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244 Cards in this Set
- Front
- Back
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Define geomorphology and pedology |
- geomorphology = earth surface landforms and processes - pedology = compositionand formation of soils |
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What is the difference between erosion and weathering. |
- erosion implies movement/transport of particles/sediments - weathering doesn’t involve transport: can be mechanical, chemical or biological, and results in a change in composition of rocks and minerals |
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Define sediments. |
- particles that precipitate out of solution and are deposited - moved by fluvial forces or gravity |
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What is positive feedback, and give a geomorphic example. |
change in output gives similar change in input - temperatures drop à more snow falls à increased albedo (less absorption of light, more reflection) à temperatures drop further |
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What is negative feedback, and give a geomorphic example. |
- change in output leads to opposite change in input - temperatures drop à less moisture in air because cold air can’t hold water vapour as readily à less snow àmore solar radiation is retained à temperatures increase |
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Is positive or negative feedback more common, and why? |
- negative feedback - often results in more stable equilibrium conditions |
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Define uniformitanism, and who defined this concept? |
- modern earth is still being shaped by same constant processes that made it what it is today (same rate but still very slow) - allows us to determine how processes worked in the past if they are working the same way today Hutton |
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What is catastrophism, and who defined this concept? |
- modern earth was formed by a series of catastrophic, high magnitude geological events that were separated by uneventful periods |
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Define and give example of steady state equilibrium systems and complexe or non-linear equilibrium system. |
- steady-state = oscillating or constant condition, more likely for shorter time scales - complexe/non-linear = more complicated and chaotic o threshold systems o saturation/depletion effects (inconsistent behaviour for similar conditions) o positive and negative feedback o dynamic equilibrium = declining rate of change to new equilibrium o dynamic metastatic equilibrium = longer time scales, changing average trend with fluctuations/disruptive events (eg flood) |
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What are the similarities and differences between rocks and minerals? |
- Both are ultimately derived from magma - minerals have a characteristic chemical structure w/ specific compounds - rocks are composed of minerals |
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What are the five most abundant elements in the Earth’s crust? (in order) |
- oxygen, silicon, aluminum, iron, calcium, sodium, potassium - O, Si, Al, Fe, Ca |
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What is mass wasting (mass movement)? |
- downward movement of rocks and soil due to gravity |
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What is lithification? |
- compaction of sediments/grains into harder rock - requires high pressure, and rock is formed at saturation when minerals precipitate |
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How are the Phi units indicative of sediment particle size? |
grain size = indicates process that deposited sediment (reveals history) - negative value if larger than coarse sand - positive value if smaller than coarse sand - backwards log scale |
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Why is grain size relevant/what does it mean? |
- indicative of the processes that occurred to make it that way (& energy required) - will determine how it can be weathered (eg whether it can be permeated by water, etc.) |
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What is the difference between beds and laminations? |
- beds are layers of sediment with structural or textural uniformity - laminations are very thin layers between beds |
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What is the difference between clastic and chemically precipitated sediments? |
- clastic = pre-existic rock fragments that have settled out of suspension (defined according to grain size) - chemically precipitated = precipitated from chemical solution (eg dissolved out of solution) |
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What is cross bedding, and where does it normally occur? |
- Different beds aligned at different zigzaggy angles - environments with migrating rippling effects (sandy rivers, coastal areas, wind-blown environments) - lee side erodes --> velocity slows at crest of “hill” --> stoss side gets depositions of sediments |
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What is parallel lamination? |
- different layers of different weights/sizes - distinct layers - due to changes in current velocities b/c of differential grain sizes - smaller grains move faster, get deposited less abundantly - sediments will be carried by fluid to areas of low velocity where they will settle - sorted! |
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What is graded bedding? |
- different layers that are graded (smallà large à small à large etc.) - no internal lamination; heavier sediments fall first - no sorting - happens rapidly, maybe due to massive flooding event etc. |
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What is massive bedding? |
- chunks of different sizes randomly distributed - has no structure or gradation or sorting - very rapid deposition - could be caused by: landslide, volcano, glacial tills and moraines |
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Give chemical formulas for carbonate, bicarbonate, sulphate, silica tetrahedral, quartz, calcite, dolomite and gypsum. |
- carbonate: HCO3(2-) - bicarbonate H2CO3 (-) - sulphate SO4 (2-) - silica tetrahedron (SiO4) - quartz SiO2 - calcite CaCO3 - dolomite CaMg(CO3)2 - gypsum: CaSO4*2H20 o formed by hydration of anhydrite |
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Which are foliated metamorphic rocks, and which are non-foliated? à slate, gneiss, marble, anthracite, quartzite, schist. |
- slate, schist, gneiss are foliated - marble, anthracite, and quartzite are non-foliated |
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Describe the difference between ultramafic, mafic and felsic minerals. What class of rock do these make up? Give examples of each |
- ultramafic; very high Fe, low SiO2 - mafic: high Fe and Mg, low SiO2, darker and denser, solidify at higher temps; lava is less viscous (flows better) o pyroxene, olivine, biotite, amphibole - felsic: low Fe, high SiO2, lighter and less dense, solidify at lower temps o quartz, Na-plagiocase, K-feldspar |
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Outline granite, diorite and gabbro, and their extrusive counterparts. |
- granite = mainly quartz, feldspars, mica, biotite, coarse grained, felsic o rhyolite when lava - gabbro = pyroxene, Na-plagioclase, olivine, denser, darker, mafic o basalt when lava - diorite = feldspar, pyroxene, amphibole, felsic o andesite when lava |
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What are the differences between extrusive and intrusive rocks? Give an example of each. |
- intrusive rocks = slow-cooling, coarse, cool before reaching surface, reach surface under other rocks - extrusive rocks = faster cooling, finer, reach surface as lava |
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Give four examples of chemically precipitated sedimentary rock, and what they are made up of. |
Chert o Organic or not o Very fine, primarily quartz
Evaporites o salt precipitated out of solution and deposited o gypsum, halites (NaCl), Mg, K
Limestone o calcite
Dolostone o dolomite = calcite and Mg (CaMg(CO3)2) o not directly precipitated = limestone that is chemically altered by Mg |
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Order the main clastic sedimentary rocks from finest to coarsest, and give their parent material/sediment. |
- finest --> coarsest shale siltstone sandstone conglomerate/breccia |
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Where/in what conditions is physical weathering most intense/effective? |
- at surface - where materials have joints/porosity/weaknesses |
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Explain two different scales of pressure induced physical weathering, and how they are different. |
- transport, uplift, removal of material cause changes in pressure - larger scale = exfoliation = removal of entire layers of bedrock (esp. batholiths) - smaller scale = spheroidal/granular disintegration = disaggregation of crystals due to decreased pressure = produces coarse sands, gravels |
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What is frost action, and where/how is it most effective? |
- because water becomes less dense as it freezes, it expands in cracks/joints in rocks and separates them - most effective on rocks with low tensile pressure, large pore size, finer grains - best for sedimentary rocks b/c of bedding planes - for igneous and metamorphic rock, must penetrate pores between minerals = leads to granular disintegration into coarse sands - can loosen soil - can form talus (accumulation of rocks at bottom of slope/valley) |
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How would salts in dry climates contribute to weathering? |
- physical weathering in form of… o water evaporates and leaves behind salts (gypsum, halite, calcite) à crystallization, leads to disintegration of bedrock § water descends through permeable sandstone to impermeable shale: salts are deposited between these layers o repeated wetting and drying (hydration-dehydration) = causes granular disintegration o repeated heating/cooling = makes fractures, damages capillaries - combination of those three |
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What is wetting/drying physical weathering? |
- for clay minerals in shale - water can penetrate space between mineral particles - causes swelling |
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What is thermal expansion weathering? |
- caused by heating and cooling which cause expansion and contraction of rock - more effective for darker minerals that heat quicker/more effectively - conduction depends on mineral makeup - physical weathering |
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Describe hydrolysis, and its effect on the parent rock. What conditions promote this? |
