Final Flashcards
Ablation Till
- Till laid down by melting ice, usually ice that has become stagnant.
- combination of englacial and supraglacial flow tills
- Thick, sandy and bouldary melt-out till
- Like basal till, but fewer fines, more gravelly, more angular, less dense, no fabric.
May have some stratification or lenses of water-borne sediments.
• NOTE: tills can easily be mixed up with colluvium!
Ablation Zone
*The lower part of the glacier.
*Zone of an active glacier where more snow and ice is lost in summer than is gained in winter.
• Snow melts seasonally here → net deficit of ice.
*Distinguished from the accumulation zone.
*Loss of snow and ice due to melting in temperate regions, but also evaporation, calving, wind and river erosion, and sublimation.
• Negative mass balance: continuously shrinking, but fed by flow of ice from above.
(• Equilibrium line: separates accumulation and ablation zones.)
-transfer of mass from the accumulation and ablation zones maintains a constant or equilibrium surface gradient.
Abrasion (Aeolian)
- Most probable mechanisms for dust generation in deserts
- The grinding or wearing action of sand and other material carried by the wind against rock surfaces
- Limited to the ability of the wind to lift abrasive sand in saltation
Abrasion (Glacial)
• Scouring of rock by glacial ice and embedded sediment (clasts)
- As clasts are move in traction, their edges and corners cut striations, while the finer abrasives polish the underlying rock surface.
- meltwater is responsible for transporting abrasive materials (along with going along with the glacier itself)
- Rates of abration may be greatest with low debris concentrations.
Rates of abration depend on frequency of contract between abrasic materials and bedrock, hardness of abrasives relative to bed, and the downward force exerted on the abrasives.
-Big angular clasts are most effective
• Rates of up to 5 mm/yr have been determined.
- Highest pressure in front of the slope, and lowest behind it.
- Cold based ice does not allow for much abrasion - and even protects the bed (because abrasion requires the presence of water) - Warm based ice is much more effective..
Abrasion (Rock Coasts)
Rock fragments and sand are swept, rolled, dragged over or thrown against rock surfaces
-Cylindrical depressions (potholes) develop where large clasts are rotated by swirling water inthe surf or breaker zones.
Accumulation Zone
*The upper part of an active, moving glacier.
• Positive mass balance: surplus of snow and ice here force the glacier to move downhill.
*snowfall accumulates and exceeds the losses from ablation
• Firn survives the summer.
(- Continental Glaciers grow outward from accumulation zones)
Aeolian Erosion processes
Abrasion
Deflation
Aeolian Transport
*** FIGURE 12.3 IN TEXT
Aggradation
- To build up the floor or slope of a river by deposition. Slopes built up in this way are described as aggradational
- Increasing amounts of sediment cause single channels to widen and aggrade, promoting braiding
Alluvial Fans
• Sloping, fan-shaped deposits built upon the floodplain of a larger river.
• Stream often splits into multiple distributary channels.
• Typically occur where streams leave steep mountain valleys and enter a larger, main river valley.
*upper fan is the youngest
*consists of sand and gravel
*Cone shaped,
Alluvium
Fluvial sediments: Valleys often have a fill of this stuff: a combination of bar and floodplain deposits
-Sediment deposited by rivers and consisting largely of sand, silt and clay
Alpine Erosional Landforms
**FIGURE 7.8 & 7.9 IN TEXT
- Cirques
- Gacial troughs
- Hanging valleys
- Truncated spurs
- Fjords
- Aretes
- Horn
Alpine Glaciers
- Long and narrow mountain glaciers which fill / carve valleys or ‘troughs’.
- Begin as “pocket glaciers” in high alpine bowls.
- Flow together like streams.
- Coalesce into piedmont glaciers when they leave the mountains.
(May feed continental glaciers, if fringes are mountainous)
(landforms are similar for both alpine glaciers and ice caps/sheets, though dimensions will differ..)
PAGE 229 for picture.. coooool.
Amplification
*Shaking levels at a site may be increased, or amplified, by focusing of seismic energy caused by the geometry of the sediment velocity structure, such as basin subsurface topography, or by surface topography.
*Two important local geologic factors that affect the level of shaking experienced in earthquakes are (1) the softness of the surface rocks and (2) the thickness of surface sediments.
Anabrancing
- Multiple, stable, low-sinuosity channels.
- Well developed levees, many vegetated islands.
- Floodplain relatively distinct
*consists of two or more fairly deep and narrow interconnected sand or gravel channels that enclose floodplain areas
*Similar to braided rivers, except these are separated by prominant natural levees, wetlands, ponds and vetegated semi-permanent islands. Also the islands are much larger than the channels, where in braided, they are similar to the size of the channel.
Angle of Repose (or internal friction)
The steepest surface gradient of loose sediment. The mass angle of repose ranges from about 32-35 degrees, generally increasing with diminishing grain size and decreasing sphericity. Individual grains, however, can have much higher angles of repose.
Arete
• Sharp-crested ridges acting as the divide between two glaciated areas.
Barchan dunes
- crescent-shaped features, horns point downwind.
- ~1 m to 100’s of m from horn to horn.
- unidirectional winds.
- Indicates that strong, competent, frequent winds
- form where sand supply is limited, and they are the fastest migrating form
*Little vegetation in the area
*Aeolian transport is more rapid across and around the sides of patches or mounds of sand than across the centres, where sand is the thickest.
Barchanoid ridges
- Barchans frequently occur in coalesced forms called barchanoid ridges
- oriented perpendicular to the wind direction.
Barrier islands
**FIGURE 14.4 IN TEXT
Coastal landscape
- Depositional landform
- vulernable to subsidence, erosion and rising sea levels
*Long narrow beach forms completely separated or detached from the mainland
-Enclose estuaries, emayments or narrow lagoons that are connected to the open sea through cannels or tidal inlets between the islands
*Some shift landward and some along the shore (due to longshore transport)
Basal Till (lodgement till)
Glacial sediemtn deposit
*Till that has been carried or depoisited a the bottom of the ice
*Dense and overconsolidated, often dominantly fine-grained, and with clasts that have rounded edges and sometimes striated or faceted surfaces.
*Have distinct till fabric, sometimes with stone dipping gently upglacier, in accordance with the direction of maximum stress.
Baymouth barriers
Coastal Landscape
-Depositional feature as a result of longshore drift.
*A spit that completely closes access to a bay, sealing it off from the main body of water.
*usually consist of accumulated gravel and sand carried by the current of longshore drift and deposited at a less turbulent part of the current.
*
commonly occur across artificial bay and river entrances due to the loss of kinetic energy in the current after wave refraction.
