Chapter 5 part 1 Flashcards
a) Divergent
plates moving apart, new oceanic crust formed @ rift, faulting
b) Convergent
: collision of plates, subduction, earthquakes, volcanoes, folding/faulting
c) Transform
plates moving past each other, earthquakes
Plate Boundaries
a) Mid ocean ridges + Continental Rifts (divergent)
b) Subduction zones, ocean crust dives down more buoyant plate (convergent)
c) Transform, lateral motion and shear
3 Types of Convergent Boundaries
a) Ocean subducts under continent (Andes)
b) Ocean subducts under ocean (Philippines, Aleutians)
c) Continent vs Continent, no subduction (Himalayas)
- Types of faults:4
a) Normal:
b) Reverse:
c) Overthrust:
d) Transform:
- Why does weathering happen
Rocks formed within the crust-high P,T
Unstable under surface conditions
Products from weathering=more stable
Controls on rate of weathering
a) Mineralogy
b) Petrology
c) Climate
d) Vegetation
- Weathering
In-situ breakdown and alteration of earth forming materials (physical and chemical)
- Weathering Front:
Interface between weathered material and bedrock
- Weathering Profile
Degree of weathering intensifies as you move closer to surface
- Soils (weathering)
• Most active part of the weathering zone’
Active processes (soil)
a) Organic accumulation + decay
b) Oxidation (of Fe + Mn common)
c) Reduction (gleying) of poorly drained soils
d) Ground water movement- moves clays and metal ions down to humid climates ~ evaporation moves salts up
e) Bioturbation-roots, animals + bugs
f) Microbial activity, fungi etc…
- Soils + Horizons O
Organics
Soils + Horizons A
Top soil
Soils + Horizons E
Zone of eluvation
Soils + Horizons B
Zone of illuvation/ accumulation
Soils + Horizons C
unlatered-ish parent material
Mechanical breakdown
Self explanitory…
Unloading
erosion removes overburden, thus rocks expand + crack
Thermal expansion
heating + cooling, needs frequent extreme fluctuations
Frost action
repeated formation + melting of ice in pores, water expands ~9% upon freezing
Wetting +drying- swell
wet, crack=dry, most effective with clay rich rocks + sediments?
Salt crystal growth
precipitation of salt crystals in rock pores, typical of dry climate + coasts
Root action
plants grow into joints etc… of rocks
- Chemical Weathering (decomposition)
• Secondary minerals (clay) are produced + more prone to dissolution/erosion
Most important agent of weathering
water
• Hydrolysis
breakdown of water into H+ and OH- ions
a) H ions replace metal cations in rock
b) Accelerated if there’s CO2 in water
• Oxidation:
a) Addition of O2 to minerals- forms oxides (rust)
b) Opposite of reduction, available O grabs electron
c) Most effective in aerated presence of air +water
• Solution:
a) Dissociation of minerals in water
b) Ions lost to groundwater/surface water-more effective in acidic waters
c) Salts, gypsum, carbonate especially prone to this… No new weathering products
• Carbonation:
a) Solution of minerals in carbonic acid (water + CO2)
b) CO2 from atmosphere, decaying organic matter
Felsenmeer
block field topography (Frost Action)=Alpine areas + Arctic/Antarctic
Karst-formed
carbonation (limestone)=humid climate
• 3 phases to sediment movement
a) Erosion
b) Transport
c) Depostion
• Sedimentary processes
requires weathering, sediment=fragments of rock that have moved from their original position
• Slopes may be:
a) Weathering limited
b) Erosion limited or
c) Equilibrium
Typical forms of slope
a) Convex upper slope (erosional)
b) Straight mid slope ( transport)
c) Concave lower slope ( depositional
Management implications (slope)
a) Erosion may increase with more surface runoff=weaker slope
b) Possible causes: Land clearing, roads, farm equipment, ranging livestock
a) Erosion may increase with more surface runoff=weaker slope
b) Possible causes: Land clearing, roads, farm equipment, ranging livestock
- Mass Wasting
Spontaneous downslope movement of soil or rock material primarily under the influence of gravity (water’s important for this role)
Erosional Mass Wasting landforms
cliffs, scarps and gullies
Depositional Mass Wasting landforms
various types of debris blocks, piles, lobes, cones etc
- Colluvium:
sediment deposited by mass wasting + other hill slope processes
- Colluvium:Properties
- Unsorted
- Low-moderate compaction
- Often angular(source material?)