- Chemical weathering - addition of H+ (replaces and then releases cations) - creates secondary/new material - primary weathering process for igneous rocks - promoted by: increased surface area, increased acidity (more H+), less cations (flushed out, etc), and increased temperature (increases reaction rates) |
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Describe carbonation and its effect on the parent rock. |
- combining minerals such as calcite with water to form carbonic acid which dissociates into bicarbonate or carbonate ions - degrades calcite in limestone - can result in karst terrains in limestones |
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Describe dissolution and its effect on the parent rock. What factors regulate this? |
- dissolving of minerals into ions, results in solution (completely dissolved) - especially gypsum, carbonates, salt/halite (NaCl) = very soluble in water - controlled by: o larger particle size = smaller surface area = takes longer to dissolve o temperature (rate of reaction) o mixing (circulation/flushing) |
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Describe oxidation and reduction and their effects on the parent rock. |
- Oxidation: adding oxygen gas to metallic elements in presence of water = forms metal oxides and hydroxides - reduction: occurs in anaerobic environments: converts metal oxides and hydroxides into metallic ions and produces oxygen |
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Describe ion exchange, and what factors control it. |
- exchanging cations that are held on negative surfaces (eg colloids, clay particles, organic matter) - not a breakdown = only an exchange
controlled by: o type of surface o charge density of cations being exchanged (negative surface will want to bind to more densely charged ions, such as H+) o concentration/amount of cations present - example: acidic soil = H+ replaces cations which reduces number of nutrients available to plants |
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What is chelation, and how does it work? |
- ligands = decomposed organic acids, etc. - ligands bind to metal cations (mineral components) - occurs in solution à being bound to ligands allows normally insoluble metal cations to be soluble = can be transported - mobilizes insoluble elements like Al, Fe to move through soil - can be used to remove heavy metals from bloodstream - changes structure/chemical composition of the minerals by binding them |
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How is gypsum formed, and how else does this process work? |
- via hydration = insertion of water between mineral particles - structural alteration - water and anhydrite combine to form gypsum (CaSO4*2H20) - similar process to convert hematite à limonite |
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What is the difference between hydration and wetting/drying weathering? |
- hydration actually inserts water molecules into the mineral structure and changes chemical composition - wetting/drying inserts water between pores = no binding, expands the structure/causes swelling, but doesn’t change chemical makeup |
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Which of the chemical weathering methods actually change chemical structure, and which are just transport or exchanges processes? |
- chelation, hydration, oxidation, reduction, carbonation, hydrolysis = actually change structure (result in new material) - ion exchange and dissolution don’t actually change chemical composition |
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What causes biological weathering? Is it physical or chemical? |
- roots wedging between rock and breaking them up à physical - release of organic acids as waste from microorganisms and plants (eg carbonic acids from respiration) à chemical |
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Describe the three main factors control weathering at a large scale? |
- climate: temperature and precipitation = controls lack or abundance of water, controls rate of reaction, heating and cooling processes etc. à climate also affects amount of vegetation and life that contribute to biological weathering o very moist, warm environments experience most intense weathering - parent material: some rocks and minerals are more resistant than others o evaporates are easily weathered because salts are very soluble in water o carbonates are intermediate (limestone better than dolomite) à susceptible to carbonation and hydrolysis o silicate minerals most resistant (igneous rocks) § quartz = most resitant
- topography – steeper slopes wash away weathering products more easily, gentle slopes accumulate products (eg salts, ions) & water can stay in contact for longer |
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Which are most resistant to weathering, and why: silicates, carbonates, and evaporites. |
- silicates are most resistant (quartz is most resistant of all) - carbonates are intermediated resistance (limestone>dolostone) - evaporites are weakly resistant (salts are easily solvated) |
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What are the four main products of weathering? Give a few examples of each. |
- resistant minerals o quartz, feldspars (Si-based means more resistant) - secondary minerals o clay minerals, metal oxides and hydroxides, chemically altered minerals o due to: chelation, hydration, oxidation, reduction, carbonation, hydrolysis = actually change structure o carbonates and evaporates are more resistant to weathering - organic material - soils |
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Describe the three main types of clay minerals and their distinguishing characteristics. |
- kaolinite (1:1 ratio of SiO4;AlO8) = low CEC, no internal surface, no capacity for swelling, very strong bonds at interactions between tetrahedron/octahedron - illite (2:1 ratio) = medium CEC, some internal surface, intermediate swelling - smectite (2:1 ratio) = high CEC, high internal surface, swells (because of alternation of Mg and Al in structure) - KIS |
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What are the main constituents of soils? |
45% mineral - 5% organic matter - 25% water - 25% air |
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How is bulk density calculated? |
- dry mass/volume |
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How is percentage saturation calculated? |
- (volume of water)/(volume of void) * 100 |
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What are the three main mineral horizons of soils, and what are they composed of? |
- A = uppermost layer, most weathered, most organic matter, leaching and eluviation - B = middle layer, medium weathering, accumulation of clays from leaching, some organic matter - C = least weathered, physically broken, gleying processes, soluble salts |
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What factors contribute to the binding and arrangement of peds? |
- negative charges on clay and organic matter produce cohesive forces |
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What are the structural characteristics of organic matter and clay in soil? |
- organic matter is spheroidal and granular - clays are blocky/columnar |
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What are the relative sizes of silt, sand and clay components of soil? |
- gravel > sand > silt > clay > colloids |
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How does texture affect soil properties? |
finer soils allow less water penetration - coarser soils allow water to flow through/downwards more easily - influences aeration - cation exchange capacity increases with higher porosity - finer soils |
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What is soil alkalinity or acidity indicative of? |
- more acidic soils = more H+, which replaces cations on colloids = less nutrients for plants = bases will be washed out of soil after removal = decreases soil fertility o typical of colder, more humid climates - more alkaline soils = less H+, in more arid/semi-arid areas - most essential/primary nutrients thrive in neutral soils |
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What does colour say about the characteristics of a soil? |
- yellow/red = oxidized iron - grey/olive = reduced iron - white/grey = salt, in arid environments - dark/black/brown = organic matter - charts are based on hue, value and chroma (intensity) |
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Define gravitational water, field capacity and permanent wilting point? How are they significant, and how are they affected by structure and texture? |
- gravitational water = water that drains within a few days from soil by gravity - field capacity = water left over after drainage, attracted to peds (held in micropores), still available to plants - permanent wilting point = water is held too tightly by soil particles due to their polarity (capillary tension) = cannot be used by plants |
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What is the significance of water in the pores of soil being a solvent? |
- solution is formed with water as the solvent and nutrients as the solutes - allows for transport of material through the soil & across horizons o material = soluble weathering products, clays, chelates (for chelation à allows mobilization of Al and Fe) |
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What is humus? |
- found in A horizon - extremely decomposed organic matter - has negative charge which allows high CEC (readily wants to exchange cations as nutrients for soil) - depends on pH = if more acidic (low pH), there’s more H+ which will lower the net charge and displace useful nutrients/cations from the colloids |
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Why is soil organic matter important? |
- helps store nutrients because of its high cation exchange capacity - very porous with charged surface - helps retain water - has cohesive structure, allows for flocculation/dispersion o flocculation = colloids exit suspension as a floc/flake |
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Name the four main mineral soil horizons, and describe them. |
- A: maximum weathering, leaching and eluviation, OM accumulation - B: less weathering, accumualation of clay, deposits of less soluble cmpds, hydrolysis and redox reactions - C: minimum weathering, accumulation of most soluble cmpds, unaffected by pedogenic processes in A and B - R: consolidated bedrock |
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Name the four main organic soil horizons, and describe them. |
- L: litter (leaves, twigs, wood) - H: humus (highly decomposed OM, black) - F: fermented litter (structures are harder to recognize) - O: highly decomposed mosses, rushes, wood |
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What is the pattern of organic composition of soils in different climates? |
- moist/warm = abundant litter, fast decay, less OM accumulation (more fresh plant material) - moist/cool = high litter, slow decay, higher OM accumulation - semi-arid/warm = low litter, medium decay rate, low OM accumulation (Grasslands) |