Bedload transport
Fluvial sedimentary process (transport)
– Almost entirely function of flow volume, velocity and turbulence
– Sand and coarse particles roll, slide and saltate (jump) at constant rate unless obstructed
– Increase in flow strength causes entrainment and a fall in velocity causes deposition
*Much slower than the flow velocity
*Sediment becomes finer downriver because size sorting in bed load and, to a lesser extent, because of abrasion and particle breakdown. Because of this, bed load becomes increasingly secondary to suspended load down the course of the river
Braided
River Channel Pattern
• Typical conditions:
o Erratic (flashy) discharge.
o Steep slope, low sinuosity.
o Relatively coarse bed material (> sand)
o High sediment load.
*Most common in high latitudes
*Very common at glacier outwash deposits
• Some characteristics:
o Multiple small, shallow channels.
o Many bars.
o Highly unstable.
*One or more channels are usually dominant in large braided rivers
Calving
Where ice breaks off glaciers in big chunks
Carbonation
Chemical weathering
carbonates are not usually the end products of weathering, but their formation represents an important step in the breakdown of feldspars and some other minerals
• Solution of minerals in carbonic acid (water + CO2).
*CO2 from atmosphere, decaying organic matter.
- Example: solution of calcite.
- Formation of carbonic acid: H2O + CO2 → H2CO3
- Solution of calcite: CaCO3 + H2CO3 → Ca2+ + 2HCO3-
• Prevalent in limestone bedrock (almost pure CaCO3).
Cascade Pool
Small Channel
• Low discharge (typically 3rd-order or less).
• Steep (S between 2º and 20º)
*Narrow
o Usually found in headwaters of a watershed.
• Usually coarse bed material.
• Common channel patterns:
o Both low sinuosity.
o Low sediment transport.
*closely spaced pools
-continuous, turbulent flow
Celerity
(Swiftness of movement)
(wave property)
(c)=lambda/T
Channel Bed Characteristics
*many local variables
o Grain size decreases and clast rounding increases progressively downstream
o Bedforms include pool-riffles, potholes, bars, dunes, ripples, etc. armoured beds
o Large woody debris important
Drainage Patterns controlled by:
o Bedrock structure (e.g. joints, faults)
o Bedrock lithology
o Sediment grain size
Channel Gradation
o Most of BC’s river valleys have been through a cycle of channel gradation since the end of last Ice Age:
i. Aggradation of glaciofluvial sediment. ii. Degradation as sediment supply dwindles.
o This has produced multiple terraces in many valleys.
Graded streams
Aggradation
Degradation
Channel Sands
Sand deposited in a stream bed or other channel that has been eroded
Chemical Weathering
Oxidation
Carbonation
Solution (leaching)
Hydrolysis
Chevron Crevasse
- develop because of drag with the valley walls, open at right angles to the max tension. Run 45 degrees downstream to the valley sides.
Cirques
- High alpine bowl where glaciers begin.
- Often occupied by small lakes called tarns.
Coastal foredunes
*Wind flow accelerates around hard objects, causing sand grains to bounce further and higher.
• Wind direction can vary as flows from a variety of incident angles are steered shoreward by changing roughness and surface slope at the back of a beach
*Saltation across the upper portion of many beaches can be enhanced by the presence of shells etc
*Dunes begin to develop above the high tidal level, where the wind is deflected around vegetation and other obstacles
*Vegetation grows (light), and encourages more accumulation of sand
- Along the coast, there is typically a foredune complex (linear, shore-parallel, vegetated dunes backing a sandy beach)
- Blowouts occur when strong onshore winds erode a gap in a coastal foredune, sweeping sand from the beach and dune inland
- These typically grade into parabolic dune
- Coastal dunes buffer against storm surges & sea-level rise
Cohesion
A force that is involved in slope stability
Col
Low pass in arete
Colluvium
Sediment deposited by mass wasting, other hillslope processes.
• unstratified or weakly stratified.
*Loose, unsorted, weathered
Map Symbol: C
Active status of formative process
Can easily be mixed up with till.
Continental Erosional Landorms
**FIGURE 7.7
Whalebacks
Rock Drumlins
Mega-Grooves
Rock Basins
Continental Glaciers
- Dome shaped glacier which buries the landscape.
- Grow outward from central accumulation zone.
- May be fed by high alpine glaciers, or have alpine ‘outlet glaciers’ if fringes are mountainous.
- May spread onto ocean → ice shelves.
- Ice caps < 50 000 km2.
- e.g. Pemberton Icefield, Columbia Icefield.
- Ice sheets > 50 000 km2.
- e.g. Antarctica, Greenland “Ice Cap.”
Convergent plate
Where tectonic plates collide → intense geological activity.
• Subduction of one plate beneath another.
• Earthquakes.
• Chain of volcanoes.
• Folding and faulting.
• Joining of continents.
Coppice dunes
- Coppice dunes are vegetated sand mounds that are commonly scattered throughout sand plains in semiarid regions where shrubs and blowing sand are abundant
- They can be incipient forms of parabolic dunes because the vegetation anchors them
- Common in coastal areas
Coulomb Equation
S = c + (σ – μ) tanΦ
S = shear strength
c = cohesion
σ = effective normal stress (=mg cosβ)
μ = pore pressure due to water
Φ = angle of internal friction (angle of respose)
Crag and Tails
Form from ice push, abrasion and plucking
can be considered a special type of drumlin in which a tail of sediment extends downstream from a projecting rock knob.
*Cavaties on the lee side of the rock obstructions can fill with sediment falling from the roof or washed in by meltwate
Creep
• Slow, shallow downslope movement of soil or rock debris.
- Rates ~ 0.1 and 15 mm/year.
- Fastest at surface.
- Main soil creep mechanisms:
- Freezing and thawing.
- Wetting and drying.
- Solifluction / gelifluction.
- Creep depends on water content, grain size, and slope angle.
- Typical indicators: uphill-bent trees, tilted poles, folded strata, small terraces.
*Pariglacial slope processes: Gelifluction and frost creep.. (solifluction..)
Crevasses
- Glacier slows at rock obstacles, surges over steps.
- Crevasses are basically normal faults in the ice where under tension.
- May form icefalls in very steep places.
3 simple types..
Chevron crevasse - drag with valley walls - 45 degrees
Splaying crevasse - meet with valley walls at less than 45 degrees
Transverse crevasse - right angles..
Cross-bedding
Fluvial sediments - small and larger scale structures.. May show flow direction.
-ripple, dunes bar architecture
*Consists of foreset beds that are steeply inclined to the main bedding plane.
*Most frequent in sandy sediments in fluvial, coastal and aeloian environments, as erosion occurs on the upstream side and deposition at the angle of repose on the downstream side of migrating ripples, sand waves and sand dunes.
