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James Hamilton

GG282 January 7, 2013 British Colombia: June and early July 2012 this part of B.C hasa lot of precipitation. The gullies on the slopes in the area became more moist and therefore more unstable. Increasing moisture in pore spaces the less strong the connect is and the material becomes more unstable. July 6 there was a mass movement in the area – created a very large debris flow. Slur of water and sediment moving down a stream channel, and as it hit a curve, you can see the materials have flown all the way through the trees and terrain. A lot of the material was deposited on the bench where people were living on these slopes. Particular event had some fatalities. Course Outline and Materials – xdrive Don’t email the prof, he wont email back. Use GG101 textbook for soils information. Weekly two hour lab, no labs this week 6 total graded components in the lab – 10 different submissions Late labs are not graded at all, labs must be in the TA’s hands – no dropbox X drive (GEOGLAB > GG 282) James Hamilton - Arts Room 2E11 Ext. 2061, office hours 12:30-1:20 pm Labs every week - not first week 50% labs, 10% midterm, 40% final GG282 January 9, 2013 Chapter 1 pg. 1-21 Geomorphology: the form of features we find on the Earth – study of landforms (landscapes) and the processes responsible for their development. Scale: Spatial scales from sub millimeter to thousands of kilometres Temporal scales from seconds to millions of years Relation between spatial and temporal scales? Relationship between space and time – Ex. Parts of the coast can be exposed during high/low tide, causing ripple features. These typesof features form very quickly, can reform in a fast amount of time. Looking at a landscape with older elements (old sediment and bedrock) a sediment and erosion history over millions of years. The smaller features have the potential to form over shorter temporal scales. Ocean trenches, sediments etc. are generally formed over longer temporal scales. Ex. ripple forms in sand caused by wind making them not symmetrical. Another small feature is an example of flutes, pits and rills on the sediment – but it takes thousands of years for these to develop from when rainfall travels down the rock over and over. Geomorphology developed as a separate branch of earth science in the late 19 century. Influences include Catarophism and Uniformalism. Catatrophism: features on the landscape caused by infrequent events. Key players: Hutton Playfair Lyell Lyell more or less became responsible for the principle of Uniformitarianism. Looking at the history of the landscape, and also learning from what the landscape is doing now has affected it in the past. Several schools within Geomorphology, including but not limited to: Historical Climatic Process Much early work focused on models of landscapes. Historical Geomorphology: Identify stages or sequences in landscape development.  cyclical models  ex. cycle of erosion Used to describe what happenson the landscape by looking at river processes and then slope processes. Function of the stream – discharge, and the gradient Look at the textbook (four diagrams showing the streams dissecting the landscape) Uplifting triggers very rapid erosion. Quickly after that, the valley floors are incised. Then gradually we lose the remnants of the flat surface until it becomes a new flat surface. Most models stressed physical erosion related to rivers and slope processes to develop planation surfaces, but there are other possibilities:  etchplains: chemical weathering processes dominant  marine planation: coastal platforms What is the problem with approaching the landscape in this way? We would look at a landscape and would expect it to be old. that is not always the case. Problems:  is there really a cycle  what actually influences form When you are looking at a landscape – don’t constrain to young vs. old landscapes. We should look at the ages of all the materials and know that everything can be different. Understand that when we look at a landscape it is made up of many different components, and we will have to look at a ton of different materials. Climatic Geomorphology: Identify important geomorphic processes and landforms associated with a given climatic region. Each climate region has a landform assemblage. Tropical rainforest: lots of chemical weathering, very deeply weathered soils (a lot of aluminum and iron components) infertile soil. We can associate climate with geomorphology of a region. But not always one feature can be assumed for every region. Process geomorphology: Identify and measure processes. Infer landform and landscape development from those observations. th John Powell, Grove Karl Gilbert late 19 century stressed the balance between process and structure in landform development. Notion of equilibrium concept (Gilbert) – importance of equilibrium, landforms represent a balance between the processes acting on a surface and the materials (structure) that comprise that surface (resist). Ex. stream channel with a sandy bed, water is moving the sand grains (some kind of feature will happen) the characteristics will represent the process of the flow and the systems being mobilizes. The form will adjust as the equilibrium changes. Late 20 century: geomorphic work grounded in the process school of geomorphology. System:  a series of components  flows of matter and energy occur between components (also identify how big is our system)  advantages: follows form the equilibrium concept Measuring – steepness, gradient, sediments, sinuosity, wavelength, velocity Characteristics of Systems:  discrete components  flows of energy and matter  feedbacks  equilibrium GG282 January 14, 2013 Feedback Example: - feedbacks occur when one variable produces a change that affects another variable - glacial feedback example of ice thickness (fig. 1.4) Equilibrium: is dependent upon time and scale Static Equilibrium: (very short time spans) develop over Steady Time (not shown on diagram) Steady State Equilibrium: (time spans of decades to millennia) Dynamic Equilibrium: (long time spans) develop over Cyclic Time Meta-Stable Equilibrium: occurs when there is a major change at a threshold (ex. landslide) Surging glacier (variegated glacier, coastal Alaska) 1964 Surging – means glacier is moving slowly, and then experiences a massive increase in velocity. From 1964-1965 the ice advanced 2 or 3km in a year. A build up of ice, and then a change in the hydraulic bed (lubricate with water the ice can move more rapidly) How can a river system change? Morphology: putting more sediment into the system it has a whole series of variables that can effect. We can change some of these controlling variables. Hydrology: building a dam youcan change the flow, but there is a lot of sediment being altered as well. What components respond quickly? What components respond slowly? Equilibrium Issues:  Not all systems are well describe by equilibrium concepts  May be multiple possible outcomes for a given set of conditions (range of possible outcomes, we cannot assume)  More than one set of processesor histories that may develop a particular feature Problems with scale: Short term process measurements (exogenic) cannot easily be scaled to longer time spans and larger features. (can’t necessarily scale up to longer periods of time) Must consider endogenic processes for larger scale features Non-linear Systems (read in textbook) Also look for –  Space for time substitution  Equifinality (form is not process)  Multiple hypotheses Modern Geomorphology: composite of ideas and approaches, new techniques and emerging fields, geochronology and digital topography (dating things, finding out how certain landscapes develop, taking detailed measurements), emphasis on endogenic processes, changing environments, non-linear responses. Review materials on:  magnitude and frequency  energy role of gravity  structure of the earth  characteristics of sediments Geomorpholoical Processes  exogenic (external processes) and endogenic (internal processes, includes tectonics)  relation between magnitude and frequency for processes  example: flooding What is a flood? When a channel is at an over full condition, when we have an overbank event. When it is full, we call it a bank full discharge: maximum amount of water that a particular channel can handle. When it spills out it is an overbank event. In a natural system: every 2-3 years we get an overbank event In a disturbed system: every year How common are high magnitude events? Not very common. What is the recurrence interval (return period) of a given magnitude? We look at the relationship between frequency and magnitude. Recurrence interval on the x axis and discharge on the y axis. High discharge events are less frequent than low discharge events. Work: product of magnitude and frequency Energy:  solar radiation  internal (geothermal) energy What drives processes?  energy in the presence of gravity Force:  force causes a body to experience acceleration (F=ma) Energy:  capacity to do work Work:  is done when a force acts on a body (matter) and causes displacement Power:  work done per unit time What resists the driving forces?  Solid earth (lithosphere)  Bedrock and sediments Endogenic: - internal earth processes include: o volcanism o tectonics or diastrophism Endogenic effects: Earth structure – simplified view in fig. 2.4 Lithosphere: oceanic is under the ocean and one is on land, they both have different composition (continental is comprised of rocks and minerals, low density) (oceanic is thinner more dense materials) Below the lithosphere is the asthenosphere: upper part of the mantle where there are solid and molten materials Model of plate tectonics: look at textbook, understand basic structure (fig. 2.5) Diastrophiism (tectonics) includes: - orogenic processes Mountain building - compressional forces that cause folding, faulting, and thrusting rock units Epeirogenis - broad regional uplift or subsidence Tectonic plates and features (fig. 2.7) Review - relation between tectonics and geological phenomena such as volcanic and seismic activity - general characteristics of bedrock types (lithology and structure) resisting framework has a major influence on the geomorphology GG282 January 16, 2013 Driving and Resisting Forces Sediments Unconsolidated materials (particles, grains or clasts), important properties include: - grain size (texture characteristics) - sorting - shape (coarse, #-dimensional characteristics) - easier to deal with larger particles - density (way they behave varies, determines where they deposit) - structures (found within materials such as layers of soil/water, used to help us reconstruct the environment) - packing ()how grains are packed together determines how much space is in between: which can maximize the content between the grains, if their is less packing