Geog final study guide
Geog final study guide Geog 1002
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This 32 page Study Guide was uploaded by Cj Sivulka on Thursday April 28, 2016. The Study Guide belongs to Geog 1002 at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months taught by Dr Stereletskiy in Spring 2016. Since its upload, it has received 31 views. For similar materials see Intro to Physical Geography in Geography at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months.
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Date Created: 04/28/16
Chapter 12: Soils • Soil – relatively thin surface layer of mineral matter that normally contains a considerable amount of organic material and is capable of supporting living plants; o About 6 inches deep o combination of mineral and organic matter, water and air, living organisms, liquid solutions, etc o 25% air, 25% water, 5% organic matter, 45% mineral matter / parent matter (rock fragments); all of which support plant growth • regolith – broken and partly decomposed rock particles; covers bedrock; kind of like a blanked over the unfragmented rock below the soil • Humus – dark colored semi soluble organic substance formed from decomposition of organic matter; “black gold;” loosens the structure and density of soil o Decomposition is the chemical or physical breakdown of a mass of matter into smaller parts or chemical elements • 5 Factors of Soil formation o Parent Material – the source of rock fragments that make up the soil § Composition has a direct impact on soil chemistry and fertility • Ones rich in nutrients (e.g., limestone and basaltic lava), are easily dissolved in water and made available to plants. • If low in soluble nutrients (Sandstone), water moving through the soil removes them and substitutes with hydrogen making the soil acidic and unsuitable for agriculture. o Influence on soil properties tends to decrease with time as it is altered and climate becomes more important o Climate § Temperature and moisture are the strongest influencers to soil formation (they influence physical and chemical reactions on the parent material) § Climate also determines the vegetation cover which in turn influences soil development by producing organic matter. § Precipitation also affects movement of matter through soil. § As time passes, climate tends to be a prime influence on soil properties while the influence of parent material is less. § Soils tend to show a strong geographical correlation with climate, especially at the global scale. o Topography § Slope and drainage influence it § When soil develops, its vertical extent is continuous and slow changing § Topography determines runoff of water, and its orientation affects microclimate which in turn affects vegetation. § For soil to form, the parent material needs to lie relatively undisturbed so soil horizon processes can proceed. § Water moving across the surface strips parent material away impeding soil development. § Steep slopes have poorly developed soils •Flatter terrain accumulates soil faster § Soil is thinner on slopes because of erosion § Steep slopes don’t have any soil development § Residual soil is developed on bedrock o Vegetation / Biological factor § Influences it through litterfall and process of decomposition because organisms add organic matter and nutrients to the soil which influences soil structure and fertility § Surface vegetation also protects the upper layers of soil from erosion § Animals live in the soil and can tunnel through it Vegetation roots provide aeration and drainage roots § Nutrient Cycling • Biotic elements of the environment need life-sustaining nutrients that find their origin in the soil. • Upon their death, organisms return these nutrients to the soil to be taken up again by other plants and animals. • Hence there is a constant cycling of nutrients between organisms and soils. • Without it, soluble nutrients would be removed from the soil by percolated water, decreasing the soil's ability to support life. o Time – slow process § Influences the temporal consequences of all of the factors described previously § Soils get better developed (Thicker, with greater differences between layers) with more time § Climate interacts with time during the soil development process. § Soil development proceeds much more rapidly in warm and wet climates thus reaching a mature status sooner. § In cold climates, weathering is impeded and soil development takes much longer. • Horizons – soil layers • Soil profile – all the soil horizons taken together; from surface to bed rock • Horizon development process; basically what goes in and out of the soil and how stuff moves around in the soil o Additions (for soil