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What is the difference between eluviation and illuviation? |
- eluviation = downward movement of fine solids (clays and oxides that move in solution as colloids, which are carried by percolating water) à require porous soils and non-swelling colloids - illuviation = deposition of eluviated particles, usually in B horizon |
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What conditions are required for leaching, and how does it work? |
- when water input (rainfall, precipitation) exceeds evaporation (evapotransiration) - increases with increased water supply and better drainage (better porosity) - organic acids (H+) displace nutrient bases (Ca++, Mg+, Na+, K+) on colloids = these are lost and descend to a Bt horizon - the bases are added to drainage water and precipitated/deposited at depth - depth of deposition depends on evaporation and rainfall rates, as well as the solubility of the mineral |
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What is the order of solubility of the common minerals that are involved in leaching? Which ones deposit the deepest? |
- from shallowest to deepest… (= least soluble to most soluble) o Fe-minerals o Al-minerals o Si-minerals o Soluble organics o Carbonates o Gypsum o NaCl |
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Which subhorizons are leached/eluviated/illuviated? |
- Ae: leached/eluviated, has pale colour due to removal of clays, OMs, salts - Bt: illuvial, clay deposits |
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What is podsolization, and how does it work? |
- water rich in H+ and colloidal/soluble OM undergoes chelation o OM complexes with Fe and Al, and allows for their transportation throughout the soil (are usually not very soluble) o Chelation increases plant nutrient availability - Requires cool, humid conditions - Humic colloids are deposited in Bf |
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What subhorizons are associated with podsolization? |
- Ae; eluviation - Bf; clay deposits and humus colloids |
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What is calcification, what conditions are required for it to occur, and which subhorizons are associated with it? |
- when evaporation exceeds precipitation (dry/arid grasslands and prairies) - accumulation of calcium carbonated in a Bca/Bk horizon due to… o humus rich Ah horizon leaches into B horizon o capillary rise of Ca solution from depth |
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What is gleying? What subhorizons are associated with it? |
- Occurs in poorly drained soils o waterlogged, cool/cold soils with low oxygen levels = slow decomposition - Upper layers = thick organic horizons - Lower layers = rgrey/green colour (due to reduced Fe) - associated with Ag, Bg or Cg horizons |
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What is salinization, and what conditions cause it? |
arid or semi arid areas where evaporation exceeds precipitation, with imperfect to poor drainage, and high groundwater table - clay rich, saline waters, no percolation/leaching - salt crust - less soluble salts deposited first - salt transmission also by capillary rise |
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Give a brief description of the main subhorizons. |
- ca = carbonate -- calcification - e = eluvation and leaching - f = podsolization - g = gleying - h = humic OM - k = carbonate (parent or minor) – calcification - m = leaching (oxidation) - n = Na clays - s = salty - t = illuvial, Si-clay - y = cryoturbation - z = frozen |
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Gleysolic and organic soils both occur in waterlogged regions: what are the difference between them? |
- gleysols are characterized by gley processes which result in Ag, Bg and Cg subhorizons, with a thin O layer - organic soils are characterized by more than 30% organic horizon, with no B or C horizon |
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Luvisols and podzols both occur in regions with coniferous forests. What are the differences? |
- they both have a leached/eluviated Ae horizon, as well LH and Ah organic horizons. - luvisols have an illuviated Bt horizon (Si-Clay accumulation) and a Ck horizon with calcareous deposits - podzols have a Bf horizon due to chelate deposits of Al and Fe |
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Which soils have a Bm subhorizon? Compare them. |
brunisols and chernozems - chernozems have no organic upper layer (LH), and have Ck subhorizon - brunisols have a much thinner Ah, as well as an upper LH |
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Compare static and turbic cryosols. |
- both close to surface of permafrost soils (tundra, sub-arctic, boreal) - static = permeable soil, no mixing/warping, no cryoturbation = no y subhorizons - turbic = are cryoturbated, have By and Cy horizons |
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Describe the structure of the interior of the Earth. |
- solid inner central core - molten outer central core - dense and mainly solid mantle, with mostly Si and O, with some Mg and Fe - crust made up of fluid asthenosphere (plastic, dense, slow-flowing) overtop the lithosphere, which is anchored to the crust (rigid, brittle, ductile) - lithosphere = continental (less dense, floats higher) or oceanic (denser |
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Explain the difference between oceanic and continental crust. |
- ocean is thinner, more dense, younger and covers more 2/3 of the earth’s surface area, and it contains more mafic material (less Si, more Mg, Fe, Ca) - oceanic crust will subduct beneath continental crust at convergent boundaries |
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What process results in a volcanic island arc? |
the convergence of two oceanic plates which results in the subduction of one beneath another - also forms a trench in fore-arc zone - aka oceanic-oceanic subducting margin |
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What landforms arise from the convergence of oceanic and continental plates? |
- orogen; mountains; Cascades, Andes - island arcs if the continental plate is submerged |
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What landforms arise from the convergence of two continental plates? |
- continental orogen, eg Himalayas - eventually becomes a suture zone - usually preceded by a continental margin orogen |
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What is a transform fault? |
- when two plates slide past each other in opposite directions - usually on ocean floor; produce zigzag plate margins - on land: San Andreas fault - either driven by shear and tension (oceanic ridges) or shear and compression |
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What features arise from transform faults? |
- earthquakes - faulting - sometimes volcanism |
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What are cratons? |
- stable regions of continental crust - not geologically active - eg Canadian shield: old metamorphic rock, slow weathering - landforms usually consist of old folds and fractured bedrock |
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What landforms arise in continental and oceanic crust as a result of divergent margins? |
Continental rift valleys o result of spreading under continental crust o end up as ocean ridges after a long time o continental crust is less pliale than oceanic crust; crust is warped and fractured
oceanic crust: ridges and rifts o spreading crust forms rifts at point of spreading o result of upwelling magma at the divergent boundary |
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What is the difference between a normal and reverse fault? |
- in normal faults, the hanging block slips below the footwall; result of tensional forces - in reverse faults, the hanging block is pushed above the footwall; result of compressional forces |
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What is a slip or transverse fault? |
- the two blocks (hanging or footwall) slide past one another |
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What is horst and graben faulting? |
graben slips below two horsts as the plates separate - horst remains at same elevation |
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What is a thrust fault? |
type of reverse fault; compressional forces - fault dip has angle less than 45deg (small angle) - forms beds that are no longer horizontal - forms recumbent folds, anticlines and synclines |
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What are hot spots? |
- volcanism that are not on plate boundaries - small but exceptionally hot and long-lasting regions below the plates - hot spots are the heat source for thermal plumes that sustain volcanoes - the volcanoes and islands formed by the hot spot are progressively older and more eroded with distance from the hot spot |
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What is a pluton? |
- magma penetrates and is emplaced within country rock - become surface landforms; become exposed due to differential erosion - the intrusive rock bodies are characterized by origin of emplacement (concordant or discordant) and size/depth of emplacement (cooling, texture) o concordant; parallel to beds o discordant; across beds |
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What are shield volcanoes? |
- made up of basaltic lava: mainly mafic, more Mg/Fe and less SiO2 - more fluid and less explosive lava - formed by successive small eruptions that form layers - eg hotspots, spreading boundaries - larger with gentle slopes |
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Name the main basaltic lava flows. |
- Aa = basaltic, most liquid flows - Pahoehoe = ropy, smooth, same lava as Aa - Pillows = rapid cooling in water creates cracks in rocks that new lava flows through - Columnar basalt = rapid cooling of basalt forms columns - Scoria |
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What are composite volcanoes? |
- in subducting margins, - andesitic or rhyolithic lava (felsic) - viscous (slow-flowing) and explosive - steep - many layers of cooled lava and tephra - sills and dykes in subsurface - very symmetrical - volcanic island arcs |
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What are plug domes? |
- viscous rhyolithic lava (felsic) - thick, no flow, very explosive - steep sided with irregular summits - eg Mt St Helens |
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What are cinder cones? |
- small features - loose tephra only - single vent - lava flows are very rare - very steep sided |
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What are calderas? |
- collapsed volcanic cone - steep sided circular depression - formed by lava draining resulting in collapse or a destructive eruption that collapsed the cone - Crater Lake Oregon |
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What are nue ardentes? |
- cloud of pyroclastic flow - high density mixtures of rock fragments and hot gases that travel downslope away from vents - superheated gas and incandescent ash - move downslope very quickly |