then the strength is not as strong) - porosity - permeability Texture (grain/particle size) If axes are measured, the shape and size can be determined Huge range of grain sizes are present (from fine clays to boulders) d is the diameter (intermediate measure) Grain Size Distribution Compare wind and wave deposited sediments: Wind - x axis is the diameter (fine/very fine sands), well sorted because the accumulated percentage graphed is occurring in a very narrow range of grain sizes (in sand range deposit) Wave - pebble deposits with a mixture of sand (coarse settlements), beach environment will have a bigger distribution of grain size, ranges from medium sand to pebbles, slope is gradual (greater spread of settlements) Structures (stratification) In an exposure of sediments we may see beds or laminations Eg. road cut - can see materials, might be able to find evidence of sedimentary features, tell us how materials were laid down Coarser materials are usually not rounded but they can be Within each bed, there is a range of fine to coarse (from a high energy event and as the energy is reduced the finer materials get deposited eg. boulders to sand layers) Cross bedding - series of lines that show the ripples of the water, older ripples show the previous ones, hummington cross-bedding is seen in coastal environments Mass Wasting Processes and Hillslope Form Read Chapter 5 Weathering Boulders present in a stream - exposed to weathering processes - becomes dissolved and is broken apart chemically and physically which we refer to as regolith which describes the surface material (used to describe the surfaces of extraterrestrial) Soils - has specific properties that have a range of processes and allow us to extract value from it Erosion processes that directly influence slopes: slope-wash and mass movement Slope-wash - water that moves across the surface relatively easy, some of it may infiltrate, will then see signs of erosion and development of rills which will turn into gullies, if they become saturated it would result in a mass movement Slope Hydrology Infiltration occurring in normal circumstances Overland flow (water moving across a surface) When infiltration capacity is exceeded by precipitation - most common overland flow Overland flow moves down flow (slope/sheet-wash) If you have a lot of overland flow - start picking up sediments If water table increases and saturates the land, overland flow will also occur Rainfall impact influences materials being moved Overland flow is what causes slope-wash (becomes concentrated in certain areas - velocity will be higher and the probability of picking up sediments is increased which creates the phenomenon of rills and gullies) Throughflow also contributes to gullies (laterally moving water through the soil) - pipes and sapping processes is what also forms gullies GG282 January 23, 2013 Forces (Cont.) Role of Water Small amount provides some cohesion in a sediment High amounts produce a slurry If fine grains in sediment - we can make a cast and manipulate it to form a ribbon (this is because of the thin film of water in between the grains As water content is increased in the sediment, the grains become separated Coulomb Equation The total resistance to shear is the coulomb equation Shear strength (resistance the material has to not move down the slope) Angle of internal friction (differs with different materials) The normal stress acts to hold the material in position on the slope Angle of slope influences the shear strength and normal stress The resistance to shear (failure) increases as cohesion, normal stress (effective normal stress) and angle of internal friction increase What about water? As the water content in material increases, the pressure of water in the pores increases This has the effect of reducing the normal stress (the water takes some of the load) Some of the weight that is directed into the hillslope so the normal stress is reduced (material becomes weaker) The Coulomb equation changes (pore water pressure variable is added) Thus, a soil that has a high water content has a lower strength and is more likely to fail Balance between the shear stress and the strength (mass movement forces) Mass Wasting Processes and Hillslope Form II Classification Many schemes/classifications that have been developed for mass movements Trenhails - based on style of motion and the types of materials involved There are 5 main classes and a 6th category Creep is classified under flows Conditions that favour falls and topples Structure (material) Joints (vertical fractures), bedding planes (fractures within material/sediment) - planes of weakness Weathering processes (chemical, physical, biological processes) Structure becomes weakened, trigger is what sets off the falls/topples (heavy precipitation, seismic event, etc.) Can be a single block of rock or many rocks falling at once Slides and Slumps Rotational - failure on curved planes Slump refers to rotational failures in sediments/bedrock with curved surfaces As material moves downslope they tend to rotate (therefore, rotational slopes) Translational failures - involve failures on a simple plain, lateral movement is a translational slide Inclined plain, failure moves across this and the name given regards the material that is moving across the slope Conditions that favour slumps: Poorly consolidated bedrock Fine grained homogeneous sediments with a high water content Conditions that