enrichment): water, oxygen, carbon, nitrogen, chlorine, sulfur, organic matter, sediments, energy from the sun o Translocation: clay and organic matter carried by water, nutrients circulated by plants, soluble salts carried in water, soil carried by animals, chemicals, o Transformation: organic matter converted to humus, particles made smaller by weathering, structure and concentration formation, minerals transformed by weathering, clay and organic matter reactions o Loss / Removal: water and minerals in solution or suspension; chemicals, particulates, organic matter • Soil movements o Eluviation – downward transport of fine soil particles, removing them from the upper soil horizon o Illuviation – accumulation in a lower soil horizon of materials eluviated from higher horizons • Soil Horizons o O horizon – loose and partly decayed organic matter o A – mineral matter mixed with some humus; dark colored horizon of mixed mineral and organic matter and with much biological activity o E – zone of eluvation and leeching; a alight colored horizon marked by removal of clay particles, organic matter, and/or oxides of iron and aluminum o B – accumulation of clay, iron and aluminum, from above; zone of illuviation o C – partially weathered parent material o R – unweathered parent material; consolidated bedrock • Soil in Boreal forests – (spodosols); pine trees have low nutrient demands so the litter is poor; little cycling of the nutrients occurs; precipitation also flushes some organic material from the soil • Soil in the warm and wet tropics – (oxisols); Bacterial activity proceeds at a rapid rate, thoroughly decomposing leaf litter; Available nutrients are rapidly taken back up by the trees; High annual precipitation flushes some organic material from the soil; Create soils lacking much organic matter in their upper horizons. • Soils in grasslands – (mollisols); some of the richest in the world; lots of rich humus; fast accumulation of nutrients; low leaching • Soil Properties o Color -‐ A product of soil forming processes; usually red, gray or white, or black or brown; colors give strong hints about soil fertility o Texture – refers to the relative proportion of sand, silt, and clay size particles in a sample of soil; sand, slit, clay refer to particle size; you use a soil texture triangle to classify the texture class o Structure – refers to the way in which soil grains are grouped together into larger masses (peds – an individual natural soil aggregate); soil structure has a major influence on water and air movement § Granular structure – where the structural units are approximately spherical and are bounded by curved or irregular faces (look like cookie crumbs!); allows water and air to penetrate the soil § Blocky structure -‐ the structural units are blocklike; the strongest blocky structure is formed as a result of swelling and shrinking of the clay materials which produce cracks § Platy structure – looks like stacks of dinner plates overlaying one another; platy structure tends to impede the downward movement of water and plant roots through soil o Soil water § Infiltration capacity is the maximum rate at which water (falling rain or melting snow can be taken in (absorbed) by soil through the surface) • Infiltration capacity – amount (depth) / time o F = d/t • Different values of F for different soil textures o EG: coarser soils have higher infiltration capacity § Field / storage capacity – maximum capacity of soil to hold water against the pull of gravity • Sand is 7%; peat is greater than 170% § Types of soil water • Hydroscopic water – water that is bound to soil particles due to molecular forces; can’t be evaporated, used by plants, or removed by any other natural process • Capillary water – the part of soil water which is held as a continuous layer around particles; most of it is available to plant roots • Gravity water – subsurface water that responds to gravitational force, percolating it through the soil o Chemistry – § some elements are required for plant growth • Calcium (Ca++) • Magnesium (Mg++) • Potassium (K+) • Sodium (Na+) § Colloids • Plant nutrients (bases) are attracted and held by very small organic and mineral particles (colloids). • Colloids generally have a net negative charge as a result of their physical and chemical composition. • One of the most important properties of colloids is their ability to attract, hold, and release ions. § Ion Exchange- the exchange of an ion in the soil for another on the surface of a colloid. • The capacity of a soil to retain and exchange ions, is called its exchange capacity. o Exchange capacity - measure of the chemical reactivity of the soil, varies inversely with particle size. Fine soils accumulate and retain many times more ions than do