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Geology: Processes, Hazards & Soils Chapter 10 35 km (21 mi.) avg., 1,200ūC Crust 100 km (60 mi.) 200 km (120 mi.) Low-velocity zone Crust Mantle Lithosphere Solid 10 to 65km 2,900km (1,800 mi.) 3,700ūC Outer core (liquid) Core Inner core (solid) 100 km Asthenosphere (depth unknown) 200 km 5,200 km (3,100 mi.), 4,300ūC Fig. 10.2, p. 212 Slide 2 Zones of earth’s sturcture • Core – solid • Mantle – thick solid zone – Aesthenosphere – under the rigid outermost part of the mantle – hot, partly melted rock that flows like plastic • Crust – outermost and thinnest zone – Contains: • CONTINENTAL CRUST - lies under continents and continental shelf • OCEANIC CRUST – under ocean basins and covers 71% of earth’s surface Oceanic crust (lithosphere) Abyssal Oceanic floor ridge Abyssal floor Abyssal plain Abyssal hills Trench Folded mountain belt Craton Volcanoes Continental shelf Continental slope Continental rise Abyssal plain Continental crust (lithosphere) Mantle (lithosphere) Mantle (lithosphere) Mantle (asthenosphere ) Fig. 10.3, p. 213 Slide 3 GEOLOGIC PROCESSES • CONSTANT CHANGES • INTERNAL PROCESSES – build up the planet’s surface – Energy provided from heat in the interior – Causes the mantle to deform and flow – Two kinds of movements: • CONVECTION CURRENTS • MANTLE PLUMES – mantle flows upward in a column Plate Tectonics • Movement of rigid plates called TECTONIC PLATES caused by convection currents and mantle plumes • Plates are 60 miles thick and are made up of continental and oceanic crust – called the LITHOSPHERE • Plates are constantly moving on the asthenosphere at different speeds Plate tectonics • Concept accepted in early 1960’s was called continental drift theory • Now called PLATE TECTONICS – PRODUCES: • VOLCANOES and EARTHQUAKES – found at plate boundaries • OCEANIC RIDGE SYSTEM • TRENCHES Help explain patterns of biological evolution Pangea Reykjanes Ridge EURASIAN PLATE JUAN DE FUCA PLATE CHINA SUBPLATE Transform fault PHILIPINE PLATE PACIFIC PLATE MidIndian Ocean Ridge Transform fault INDIAN-AUSTRLIAN PLATE Southeast Indian Ocean Ridge NORTH AMERICAN PLATE COCOS PLATE East Pacific Rise MidAtlantic Ocean Ridge EURASIAN PLATE ANATOLIAN PLATE CARIBBEAN PLATE ARABIAN PLATE AFRICAN PLATE SOUTH AMERICAN PLATE Carlsberg Ridge AFRICAN PLATE Transform fault Southwest Indian Ocean Ridge ANTARCTIC PLATE Convergent plate boundaries Plate motion at convergent plate boundaries Divergent ( ) and transform fault ( boundaries ) Plate motion at divergent plate boundaries Fig. 10.5b, p. 214 Slide 6 Volcanoes Earthquakes Fig. 10.5a, p. 214 Slide 5 TYPES OF BOUNDARIES • DIVERGENT PLATE BOUNDARIES plates move in opposite directions • Builds up the earth’s crust Lithosphere Asthenosphere Oceanic ridge at a divergent plate boundary Fig. 10.6a, p. 215 Slide 7 Mid-Atlantic Ridge system • Convergent plate boundaries – plates are pushed together by internal forces • Oceanic lithosphere is subducted under the continental at subduction zones • Trenches normally form at the boundary Trench Volcanic island arc Rising m agm a Subduction zone Lithosphere Asthenosphere Trench and volcanic island arc at a convergent plate boundary Fig. 10.6b, p. 215 Slide 8 Convergent Plate Boundary • Transform faults – occur when plates slide past one another along a fracture (fault) in the lithosphere Fracture zone Transform fault – Most are on the ocean floor Lithosphere Asthenosphere Transform fault connecting two divergent