favour slides: More cohesive bedrock units where bedding planes are parallel to the surface Assume it is a translational slide (units failing on a simple plain) Weathered shallow depth sediments that experience an increase in their water content GG282 January 28, 2013 Lateral Spread - a lateral spread involves the outward expansion of fractured material - variety of styles of motion (slide, flow etc.) Look at Chapter 5 – Types of Movement - spreads may occur when coherent materials move laterally on underlying deformable materials Flow – a combination of sediment, rock, organic debris and water that deforms and shears as they move downslope with higher velocities at surface Creep – is the slow downslope movement of materials by a variety of processes Solifluction – very slow Evidence of deep seated creep – scarps that dup into the slope, these features are called Sackung Earthflows – mainly fine textured sediments, variable water content, slow to very rapid, well defined source area, transport zone and depositional areas Parts of Southern Quebec and Eastern Ontario have deposits of fine mineral and clay materials from the last glaciation. Locally it is called Leda Clay. It is called quick clay, it tends to behave quickly as it weathers and moisture content changes. Poor sediments with a loose matrix that become exposed as land that was once underwater, then fresh water flowing over and over erodes the good materials and minerals like sodium? ions or sulfate? And changes the whole dynamics of the material and the sediments become weaker. This can happen very quickly, which is why they are called quick clays. Debris Flow: typically looking at mountainous terrain, rapidly moving, sediment, high water content (slurry), may travel long distances in channels in steep mountains, triggered by rain or snowmelt, deposits in fans or cones Starts with heavy rainfall swelling the stream, then sediments slump into stream, forming a slurry (debris flow) Debris flow increases volume as it picks up additional sediment Mudflows vs. Debris Flows - Avalanche (not snow avalanche) o A rapid flow of material (rock or debris) on an open slope (not generally in a channel) o May have low water content o Called debris or rock avalanche The difference is the material flowing. Rock Avalanche - with very large… - Rock avalanches are considered complex Glacial Processes Chapter 6 For glaciers to evolve, we must have snowfall go to firn snow. Then gradually this firn changes from firn to ice so long as it becomes compacted with a higher density. Learn the different types of glaciers in the textbook. Glacial Ice – coarse polycrystalline structure, ice with small amount of gas and water With increased depth, ice becomes coarser textured Mass Balance Budget between inputs (accumulation) and outputs (ablation). GG282 January 30, 2013 Glacial Processes I Mass Balance Budget between inputs (accumulation) and outputs (ablation) Figure 6.2 South East and West of Alaska, BC and Alberta - need to develop a system where there is more snowfall than glaciers - not all snow is evaporated - some is lost to glaciers and is built up into glacial ice More precipitation is cooler areas (mountains) is in the form of snowfall Why is there glacial ice in the East of Baffin island - because of precipitation - more snowfall in the eastern part of the arctic than the west (Baffin bay is open for longer periods of time) and therefore glaciersare formed Fig. 6.3 in the 5th edition - ice sheet is dome in its size - the accumulation zone is where the mass balance is deposited (the top of the dome) When looking at the mass balance of a system - have to look at accumulation zone, ablation zone and how the mass is moving within this As move from accumulation snow at the top to the bottom the ice becomes more visible - at the top it is covered with snow (precipitation) Fern line/snow line/equilibrium line - look at these lines at the end of glacial periods (end of summer - Aug/Sept) - the line from where we move from snow to ice (accumulation zone to the ablation zone - transition period) Accumulation Processes Snowfall (adds mass to the glacier) Rainfall (freezes in glacier) Drifting snow and snow avalanches Superimposed ice - temp. of glacier is below freezing with a water source coming onto the glacier (eg. stream from a valley) and this water can freeze onto the glacier Ablation Processes Melting Evaporation - number of water bodies on the ice - losing mass Sublimation (solid to the vapour phase directly) Streams Calving Measurement Techniques Direct measures - measure the snowfall and density - can determine the amount of water that has been added to the glacier - (do this after the glacial period as well which allows to determine the amount that remains) Snow and ice stakes, cores, trenches and surveying Indirect measures: hydrology (main output - melting), remote sensing (aerial photography, satellite imagery) Accumulation and ablation monthly values - Fig. 6.4 Positive mass balance: active ice indicators - glacier is gaining mass (gets larger) and moves down slope into lower elevations Negative mass balance: stagnant ice indicators (has blocks of ice that are left behind, might not be able to find the elevation line because the snow line is below elevation) (Fig. 6.5) Region differences - climate (mass balance gradient) - Fig. 6.6 - if mass balance is positive, it isgaining mass, if it is zero it is staying the same and if it is negative