coarse soils. The exchange capacity of the soil's colloidal particles is of tremendous importance. Nutrients that would otherwise be washed away are held in reserve and become available to the plant. § Cations differ in their ability to replace one another; if present in equal amounts, H+ replaces Ca++ replaces Mg++ replaces K+ replaces Na++. If one ion is added in large amounts it may replace another by sheer force of number. This is largely what occurs with the addition of fertilizer. The release of hydrogen ions in soils tends to promote the exchange of ions, making them available to plants. § Ph -‐ H+ concentration in the soil is measured in terms of the pH scale. Soil pH ranges from 3 to 10. Pure water has a pH of 7 which is considered neutral, pH values greater than seven are considered basic or alkaline, below seven acidic. Most good agricultural soils have a pH between 5 and 7. § Pdeogenic regimes – • Laterization Eluviation and leaching of A horizon in wet warm climates (red soils, Fe, Al) • Podzolization Eluviation and leaching of A horizon in cold temperate climates (ash like A, yellow B) • Gleization Reduction of Fe+++ to Fe++ in anaerobic environment • Calcification Calcic hardpans (prairies/steeps) in dry conditions • Salinization Accumulation of chlorides, sulfates in desert climates • Naming and Labeling of Soils o Soil taxonomy – generic; soil is organized based on observable soil characteristics; focus on the existing properties of the soil rather than on the environment, process of development, or other properties • Classifications o Alfisols § Al stands for aluminum and F stands for iron; lots of these 2 elements in the soils; clay accumulation with high bases; most wide ranging of mature soils o Andisols § Andesite, rock formed from a type of Magmum in the Andes Mountans volcanoes; lots of ash o Aridisols § Dry soils; 1/8 of the earth’s surface; requires irrigatoin o Entisols § Very little profile development; sandy / droughty conditions; 12% in Us mostly in west; were recently formed (recENT) o Gelisols § Permafrost layers; in the polar and alpine regions; freezing § Soils of very cold climates that contain 2 meters of the surface § These soils are limited geographically to the high latitude polar regions and localized areas at high mountain elevations § Has a high percentage of organic matter because of the slow rate of microbial decomposition in cold climates o Histosols § Organic soils; cover a small area (2% of US); essentially peatlands, large carbon; living tissue; mostly organic matter o Inceptisols § Few diagnostic features; adolescent in various environments, young soils; beginning of soils in their life o Mollisols § Soft, dark, 22% of the US; excellent for agriculture o Oxisols § highly weather and leached; warm, rainy areas; soils with large amounts of oxygen containing compounds o Spodosols § Acid, sandy forest soils; coniferous forests; wood ash; ashy soils o Ultisols § Soils that have had the last of their nutrient bases leached out; clay accumulation with low bases o Vertisols Chapter 13: Introduction to Landform Study • The Earth interior o Crust – outermost solid layer § 1% of the earth’s volume § 7-70km o mantle – beneath the crust and surrounding the outer core; 2900km, 84% volume § Lithosphere – crust and uppermost zone of mantle § Asthenosphere – layer of the upper mantle and underlying lithosphere; very hot, weak, and easily deformed § Mesosphere – rigid part of the deep matle o Outer core – molten shell beneath the mantle that encloses Earth’s innter core o Inner core – primarily solid: iron nickel alloy • The Composition of the Earth – 100 natural chemicals in the Earth’s crust, mantle, and core o Minerals are the building blocks of the rocks o Solid when – atoms are arranged in a regular pattern to form solid crystals o Naturally found in nature and are organic o Have a specific chemical composition § Silicates, oxides, sulfides, carbonates, halides, native elements o Rocks are consolidated combinations of minerals • Bedrock – buried layer of the residual rock that has not experienced erosion (underneath regolith and soil) • Igneous rocks are formed by solidification of molten magma o Extrusive – volcanic rock; molten rock aka magma is ejected onto the earth’s surface and solidifies in the open air; (lava is when it is out of the earth); pyroclastic § Can see the horizontal layers like on river beds o Intrusive – plutonic; rocks that cool down and solidify beneath the earth’s surface; granite is intrusive • Sedimentary Rocks – formed by sediment consolidation; pressure and cementation o Sediment is material that is broken down by natural processes and is subsequently transported by the action such as wind, water, and ice o