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What is lahar? |
- pyroclastic debris with water (from rain and snow): flows fast and far - cold or hot water - source is snow or rainfall |
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What is tephra? |
- pyroclastic fragments that range in size - can remain as sediment or fuse into rock - smaller fragments travel farther, larger boulders stay near origin - can cause volcanic winters or acid rain - very fine = tuff - serve as temporal marker horizons (allows you to guess age of eruptions) |
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What is pumice? |
- pyroclastic debris that undergoes rapid cooling and rapid depressurization - releases gases and creates air bubbles - can be very low density (might float) - felsic and andesitic |
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What is tuff? |
- consolidated, fine-grained tephra (ash, dust) - soft and erodes easily - andesitic or rhyolithic (sometimes basaltic) |
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What is breccia? |
- large angular clasts – can be sedimentary or volcanic - volcanic: rocks can be picked up lava flow = autobrecciation |
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What are mass movements/mass wasting, and what drives them? |
- downslope movements of earth materials under influence of gravity - force = mass x acceleration - acceleration is due to gravity (a=g), which is the driving force |
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What are the shear and normal forces involved in mass wasting? |
- the driving force is gravity - shear = gravity distributed along slope, pulls things down slope parallel to the surface - normal = gravity acting perpendicular to slope, holds things to the slope |
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What are the equations for shear and normal forces? |
- B = angle of slope - normal o sigma = mgcosB - shear o tau = mgsinB |
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What is the difference between a force and a stress? |
- forces can be localized to one point or particle - forces become stresses when talking about a block or sheet of material = a force applied over an area - stress = force/area - units: N/m - for stresses, the thickness of the material must be taken into account |
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What are the equations for shear and normal stresses? |
- stress = force/area - gravitational stress o hycosB = hgpcosB o h = vertical thickness o y = gp = gravity * density o B = slope angle - normal stress o hycosBsinB - shear stress o hycosBcosB = hycosB^2 |
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What are the differences and implications of normal and shear stresses? |
- normal and shear stress are in direct opposition to induce (shear) or prevent (normal) movement - every object on a slope (not on a horizontal plane) is subject to shear stress = all landscapes eventually become flatter - strain results in deformation, which is a result of stress - depends on the physical properties - matters because… o want to avoid death & destructuion o mitigate and adapt o recognize risk factors (geological structures, climate, previous mass movements) |
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What is shear strength? |
- S = c + sigma-e tanphi o c = cohesion o sigma-e = effective normal stress = normal stress – water pressure o tanphi § coefficient of friction § internal resistance to movement, sliding |
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What is effective normal stress? |
- normal stress – water pressure - normal stress increases with mass - water pressure opposes normal stress; reduces strength o high water pressure supports grains and counters normal stress - effective normal stress is caused by gravity - produces friction at contact with slope - exception: low moisture (dry) o cohesion increases when a little water is added o surface tension of water binds grains together (think sand castle) |
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What is cohesion? |
attractive forces between grains - binding by electrostatic forces - moist silt and clay (small) are especially cohesive o clay is fluid when saturated, cohesive when wet, brittle when dry - dry sand (large) has very little cohesion |
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What is tanphi and how is it important? |
- tanphi = coefficient of friction, Cf - phi = angle of repose = slope angle where particles stop sliding (anything higher, they’re sliding) - depends on size, shape, roughness, and packing of the unconsolidated material - consolidated material is bonded/cemented together very tightly; has very high Cf |
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What is slope stability, and how is it measured? |
- competition between driving (shear stress, tau) and resisting (shear strength, S) cause differential slope stabilities - measured by safety factor, F |
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What is the safety factor, F, and what does it measure? |
- measures the slope stability - F = S/tau o S = shear strength o Tau = shear stress - if F>1.3, slope is stable - if F<1, slope becomes unstable - between 1 and 1.3, there is conditional instability (needs some other factor) |
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Outline the processes that increase stress. |
loading slopes with water, fill, or buildings - removing lateral support = increases slope angle o due to erosion (river or waves) and excavation (building) - removing support from below (karst, mining) |
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What are stress, strength and strain? |
- stress: force applied over area - strength: ability of the material to withstand a stress - strain: response to stress; usually involves change in shape or volume |
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Outline the processes that decrease strength. |
- increased pore water pressure (saturating pores with water) - dissolution of cementing material (breaking of bonds) - weathering - fissuring, earthquakes |
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What is strain? |
- a response to stress - change in shape or volume due to applied stress, a deformation - can be brittle, elastic, plastic or viscous. |
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What is brittle strain? |
o breaks with little deformation |
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What is elastic strain? |
o regains shape o stress = strain (hooke’s law) o constant stress means constant strain o recovery with removal of stress o if too much stress, elastic limit is reached § results in fracture = becomes plastic behaviour o most rocks have limited elastic behaviour à deformation is imperceptible up to elastic limit |
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What is plastic strain? |
o retains shape o no strain until threshold (yield stress) o strain rate is constant if the stress is constant, but get loss of strength o permanent deformation o common in clay, weak rock and soils |
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What is viscous strain? |
o behaves as a fluid o viscosity = the internal resistance to flow o viscous materials have strain rate (flow) proportional to stress o no yield strength o in liquids, some ice |
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How are types of mass wasting classified? |
- by mechanism, material and speed |
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What are the characteristics of rock falls and topples? |
rapid movement - descend through air - falls fall directly, while topples rotate as they fall - common in jointed or fractured beds due to… o pressure release, root wedging, frost, erosion, overhang - topples: o block will rotate and fall when the place of the center of gravitylies outside the base of the block o joints or faults dip steeply; blocks rotate o brittle fracture o creates talus - falls: o caused by undercutting, wave erosion, thermal erosion (permafrost) |
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What is talus, and what causes it? |
- result of rock topples - slope with a characteristic angle of repose - angle of repose is increases for… o larger debris, compaction, angularity, roughness |
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What are the characteristics of creep? |
imperceptibly slow-flowing deformation of a slope - sum of heave and/or flow: expansion/contraction o due to freezing/thawing or wetting/drying - involves surficial material (rock, soil or colluvium) - includes… o soil creep (unconsolidated) o rock creep (flow) § poorly defined shear plane § plastic deformation of weak rock below creeping soil o rock glaciers - rapid if there is tension: steep, convex slope segments - slow if there is compression: concave, low slopes - common in presence of o ice lenses, earth worms, swelling clays, permafrost - pure heave o very slow, imperceptible o if some flow, it is evident as lines, lobes (rock glacier) o rock glacier = heave w/ some flow |
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What are the characteristics of slides? |
- rapid and discontinuous - discrete mass on well defined surface o mass of sediment/rock sticks together as a coherent block as it travels along slope - can be planar or rotational (slump) - planar slides
- all slides are… o longer than wide (L:W ratio ~10:1) o moderate to low moisture o fairly fast o discontinuities or planes of failure (beds, joints, unconformities, base of active layer) o can be triggered by earthquakes, rock falls, frost or water) |
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What are planar slides? |
o planar shear surface o rock slide = fractured or unfractured rock o debris slide = unconsolidated soil, debris
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What are slumps (rotational slide)? |
o rotational shear surface o concave sections o deeper than slide o thick clay deposits o can have multiple o water collects below scarp o distinct slide movement attenuates at toe o usually some plastic deformation = becomes flow at this point |
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What is flow? |
- shear occurs throughout = no single shear plane - max shear at base - water is usually involved - many begin as non-viscous failures (slides, slumps or falls) - flows are classified by their velocity, moisture and sediment content - dry flows = rock creep, debris avalances |
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What are avalanches? |
- dry flow involving snow, rock or debris - initiated by slides (shear plane) followed by flow (due to trapped air = no friction; involves erosive power; displaces air and wind) - have hummocky lobes of debris at base, chaotic mix - example: halfway river |
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What are earth flows? |