*Fluctuation in discharge and velocity cause bed erosion and the formation of depressions that are later filled with sediment
Trough cross-bedding - produced by bedforms with curved or irregular crests
Planar cross-bedding - bedforms with linear or straight crests
Cutbank
Erosional landform (sediment)
- found in abundance along mature or meandering streams
- located on the outside of a stream bend, known as a meander, opposite the slip-off slope on the inside of the bend.
- shaped much like a small cliff, and are formed by the erosion of soil as the stream collides with the river bank.
- Often erosion proceeds to turn the meandering river into an oxbow lake
Debris Avalanche
- Long-runout rockslides
- the debris of rock fragments assumes a transition streaming or flowing motion followed by falls and flows (cushion of compressed air, dense cloud of dust, vapourized intersitial water, or wet mud)
- can have rates of more than 300 km/hr, and distances of 5-20 times the height of the vertical descent
- In canada - tend to occur in well-jointed, steep rock dippings at angles 25-40 degrees.
- triggered by heavy precipitation, frost action or seizmic event
- Direction of slip movement is almost always normal to the anticlines, synclines, thrust faults etc.
• Snow avalanches sometimes included here…
Debris Flow
• Rapid flow of muddy water with large amount of coarse material (e.g. boulders, trees, cars).
• Less water than mud flow.
• Poorly sorted.
*In valleys and mountainslopes
*From heavy seasonal rainfall or snowmelt
*Travel considerable distances
*may form ridges or levees along the sides of the valleys when they decelerate. (large cones or fans at the front of the flow)
Deglaciation
*glacialmarine -> non-glacial sediments
• Beware of unconformities: erosion boundaries between strata → loss of information.
• Erosion may go right to bedrock.
*Movement of the glacier ceases when there is no longer an accumulation zone.
*Deglaciation over large areas was accomplished by ice thinning and ice disintegration rather than the steady retreat of the ice margins..
*Dominant features are a vaiety of ridges and plateaus
• These deposits and other landforms are the clues with which our glacial history was reconstructed!
Degradation
Lowering of the land surface by erosion
In River..
=excessive erosion of the river bed (downcutting).
o Channel is locally lowered → slope decrease.
o Possible causes:
• Decrease in sediment load (e.g. end of glacial stage).
• Increase in flow (e.g. inter-basin flow diversion).
• Fall in base level (e.g. tectonic uplift).
Delta
Glaciolacustrine depositional landform
- Fan-shaped deposits where streams enter proglacial lakes.
- May be abnormally large due to the enormous load of sediment.
• Built where a river enters standing water (lake or ocean).
• Flatter, finer grained than alluvial fans.
• Exact shape depends on coastal processes.
*River drops load as enters a body of standing water (sea or lake)
*Fail to develop in areas with strong waves, currents or tides, or where the river carrier little sediment
Depositional Aeolian features
Ripples
Dunes
Loess deposits
Determinants of Channel Form
Discharge
Sediment Load
Sediment calibre
Slope
Diamiction
*Any poorly sorted mixture of mud, sand and rock fragments
*Tills are glacial diamictons
discharge
-Volume rate in water flow - includes loads that are transported in the volume
(Q) - the most important variable in determining channel morphology.
o Related to climate, position in watershed.
o Amount determines channel size; timing is important in determining style of channel.
- Q is the volume of water per unit time passing through a cross-section of a stream.
- Q = Av
- A = cross-sectional area (Wd), v = mean velocity.
- Or Q = w d v
• Maximum velocity occurs almost at the top / centre (or outside of a bend).
- Temporal: varies in response to changing precipitation, snowmelt inputs (seasonal, storm-scale).
- Discharge Hydrographs show changes in Q with time.
Dissociation
In chemical weathering (solution - leaching)
The separation of cations and anions and their dispersion in water.
- Dissociation of minerals in water.
- Ions added to groundwater, surface water.
- E.g. basaltic rocks in Hawaii → karst-like features
- mostly salts, gypsum, carbonate esp.
Dissolved Load
Sediment transport..
• Dissolved (solutional) load
– solute concentration is often estimated from the electrical conductivity of the water (doesn’t include dissolved silica, important in tropical rivers)
*Solutional load concentrations usually decrease with increasing discharge (high discharge also has less opportunity to pickup solute)
*During periods of low flow, concentrations increase as a result of evapotranspirational losses from chanls and the supply of groundwater
*Higher solutional load over limestone, dolomites or evaporites and low in areas of shield bedrock.
Distributary Channel
A river channel usually deltaic, that splits off from the main channel and does not rejoin it
Divergent Plate
Divergent margins:
o The ocean bottom is a vast lava plateau.
o Lava plateaux may also form when large cracks in the crust form in non-divergent settings.
*Large ridges or mountainchains develop beneath the oceans along the divergent margins
*New crust is created from volcanic material welling up into the gap
Drumlins
Continental Erosional Landform (Ice contact)
Rock drumlin:
• Like whalebacks, but asymmetrical.
• Steeper end up-glacier
• Dimensions: height up to 50 m, length up to several km.
- Drumlins
- Streamlined hills of till up to 60 m high.
- Usually teardrop-shaped (steep side up-glacier).
- Usually occur in groups (swarms or fields).
Drumlins formed under ice sheets are often distributed in bands that are paralell or perpindicular to the direction of ice movement. Direction of ice flow should not be based on a single drumlin, as a small proportion of the forms in drumlin fields have reversed profile shapes in relation to ice flow.
Dunes (Aeloian)
Aeolian landscape and landforms
Hills of windblown sand
Variable types of dune depended on sand availability, grain size and distribution, wind energy, vegetation etc.
Depositional form:
Barchans
Barchanoid ridges
Transverse dunes
Parabolic dunes
Coppice dunes
Coastal dunes
Longitudinal dunes
Star dunes
Loess deposits
Dunes (River)
Larger features, ranging up to a meter or more in height and spacing
*Rarely found in rivers with gravel beds
*Eddies form on lee side of Dunes
*Dunes advance downstream
At Higher velocities, antidunes develop, with a great increase in the amount of sediment moving along the bed.
*Antidunes move upstream because sediment is lost to saltation and suspension on the downstream side faster than it can be replaced
Earth flow
- Moderately rapid downslope movement of saturated soil / sediment. (Between creep and mudflow)
- Very common in old marine deposits (clays liquefy).
*Often develop from spreading of slumps and are also common where there are moderate gradients and clay or clay-bearing rocks.
Convergent plate
Where tectonic plates collide → intense geological activity.
• Subduction of one plate beneath another.
• Earthquakes.
• Chain of volcanoes.
• Folding and faulting.
• Joining of continents.
Effective normal stress
Effective Stress is a force that keeps a collection of particles rigid. Usually this applies to sand, soil or gravel.
ex. a pile of sand keeps from spreading out like a liquid because the weight of the sand keeps the grains stuck together in their current arrangement, mostly out of static friction. This weight and pressure is the effective stress.