Sediment is formed by particles deposited by wind or water and it builds up layers and compacts; cementation happens when pores between the dirt are filled by cementing agents like silica, calcium carbonate, iron oxide o Sedimentary rocks form: § In terrestrial environments – rovers and flood plains (fluvial and alluvial); lakes (lacustrine); deserts (Aeolian environment) § Marine environments – continental shelf; continental slope; abyssal plain; beach and barrier islands o Abundant types of sedimentary rocks • Sandstone – compacted sand grains o Shale – compacted silt and clay particles; most abundant o Limestone – chemically or organically produced (calcium carbonate; skeletal remains lime secreting creatures) • Metamorphic rocks – originally was a different type of rock (like sedimentary or igneous) but was changed by heat and / or pressure within the earth • Ocean floor rocks o Basalt (dense rock) covered with thin layer of sediments o Ocean crust sima rock • Isostasy – isostatic equilibrium o Huge plates of crustal and upper mantle material (lithosphere) “float” on more dense, plastically flowing rocks of the asthenosphere. The “depth” to which a plate, or block of crust, sinks is a function of its weight and varies as the weight changes. This equilibrium, or balance, between blocks of crust and the underlying mantle is called isostasy. The taller a block of crust is (such as a mountainous region), the deeper it penetrates into the mantle because of its greater mass and weight. Isostasy occurs when each block settles into an equilibrium with the underlying mantle. Blocks of crust that are separated by faults will “settle” at different elevations according to their relative mass (Figure ) o Crust floats on the denser, deformable mantle below o There is a gravitational equilibrium at Earth’s crust; where material is added, crust will sink, remove and the crust will rise Geomorphological Processes • Geomorphological processes – what changes the earth o Endogenic – energy from within the earth that changes it § Internal § Geothermal energy § Tectonics, igneous activity, metamorphism § Orogeny / orogenesis (vertical displacement; mountain ranges) § Epeirogeny / Epierogenesis (vertical displacement; entire continents) § Mainly relief construction o Exogenic – energy outside the earth (like atmosphere) that changes it § External § Solar radiation § Denudation: weathering, erosion, transport, deposition § Mainly relief reduction • Erosion wears down a landmass through a predictable series of stages, to a surface of low relief; landscapes can be young and old (relative) • Internal Processes – originate from within the earth; initiated by the internal energy that generates forces that apparently operate outside of any surface or atmospheric influences o Plate tectonics o Volcanism and plutonism o Folding o Faulting o Earthquakes • External processes – operate at the base of the atmosphere; draw their energy mostly from source above the lithosphere, either in the atmosphere or in the oceans o Weathering o Mass wasting o Erosion / deposition • Continental drift – theory to explain Pangea o Originally proposed by Alfred Wegner in 1912; his theory was rejected b/c the ocean floor was too strong to be plowed aside; and because wegner had not proposed a plausible force that could induce the continents to drift o Evidence for continental drift § 1. Fit of coastlines – coastlines of the continents fit together like puzzle pieces § 2. Godwana ice age – finding of tilltes (glacial sediments) in similar places where Pangea was near the south pole § 3, mesosauurus – same animals found on coasts of continents – would’ve been impossible if these continents had not once been touching § 4. Matching mountain ranges § 5. Pole wandering § 6. Sea floor spreading – cracks in the seafloor where they split; midocean ridges are formed by currents of magma rising up from the mantle; volcanic eruptions create new basaltic ocean floor that spreads away from the ridge § 7. Global seismicity – earthquake cracks • Plate tectonics – the combination of the concept of transform faults with the hypothesis of sea floor spreading led to the construction of the theory of plate tectonics; the theory states that the lithosphere is divided into an interlocking network of blocks named plates • Plate boundary movements o Divergence – seafloor spreading o Convergence – collision o Lateral – transform (one goes up one goes down) • Divergent plate boundaries (where they split apart) – are the origin of ocean basins • Rift valley formation - near-shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault; formed on a divergent plate boundary, a crustal extension, a spreading apart of the surface, which is subsequently further