- viscous flow of saturated, fine materials - mix of clay, sand and silt - from solifluction speeds to mudflow; high water content - have thick, bulging lopes o lobes dry out as they flow o thicken at toe o hummocky = uneven surface o often slump headwards |
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What are debris flows? |
- flow of non-saturated, coarse to fine materials - mix of grain sizes - speed varies, but usually quite fast - high water content: slurry flow - fans or tracks in existing valleys |
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What are fine flows? |
- mudflow = more than 80% clay-sized particle (wet and slow) - movement depends on water content - loss of cohesion: bonds between clay articles are broken as water is absorbed (liquefies) - quick clays = have limited cohesion when wet - may begin as a slide or slump |
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What are mudflows? |
- arcurate (semi-circular ) scarps - irregular, hummocky floor, bottlenecks - most are a mix of a slump that flows on a bed of clay - common in St. Lawrence valley (glacial clay overlain by fluvial sands) - may involve quick clays - or.. clay-sized minerals: quartz, mica, feldspars (few clay minerals, no negative charge, low cohesion) - sandy surfaces are porous = saturation of the clay material |
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What is solifluction? |
soil flow - slow - saturated, viscous surfaces - creates lobes, ripples and waves - some degree of sliding |
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What is skin flow? |
- active layer detachment slide - arctic regions |
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What is a glacier? |
mass of ice with high snowfalls that persist - moves under its own weight (shear stress) - pretty much confined by the topography around it |
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What are the stages in formation of glacier ice? |
What are the stages in formation of glacier ice? - snow o is porous and has low density o can be transformed by sublimation, melting and infiltration because the pores can still be saturated by water, as well as other materials (sediment, debris) - firn o multi-annual snow = snow that has survived one summer o middle state between snow and ice o loosely packed, randomly oriented ice crystals o can be compacted, crushed, rounded and regelated (melting under/due to pressure) o higher density than snow - ice o further compaction and recrystallization of firn o higher density than firn and snow |
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How are glaciers formed? |
- Mass increases due to increased snow fall and more refreezing (increases density as it becomes more icy) - Mass decreases due to sublimation, melting/runoff and calving |
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What is the accumulation and ablation zone of a glacier? |
- accumulation zone = where glacier gains mass (more snow than melting) - ablation zone = where glacier has a net lost of mass (more melting than snow) |
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What is mass balance, and what does it tell you about a glacier? |
can be defined for the whole glacier, or a certain zone of altitude (= specific mass balance) - MB = (snowfall + refreezing) – (melt + sublimation + calving) o = all mass gains – all mass losses - influenced by slope orientation and aspect - if MB is POSITIVE.. there is net accumulation (glacier is gaining mass = glacier is thickening and advancing) - if MB is NEGATIVE… there is net ablation (glacier is losing mass = glacier is thinning and retreating) |
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What is the equilibrium line? |
- an elevation in the glacier where the mass balance = 0 - no net accumulation OR ablation |
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What is a mass balance gradient? |
- graph that shows mass balance vs altitude - steeper line for continental climates than marine climates |
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What are ice sheet/ice caps? |
- extensive, dome-shaped glaciers on a continental scale - ice sheets are larger than ice caps - sheet: more than 50,000km^2, cap is anything less - limited by topographical constraint: will have domed, convex shape - reflects unrestricted flow of ice that goes outward in all directions - continental ice sheets will have accumulation in the middle with ablation zones going outwards in all directions |
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What are ice fields? |
- smaller than ice sheets and ice caps - may have dome in centre but overall shape is controlled by the surrounding land - eg covering mountain basin or low-relief plateau - may feed a series of valley glaciers |
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What are cirque and valley glaciers? |
- Cirque = form bowl-like hollows in the sides of mountains - Valley = form in valleys, can be fed by cirques |
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What are piedmont glaciers? |
- flow from mountain onto a plain: fan outwards - unconfined flow in the lower reaches |
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Outline the relevant periods of geologic time to glaciation. |
- in Pleistocene (1.65-2.4 mya) o series of glacial and interglacial stages o Wisconsin = recent glacial period; interstadial, 10 deg colder § Early § Middle (alternating cold-warm) § Late (last major advance of glaciers) o Sangamon = interglacial period; stadial; ice sheets disintigerated § Similar temps to Holocene o LGM = last glacial maximum = 23,000-10,000 years ago § Abrupt changes following this o Younger dryas stadial, 13,000 ya § Cooling from drainage of lake agassis through the St. Lawrence § Rapid change in climate o Cooling event 8200 ya, 5degC drop, drainage of L.A and Ojibway = reduced the salinity of N. Atlantic, slowed the current - in Holocene o most recent epoch - interstadial = cooler periods during a glacial stage - stadial = warmer periods during a glacial stage |
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What causes glaciations? |
cyclical changes in the wobble (precession), tilt and orbit (eccentricity) of the Earth o Milankovitch cycles - Non-cyclical changes” o Changes in land elevation o Arrangement of continents (tectonics) o Changes in albedo or other feedbacks |
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How is the thermal regime of glaciers controlled at different points? |
- at surface: o controlled by air temperature, snow cover (provides insulation) and solar radiation - internally: o refreezing and friction = heat the ice - at bed: o geothermal heat flux (underground) and friction from movement (pressure) |
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Why does the thermal regime of a glacier matter? |
- the temperature at the bed controls erosion and movement, as well as the transport of debris and the deposition of it |
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What is the pressure melting point? |
- melting point (greater than 0deg C) decreases as pressure of ice increases - more ice pressure on top = melts at colder temperatures |
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Explain the differences between polar, subpolar and temperate glaciers. |
- temperate o warm throughout o at the bed, water is at pressure melting point - subpolar = polythermal o warmer at surface o frozen in places year round o at pressure melting point in places - polar o frozen at bed o cold throughout |
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Summarize the three main ways glaciers move. |
flow (creep) o movement between and within crystals o driven by shear stress (parallel to slope) o deformation higher in warm ice - fracture o crevasses and shear fractures o more prevalent in… § thin ice § near terminus § deep cold ice - sliding o depends on slope, basal substrate, water |
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What is creep? |
plastic flow - movement between or within ice crystals - strain depends on stress and temperature of ice
shear stress of ice is… To = (Pi)gt(sina) t = thickness a = slope of ice surface Pi = density of ice
E = At^n t = shear stress A, n= constants (increase with temperature) E = strain rate
The plastic limit of ice o ~strength of ice o Tcrit = 1-1.5 kg/cm^2 o Generally t>60-90m |
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How does mass balance affect creep? |
greater accumulation (+ MB) yields thickening and flow - higher slope = higher stress = higher strain = higher flow |
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What is fracture? |
glacial movement mechanism - ice fractures when strength of ice is exceeded (=plastic limit) - depends on… ice temperature, type of stress (tension or compression), more abrupt accelerations or deccelerations in colder ice = higher chance of fracture - fracture is more common along walls, at terminus and on surface (not in the middle of glacier) - colder ice = higher stress = higher chance of fracture - stress depends on velocity
acceleration o causes tension stress in accumulation zone or steep bed o creates crevasses
deceleration o causes compression stress = causes thickening o in ablation zone or the concave bed o creates thrust faults o brings debris to surface |
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What are crevasses? |
result of tensional stress - upper layers of ice fracture (where ice is cold) - below ~30m of depth, plastic flow closes the fractures - different types: o transverse = steep slopes = ice falls o chevron = high friction along valley walls o longitudinal = lateral spreading, tension o radial = often piedmont glacies, radial spreading |
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What is sliding? |
- glaciers slide and slip over their beds - depends on slope, thickness, temperature of ice, and nature of underlying surface - facilitated by layer of meltwater underneath glacier = lubricates and reduces bed roughness - more sliding if sediment below glacier is more deformable - steeper slopes = more sliding - colder ice doesn’t slide - t > S à shear stress must be greater than shear strength o recall S = c + (sigma – mu)* tanphi |
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What is regelation? |
sliding due to melting and freezing - melting and refreezing of ice (due to pressure changes) around obstacles at the bed o changes in pressure due to differential mass = changes the melting temperature o more pressure = lower melting temp - ice can melt at temperatures less than 0 deg C at higher pressures - this depends on… o mass and thickness of overlying ice o obstacles o the fact that there is higher pressure on the upstream side of obstacles = higher stress = lower melting temperature § this facilitates deformation and therefore sliding |
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What factors affect water flow in glaciers? |
- ice temperature - permeability of bed material - surface melting o supraglacial streams feed englacial conduits and fractures o subglacial drainage develops |
