UBC GEOB 103
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Created by:
riccatina on April 20, 2010
Subjects:
Rivers, glaciers and mass movement
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186 terms
Terms | Definitions |
|---|---|
 sediment | material that is eroded and enters the channel and is a) deposited in and around the channel b) eroded following deposition or c) transported downstream |
| What does sediment transport depend on? | velocity of flow, sediment size, if it is dissolved or not |
| Hillslope erosion | entrainment, transport and deposition. |
| Erosion equation | Driving forces/Resisting forces |
| 3 types of erosion | rainsplash erosion, sheet erosion, rill & gully erosion |
| Rainsplash erosion | impact of falling drops, effective with sparce vegetation, amount of erosion depends on kinetic energy - not effective in transport of sediment - depends a lot on slope! |
| Sheet erosion | erosion from overland flow over smooth surface - depends on slope angle and water depth - effective in transporting eroded material + no evidence of canalized flow |
| Grade I have to get | 85% |
| Rill erosion | along small channels, density declines with slope length and less steepness. Depends on - slope angle, water depth and soil erodability |
| Gully erosion | deep, V-shaped channels. Develop due to surface and subsurface flow |
| How does sediment enter rivers? | - slope erosion (sheet, rill, gully) - mass movement (landslide, etc) - recruitment of sediment from bed and bands |
| What happens once sediment enters rivers? | - Deposition = force of flow < resistant force & Transport = force of flow > resistance force |
| Discharge | volume/unit of time - increases when velocity increases and cross-sectional area increases |
| Load | amount of sediment transported at a given discharge |
| Competence | max. particle size that rivers can move - increases with velocity, depth and slope |
| Capacity | max. amount of solid sediment that a river can move at a given discharge |
| 3 types of loads | Solution (dissolved) - suspended load - bed load |
| Total load | bedload + suspended load + dissolved load |
| Sediment load | bedload + suspended load |
| Dissolved load | solutions and chemical weathering - groundwater in contact for long periods of time - 60-80% of total load |
| Suspended load | suspended because of turbulent eddies, very fine (silt, clay) - 90% of sediment load - from slopes, banks and channel bed - depends on discharge and sediment availability |
| + discharge = + load | more water (volume) to carry - more erosion of bed (higher velocity) - more and larger sediment (higher turbulence) - more available sediment (flooding) |
| Bedload | sediment travels bouncing (saltation), rolling or sliding over the streambed - move short distances - large particles or low discharges - coarse - 10% of sediment load |
| 2 channel types | Bedrock and Alluvial |
| Bedrock channel | no sediment accumulation, bed and banks of rocks, upland of drainage, steep slopes and high erosion |
| Erosion in Bedrock channels? | Chemical weathering, abrasion, hydraulic action |
| chemical weathering | solution and other chemical processes remove material |
| abrasion | physical action of the sediment moving over the bedrock |
| hydraulic action | flowing water pushes and pulls on rock blocks |
| Alluvial channel | sediment accumulation, channel cuts into alluvium, bed and banks are material deposited by river, lowlands, low gradient - sorting (downstream, well sorted, usefull for aquatic environments) |
| Thalweg | deepest and fastest part of flow |
| pool | deep slow flow besides center |
| riffle | shallow rapid flow near downstream end of bar |
| Flood plains | broad, flat deposits of alluvium that extend from one valley wall to the other. Are the peak flow in water level and is inundated during floods (aprox. 1 every 2 years) - mainly composed of silt, clay and fine sand |
| 3 alluvial river patterns | straight, meandering, braided |
| Meandering Rivers | constantly erode on cut bank and deposit in point bank. Creates floodplain that is wider than the channel and changes course gradually. |
| oxbow lake | bow or crescent shaped lake that forms when meandering erosion cuts off bends |
| braided river | multiple=thread channel. High sediment load, floodplain completely occupied by channel. constantly changing course. usually coarse sand and gravel deposits, many bars |
| bar | small island that form when there is a high load of sediment |
| 2 terraces | alluvial and bedrock |
| alluvial terraces | bench-like landforms that are carved in alluvium by a stream during degradation |
| degradation | downcutting of a stream channel by stream erosion |
| bedrock terraces | created by tectonics, climatic change, variations in base level, variations in flood magnitude |