it is losing mass - eg. as the elevation is low we have a negative mass balance and as the elevation increases it becomes positive (continental climate) - more melting at lower conditions White glacier Example - mass balance gradients (2005-06, 2006-07) - by doing measurements from the base to the top of the glacier we can determine the distribution of the mass balance - more mass was lost in 2006/07 In the recent years - data shows >80% of monitored glaciers have negative mass balance (global data) Ice Temperature Temperature (Thermal Regime) Influences motion and erosion Controls of ice temp: - Surface air temp - Snowfall - Geothermal heat Cold and warm based glaciers, temperature profiles (Fig. 6.7) - if temp is below freezing then it is a cold-based glacier, has a frozen bed, at surface the melting point is 0 degrees - as the pressure is increased, the melting point changes, cold in the summer and winter - a warm based glacier has an unfrozen, wet bed, is warmer in the summer and colder in the winter GG282 February 6, 2013 Midterm: MC, definitions (with choices - give the definition, not the description, what it does, etc., ), short answer (read carefully - explanation, describe, etc.) Motion Surging Sudden increase in velocity Occurs where ice is warm based May be related to a sudden increase in the amount of basal water (reduces friction, causes rapid basal slip) Elaborate surging pattern Crevasses and Structures Crevasses may develop where the ice fractures Ablation zone Occur near valleys Motion Many crevasses occur where the rate of motion is greater than the ability of the ice to deform (by creep): fractures result Less pressure because of the ice above it - so fractures are developed Commonly seen where ice is flowing over a steep slope - seen in New Zealand Seen on ice margins as well - valley glacier coming off from ice pool, and significant crevasses are in these areas (seen in BC) Ogives show one years movement off the glacier down the mountain - thicker, lighter coloured layer is the ice that has moved during the summer period Extending flow of ice is when ice is under tension Placement of ogives is not evenly spaced Glacial Processes: Water Water influences motion and erosion Water is more important in ablation zones (particularly for temperate ice) Where water is found, usually warmer ice and how sediment is transported in this environment Supraglacial - ‘on top of’ - surface of glacier and upper meters of the ice Englacial - ‘within’ - environment within ice mass its self Subglacial - ‘base’ - contact zone between glacier and its bed Nye (n) and Rothlisberger (R) channels - difference is between beds and how they are developed N channels - erosional channels in the underlying bed (bedrock/consolidated sediments) R channels are cut into the ice above the bed (have the appearance of tunnels) R channel - takes water along the base of the glacier (Cordillera, Blanca - Peru) Tunnel Valleys Large N-channels typically developed in sediments Water can erode R channels which can form N channels which can be kilometers in width Occurs beneath glacier Broad valleys with flat bottoms, formed sub glacially Spillways and Channeled lands (scablands) - melts meltwater channels - valleys carved out by meltwater Channeled lands - high discharge events can produce spillways in the proglacial environment, in extreme cases cutting the landscape into a network on canyon features - flood events are associated with these Erosion Erosional processes: - Abrasion (scour) - Plucking (quarrying) - Fracturing - Meltwater Abrasion A process that occurs where basal ice is warm and sliding Clasts may be frozen into the basal ice, or may be lodged between the ice and bed As the ice moves, the clasts roll, slide and are dragged over the bed, scouring that bed surface Many factors that influence the abrasion rate With increased thickness of ice, pressure increases as well as the rate of abrasion Rate of abrasion becomes negative, sediment is being deposited (Fig. 6.15) - when pressure gets too great the rate of abrasion is decreased Need sliding ice, warm basal waters, pressure environment - for abrasion to occur Evidence of abrasion: striations Plucking Pressure distribution at bed (Fig. 6.16) Distribution of pressure: b in diagram shows that the pressure is very great, c in the diagram has a lower pressure point - rock can be fractured Evidence of process - basal ice (regelation ice) often has a high debris content - freezes into the base of the glacier Variety of landforms result from plucking (stoss and lee forms) - stoss side becoems smooth and lee side becomes plucked Fracture Pressures exerted by clasts in the ice may be sufficient to fracture underlying bedrock May produce a variety of forms, often due to a combination of abrasion GG282 February 11, 2013 Midterm - short answer - trying to formulate a reasonable response writing in sentences and not point form Glacial Erosion: Fracture Pressures exerted by clasts in the ice may be sufficient to fracture underlying bedrock May produce a variety of forms, often due to a combination of abrasion and fracture Small scale features that can develop in bedrock due to fractures Clasts can come into contact with bedrock and causes fractures Series of fractures are transverse Erosion and Ice Temperature Erosion most effective under warm ice, there is very little or no abrasion under cold ice
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