plate boundaries Fig. 10.6c, p. 215 Slide 9 External Geologic Processes • Based directly or indirectly on energy from the sun and gravity • Tend to wear down the earth’s surface • Two types: – EROSION - material is dissolved, loosened, or worn away at one part of the earth’s surface and deposited somewhere else • Caused by wind, water, and human activities – WEATHERING – produces loosened material that can be eroded • MECHANICAL – large rock fragments broken into smaller pieces – One type called FROST WEDGING- caused by freezing, expansion, and splitting of rock • CHEMICAL – chemical reactions decompose a mass of rock mainly reacts with oxygen, carbon dioxide, and water in the atmosphere and ground Minerals • Either an ELEMENT or INORGANIC COMPOUND – naturally occurring and a solid • Some are single elements – Au, Ag • Most are compounds – mica, salt, quartz ROCKS • Any material that makes up a large natural continuous part of the earth’s crust • Can contain only one mineral but most consist of two or more minerals – Example: GRANITE – quartz, mica, and feldspar IGNEOUS ROCKS • FORMS FROM MOLTEN ROCK MATERIAL (MAGMA) – Wells up from upper mantle or deep crust – Cools – Hardens into rock – EXAMPLE: GRANITE • FORMS FROM LAVA – Forms above ground when magma coold – Main part of earth’s crust – Source of many nonfuel mineral resources The Rock Cycle Transportation Deposition Sedimentary Rock Slate, sandstone, limestone Erosion Heat, pressure, stress Weathering EXTERNAL PROCESSES INTERNAL PROCESSES Igneous Rock Granite, pumice, basalt Cooling Heat, pressure Magma (molten rock) Metamorphic Rock Slate, marble, quartzite Melting Fig. 10.8, p. 217 Slide 11 Natural Hazards • Earthquakes caused by stress in crust which deforms rock until it fractures producing faults. This faulting or abrupt movement causes EARTHQUAKES CHARACTERISTICS OF EARTHQUAKES: • ENERGY IS RELEASED AS SHOCK WAVES WHICH MOVE OUTWARD – FOCUS - POINT OF INITIAL MOVEMENT – EPICENTER – POINT ON EARTH’S SURFACE ABOVE THE FOCUS. • MAGNITUDE – MEASURES SEVERITY OF EARTHQUAKE – RICHTER SCALE- MEASURED ON A SEISMOGRAPH – RANKED AS: INSIGNIFICANT – LESS THAN 4 MINOR (4.0 – 4.9) DAMAGING (5.0 – 5.9) DESTRUCTIVE (6.0 – 6.9) MAJOR (7.0 – 7.9) GREAT (OVER 8.0) *AMPLITUDE FOR EACH IS 10 X GREATER THAN THE NEXT SMALLER UNIT MORE … AFTERSHOCK S– smaller earthquakes that follow – often over a period of months FORESHOCKS – seconds to weeks before the main shock PRIMARY EFFECTS - shaking, sometimes permanent vertical or horizontal displacement of earth SECONDARY EFFECTS - rock slides, fires, flooding, tsumanis, REDUCING EARTHQUAKE DAMAGE • EXAMINE HISTORICAL RECORDS AND MAKE GEOLOGICAL MEASUREMENT • MAP HIGH RISK AREAS • ESTABLISH BUILDING CODES • TRY TO PREDICT WHERE AND WHEN EARTHQUAKES WILL OCCUR VOLCANOES • MAGMA REACHES THE EARTH’S SURFACE THROUGH A VENT OF CRACK – RELEASES: • EJECTA – CHUNKS THROUGH ASH • LIQUID LAVA – • GASES – water vapor, carbon dioxide, sulfur dioxide – USUALLY FOUND IN SAME AREAS AS EARTHQUAKE ACTIVITY – BENEFITS: • FORM MOUNTAINS, LAKES, AND PRODUCE FERTILE SOILS AS LAVA WEATHERS REDUCE VOLCANIC HAZARDS • LAND – USE PLANNING • BETTER PREDICTION • EFFECTIVE EVACUATION PLANS Oak tree Fern Word sorrel Lords and ladies Dog v iolet Earthworm Millipede Mole Honey f ungus Grasses and small shrubs Organic debris Builds up Moss and lichen Rock fragments O horizon Leaf litter A horizon Topsoil Bedrock B horizon Subsoil Immature soil Regolith Young soil Pseudoscorpion C horizon