| deposition at river mouths | occur when a river reaches base level, flat surface or standing water. Alluvial fans or Deltas. Due to reduced velocity. Many tributaries appear. |
| Deltas | formed when river flows into standing water, rapid deposition of the alluvial sediment. mostly sand and finer material, low angel forms from top, has steep fronts that go into the water body, producing forest bedding |
| Alluvial fans | cone shaped, steep alluvial deposits that form when stream channel emerges from a steep, confined valley onto a broader flatter. Coarse sediment (gravel and boulders with sand). moderately steep, if it is subject to debris flow it may be alluvial material and colluvial material |
| Base level | ultimate sea level, in local areas it may be a dam. the theoretical limit for stream erosion |
| knicpoint | discontinuity of of profile because of tectonic, change in rock erodibility and change in base level |
| graded stream | stream that has a succession of lakes, falls, rapids and discontinuities. Achieves a balanced state (average export of sediment is also average import) |
| landscape evolution | upland stream (steep, rapid flow = sediment sources, coarse materials), lowland river (slower flow, high sediment load, sediment accumulation, fine materials) |
| Denudation | amount of sediment eroded from the basin. Assumes sediment is completely eroded from the basin. Estimated as total volume of sediment divided by total basin area. Equal lowering over entire basin area. |
| Sediment yield | amount of sediment eroded per unit basin area per unit time. Does not equal total sediment eroded from upland areas. Arrives to mouth without being deposited in valley bottom. |
| Controlling factors of sediment yield | climate and vegetation, basin size, elevation and relief, rock type, land use and human activity. Small basins have more sediment because of steep slope and mass movements. If basin is large there is less force and more places for deposition |
| glacier | a mass of ice that forms on land due to a multilayer surplus of snowfall over snowmelt. Effective agents of erosion and deposition. |
| 2 glacier types | Alpine (mountain) and continental (ice sheets and caps) |
| how do glaciers form? | there is a surplus of snow which is compacted by more snow and rain, re-crystalizes into firn and ice. Gravity moves mass downslope, slowly forming a streamlike pattern |
| What are the climate inputs in glacier? | Temperature and Precipitation |
| snowline | elevation above which snow persists year round, lower limit of perennial snow |
| annual mass balance | net accumulation - net ablation |
| Alpine glacier | "mountain glacier" - confined to a narrow and thin topography in valley. Piedmont and tidewater. river of ice confined in valley, transports debris downstream, originates in cirque and terminates in a body of water |
| cirque | origin of alpine glaciers, bowl-shaped at head of valley. Eroded during extended glaciation |
| continental glacier | continuous mass of ice, creates own topography over huge area. Ice sheets, caps, fields and shelves |
| ice sheets | most extensive |
| ice caps | round ice with dome |
| ice fields | not enough ice for dome, flow is constrained by topography |
| ice shelves | sheets attached to land, oversea floats on water. has steep cliff facing seawater |
| Glacier ice formation? | from snow that doesn't melt in summer. snow plus water = more weight and pressure and snow transforms to ice. Why? pressure decreases air space, increases density and leads to consolidation and re-crystallization of snow into large crystals of snow ice (rough and granular) |
| firn | granular old snow, forms surface layer in accumulation zone, intermediate between ice and snow |
| accumulation zone (glacier) | upper part of glacier, net snow accumulation |
| ablation zone | lower part of glacier, net melting and sublimation |
| glacier mass balance | change in mass of a glacier over time = total accumulation - total ablation . Either at a point, or total mass change of glacier or over an area. |
| glacier condition | gaining (+), losing (-) and equilibrium line in middle |
| glacier retreat | terminus have been retreating since little ice age |
| determinants of glacier movement | weight- pressure on top forces ice to spread out. Flow - ice is slippery when it is lubricated by water between rock and ice as well as between grains |
| crevasses | formed because lower part of glacier moves slower than higher part but causes more deformation. differential velocities cause surface to crack |
| velocity of movement depends on... | distance from bed and valley sides (friction), surface slope (steepness), free water at bed (lubrication) - most movement occurs internally at upper levels |