End moraines
produced at front of actively flowing glacier.
• Terminal moraines: mark the farthest advance.
• Recessional moraines: mark temporary halts or re-advances of ice in a period of general recession.
*Made in front of an active or inactive glacier.
*consist of debris that was carried mainly at the bottom or on the top of the ice.
*Another type was formed where frozen sediments and bedrock were pushed and thrust upward into faulted blocks by the advancing ice sheet.
Englacial Till
-Located or occurring within a glacier, as certain meltwater streams, till deposits, and moraines
Equilibrium Line
separates accumulation and ablation zones.
• ~ the firn line.
• In reality, this is more like a zone.
*At the ELA - the snow and ice added in a balance year is exactly equal to the amount that is lost.
*Balance year is generally taken to be the time between two successive annual minimums in the mass of the glacier)
Erosion limited
A part of hillslope erosion
*weathering / sedimentation is faster.
- Unconsolidated material accumulates, covers bedrock.
* Typical of gentle-moderate slopes.
Erosional Landforms (Glaciers)
(Mechanisms and small features)
Mechanisms: Ice push, Abrasion and Plucking
Small Features: Polish, Striations, Grooves, Crag and Tails, Roch Moutonnees
Eskers
• Winding ridges produces by streams in tunnels beneath or upon the ice. (Glaciofluvial material)
*Mostly sand - but with gravel and cobble materials also
*Usually found relatively close to source - ~15kms
-Glaciofluvial deposits: like braided river, but maybe thicker - often disturbed due to loss of ice support (eskers)
Eustatic
**SEE TEXT FIGURE 13.11
o Glaciation → water stored in glaciers → sea level fall.
o Deglaciation → meltwater in oceans → sea level rise.
- Late Cenozoic:
- Sea level dropped eustatically by at least 100 m.
A global change of sea level resulting from a rise or fall of the ocean level rather than of a change in the level of the land.
*Eustatic changes in sea level in the Pleistocene were mainly cause by the growth and decay of ice sheets, but the changes in the volume of the ocean basins due to tectonics and sedimetation were important in the Tertiary.
Exfoliation
- Rocks tend to split into sheets parallel to the topography.
- e.g. granitic exfoliation domes (Yosemite)
- Produces ‘dilation joints’.
- Note: small-medium scale peeling off of rock slabs = ‘spalling’.
- Freezing water or chemical precipitation in cracks can assist exfoliation.
- Compression can also help.
Factorof Safety
(Fs) is used to define slope stability.
• Fs = S / τ.
• Fs > 1 → stable slope.
• Fs < 1 → unstable slope.
• Some slopes may exist temporarily in an unstable condition.
term describing the structural capacity of a system beyond the expected loads or actual loads. Essentially, how much stronger the system is than it usually needs to be for an intended load.
Faulting
fracturing of brittle rock from unequal stress; usually involves displacement along fault plane (plane of fracture).
• Sudden slippage along fault plane results in earthquakes
• 4 major types of faults:
1. Normal: relative vertical movement of crustal blocks along steep fault plane. Associated with rifting.
2. Reverse: associated with compressional forces. One block riding up over the other, producing very steep fault scarps.
3. Overthrust: akin to a low-angle reverse fault, one block rides up on top of the other along a near-horizontal fault plane.
• E.g. Canadian Rockies → 100s of km.
4. Transform (transcurrent or strike-slip): relative horizontal movement of crustal blocks along nearly vertical fault plane.
• E.g. San Andreas Fault
Fetch
- Fetch (area of water over which wind blows).
Wave energy is dependent on fetch, among other variables
Fining upward sequence
grain size is decreasing upward in the sandstone core/rock/outcrop.
A good example of a fining-upward succession is a river point bar
Point bars get their unique shapes because of the way water flows through curving channels like bends in a river. As the water enters the bend of the river the flow spins in a spiral. The flow is strongest on the outside of the bend causing erosion of the outer bank. As the water flows away from the outer bank and rises up the slope of the inner bank, or point bar, it loses some of its energy and begins to deposit sediments eroded from the outer bank. First the coarse grains are deposited near the base of the point bar and then the finer grains as the water flows towards the top of the point bar.
Firn Line
*firn is partially compacted snow or ice that is at an intermediate stage between snow and glacial ice
the zone of a glacier between the lower region of solid ice and the upper region, above which ablation occurs
Fjords
- Troughs invaded by rising ocean water.
- Very common on the BC coast, e.g. Alberni Inlet, Howe Sound.
Flashy Discharge
Flashy discharge is a type of flood characterized by short lag times between rainfalls and the
rapid rise and fall of floodwater because of urbanization.
Flash discharge is of higher magnitude (higher peak of discharge) because water is discharged
in a shorter time period.
Flows
• Movements of liquefied material → lots of water required.
- Failure usually begins on a plane.
- Often rotational.
• Debris is deposited in a lobe.
- Flows occur when:
- Large amounts of weathered material are available.
- Large amounts of water.
- Steep slope (if only locally).
Three principal types:
Mud flow
Earth flow
Debris flow
Folding
- Initial, plastic deformation of rocks under compressional stress (convergent margins).
- Most common / evident in sedimentary rocks.
- Anticlines (ridges) and synclines (troughs or valleys).
Foreset beds
A foreset bed is one of the main parts of a river delta.
It is the inclined part of a delta that is found at the end of the stream channel as the delta sediment is deposited along the arcuate delta front.
As the sediments are deposited on a sloping surface the resulting bedding is not horizontal, but dips in the direction of current flow toward deeper water. A cross-section of a delta shows the cross bedding in the direction of stream flow into the still water.
The foreset bed is formed when a stream carrying sediment meets still water.
When the stream meets the still water, the velocity of the water is decreased enough so that the larger sediment particles can no longer be carried and are therefore deposited.
The deposited sediment builds up over time, and a delta is formed.
Fraser Glaciation
- Peak of Fraser Glaciation = Vashon Stade (~ 14,500 years BP).
- Alpine glaciers expand, coalesce into major valley and piedmont glaciers.
- Large ice sheet advances down Strait of Georgia past Seattle.
- Overrides Vancouver Island, fills Strait of Juan de Fuca, may extend to continental shelf off west coast.
Associated Sea leve changes… Eustatic and Isostatic
Friction
Angle of internal friction/repose
- Texture
- Angularity of sediment
- Compaction
- Involved in sediment erosion
Frost action
- Repeated growth and melting of ice crystals in the pore spaces of rock.
- Liquid water seeps into joints.
- Expands 9% upon freezing → powerful force (e.g. Quebec highways).
- Factors in effectiveness:
- Ample water supply is critical.
- Frequency, speed and duration of freeze/thaw cycles may be important.