Parent material Mite Nematode Actinomy cetes Root system Mature soil Red earth mite Springtail Fungus Bacteria Fig. 10.12, p. 220 Slide 15 Characteristics of soil • TEXTURE – DETERMINED BY SIZE AND TYPE OF MINERAL PARTICLES – CLAY - VERY FINE PARTICLES – SILT - FINE PARTICLES – SAND - LARGE PARTICLES – LOAM = EQUAL MIXTURE OF CLAY, SAND, SILT AND HUMUS 100%clay 0 80 clay 20 60 Increasing percentage clay 40 silty clay sandy clay 40 60 sandy clay loam 20 clay loam silty clay loam loam silty loam sandy loam 0 sand 100%sand Increasing percentage silt loamy sand 80 80 silt 60 40 Increasing percentage sand 20 100%silt Fig. 10.16, p. 224 Slide 20 Soil Porosity • SIZE, SHAPE AND DEGREE OF CLUMPING DETERMINE THE NUMBER AND VOLUME OF SPACES FOR AIR AND WATER IN SOIL • Called SOIL STURCTURE – – – – How soil particles are “glued together” Granular – large rounded clumps Crumb – irregular clumps Platy – thin horizontal plates • MORE PORE SPACES, MORE AIR AND MORE PERMEABLE TO WATER FLOW. • Porosity determined by soil texture PERMEABILITY & STRUCTURE AFFECTS MOVEMENT OF AIR AND WATER THROUGH THE SOIL PERMEABILITY – rate at which water and air move from the surface down PERCOLATION – Ability of water to soak into the soil CAPILLARY ACTION – movement of water upward against the pull of gravity Water High pe rmeability Water Low pe rm eability Fig. 10.17, p. 224 Slide 21 • TEXTURE, POROSITY, AND PERMEABILITY DETERMINE THE WATER HOLDING CAPACITY OF THE SOIL , THE AERATION OF THE SOIL, AND THE MOISTURE CONTENT OF THE SOIL. pH • PLANTS CAN ONLY ABSORB WATER, ETC. THROUGH ROOTS IF PH IS WITHIN A CERTAIN RANGE • MOST PLANTS PREFER 6.5 TO 7 – at this point the minerals are fairly soluble. • EAST COAST - ACIDIC - DUE TO MORE RAINFALL - USE LIME TO NEUTRALIZE bue must add manure or fertilizer. • WEST COAST - ALKALINE - LESS MOISTURE – reduces uptake off phosphorus and zinc - USE SULFUR • pH INFLUENCES THE RATE OF NUTRIENT UPTAKE • ACIDIC SOILS USUALLY LOW IN NITROGEN & PHOSPHORUS – BELOW 5.5, BELOW 4.0 VERY LOW! What causes soil erosion? • Erosion - movement of soil components from one place to another. – Results in buildup of sediments and sedimentary rock on land and in water. • The two main agents: – Wind and water • Some is natural, other is caused by man – Plant roots help to anchor the soil. Main human causes of erosion • • • • • • • Farming Logging Construction Overgrazing Off-road vehicles Burning of vegetation MOST EROSION IS CAUSED BY MOVING WATER! Types of erosion • Sheet erosion - movement of water across a slope or field in a wide flow • Rill erosion - water forms fast flowing rivulets that cut small channels in the soil • Gulley erosion - rivulets of fast moving water join together and erode deeper and deeper until you have ditches and gullies. – Usually occurs on steep slopes where vegetation has been removed. Fig. 10.18, p. 225 Major harmful effects of erosion: • Loss of soil fertility and it ability to hold water • Runoff of sediment that pollutes water, kills fish, and clogs irrigation ditches and builds-up in waterways • Increased use of fertilizer to keep soil fertile • EROSION IS A SERIOUS WORLD PROBLEM! – TOPSOIL IS ERODING FASTER THAN IT FORMS ON ABOUT ONE-THIRD OF THE WORLD’S CROPLAND. Areas of serious concern Areas of some concern Stable or nonvegetative areas What is Desertification? • When the productive potential of arid or semiarid land falls by 10% or more. • Can be caused by climate or human activities • Moderate - 10-25% drop in