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Outline the processes by which glaciers erode. |
Abrasion (scuffing away) o scratching, grooving, polishing bed - plucking/ quarrying o in jointed rocks o jointing may have occurred prior to glaciation or be a result of it o due to pressure release and frost wedging - friction cracks and fractures o cresent shaped cracks and grooves o blocks sheared off fresh bedrock by large bed debris - erosion by running water |
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What is glacial abrasion? |
- Debris carried by ice will wear down at bedrock - requires debris, sliding ice and debris renewal - rate is affected by: o velocity of moving ice o thickness of moving ice (thicker = increases abrasion rates) o basal meltwater § water at bed that lubricates movement § increases velocity and decreases friction o debris (too much debris increases friction too much) o hardness of the debris compared to the bedrock § basalt is twice as hard as marble, marble will abrade three times more than basalt § aka softer bedrock will abrade more easily o shape and size of debris § larger and more angular debris is more effective at abrasion |
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What is plucking and quarrying? |
erosional processes that allow glacial ice to pick up (“pluck”) large rock units from the bedrock o aka freezing of ice to loose blocks o abundant fractures o may be caused by unloading, or may already be present - plucking is dominant on hard rocks with a dense joint patter o abrasion is more dominant on softer rocks with wider joint spacing - jointing may have occurred before or after glaciation - jointing can be caused by pressure release or frost wedging - regelation = pressure variations around obstructions |
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What are friction cracks and fractures? |
- Friction cracks and chattermarks = small (10-15cm) fractures with concentric features - Crescent shaped cracks and grooves - Blocks sheared off fresh bedrock by large bed debris - suggests intense stress and jerky motion - requires basal rocks - ice too soft |
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How does running water erode glacial bedrock? |
- meltwater from surface reaches beds via moulins and crevasses in ice - basal meltwater will facilitate sliding, abrasion and scouring of bedrock - erosion by water can create potholes, flowmarks around obstacles and sinous, swirling channels |
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Give two examples of streamlined erosional landforms. |
they are typically smooth, striated and streamlined
whalebacks (stoss and lee) o caused by abrasion o striated and polished bedrock or debris o wave-like, multiple humps o a smoother roche moutonee
rock drumlins o also caused by abrasion o smooth, taller hump o larger than whalebacks o smooth bedrock (not till)
roche moutonee o caused by regelation and plucking o flatter hump with scraggly end o stoss side due to compression and abrasion o lee side due to extension and plucking o crevasses in ice that covers the hump |
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What is the difference between the entrainment and transport of debris? |
entrainment = taking up debris from surrounding areas into and onto a glacier - transport = the way ice moves debris around |
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What is the difference between subglacial, supraglacial and englacial debris? |
subglacial = generated from erosion at bed - supra glacial = generated from rock falls and erratics - englacial = inside glacier, burial of supraglacial debris or…thrusting/folding of subglacial debris |
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What are erratics? |
- type of supraglacial debris - eg Big Rock, Okatok o made of Quartz o carried 500km |
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How is englacial debris entrained? |
- may be supraglacial debris that has been buried o in the accumulation zone o high accumulation rates = high rate of ice formation - may be subglacial debris that has been encorporated from underneath o eg thrust faults o would be in the compression zone near the terminus of the glacier |
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What is till, and what causes its formation? |
- glaciers generate sediment of many sizes (boulders to rock flour or fine clays) - these sediments are generated by glacial erosion, entrainment and deposition - can created till, drift or diamict - till o sediment laid down by glacial ice o usually not well stratified and unsorted o many ways to form it (depositional processes) o when it is reworked it can become diamict § diamict = general term for reworked till (unstratified, poorly sorted sediment) o highly variable and difficult to classify; often reworked (=diamict) - common characteristics of till… o poorly sorted, bimodal o very fine sediments mixed with very coarse sedimetns o erratic lithologies from elsewhere o faceted, polished, striated clasts o oriented, subangular stones o deformed sediments, shear planes |
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Explain the differences between till, drift and diamict. |
all are glacial sediments - till o unstratified o unsorted o carried and deposited on land by ice - drift o stratified (laid down by or in glacial meltwater) o sorted due to gravity, etc. o unstratified drift = till o laid down in water by glacial ice or meltwater - diamict o unstratified o poorly sorted o includes till and drift: a general term for unsorted glacial sediments o usually used when till and drift have been reworked: initial form and processes cannot be distinguished |
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Describe the types of sediment deposited by moving ice. |
lodgement o plastered to bed - melt-out o melts from slow-moving ice - gravitational o debris released into subglacial cavity that settles by gravity into a stagnant pool of water |
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What is lodgement? |
ice is sheared away - friction is greater than the shear strength of the cie - ice smears debris or debris rich ice to the bed - usually requires thick, warm ice to generate friction - large clasts oriented parallel to flow o dip up glacier o shear planes may be evident in fine sediment - soft bed o soft sediment will be forced up around large clasts o positive feedback |
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Describe ablation processes. |
ablation = melting and washing away of ice - melt out = melting of slow moving, debris-rich ice - supraglacial = coarse, angular (on top) - subglacial = acted on by gravity; basal melt drops debris into cavities; sediment is layered, mixed grain size - proglacial = unsorted o flow till melts near margins and saturates sediment o internal mixing, flow structure, fine matrix - can tell difference btw the three based on the size and angularity of sediments |
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Name the two main ways tills are classified. |
- by position relative to ice (ice-marginal, supraglacial, subglacial) - by the processes by which they are made (primary: lodgement, melt-out, sublimation, deformation, squeeze-flow, and secondary: flow till) |
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Describe the different types of till classified by the process by which they are made. |
- lodgement till o formed at base of ice o dense o dominantly fine-grained o rounded clasts due to shearing - melt-out till o supraglacial = coarse, angular, loosely-packed clasts o subglacial = clasts are more like lodgement till o proglacial = not sorted; flow till, internal mixing - deformation tills o dense, consolidated o fault or thrust structures - flow tills o poorly consolidated o sand and silt |
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What is glaciotectonics? What are the two types of glaciotectonic activity recognized? |
- the structural deformation of bedrock or sediment masses as a direct result of glacial movement or loading - proglacial deformation = at the ice margin o shear and compressional forces o forms large-scale compressional folds, thrusts and nappes o deformation along ice margin will form ice-thrust ridges or push moraines o may be overridden by ice (can’t be seen) - subglacial deformation o takes place beneath ice o shear and extensional tectonics o forms attenuated (thin) folds, small inclusions, augens o occurs when stresses exerted by ice exceed the shear strength § recall shear strength = max shear stress a material can withstand § aka basal shear stress > strength of sediment o more likely to occur in finer materials (silts and clays, not sands and gravels) o melt water and high pore water pressure o can also form deformation till = product of deposition and deformation o squeeze fill = pressure of ice forces saturated sediment into cavities |
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Explain the three main ways till can be deposited on land by ice. |
Lodgement o Debris is plastered onto the bed o Frictional drag exceeds shear stress imposed by moving ice - melt-out o deposition made by melting ice: stagnant or very slow moving - gravitationally o falling, sliding or flowing material |
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Describe the main characteristics of waterlain drift. |
- poorly sorted - no stratification - farther from ice margin = more sorting and stratification - faceted, striated, polished clasts - glaciomarine (salt water) = looser, extend farther, high Na+ - glaciolacustrine (fresh water) = no marine fossils, don’t extend as far, higher Ca+ o includes distal deposits of silt and clay that settle slowly in winter months o also… varves = annual layers of silt and clay § finer in colder months, coarser in spring |
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What is a moraine? |
- at the maximum extent of ice advancement - in glaciers that are still advancing… o conveyor belt deposition creates steep, sharp ridge moraine o bulldozing deposition = push moraine § shearing creates severe internal deformation § more basal (bottom) debris - in glaciers that are receding… o advance or standstill position behind terminal moraine o broader, less height than regular terminal moraines - in glaciers that are stagnant (not moving)… o broad, irregular o melt deposition off terminus (often flow till) o or thrust zone |
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What is a ground moraine? |
- composed of basal till (at bed) - lodgement till - often draped in supraglacial till |
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What is a lateral moraine? |
at margins of valley glaciers - mix of supraglacial and subglacial debris |
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What is a medial moraine? |
- merging of lateral moraines from tributary glaciers - mainly supraglacial |
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What is an interlobate moraine? |