• Actual mechanism may be related to crystal growth and/or water pressure.
Gelifluction
Soil flow that refers to the movement of freeze-thaw surface material over permanently, seasonally or even diurnally frozen ground.
*Gelifluction usually periglacial land (sides of glaciers)
Geomorphic processes
Terrain symbol mapping..
• Natural mechanisms of weathering, erosion and deposition that result in the modification of the surficial materials and landforms at the earth’s surface.
mostly assumed to be active
Glacial troughs
- Glacier-carved valley.
- U-shaped cross-section .
- Typically straighter than unglaciated valleys
Glacier mechanisms
ice push
abrasion
plucking
Glaciers
**FIGURE 6.3 & 6.6 IN TEXT
- A glacier is a moving mass of ice that has its genesis on land.
- Glaciers are powerful geomorphic agents:
- Friction caused by moving ice → erosional landforms
- Deposition of eroded sediment → depositional landforms
Formation overview…
- Glaciers may form in any area with a year-to-year surplus of snow.
- Successive layers of snow are slowly compacted
- Snow crystals gradually become more dense, bonded with increasing burial depth and age (becoming ‘firn’).
- Firn crystals melt / squeeze together into glacial ice.
- Gravity slowly deforms and moves this mass of ice.
- Weight of glacier forces ice to deform in a plastic way → flows!
Glaciofluvial
Material Name - Fg (inactive)
- Produced by meltwater streams around glaciers.
- Deposits = ‘outwash.’ - sand and gravel
Deposits: Like braided river, but maybe thicker. Often disturbed due to loss of ice support (eskers, kames).
Outwash Plaines
Eskers
Kames
Glaciolacustrine
- Proglacial lakes often formed by the damming of a valley by a moraine or ice.
- Striking turquoise colour due to glacial rock flour in suspension.
Material name: Lg (inactive)
deposits: Fine-grained (clayey to sandy muds), finely stratified, unconsolidated, often including larger ‘dropstones’.
Deltas
Kames deltas
Kettles
Glaciomarine
deposits: As glacial lacustrine, but with more clay, marine fossils.
Material name: Wg (inactive)
Associated with meltwater streams in contact with the sea.
Graded Stream
o Over a period of years, slope is delicately adjusted to provide, with available discharge and prevailing channel characteristics, just the velocity required for the transportation of the sediment load supplied from the drainage basin (Mackin, 1948). but with no extra energy for erosion*
o i.e. stream has equilibrium slope
Gravel
A mixture of two or more size ranges of rounded particles greater than 2 mm in size (e.g., a mixture of boulders, cobbles and pebbles); may include interstitial sand.
Material: g
Ground Moraine
*plastered over the ground in the path of the glacier.
*consists of an irregular blanket of till deposited under a glacier.
*Composed mainly of clay and sand, it is the most widespread deposit of continental glaciers.
*Although seldom more than 5 metres (15 feet) thick, it may attain a thickness of 20 m.
Hanging Valleys
- Truncated where they meet a larger glacial trough.
- Often the sites of waterfalls.
Hot spots
Create Shield volcanoes and Intrustions
Shield Volcanoes: form when a plate passes over a stationary mantle plume. Usually built almost entirely of fluid lava flows
Intrusions: may form if magma cools before reaching surface. - igneous rock that was pushed into cavities of rock during its magma form.
• May be exposed by erosion later.
Isostatic
**SEE TEXT FIGURE 13.11
A state of balance that is maintained in the crust of the Earth. Distrubrance of this balance causes isostaic movements, which act to restore the balance. These movements, which act to restore the balance. These movements may involve uplft of the land to comepesate for erosion, or depression of the land to accomodate the weight of accumulated sediment.
Glacio-isostasy involves the depression of the land owing to the weight of a large body of ice, and uplift or rebound as a result of the disintegration or retreat of the ice.
Sea level changes..
o Glaciation → isostatic depression of crust into mantle → sea level rise.
o Deglaciation → isostatic rebound → sea level fall.
- Late Cenozoic:
- Land was isostatically depressed even more in places (variable).
Kame Deltas
• Deposited against ice in proglacial lakes.
*Glacial landform made by a stream flowing through and around glacial ice and depositing material as a kame(stratified sequence of sediments) upon entering a lake or pond at the end or terminus of the glacier, thus “in front” of it, a proglacial lake. *It is distinctive because it has been sorted by the action of the stream. This sorting is responsible for the stratified layers of silt, sand and gravel at the ice margin which create the delta. This landform may often be observed after the glacier has melted and the delta is visible.
*Often upon melting of the glacier the edges of the delta may subside as ice under it melts and glacial till may be deposited in the lateral or side area also as material is deposited from the melting glacier.
Kames
- Isolated hills of glaciofluvial sediment originally deposited in depressions in the ice.
- If between ice and valley wall, form is called a kame terrace.
- Often unstable after ice support is removed.
Kettles
- Depressions produced by melting blocks of ice.
- Ice block was buried in till and then melted.
- Usually occupied by a lake.
Lagoons
Coastal lagoons form along gently sloping coasts where barrier islands or reefs can develop off-shore, and the sea-level is rising relative to the land along the shore (either because of an intrinsic rise in sea-level, or subsidence of the land along the coast). Coastal lagoons do not form along steep or rocky coasts, or if the range of tides is more than 4 metres (13 ft). Due to the gentle slope of the coast, coastal lagoons are shallow. They are sensitive to changes in sea level. A relative drop in sea level may leave a lagoon largely dry, while a rise in sea level may let the sea breach or destroy barrier islands, and leave reefs too deep under water to protect the lagoon. Nybakken describes coastal lagoons and barrier islands as a “coupled system”. Coastal lagoons are young and dynamic, and may be short-lived in geological terms. Coastal lagoons are common, occurring along nearly 15 percent of the world’s shorelines. In the United States, lagoons are found along more than 75 percent of the eastern and Gulf coasts.[3][4]
- usually connected to the open ocean by inlets between barrier islands.
- The number and size of the inlets, precipitation, evaporation, and inflow of fresh water all affect the nature of the lagoon.
- Lagoons with little or no interchange with the open ocean, little or no inflow of fresh water, and high evaporation rates, may become highly saline.
- Lagoons with no connection to the open ocean and significant inflow of fresh water, may be entirely fresh.
- On the other hand, lagoons with many wide inlets, have strong tidal currents and mixing.
- Coastal lagoons tend to accumulate sediments from inflowing rivers, from runoff from the shores of the lagoon, and from sediment carried into the lagoon through inlets by the tide.
- Large quantities of sediment may be occasionally be deposited in a lagoon when storm waves overwash barrier islands. Mangroves and marsh plants can facilitate the accumulation of sediment in a lagoon. Benthic organisms may stabilize or destabilize sediments.