| seracs | blocks/columns of ice formed by intersecting crevasses. are found on base of glacier |
| supraglacial meltwater | water flow on top of glacier, melts surface and can melt through glacier |
| moulin | where a supraglacial meltwater stream melts a vertical tunnel through ice |
| subglacial meltwater | generated in 2 ways - at surface flowing through moulins and tunnels to bed and by friction of ice moving over the bed. Lubricates bed and increases slip, erodes and transports sediment. |
| glacial landscapes | v shaped before glacial and u shaped after |
| 3 glacial erosion | ice push, plucking and abrasion |
| ice push | glacier acts as a bulldozer, pushing limited amount of loose rock debris |
| plucking | removal of rocks from outcrop (water along fractures) |
| abrasion | grinding of bedrock surfaces using rock carried by ice - polished and scratched rock surface caused by moving sheet |
| glacial striations | long, straight scratches (evidence of glacier) - rates of up to 5 mm/yr. influenced by amount of debris, basal sliding velocity, ice thickness (pressure), hardness of bedrock, basal water pressure and removal of rock material |
| cirque | semi-circular shaped created as glacier sources back toward mountain - at the head, depends on level of activity of glacier, duration of glaciation and composition and structure of bedrock |
| arete | steep-sided, shard edged bedrock ridge formed by two glacials eroding on oposite sies of a ridge |
| col | low areas, or passes, through a ridge that once had claciers on either side |
| horn | 3 or more cirques adjacent to one another (the peak that survived glacier erosion all around) |
| tarn | small lake that occupies a rock basin in a cirque or glacier through |
| glacier trough | eroded by passage of valley glacier - longitudinal profile is steep, irregular and stepped - u-shaped and typically straight |
| hanging valley | tributary that no longer meets the main valley at the same level - where now there are waterfalls |
| fiords | glacier troughs partially filled with ocean water |
| evidence - erratic | boulder-size rock dumped by glacier in a landscape of different composition |
| evidence - till | unsorted material deposited by glacier (multiple grain sizes) |
| evidence of glacier | erratic, till, striation and polished bedrock |
| glacier deposits | loose or fragmented rock - any size, eroded from underlying bedrock or deposited by previous glacial advances. Meltwater stream carries fine grained material |
| fall-in | rocks fall into the glacier from surrounding slopes and are carried like a conveyor belt |
| tributary glaciers | ice carried from smaller, contributing glaciers |
| outwash | materials carried away from the glacier snout and deposited by stream deposits. sorted, stratified deposits from glacial streams as glacier melts |
| glacial drift | all debris deposited by glacier. |
| lodgement till | deposited under the ice, dense and clay ric, compacted by overriding ice |
| abblation till | deposited in front of the ice as glacier retreats, usually sand and silt |
| Morraines | glacially deposited sediment piles |
| ground morrain | beneath ice a.k.a. lodgement till |
| lateral morrain | pile up along the sides of glaciers |
| medial morraine | material in middle of glacier (when two lateral morraines come together) |
| end/terminal morraine | at ice front (marks glacier's farthest advance) |
| recessional morraine | slow retreat of terminus leaves series of end morrain |
| drumlin | low oval hill made of deposited till, molded by overriding glacier, upstream side is steep, downstream side is tapered - long axis parallel to direction of ice flow |
| esker | narrow ridge of coarse sand and gravel formed by subglacial meltwater channel (tunnel) sinuous but parallel to glacier flow, not always continuous |
| kettle | steep-sided hole formed by gradual melting of large ice block left behind by glacier with sediment accumulated "kettle lake" when it has water |
| kame | any stratified ice deposit - sediment deposited on ice surface is lowered onto landscape as it melts - within or between ice blocks (IC), also from delta of outwash stream (SD) |
| outwash plain | depositional plain of stratified drift |
| periglacial | processes, landforms, topography and climate of cold regions, along margins of past and present glaciers. freeze-thaw processes common features: permafrost, pattern ground and ground ice |
| permafrost | <0 for more than 2 years, |
| cryotic ground | frozen ground |
| noncryotic ground | unfrozen ground |
| active layer | seasonally frozen ground |
| talik | unfrozen patches. through, closed or open |
| through talik | connects active layer and groundwater |
| closed talik | within continuous frozen layer |