productivity • Severe - 25 - 50% drop • Very severe - drop of 50% - usually results in gullies and sand dunes. • A SERIOUS PROBLEM WORLDWIDE! What causes Desertification? • • • • • • Overgrazing Deforestation without reforestation Surface mining without land reclamation Salinization and waterlogging of soil Bad irrigation techniques Farming on land with poor soil Moderate Severe Very Severe Fig. 10.21, p. 228 Consequences: • • • • • Worsening drought Famine Declining living standards Economic losses More environmental refugees Major symptoms: • Loss of native vegetation • Increased erosion of dry soil - mainly by wind • Salinization • Lowered water tables • Reduced surface water as streams and ponds dry up. What can we do? • Reduce overgrazing • Reforestation programs – Plant trees and grass • Reduce the threat of global warming What is Salinization? • Accumulation of salts in topsoil due to irrigation • Most irrigation water is a dilute solution of various salts picked up as the water flows over the earth. • Small quantities are essential but in large amounts is toxic. • • • • • Stunts plant growth Lowers crop yield Eventually will kill plants Ruins the land Severe salinization has reduced the world’s irrigated cropland by 21%. • In U.S. it has reduced cropland by 23%. What can we do? • Flush salts with more water but this is costly and wasteful • Take land out of production for from 2-5 years • Install an undergound network of perforated pipes and flush soil with low-salt water • All of this is expensive! More… • Reduce use of water in irrigation • Switch to more salt tolerant plants • Plant salt loving plants and convert the land to grazing land. • There is no cure for salinization. Waterlogging • Caused when large amounts of irrigation water leach water deeper and deeper into the soil. • Without drainage underground water rises higher and higher. • Eventually the salt water envelopes and kills the deep roots of the plants. • About 1/10 of all irrigated land suffers from water logging. Transpiration Evaporation Evaporation Evaporation Waterlogging Less permeable clay layer Fig. 10.22, p. 229 SOIL CONSERVATION • REDUCES SOIL EROSION AND RESTORES SOIL FERTILITY • CONVENTIONAL-TILLAGE –plow in fall and plant in the spring – leaves soil bare through winter and vulnerable to erosion • CONSERVATION-TILLAGE – disturb the soil as little as possible OTHER SOLUTIONS • TERRACING – use a series of broad, nearly level terraces – run across the land’s contours – Retains water at each level – Reduces soil erosion • CONTOUR FARMING – plowing and planting in rows across the contour of gently sloped land – helps to hold soil and slow water run-off • STRIP CROPPING – planting alternating strips such as corn & a legume – traps soil, catches water runoff, helps prevent spread of pests and disease • WINDBREAKS or SHELTERBELTS – trees planted – reduce wind erosion, helps retain soil moisture, supplies wood for fuel, provides animal habitats RESTORING SOIL FERTILITY • ANIMAL MANURE – improves soil structure, adds organic nitrogen, stimulates beneficial soil bacteria • GREEN MANURE - fresh or green vegetation plowed into soil – increases organic matter and humus • COMPOST – • INORGANIC FERTILIZER – EASY TO TRANSPORT, STORE, AND APPLY – DON’T ADD HUMUS TO SOIL – REDUCE SOIL’S ORGANIC MATTER AND WATER HOLDING ABILITY – LOWERS OXYGEN CONTENT OF SOIL – ONLY SUPPLY 2 0R 3 OF ESSENTIAL NUTRIENTS – REQUIRE MUCH ENERGY TO PRODUCE – RELEASE NITROUS OXIDE A GREENHOUSE GAS