Lahars
volcanic mudflows initiated by rapid melting of snow and ice.
• e.g. Nevado del Ruiz, Colombia, 1985 → lahar 40 m high wiped out town of Armero, killed 23,000 people.
• Danger from Mount Rainier.
Lateral Moraines
near the side margin of a valley glacier.
*Lateral moraines are parallel ridges of debris deposited along the sides of a glacier.
*The unconsolidated debris can be deposited on top of the glacier by frost shattering of the valley walls and/or from tributary streams flowing into the valley.
*The till is carried along the glacial margin until the glacier melts.
*Because lateral moraines are deposited on top of the glacier, they do not experience the postglacial erosion of the valley floor and therefore, as the glacier melts, lateral moraines are usually preserved as high ridges.
Lava Plateau
Ocean bottom is a vast lava plateau at divergent margins
-May also form when large cracks in crust form in non-divergent settings
*Basic lava produce very flat plateaus when in enormous quantities
Loess Deposits
- windblown silts – cover large parts of the globe
- during the deglaciation, large volumes of wind-blown silt or loess gets blown onto the unglaciated landscape
- low latitude deserts also are a major source of global loess much of which gets deposited widely in the oceans
- Loess often makes up a significant component of the B-horizon and is considered a dilutant to the native weather bedrock regolith.
Longitudinal (linear) dunes
- Linear dunes are straight or irregularly sinuous, elongate sand ridges
- They are aligned parallel to the forming wind and are often wider and steeper at the upwind side, gradually tapering until they merge with the desert surface.
- often wider and steeper at the upwind side, gradually tapering
- Curving linear dunes sometimes called ‘seif dunes’
- Form in unvegetated areas, often on bedrock.
- Occur in warm deserts
- Wind regimes responsible for linear dunes are usually more directionally variable than those associated with barchans or parabolic dunes
Longshore bar
A ridge of sand, gravel, or mud built on the seashore by waves and currents, generally parallel to the shore and submerged by high tides. Also known as offshore bar.
Visible at low tide as a sand bar, or a ridge of beach sediment sharing the general contour of the shoreline itself, a longshore bar is actually a feature sculpted by the push and pull of years of waves. It only seems to share the general contour of the shoreline because the break point of the waves (a point determined by depth) tends to be equidistant from shore—which itself has of course been rounded off or leveled by waves—lending any bar that shares its contour a generally level, or straight, appearance. However, this is just a function of the break point: the bottom current necessary to feed the shoreward current of a wave pulls silt in with it, then, the moment the wave breaks, deposits it, in the same place, time after time. That deposit—that steady accretion of silt—is the longshore bar. Due to the redistribution of silt, there will often be a trough between the longshore bar and the beach itself. Seaward of the longshore bar are other longshore bars at the break point of larger waves.
Longshore drift
**FIGURE 13.4 IN TEXT
- Sideways = longshore or littoral.
- This occurs because waves rarely arrive perfectly normal to shoreline.
- Often there are prevailing longshore currents in an area.
- May vary seasonally (e.g. Ross Bay).
Varying texture along beaches
Meandering
**FIGURE 11.10 IN TEXT
Symbol: M
• Typical conditions:
o Predictable discharge.
o Low-moderate slope, moderate-high sinuosity.
o Sediment calibre up to sand or fine gravel.
• Some characteristics:
o One main channel.
o Classic cutbank / point bar / pool / riffle sequences.
Medial Moraine
between two coalescing glaciers.
Often extend downstream on the ice surface from the point where two lateral moraines join at the spur of valley confluences
*Essentially ice ridges protected from the Sun’s heat by a surface layer of debris, they are conspicuous features of contemporary valley glaciers
*Most have not survived deglaciation in a recognizable form, though they may produce chains of kettles and hummocky topography on the floors of mountain valleys
Neap Tide
Smallest range (moon and sun at right angles)
*Tides vary depending on the positions of the sun, and moon around the Earth..
*the opposition of the graviational attractions of the moon and sun produces tides with a minumum tidal range
Normal Fault
A geologic fault in which the hanging wall has moved downward relative to the footwall. Normal faults occur where two blocks of rock are pulled apart, as by tension.
A normal fault occurs when the crust is extended. Alternatively such a fault can be called an extensional fault. The hanging wall moves downward, relative to the footwall.
Outwash Plain
• Broad plains formed by deposits from proglacial braided streams at or beyond the ice terminis
*sands and gravels
• Very wide, active.
• When dry, becomes the source for fine wind-blown material called loess.
Oxbow Lake
An oxbow lake is a U - shaped body of water formed when a wide meander from the main stem of a river is cut off to create a lake.
This landform is so named for its distinctive curved shape, resembling the bow pin of an oxbow.
Parabolic dunes
- In plan view, parabolic dunes are u-shaped mounds of well-sorted sand with two elongate arms that extend upwind.
- Slip faces occur on the outer (convex) side of the nose and on the outside slopes of the elongate arms
- often occur in semiarid areas where some precip is common (and Vegetation)
- arms are typically anchored by vegetation, and wind erodes sand from the central zone, and deposits it on the leeward slope - central part migrates downwind.
- often associated with blowouts, which provides the sand.
Plucking
- Removal of blocks of rock from outcrops by ice.
- Exploits rock weaknesses along existing fractures / joints.
*As a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints in the bedrock. The freezing and thawing action of the ice causes cracks in the bedrock through hydraulic wedging. Eventually these joint blocks come loose and become trapped in the glacier.
Point Bar
*Depositional feature made of sand and gravel that accumulates on the inside bend of streams and rivers below the slip-off slope. Point bars are found in abundance in mature or meandering streams.
*They are crescent-shaped and located on the inside of a stream bend, being very similar to, though often smaller than, towheads, or river islands.
*well sorted sediment that typically reflect the overall capacity of the stream.
*very gentle slope and an elevation very close to water level.
*often overtaken by floods and can accumulate driftwood and other debris during times of high water levels.
*A point bar is an area of deposition whereas a cut bank is an area of erosion.
*Point bars are formed as the secondary flow of the stream sweeps and rolls sand, gravel and small stones laterally across the floor of the stream and up the shallow sloping floor of the point bar.
Proglacial lakes
often formed by the damming of a valley by a moraine or ice.
• Striking turquoise colour due to glacial rock flour in suspension.
*Is in contact with the ice front along part of its margins.
Reverse Fault
A reverse fault is the opposite of a normal fault—the hanging wall moves up relative to the footwall. Reverse faults indicate compressive shortening of the crust. The dip of a reverse fault is relatively steep, greater than 45°
Riffle-pool
the usual channel pattern.
o Low-moderate sinuosity.
o Moderate sediment transport.