| open talik | below a lake, inside frozen layer |
| continuous permafrost | perennial, severe cold, poles |
| discontinuous permafrost | disconnected patches of frozen land |
| alpine | at high altitudes |
| perennial process | frost heaving, frost thrusting, cryoturbation and ice wedge |
| frost heaving | vertical movement of soil and rock |
| frost thrusting | horizontal movement of soil and rock |
| cryoturbation | soil layer churned by frost action |
| ice wedge | water enters crack and freezes, crack enlarges with repeated freeze and thaw |
| ground ice | frozen subsurface water - pore ice (soil pores), lenses and veins (channels of ice), segregated ice (layers), intrusive ice (water injected under pressure) and wedged ice (cracks) |
| patterned ground | rocks form polygon at surface |
| pingo | heaved, circular ice-cored mound |
| palsa | mount of peat with thin perennial ice lenses |
| loess | accumulation of wind-blown fine sediment from cold regions with no vegetation. can be derived from galcial outwash deposits or glacial erosion |
| pingo formation | 1. lake drains and fills with sediment 2. talik beneath lake freezes 3. pressurized water is forced toward surface and freezes 4. frozen water expands, heaving land upward, rupturing surface 5. covered with soil |
| paleoclimatology | study of past climates - pleistocene, holocene, last ice age, medieval warm, little ice age, post = drastic warming |
| weathering | decay, disintegration, and dissolution of fresh rocks and minerals - no transport. Alters original lithological characteristics. Produces an unconsolidated material consisting of: new minerals, minerals that resisted destruction (stable minerals) and organic minerals added to weathered zone |
| types of weathering | physical, chemical and biological processes |
| erosion | removal of weathered material from one place to another - transport |
| soil thickness | depends on balance between production (weathering) and removal (erosion). Weathering without erosion = soil development. Erosion without weathering = no soil development |
| regolith | - layer of loose, heterogenous material covering solid rock (produced by 3 types of weathering) |
| weathering front | interface between weathered material (regolith, soil) and bedrock |
| physical/mechanical weathering | disintegration - no chemical reactions, produces smaller particles from larger ones, rock breaks continuously as stress is exerted, preserves the chemical characteristics of rock |
| chemical weathering | decomposition - mineral alteration or decomposition, involves chemical reaction and change in chemical composition of minerals - new minerals are created (secondary minerals like clay) - organic acids produced by plants enhance chemical weathering |
| Biological weathering | biological activities directly break down rocks (people, animals, plants) - roots exert force - lichens contract during dry season |
| factors that influence weathering... | simultaneous physical and chemical weathering. character of bedrock (resistance, solubility, jointing/fractures), climate (temperature and precipitation), slope aspect, vegetation cover |
| main controls on weathering | water, temperature, mineral type, features of surface area |
| physical weathering - unloading | 1. deeply buried rocks are under high pressure, 2. erosion removes overburden - decreases pressure - physical heaving of rock 3. layers of rock peel off into widely spaced sheets - sheeting structures and exfoliation domes, granular/disintegration (grains loosen and fall out) |
| physical weathering - crystallization | growth of salt crystal in rock pores. dry climates on coasts, forms caves and niches. Sources of salt are precipitation (seawater) and dust and volcanic acids. Salt expands as water evaporates. |
| entrainment | changing of sediment from static to transportable |
| physical weathering - frost action | ice crystal growth and frost wedging. Freezing water to ice crystal grows 9% - mechanical force applied > tensile strength of rock. Frost wedging = push joints/grains apart. - stress of water as it freezes and expands |
| freeze-thaw | freezing - expansion. thawing - contraction. repeated growth and melting of ice crystals in the pore spaces of rock. |
| lithology in break | determines break. Sedimentary, joint block separation. Igneous, granular block separation |
| talus slopes | poorly sorted, cone-shaped debris at base of steep slope |
| physical weathering - thermal expansion | volume change due to change in temperature. Heating - expansion. Cooling - contraction. rocks and minerals expand in response to daily heating and cooling, seasonal heating and cooling and wildfires. For effectiveness requires frequent and extreme fluctuations. |