deepened by the forces of erosion o Begins on a continent o Grows to be come linear sea o A constructive boundary out of rock is created • Convergent plate boundary: ocean to continent – subduction trenches (the slab is pulled next to continents) o The rock is destroyed by subduction; one plate going over the other o Continent plate goes over sea plate o Andes mountain • Convergent plate boundary: ocean to ocean o Subduction trenches deep in the ocean o Rock is destroyed via subduction o Aleutian islands, marina islands • Convergent plate boundary: continent to continent o No subduction o Conservative boundary- rock is neither created or destroyed but pushed up o Makes mountains like the humalayas • Volcanism o Lava – exposed magma o Magma – molten mineral material below the surface that is extruded onto the surface of the earth o Pyroclastic material – solidified materials such as solidified lava blobs, rock fragments, ash, and dust thrown into the air by explosive volcanoes • Types of landforms associated with volcanic activity o Shield volcano – never steep sided; wide; big, largest; high layer upon layer of solidified lava flows; gentle angles; large base; created from basalt; characteristic of the midocean region; basalt has a lot of sand so the lava flow is slow o Composite volcano – steep sided, large, symmetrical cone, layers of pyroclastic material; erupt explosively; can grow tall but not as tall as shield volvanoes o Cinder cone – smallest; steep sided; loose pyroclastic material; 500 meters tall; result of a single eruption • Plate tectonics and hot spots o Hawaii, along the coast of cali, along plate tectonics o Volcanoes are distributed based on the locations of plate tectonics o Volcanoes that aren’t along the edges of the plates are called hotspots – spots that have mantal flumes (much higher temperature of magma); these are the special areas because they sit in the same location regardless of where the plates are moving • Plutonism: ingenous intrusions o Vertical ones are called dikes o Horizontal intrusions are called sills o Baleolith – a very large igneous intrusion extending deep in the earth’s curst • Tectonism or Diastrophism o General term referring to the deformation of the earth’s crust; implies the material is solid and that there’s plate boundary movement § Implies the material is sold § Plate boundary movement – variety to unknown causes § 2 types: folding and faulting • Folding – lateral pressure causes bending in the sedimentary rocks; happens when the rock bends and not breaks o Syncline – a sequence of folded rocks with the youngest rocks on the inside of the fold (at the surface) o Anticline – a sequence of folded rocks with the oldest rocks on the inside of the fold (below the surface) o In the Appalachian mountains in the eastern US, most anticlines and synclines are plunging folds ( V fold goes into the ground) rather than horizontal folds (remains parallel with the ground) o Ridges – when the folded rock turns sharp and stiff o Valleys – when the folded rock turns out smooth and wavy • Faulting – breaking apart of crustal material o Displacement o Occurs in zones of weakness in the crust at the fault line or zone o Types of faults – regardless of size, all faults are classified by the direction of the relative movement which is called the slip § Dip slip faults (normal and reverse) – pulling away at the faults or pushing together at the faults • Motion of the blocks is parallel to the direction o Normal movement is down dip o Reverse movement is up dip § Strike slip faults (left and right lateral) • Horizontal side to side grinding at the fault • Right lateral and left lateral § Oblique slip faults • Displacement both vertically and horizontally § Reverse fault – when 2 blocks collide together and one is pushed on top of the other • Earthquakes – vibration of the earth produced by shock waves resulting from the sudden displacement usually along a fault; release tension accumulating across the plate tectonics o Earthquake waves § P waves – fastest moving, alternately compressing § S waves – slower moving, producing both side to side and up and down motion o Seismic waves – energy waves in an earthquake that originate at the center of the fault motion o Magnitude – calculated on a logamartihic scale § Least understood § Difference between a 3 and a 7 is 1,000,000 times energy § Common scale is richter scale CH15: Preliminaries to Erosion: Weathering and Mass Wasting • Denudation o Overall effect of the disintegration, wearing away, and removal or rock material (i.e. lowering of the surface of continents) o Three processes § Weathering – breaking down rock into smaller components by atmospheric and biotic agencies § Mass wasting – short