*Undulating beds of gravel that form a sequence of bars, pools, point bars and riffles. The pools are rhythimically spaced, about five to seven channel widths apart. They have moderate to low gradients and are generally unconfied, with well-established
Rill Erosion
- If slopes are steep enough and rain intense enough, sheet flow will concentrate into little streams.
- These can cut small channels called rills.
- Several cm wide / deep
- Occur on relatively smooth surfaces.
- Parallel rills develop along the slope.
Rills may join to form gullies
Rip current
*a strong channel of water flowing seaward from near the shore, typically through the surf line
*Typical flow is at 0.5 metres per second (1–2 feet per second), and can be as fast as 2.5 metres per second (8 feet per second), which is faster than any human swimmer.
*They can move to different locations on a beach break, up to tens of metres (a few hundred feet) a day. They can occur at any beach with breaking waves, including oceans, seas, and large lakes.
*When wind and waves push water toward the shore, that water is often forced sideways by the oncoming waves. This water streams along the shoreline until it finds an exit back to the sea or open lake water. The resulting rip current is usually narrow and located in a trench between sandbars, under piers or along jetties.
*This strong surface flow tends to damp incoming waves, leading to the illusion of a particularly calm part of the sea, which may possibly lure some swimmers into the area.
Ripples
Depositional landforms from Aeolian process
*smallest landform, asymmetric
• 5–25 cm, h 0.5–25 cm
• indicate flow & transport direction
• size (h) & spacing (λ) controlled by grain size & windspeed
• height controlled by ability of wind to entrain coarser particles from crest
• ripple crests are typically coarser on ‘active’ upwind slopes with finer grains in the sheltered lee zone
Fluvial Ripples…
*on riverbeds, they may be up to several cm in height and spacing
*Low river velocity and placid water surfaces
*the small amount of sediment that is moved under these conditions is restricted to single grains on the riverbed.
Roche Moutonnees
Small Erosional Feature
• Asymmetrical rock knobs.
• Smooth, gentle up-glacier slope (due to abrasion) - with striations in the direction of flow
• Features grooves, striations and polish.
• Rough, steep slope down-glacier (due to plucking).
*Most likely to develop near the termini of warm glaciers, where the glacial ice is thinner
Scroll bars
*Result of continuous lateral migration of a meander loop that creates an asymmetrical ridge and swale topography on the inside of the bends.
*The topography is generally parallel to the meander and is related to migrating bar forms and back bar chutes which carve sediment out from the outside of the curve and deposit sediment in the slower flowing water on the inside of the loop, in a process called lateral accretion.
*Scroll-bar sediments are characterized by cross-bedding and a pattern of fining upward.
*These characteristics are a result of the dynamic river system, where larger grains are transported during high energy flood events and then gradually die down, depositing smaller material with time.
Sea Stacks
Erosional Coastal Landscape
*consist of steep and often vertical column or columns of rock in the sea near a coast, isolated by erosion.
*Formed over time by wind and water, processes of coastal geomorphology.
*They are formed when part of a headland is eroded by hydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks and even a small island.
Shear Stress
Driving force = downslope component of weight (mass X gravity)
-variable on factors like grain size, packing coefficient, sediment density, angle of internal friction
*The downslope component of the fluid weight exterted on a particle on a bed.
-• τ = h*y*sinβ*cosβ where
τ = shear stress
h = vertical thickness of material above the potential failure plane
y = specific weight of material
β = slope angle
Sheet Erosion
A type of hillslope erosion
- Erosion as a result of sheet flow: overland flow that forms a thin layer of water over a smooth surface.
- Removes particles in thin layers by precipitation and overland flow.
Slump
Deep seated rotational slide, but not much downslope movement. eg - Dallas
*slumps take place along curved surfaces that are concave upward, and tehy usually extend to greater depths that translational slides.
*Slumps usually require deep perolation of water and thus may take place long after the rain has ended.
*Clay and shale deposits esp vulnerable
*Leaves a steep scarp
*further slumping will continue until a more stable slope of low gradient is attained.
Solifluction
‘Soil flows’
*refers to a wide range of mass movements in a variety of climatic environments.
Spit
Depositional Coastal Landform
Long narrow ridges of sand and pebbles attached at one end to the coast and terminating at the other in the sea
*Sediment moving alongshore often builds spits at the mouths of estuaries and at other places where there is an abrupt change in the direction of the coast.
*Most spits extend along the original line of the coast, reducing irregularities
Spring Tide
= largest range (moon and sun together or opposed).
Tidal range is at it’s maximum.
*occurs twice a month, when the sun, moon and earth are roughly aligned.
Star Dunes
- Star dunes are isolated, pyramidal, somewhat irregularly shaped to symmetrical mounds of sand with three or more arms radiating from a central high point (with approx radial symmetry)
- arms can vary in length, width, number, and shape, but each has a slip face
- develop from winds that blow from several opposing directions, either a result of seasonal shifts or where secondary wind flow patterns are produced by topographic barriers
- isolated star dunes grow mostly upwards and it’s not uncommon for them to reach heights of 200-300 m.
- very low lateral migration rates (cm/yr)
Step-pool
morphologically comparable to rapids in small headwater channels
*consist of a staircase series of steps formed by accumulations of large cobbles and boulders that ay be trapped against bedrock obstructions.
*scour pools containing finer material develop downstream of the steps, creating high energy zones, of a characteristic length in which it is unlikely that other steps would be able to form.
*Distance between pools is typically between one and four times the width of the channel.
Straight River
- Uncommon in nature → usually in areas of very low stream power (i.e. low slope) or geologic control.
- Typically contain alternating pool / riffle sequences.
*usually have bars that alternate as they down downriver and the thalwag meanders a little
*
Stratified drift
Glacial meltwater (proglacial streams and lakes)
-Depositional landforms occur via transportation of either Ice or Glacier meltwater…
Sediments deposited by glacial meltwater that are sorted and layered; a major subdivision of glacial drift that includes river, lake, and marine deposits
Stratovolcanoes
Convergent margins..
Subduction -> plate melts -> rising magma forms stratovolcanoes
*cones consisting of interbedded lava flows and pyroclastic layers
*Their lava is less fluid like than shield volcanoes and their eruptions are therefore more explosive
*Steep sides - 10-35 degrees
Striations
Small erosional feature
due to abrasion
Generally in the direction of glacial flow
*ca sometimes be seen on clast surfaces
*absent on supraglacially or englacially tranported debris and are found on only a small porportion of the meterial carried at the base of the ice
*Most common on facets and on stones embedded in lodgement till and overridden by the ice
*Some striations may cross in areas where the rocks were rolling.
Strike-slip
Faulting: Relative horizontal movement of crustal blocks along nearly vertical fault plane eg - san andreas fault
Movement parallel to the strke of the fault surface, so that the blocks on either side of the fault move sideways past each other.