- formed between two adjacent glaciers - large volumes of meltwater involved - primarily sorted and stratified sand and gravel - aka KAME moraine |
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What is the water budget, and what are the components? |
- RO = P – IN – ET – deltaS o RO = runoff o P = precipitation o IN = surface infiltration o ET = evapotranspiration o deltaS = change in storage (in ground)
any water entering the system must be removed by evaporation/transpiration, runoff, infiltration, or stored in the ground o aka... P = IN + ET + RO + deltaS |
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What is Q and it’s significance on the stream’s properties? |
Q = discharge - Rate of water flow - Determines the erosive power of the river - Q = AV - Discharge can have seasonal or diurnal variability |
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How is discharge measured? |
- the river is divided into many cross-sections, with different widths (Sw) and depths (Sd) - velocity is measured at each of these sections - The sum of each of the sections’ Q’s is found and a rating curve is made - Rating curve is usually exponential o It shows the relationship between discharge and depth |
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What is a discharge hydrograph and what does it show? |
- graph of Q vs time - shows discharge over time - depends on… o rate of precipitation and infiltration o shape and size of drainage basin o interception and evaporation |
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What are the main factors that affect the shape of the hydrograph? |
- drainage basin size and shape - soil and rock type - vegetation cover - human activity - weather & climate |
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How does infiltration affect discharge? |
- it is the water that penetrates the surface of the ground - it reduces runoff (water is temporarily stored in ground/soil) - depends on permeability (porosity), slope, soil saturation, and vegetation/OM |
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How does the shape and size of the drainage basin affect discharge? |
- watershed divide = perimeter that marks the limits of a drainage basin - determines volume of precipitation possible to receive - and… time it takes for water to get to drainage outlet - more circular drainage basins will have steeper peaks o all points in the basin are roughly equidistant from the river; get equal flooding after precipitation - larger basins will have higher peak discharges but longer lag times o lag time = time between precipitation event and when discharge increases on hydrograph |
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What is hortonian flow? |
- infiltration excess overland flow - more rainfall than the ground can store - or.. ground/soil with little vegetation, compact soils, (=permafrost, agricultural fields, arid regions) - susceptible to severe flooding - after a storm, will have very high peak in hydrograph - more eroded |
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What is saturation overland flow? |
Generated by rainfall/precipitation in saturated zone - rainfall infiltrates and saturates subsurface so much that it leaks into groundwater which raises the water table - water is expelled as overland flow - more gradual changes in the hydrograph after storm events; o depends on extent of saturation after rain o can be initially steep followed by gentle recession limb - less eroded areas |
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What is subsurface flow? |
- has low, broad peak in Q on hydrograph - slow release of storm flow - not on surface - its subsurface |
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How are river velocity and flow related? |
- potential energy becomes kinetic as velocity - flow is driven by gravity and opposed by friction - velocity is greatest in the middle of the channel near the surface - velocity is lowest on the sides of the channel o riverbed resists movement due to shear stress |
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What is hydraulic shear? |
- a result of the change in velocity with depth - highest at the bed (edge of river) - creates lift = causes particles to be carried |
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What formulae are used to measure velocity? |
- Chezy: v= Ch(Rs)^0.5 o Ch = Chezy coef, friction factor o R = hydraulic radius o S = slope - Manning: v= (R^0.66*S^.5)/n o R = hydraulic radius o S = slope o N = manning roughness coef. - Also: Darcy Weisbach |
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What is laminar flow? |
- When water moves down channel in parallel paths - No mixing - Layers “slide” past each other - Rare for natural channels; more common in viscous fluids or groundwater - Natural channels have quasi-laminar flow near bed or banks (laminar sublayer, see below), very thin layer - Flow velocity increases as depth increase |
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What is turbulent flow? |
water moves down channel in chaotic, irregular paths - higher friction against boundary of bed - fluctuations in velocity - eddies = mixing; superimposed on the main forward movement; helps suspend particles - flow velocity increases roughly as depth increases - laminar sublayer is thicker if: § lower temp § higher viscosity § lower velocity |
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What is the laminar sublayer? |
thin layer of laminar flow near the bed of the river (everything else is turbulent) - requires small reynold’s number, R, and low velocity - smooth bed - becomes thicker and temp and velocity decrease, and as viscosity increases |
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What is the Reynolds number? |
- defines type of flow - Re = VR/u - V = velocity - R = hydraulic radius - u = kinematic viscosity; resists flow = viscosity/density |
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What is river power? |
- rate of energy dissipation - energy available to drive geomorphological change in river systems - Power, P = W/t, W= force applied over distance - River Power, p = density x slope x gravity x discharge - Rivers are most powerful near |
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How does river power differ in different areas of the river? |
most power in middle along length (profile) - at headwaters, there is a steep slope but low discharge = lower - at mouth, there is a gentle slope but high discharge = lower |
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What is sediment transport, and what factors determine the amount of it? |
- rivers can transport rock, regolith, soil, and sediment from their upper portions to their drainage basin - more energy needed to transport larger, coarse sediments than fine ones - transport rates/amounts depend on o river power (energy) o sediment size and availability
- sediment is transported if: o shear stress exceeds resisting forces o resisting forces = friction, cohesion, gravity o shear stress allows particles to be carried; causes lift |
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What are the modes of sediment transport? |
- suspended or bedload rolling - saltation - sliding
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What is threshold shear stress? |
- shear stress = parallel to surface - causes grains to move once the critical/threshold shear stress is applied - actual critical/threshold shear stress can be difficult to determine/predict - this is because there is small-scale heterogeneity in velocity, grain size, density, and packing and shape of sediments - measured using bernoulli’s equation |
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What is bernoulli’s equation and what does it predict? |
it predicts stress needed for motion - Tcr = (pi/6)(Ng*D^2)g(Ps-p)Dtan(phi) o Ng = grains/area o D = grain diameter o Phi = angle of repose o Ps = sediment density - The shields parameter for rough beds is: o Tcr = 0.06g(Ps – p)*D |
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What relationship do threshold/competency curves show? |
- Hjulstrom’s curve shows the relationship between velocity and grain size o There is a velocity for motion (erosion, transport, deposition) of sediment that depends on grain size o Erosion velocity = threshold velocity (when grains start to move) § Higher for lower diameter particles (due to lower cohesion) § Lowest for medium diameter particles § High for large diameter particles as well o Depositional velocity = velocity needed for deposition § Lower velocity needed to deposit smaller particles § Higher velocity needed to deposit larger particles § Depends on size (calibre) of sediment, velocity, and amount of turbulent flow § If turbulent velocity (Vt) is larger than settling velocity (Vs), then the sediment can’t settle and remains in suspension § Stokes Law: larger, denser particles settle faster o Competency = coarsest (largest) size a flow can transport (Max size at max velocity) § Vs capacity = max amt of sediment of a certain size a river can transport o See pg 324 textbook graph |
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What is Stokes Law and what does it tell you? |
- Vs = 0.22(Pp-p)gD^2/mu - Tells you that larger, denser particles settle faster |
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How are sediment loads (mass of sediment) and Q (discharge related)? |
- qs = pQ^j o qs = suspended load o p, j = constants o Q = discharge - Shown by sediment rating curve: plot of concentration of suspended sediment against river discharge - Suspended-sediment concentrations (SSP) are determined by: o Sediment availability (more easily erodible material) o Usually lower than max. transport capacity o The relationship between SSP and Q thus is more related to the varying amount of available sediment (not shear stress or turbulence) § May change due to storm evens, large rainfalls etc. § SSP declines after prolonged rainstorm |
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What is the significance of the development of bedforms? |
Bedform = “structures” at the bottom of the river in shallow areas; fine-grained - flowing water affects bed roughness, friction and currents near the bed - this will then affect what the bedform looks like - the type of bedform depends on… o grain size, velocity, water depth/shallowness |
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What are the four main types of bedforms? |
Ripples (small) - Dunes - Antidunes (large) - Flat bed
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What is the Froude number, and what is its significance? |
determines the nature of bedforms - depends on the turbulent nature of flow - Fr = v/(gd)^0.5 o V = velocity o G = gravity o D = depth - If F<1 (small), there is tranquil flow (subcritical) - If F>1 (large), there is erosive, shooting flow (supercritical) |
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What are ripples, and what conditions do they require for formation? |
