximately 1/3 of topsoil has been lost“Dustbowl” in the 1930s

Overgrazing, conventional tillage, drought

Soil Conservation Act (1935)

Good news:Loss has been slowed by 40% last 20 years.

Bad news: Dustbowl in China?



Global Soil Erosion

Areas of serious concern

Areas of some concern

Stable or nonvegetative areas



Soils: DegradationDesertification

Productive potential of arid landdecreases

Natural climate changes : prolonged droughthuman activities

POSITIVE FEEDBACK MECHANISM!Drought -> increased reflectivity ->change local climate -> increase drought



Soils: Degradation

SalinizationIrrigation and

evaporationAccumulated salts

From unabsorbed water

WaterloggingPrecipitation/irrigation causes water

table to rise, salt sits in soil until

EvaporationTranspiration

Evaporation

Waterlogging

Less permeableclay layer



Solutions: Soil ConservationConventional Tillage

Leaves soil bare in the winter

Conservation Tillage (Minimum/No-Till)Disturbs soil as little as possible

Cropping methods

Strip/contouring to protect soilWindbreaksReduce soil erosion/retain moisture

Land Classification: ID delicate areas



(a) Terracing(b) Contour planting and strip cropping

(c) Alley cropping (agroforestry) (d) Windbreaks



Soil RestorationOrganic Fertilizer

Animal manureGreen manureCompost

Crop rotation: alternate crops/legumes

Commercial inorganic fertilizerNitrogen/phosphate/potassiumD ’t t g i t i l

chapter 14 notes power point

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