Earthquakes along strike slip faults:
As two plates try to slide past one another, friction prevents them from moving. Strain builds as a result. Eventually the rock breaks and suddenly releases all this built-up energy in the form of vibrational, or seismic, waves. The seismic waves spread in all directions away from the breaking rock. When these waves reach Earth’s surface, they cause the ground to move. This is called an earthquake.
Subduction Zone
*Subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate and sinks into the mantle as the plates converge.
*Regions where this process occurs are known as subduction zones.
*That is, the subducted lithosphere is always oceanic while the over-riding lithosphere may or may not be oceanic. Subduction zones are sites of high rates of volcanism, earthquakes, and mountain building.
Swash
Wave induced current..
Forward=swash
-Turbulent layer of water that washes up on the beach after an incoming wave has broken.
*The swash action can move beach materials up and down the beach, which results in longshore transport
*The time-scale of swash motion varies from seconds to minutes depending on the type of beach.
*Greater swash generally occurs on flatter beaches.
*The motion plays the primary role in the formation of morphological features and their changes in the swash zone.
*The swash action also plays an important role as one of the instantaneous processes in wider coastal morphodynamics.
Swell
• Swells (summer conditions) tend to build the berm, steepen the beach face (depositional).
*Swell waves are fairly consistent in frequency and direction, especially in the Southern Hemisphere - longshore sediment transport is therefore more constant that in storm wave environments.
Tectonics in BC
Terrain Mapping
o Divide landscape into morphological units.
o Classify terrain polygons.
o Uses: landslide hazard, suitability for building, forestry, etc.
Three types of sediment transport
- suspended (wash) load transport
- Bedload transport
- Dissolved (solution) load
- Sediment load is highly pulsed – dependent on sediment supply
- As Q rises, so does river’s ability to erode and transport sediment
- Sediment load (Qs) generally increases with Q.
- Assuming adequate sediment supply exists… may vary seasonally or between watersheds.
- River-bed sediment has shear strength related to texture, bed structure, lithology, etc..
Tombolos
Depositional Coastal landscape
*Beach formations that connect islands to the mainland or islands to islands. Tombolos develop on the lee side of islands because of the shelter provided from strong wave action and the refraction and convergence of the waves behind islands.
Translational slide
*The planar rupture surface is roughly parallel to the ground surface and at fairly shallow depths
*fault lies along discontinuities in the sediment or soil
Transverse dunes
- Transverse dunes are a variety of crescentic dune ridge similar to barchanoid ridges, but are much straighter in plan view
- most likely dune pattern if winds are unidirectional and sand is free to migrate
- usually free of vegetation and form long ridges
- the two flanks of transverse dunes have different angles: a gentler stoss side and steeper lee side
- Resemble linear dunes, except that they are aligned normal to wind direction and linear dunes have equally steep flanks.
- Migrate in a direction normal to their ridges (e.g. along wind direction), while linear dunes migrate longitudinally along the long axis of the ridge.
Truncated spurs
Glaciar has chopped off ends of rock ridges to form smoother, truncated spurs.
Tsunami
Very long waves that are generated by earthquakes associated with vertical crustal movements.
Then, when it hits the shallow water, the wave grows larger, as it still has the energy it did in the deep end, but not the wavelength, so it goes higher.
Two main components of moving glacier
Accumulation zone abover the equilibrium line altitude, where snow and ice is gained in winter than is lost in the summer
Ablation zone below the ELA, where more snow and ice is lost in the summer that is gained in the winter.
Types of river channels
**FIGURE 11.8 IN TEXT
Unloading (pressure release)
- Deeply buried rocks are under high pressure
- Erosion removes overburden → rocks expand!
- Rocks tend to split into sheets parallel to the topography.
- e.g. granitic exfoliation domes (Yosemite)
- Produces ‘dilation joints’.
- Note: small-medium scale peeling off of rock slabs = ‘spalling’.
- Freezing water or chemical precipitation in cracks can assist exfoliation.
- Compression can also help.
Ventifacts
Aoelian abrasional process.. created by abration by saltating sand grains
-wind eroded forms of various shapes and sizes
abrasion concentrated at the foot of rocks. creating a pedistal
Volcanic Landforms
- Landforms built by extrusion of magma from constricted openings in earth’s surface
- Lava and tephra (solid fragments from ash to boulders) cool and form a variety of features.
Divergent margins
Convergent margins
Hot spots
- Intrusions may form if magma cools before reaching surface.
- May be exposed by erosion later.
Wandering Gravel Bed River
- Transitional form between braided and meandering.
- Occasional, stable, vegetated islands.
*A common type of iver pattern in mountainous regions is transitional between the braided and meandering states
*laberally unstable gravel-bed rivers consist of stable reaches with single channels alternating with unstable, sometimes breaded reaches with multiple channels
*develop as the supply of coarse, generally glacial sediment is gradually exhausted
Wave Refraction
**FIGURE 13.2 IN TEXT
- Shoaling causes wave crests to conform to bottom topography. DIAGRAM
- They are almost parallel to shore by the time they break.
- Wave energy is concentrated on headlands, diffused in bays.
- This tends to promote coastal straightening over time (assuming homogeneous coast materials and topography).
Wave Shoaling
- Due to bottom friction, waves slow down. or ‘shoal’, when they enter shallow water.
- Individual waves in wave sets begin to ‘catch up’.
- E must be conserved → C and λ are reduced, so H must increase.
- When steepness > 1, wave is unstable and begins to break.
*the effect by which surface waves entering shallower water increase in wave height (which is about twice the amplitude). *caused by the fact that the group velocity, which is also the wave-energy transport velocity, decreases with the reduction of water depth.
*Under stationary conditions, this decrease in transport speed must be compensated by an increase in energy density in order to maintain a constant energy flux
*Shoaling waves will also exhibit a reduction in wavelength while the frequency remains constant.
Wave-cut terraces
Erosional coastal landform
*narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by the erosion of waves.
*Wave-cut platforms are often most obvious at low tide when they become visible as huge areas of flat rock.
*Sometimes the landward side of the platform is covered by sand, forming the beach, and then the platform can only be identified at low tides or when storms move the sand.
Weathering Front
Interface between weather material and bedrock
*point of contact between regolith and underlying rock
Weathering Limited
A part of hillslope erosion process
erosion is faster than weathering / sedimentation.
• Usually, bare rock is exposed.
• Typical of steep slopes.
Whalebacks
- Streamlined, glacial-smoothed hills oriented parallel to ice flow.
- Height of 1 to 10 m and a length of 1 m to several km.
Yardings
Aeolian abrasion process..
-elongated, wind & sand eroded ridges that tend to occur in groups