- small features on shallow beds - Fr<<1 (very small) - Low flow velocity - Single grains are eroded and deposited such that ripples migrate downstream - Have crests + troughs - Can be planar or linguoid - Spacing between each ripple is <60cm - See diagram in lecture 1, page 8 - Smaller height than dunes and antidunes - Very shallow flow depth (a few cm) |
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What are dunes, and what conditions do they require for formation? |
- similar to ripples, but larger - Fr<1 (small) - Grains move in groups and the dunes migrate downstream - Gentle stoss, steep lee slope - Rarely found in rivers with coarse (gravel) beds - Spacing between each dune can be 60cm-100s of ms (much larger than ripples) - Larger height than ripples - Don’t need as shallow flow depth |
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What are antidunes, and what conditions do they require for formation? |
- as velocity increases in dunes, they become standing waves then antidunes - Fr >1 (larger) - Antidunes migrate downstream - Erosion and suspension in downstream direction than supply and deposition upstream - Plane bed will develop as velocity increases - Spacing between antidunes can be 10s of cm to ms (variable) - Also has variable height - Require more shallow flow depths |
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What are drainage basin patterns, and what are they controlled by? |
- the arrangement of streams in a drainage basin - controlled by: o structure: domed vs tilted bed § slope drives flow into the basin o lithology: weatherability and erodibility of material that makes up the basin § if rock is easily weathered, this will be a lower point of the land: water can build up here - understanding the drainage pattern allows us to interpret rock type, structure - use patterns on air photos and topographic maps |
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What are the characteristics of a dendritic drainage basin pattern? |
- random headward erosion - tree-like pattern - lithology (rock) indicates homogenous bedrock = no signficiant structure - insequent streams - all areas are equally weathered/eroded - there are flat areas, not many hills |
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What are the characteristics of a radial drainage basin pattern? |
- streams flow in all directions from a central point - indicates high relief (slope) domes and peaks - in areas with recently formed volcanic cones or uplifted domes - have consequent streams - eg Volcanic domes in guatamala |
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What are the characteristics of a trellis drainage basin pattern? |
- parallel tributary streams at high angles to trunk streams - long main stream with lots of trunks at ~90deg - indicates folded or tilted sedimentary beds - beds will vary in resistance; most resistant beds will form trunk streams - consequent (structure) AND/OR subsequent (lithology) - eg Banff |
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What are the characteristics of a rectangular drainage basin pattern? |
similar to trellis - trunks form right angles with tributaries - indicates fractured/jointed rock: igneous or metamorphic; or flat, jointed sedimentary beds - subsequent streams: streams will flow in the fractures and joints (depends on lithology) - eg NE New York, or shield environments in the NW territories |
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What are the characteristics of an annular drainage basin pattern? |
streams curve or flow in circular pattern - indicates breached domes or beds of alternating resistance - circular outcrop (bull’s eye pattern) - may have radial pattern if the centre if there is dome present (radial and annular pattern together) - subsequent drainage: follows most weathered beds |
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What are the characteristics of a multibasinal drainage basin pattern? |
there are many small ponds and alkes - irregular flow and basing connection - indicative of permafrost (thaw lakes), karstic regions and hummocky deposits (dead ice moraine) - kettle-type lakes |
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What is the different between insequent, consequent, and subsequent streams? |
insequent stream = stream extension and erosion NOT guided by structure OR lithology - consequent stream = stream extension/patter and direction of low is controlled by slope of land (=structure, not lithology) - subsequent = streams extend/trunk depending on lithology: trunks form where there is least resistant (most easily erodible) rock |
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What are contorted and parallel drainage basin patterns? |
contorted: contorted metamorphic rocks; squiggly - parallel: modertate to steep slopes or parallel elongated landforms |
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What is the difference between non-alluvial and alluvial channels? |
non-alluvial = controlled by bedrock o physically confined, steep o resistant, rough banks and beds o can just be presents in a largely alluvial channel o would change very slowly due to resistance of bedrock - alluvial = less resistant bedrock o channel changes much more rapidly o adjust in size, shape and pattern o bank and bed material easily transported and depositied by flow (looser, gravel or fine sediment) o form in floodplains (portion of valley floor built by the stream) o have deposiitons of alluvium which is continuously reworked - bedrock may have more resistant and less resistant parallel strata o waterfall will form where weaker strata are exposed (eg shale) o more resistant strata will have steeper walls and be flatter/more uniform |
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What is the difference between cascade, step-pool and plane-bed channels? |
- cascade o steep, narrowly confined o rough turbulent flow (white water around boulders) o rocks and boulders of different sizes scattered irregularly along channel o forms small, closely spaced pools and channels - step-pool o staircase of boulders/cobbles separated by scour pools with finer material o spacing determined by discharge, slope and height of the steps - plane channel o no bedforms o moderate gradient o gravels cobbles spaced evenly and flatly along bottom |
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How does alluvial channel morphology vary, and what factors cause this? |
- can be straight, meandering, braided or anabranching - vary due to… o sediment load type o current velocity o channel bed and bank material (erodability, weatherability, size, etc.) |
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What are the characteristics of straight channels? |
alluvial - don’t persist over long reaches - share characteristics of other channel types: bars, riffles and pools |
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What are bars, riffles and pools? |
- bars o zones of fine deposition along banks o slower flow - riffles o zones of channel bedload deposition o flow reduced - pools o zones of flow convergence o scour |
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What are the characteristics of meandering channels? |
- straight, unstable flow o flow is deflected and reflected o flow is directed to outside of meander; raises water level there o sets up helical (spiral) o outer bank erodes; inner bank gets deposition of sediment - positive feedback: o more erosion = more bending of channel o more bending = higher velocity o more erosion = increases bending - point bars: o inside of bends o zones of low flow and deposition o fine particles (sand, silt) - oxbow lakes, fills o when stream is abandoned, forms a curved lake that is eventually over-vegetated - chutes/cutoffs - these landforms occur when… o there is a well-developed floodplain o low slopes o fine sediment (clay rich, cohesion) |
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What are the characteristics of braided rivers? |
- occur in areas where… o there is abundant sediment o banks easily erode o discharge is high and sporadic o == mountain regions, glacial outwash plains, alluvial fans - development: o during high discharge, stream channel is choked with coarse bedload o coarser materials (gravel, sand) are deposited as bars when stream reaches sediment capacity o stream is diverted around coarse deposits - have numerous dividing and reuniting channels - less sinuous than meandering channels - intervening deposits of bars/islands o bars = less stable; made of sands and gravels o islands = more stable |
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What are the characteristics of anabranching channels? |
- multiple branches/channels diverge and rejoin - channels are primarily erosional; often by avulsion o starts with meandering river with oxbow lakes o break in levee of meander; flow is diverted o new channel is formed = different than oxbow lakes o two active channels - discrete channels separated by stable alluvium - islands: semi-vegetated or exposed bedrock - islands are wider than channels - compared to braided… o depositional o single channel; flow is diverted around obstructions that are flooded annually |
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What are the four ways that channels form is controlled? |
discharge - slope - erodibility, stability - sediment load |
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How does bank and bed erodibility affect channel form? |
deposits of alluvium in valley floor - experiences flooding during periods of high discharge - accretion = layers are formed as material is deposited over time o lateral accretion: channel deposits and point bars o vertical accretion: overbank deposits, levees, channel fill, crevasse-splay http://en.wikipedia.org/wiki/Crevasse_splay |
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What are the characteristics of terraces? |
flat surfaces/benches perched on the sides of valleys - caused by change in environment that causes down cutting - depositional = abandoned alluvial flood plains - erosional/cut = down-cutting through bedrock - structural = differential erosion of beds of varying thickness o layers of stronger or weaker rock - will slope downriver (follow slope of the actual river) - result of… o increase in slope due to… § tectonic uplift § drop in sea level (eg glaciation) § changes in morphology = removing obstructions, meanders o increasing Q § climate change (de-glaciation) o decreasing sediment load = increases erosion |
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What are the characteristics of deltas and fans? |
- delta o where river drops sediment load as it enters a standing body of water (large lake, ocean) o flow decreases in velocity = sediment is depositied o triangular, fan or branching channels (birds foot) - fan o formed on land o river debris flows leaving a valley and flow over the plain o sediment is deposited because channel width is increasing o this increases depth and velocity as well |