distance, downslope movement of broken rock material due to gravity § Erosion – more extensive and distant removal, transportation of fragmented rock material • Weathering (rocks are broken down) -‐-‐> Mass Wasting (gravity moves deb ris)-‐-‐> Erosion (weathered debris is removed) -‐-‐> Deposition (debris is deposited) • Weathering is the initial stage o It’s the disintegration and decomposition that destroys rock ; rock is fragmented into small pieces, the atmosphere is a key agent in weatheri ng o 3 main types (mechanical chemical and biological) § Mechanical / physical weathering -‐ the mechanical disintegration of rock without a change in its chemical decomposition • Thermal expansion and contraction -‐ enlargement and reduction in volume in response to heating and cooling; when a rock is heated it expands, when it is cooled it contracts; different minerals expand and contract at different rates • Exfoliation – o Mechanical exfoliation -‐ rock expands and cracks as pressure is reduced due to removal of overlaying material; rocks below the earths surface support the weight of the overlying column of rock; buried rocks are slightly contracted under pressure; erosion or tectonics strops away overlying rock and decreases pressure on buried rocks; this results in release of the pressure that forms parallel to the surface; with continued exposure of buried rock slabs of rock break long the pressure release fractures; this is called unloading o Unloading exfoliation -‐ Stripping away of roughly parallel, cocentric rock slaps; curved layers peel off bed rock ; deformation of rock due to the relief of confining pressure of overlying rock • Frost wedging -‐ expansion of water in the rock and cracks the rock • Crystal growth – salt crystals grow from evaporated salty water; in desert an semi desert environments, water on the surface or in th e soil is often evaporated; as water evaporates, salts that were dissolved in the water are forced to crystalized § Chemical weathering -‐ reactions involve exchanges of materials between reactant and the rock; principal agents of chemical weathering: oxygen, water, carbon dioxide • Agents in chemical weathering: oxidation, hydrolysis, carbonation o Oxidation -‐ Oxygen attacks the minerals containing iron, forming red oxides = reddish rock o Hydrolysis -‐ Water attacks hydrogen and hydroxide in rock, displacing potassium, sod ium, calcium and magnesium ions; hydrolysis is the most common weathering reaction on earth o Carbonation -‐ A weak carbonic acid converts limestone to dissolved calcium and biocarbonate s; deeply pitted surface of the limestone; rainfall erodes the limestone into pits and channels by dissolving it • Spherodial weathering – when the chemical weathering makes rocks spherical • Rates of chemical weathering -‐ Australians do this with rocks in graveyards and dates § Biological weathering • Direct • Biophysical Biochemical Root pressures, growth stresses, Bacterial redox, chelation, wetting and drying, mechancial cation exchange, solution boring • Indirect -‐ soil mixing; production of organic acids and CO2; organic layers protecting a surface • Biological agents in weathering • Root weathering -‐ where tree roots influence pavement • Lichens and mosses open fissures and rocks and scrounge nutrients • Rates of weathering • Relative resistant • Permeability / porosity • Quartz content • Jointing • Relative exposure • Increasing surface exposure of rock accelerates weathering • Vegetation • Interception rate; infiltration rates; organic matter production • Altitude • Mechanical (freezing / thawing) increases in importance with higher altitude / elevation • Chemical increases in importance at lower altitudes especially with increase in vegetative cover • Slope • Inverse relationship between slope and interception, infiltration, vegetative cover • Direct relationship between slope and materia l transport o Regolith – a product of rock weathering – the amount of weathering increases towards the surface • Mass wasting is step 2 of denudation (after weathering = 1 stage) st o Intermediate stage is the mass wasting; gravity is the energizing force behin d mass wasting o Mass movements -‐ any unit of movement of a body of material, propelled, and controlled by gravity (2 major categories: landslides (rock and soil); avalanches (snow and ice) o Major mass movements -‐ seismic activity, atmospheric elements o Increasing risk of this worldwide -‐ land hunger (Barrio settlements) § Up to 90% of landslide deaths occur on the pacific rim § US economic loss well over $1 billion a year § Death total is usually low, speed off the slide o Landslides – downslope movement of rock and s oil debris that have been separated from the underlying slope; occur