| Chemical weathering main factors | temperature, water, surface area, mineral type, time (5 main types) |
| chemical weathering - hydration | combination with water, may cause expansion, mechanical weathering. hydration, dehydration cycles - granular disintegration |
| chemical weathering - hydrolysis | chemical reaction with water produces new compounds is significant in weathering of silicates |
| chemical weathering - oxidation | chemical combination with oxygen - rust |
| chemical weathering - solution | mineral dissolves- water and carbonic acids. forms no new weathering products, groundwater dissolves bedrock ions in solution added to water and becomes dissolved load. limestone caves - crystallization of calcite, stalctite and stalagmite formation - dissolution of calcium carbonate is erversible process |
| chemical weathering - carbonation | solution in carbonic acid, formation of carbonic acid - water, vapour + carbon dioxide |
| Karst topography | landscapes of limestone, susceptible for chemical weathering, distinctive features - sink holes, underground, caves and channels, disappearing streams |
| karst | long-term solution weathering of limestone bedrock by surface and ground water |
| biological weathering | highly fractioned sandstone - penetrative woody tree roots - root wedging and biotic leaching |
| mass movement/wasting | downslope movement of soil or rock material under the influence of gravity without the direct aid or water, wind or ice. Spontaneous, bedrock, debris and/or soil. at surface and submarine |
| mass movement - equation | driving force > resisting force (gravity > shear strength, cohesiveness and internal friction). Gravity (mass, acceleration due to gravity, weight, friction force, coefficient of friction) |
| angle of response | max. angel that loose material forming a slope can maintain without shipping. balance between driving forces and resisting forces. function of grain size and texture (solid rock could be 90, loose material and soil between 13 and 24 and coarse san 30-33) - a pile of sediment resting on the angle of response represents the threshold condition, any slight disturbance causes a failure |
| slope stability | driving forces (gravity) increase as slope angle increases. resisting forces (friction and cohesion) decrease as water content increases. |
| factor of safety | defines slope stability (Fs) = sum of forces resisting movement/sum of driving forces. Fs>1= stable slope. Fs<1= unstable slope |
| Major players | 1. Climate and meteorological events 2. Lithology, layering, structural control, gradient and surface material 3. vegetation and land use effect |
| criteria to distinguish in mass movement | material (soil/rock, coarse/fine), water content (dry/wet/fluid), rate of movement (slow/fast), type of movement (fall/slow) |
| triggering mechanisms of mass movement | earthquakes, increased water content, decreases in slope strength due to weathering. Physical, chemical, anthropomorphic and biological |
| low risk vs. high risk | low = unsaturated sediment dips upslope with no development. high = saturated igneous dips downslope with extensive development |
| Rock fall and Soil fall | free fall of soil and rock. steep slopes or cliffs, accumulates at base of slope, forms talus cone or scree slope. material in talus is at angle of response aprox. 35 |
| Slides | rapid sliding of a cohesive block of material (rock or soil), moves along a slippage line, steep slope usually after heavy rain because water reduces resistance, increases weight and pressure. movement depends on lithology, rock structure, vegetation, earthquakes. |
| 2 types of slope | translational and rotational |
| Flows | viscous flows occur when soil/debris/clay are liquified. 3 types: mudflow, earth flow, debris flow |
| mudflow | rapid downslope flow of water and soil (mostly clay) |
| earth flow | moderately rapid downslope movement of masses of saturated flow |
| debris flow | flow of muddy water with large amount of coarse material (coarse material, less water and more material than mudflow, poorly sorted) - happens when there are large amounts of regolith and water. Common in coastal mountains (heavy rains, steep slopes, mantled by loose sediment) |
| soil creep | alternate feeze/thaw or wet/dry cycles - needle ice, as water freezes it pushes particles up, they fall downslope with gravity when they unfreeze. Slow downslope movement of soil and rock due to expansion and contraction (.1 to 15 mm a year). Very shallow - only upper part of soil, irregular movement that depends on slope angle and soil type |
| solifluction | rapid soil creep, soil and rock are saturated and flow downslope. common in subpolar regions, where drainage is inhibited. |
| gelifluction | solifluction over permafrost |
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