when the strength of the material comprising the slope is exceeded by a downslope stress § Mechanics of landslides • D=driving force or shear stress • S = resisting force or shear strength • Landslides occur when D>S • N = normal force; force perpendicular to the slope • W = weight of the material, vertical pull of the vravity • A = angle of the slope • Angle of repose -‐ the maximum angle at which a material can remain at rest on the slope § Landslides occur in areas where there is: seismic shaking; high relief, mountainous environments; moderate relief, severe land degradation; areas with loose deposits; areas with high rainfall o Types of mass wasting -‐ movement of debris (mainly rock) transported through the air § Fall – movement of debris (mainly rock) transported through the air; presence of water freeze-‐thaw cycle; earthquakes; slopes steeper than 40 degrees; on some roadways, there is mesh that prevents rock from covering roadway § Slide – can be rock or land; • Rockslides can happen suddenly with rapid downslope movement of talus • Landslides – happen when the movement of rock and soil slip along surfaces due to gravity o Two main types § Rotational slides (slumps); curved slip surface § Translational slides – relatively uniform, planar surfaces; block glides and debris slides o Landslide warning signs: doors or windows jam for the first time; new cracks appear in plaster, tile, brick, or foundations; outside walls or stairs begin pulling away from building; slowly developing widening cracks appear; underground utility lines break § Flow – when there is water or ice to lubricate the movement of slope material • Debris (Mud flow) – movements of fluidised soil and other material acing in a viscos mass o occurs when there is lo ose slope material that becomes saturated o high water content – fast moving; generally follow stream channels; deadly § creep – the imperceptibly slow down-‐slope movement of material; usually has to do with freezing and thawing of the soil; can be indicated by tilted fence posts • soilfluction – involves the freezing and thawing of soil above the permafrost, causing the slope to sag downslope § Other triggers of mast wasting: events ice wedging; biological activity (human pushing a rock down a hill); shocks (like an earthquake) • Slope modification – modification of a slop by either humans or by natural cause can result in changing the slope angle so that it is no longer at the angle of repose; a mass wasting event can then restore the slope to its angle of repose • Undercutting – streams eroding their banks or surf action can undercut a slope making it unstable • Overloading – involves an increase in weight which may increase the shear stress on the slope or may increase the water pressure and decrease friction causing slope failure; this factor is almost always the result of human activity including the weight of buildings, or things like dumping, filling or piling up material • Removal of vegetation – can cause erosion of soil more easily • Exceptional precipitation – heavy rains can saturate regolith reducing grain to grain contact and reducing the angel of repose, thus triggering a mass wasting event Fluvial processes • Running water over the land • Fluvial -‐ system is powered by conversion of the potential energy of sol ar radiation and gravity to kinetic energy of motion and heat; most energy is lost to friction and turbulence, but small fraction is converted to mechanical work of erosion and transportation o Contributes more to shaping landforms than all the other externa l components combined • Agents of continental denudation o Rivers 85-‐90% o Glaciers 7% o Waves 2% o Wind 1% • Stream -‐ a long narrow body of water that flows in a trench like depression (channel) under the force of gravity • Classical Fluvial Classification Systems o By constancy of flow • Perennial streams -‐ constant flow; streams that we see in mid latitudes; base flow is provided by ground water seepage into the channel • Intermittent (seasonal) streams -‐streams which only flow during wetter times of the year • Ephermal Streams -‐ a stream that carries water only during and immediately after periods of rainfall or snowmelt • The stream system o Drainage basin / watershed -‐ an area of land that contains a common set of streams and rivers that all drain into a singer larger body of water, such as a larger river, lake or ocean o Drainage divide -‐ represents the boundary between adjacent drainage basins and determines into which basin precipitation flows o Tributary systems -‐ are small streams that enter into the main stream o Endorheic basins do not drain into the ocean • Stream characteristics o Channel slope or gradient -‐ the difference in elevation between two points on a stream divided by the distance between them measured along the stream channel o Flow velocity -‐ how fast the water is movin g through a cross section; determined by the balance between the down slope gravitational stress as a result of the slope of a stream, and the loss or expenditure of energy in the overcoming the frictional resistance of the channel bed and side o Stream discharge (Q) -‐ the volume of water passing through a particular cross section in a unit of time, measured in units like cubic meters per second or cubic feet per second • Q = A*V § A -‐ cross sectional area; V -‐ velocity • The work of streams o Erosion -‐ the group of processes whereby earth material is loosened or dissolved and removed from any part of the earth's surface; stream erosion is the detachment of material from bed or sides of the channel • Erosional landforms -‐ landforms shaped by removal of regolith or bedr ock by erosion o Transportation -‐ once material is detached from the channel it can be transported; transportation is the movement of earth material, in this case, by water o Deposition -‐ the laying down of potential rock forming material in the form of sedim ents • Depositional landforms -‐ landforms made by the deposition of sediment o Hydraulic action -‐ the impact of water on the sides and bed of a channel; it dislodges unconsolidated materials and makes them available for transport o Abrasion -‐ the mechanical wearing down of rock by the rock fragments that are being transported by the stream o Corrosion -‐ the chemical reaction of moving water with the material on the stream bed o Rainsplash erosion the process of disturbing the soil surface by the direct force of fal ling rain drops o Overland flow -‐ unconfined flow of water running across the surface in very shallow depths; occurs on relatively smooth slopes • Rill erosion -‐ If there are small irregularities at the surface, the water tends to concentrate in small channels called Rills. Because water is confined it moves much faster § Rill erosion is the removal of material by concentrated erosion running through little streams o Gullies -‐ steep sided trenches formed by the coalescence of many rills o Ravine -‐ a deep narrow steep-‐sided valley formed by running water o Progression of erosional landforms associated with streams • Rills -‐-‐> gullies -‐-‐> ravines -‐-‐> valleys o The base level of a stream is defined as the lowest level to which a stream can erode its channel; lowest level at which erosion is impossible (aka like the mouth of the river where it meets the ocean) • For most streams, base level is sea level (Absolute (ultimate) base level) • Variations in bedrock and topography will often result in a temporary base level (local base level) • Examples of local base levels: lakes, larger streams, resistant rock • Sediment transport in a stream -‐ the material transported through a stream is called the stream load: o Dissolved -‐ part of the fluid; comes from groundwater seepage into the stream; also comes from the solution of materials that line the channel; particular important in limestone areas o Suspended -‐ comprised of sediment and transported through the stream; composed of silt and clay particles suspended by flow o Bed (or traction) load -‐ that which is moved across the bed of the channel • Can be transported by § Traction -‐ scooting and rolling of particles along the bed § Saltation -‐ a bouncing like movement • Stream competence -‐ the size of the largest particles a stream can move; competence is ex pressed in terms of mass; it is a function of stream velocity • Steam capacity -‐ the total sediment load a stream can move or transport in a given length of time; expressed in terms of mass per time; it is a function of stream discharge • The functions of velocity o Deposition in regards to velocity -‐ as velocity and discharge decreases, the ability of the stream to move sediment through it decreases, the heaviest particles deposit on the bed first, with the smaller and lighter particles transported much further b efore accumulating • Alluvium -‐ materials deposited by streams o Erosion -‐ if velocity goes up then rate of erosion goes up o Transportation -‐ stream capacity (the total sediment load a stream can move or transport) is a function of stream discharge (Q -‐ the volume of water passing through a particular cross section in a unit of time); if stream discharge, Q, is increasing, then so is stream capacity • AKA: the more water passing in a rover, then the more sediment load a stream can move and transport o Streams can undergo substantial changes in their geometry in response to changes in the velocity, discharge and
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