- Un-stratified or weakly stratified
Mass Wasting occurs when
driving forces > resisting force
a Driving force
downslope component of weight (shear stress) [mgsinβ]
b) Resisting force
(shear strength) (S) with components; [ mgcosβ
c) Friction (angle of internal friction/response)… has to do with (mass Wasting)
texture, angularity and compaction
e) Water content
pore pressure
f) Factor of Safety
used to assess slope stability. If
1) Fs>1 stable slope
2) Fs,1 unstable slope
Thus stable slopes eventually fail because
rain/snowmelt, over-steeping, loading, earthquakes or just weathering
Creep Def:
1) Slow, shallow downslope movement of soil or sediment.
Creep Main mechanisms
a) Freezing/thawing
b) Wetting/drying
Creep indicators
: uphill-bent trees, tilted poles, folded strata, small terraces
Slides Def:
sliding of masses of rocks and or sediments with variable speeds
Characteristic of slides
a) Failure with a distinct plane
b) Usually a pre-existing weakness
c) Opening for water, thus less friction
d) Translational or rotational
e) Slumps-deep seated rotation with minimal downslope movement (Dallas rd)
Debris Avalanches
sliding material often disintegrates, fast, and referred to snow/ice
Flow
Movement of liquefied material with debris forming a lobe.
Flow Occurs when
a) Large amounts of weathered material available
b) Lots of water
c) Steep slopes
Mud flow
Rapid, mostly fine sediments and water that’s common with steep, arid regions ~ Lahars with volcanoes
• Earth Flow
slow to moderately rapid movement with saturated soils/sediments and are common with marine clays
• Debris flow
Rapid, muddy water with course material (trees, boulders, dead animals etc..) and are common in BC mts that deposit poorly sorted material
Falls
Free fall of soils or rock (very steep slopes) form talus(scree) @ base of cliffs
Types of mass wasting
Creep
slides
Debris Avalanches
Flow-mud,earth, debris
- Streams/rivers
channelized flow/runoff
Functions of streams
Sediment dynamics create channel form
Important for fish habitat, engineering, water supply, irrigation etc…
Drainage networks/watersheds (Horton system of stream ordering)
Flow amounts
Most important variable
• Discharge (Q=wdv)
• Related to climate +position in watershed
• Determines channel size/style
- Flood prediction
Magnitude-frequency analysis
Bad flood prediction because
problems are that records are short, spread out and often heterogeneous
• Sedimentary processes Streams (erosion)
1) Erosion of material that was removed from bedding or banks with erosional landforms such as cutbanks, thalwags, scour, pools and canyons.
• Sedimentary processes Streams (Transport)
2) Transport meaning either, suspended in water column or dissolved
• Sedimentary processes Streams (Deposition)
3) Deposition when water slows down… sediment texture reflects flow velocity with depositional landforms such as: bars, floodplains etc..
- Determinants of Channel form (variables)
Discharge (Q), sediment load (Qs) Texture (D) and slope (S) ~ sinuosity
Small Channels:
a) Low stream order/discharge
b) Usually steep=high velocity
c) Usually course bedding material
d) Width>depth
e) Common patterns: step-pool(steepest) or Cascade-pool. Both have low sinuosity + low sediment transport
Intermediate Channels
a) Higher order/discharge
b) Moderately steep slope
c) Width»depth with large woody debris + stones
d) Riffle pool channel most common (low sinuosity, sediment transport)
Large Channels
a) Higher discharge
b) Wider valleys/floodplains
c) Slope usually < 1°
d) W»>D
• Straight (channel)
low sinuosity with a single channel a) Uncommon in large rivers, usually steep slopes (small stream) or geologic control (large) with Pool/riffle sequences
• Braided (channel)
low sinuosity with multi channels c) Multi small shallow and low-sinuosity channels with many bars and usually unstable with floodplain less distinct. Typical of an erratic discharge regime and a relatively steep slope with course bedding material( >sand) and has a large sediment load
• Meandering
b) Regular cutbank/point bar/pool/riffle sequences and a distinct floodplain. Typical with regular discharge regime and sediment texture (sand-fine gravel)
• Anastamosing
d) Intermediate or between braided and meandering that forms multi, stable and low sinuosity channels with well-developed levees and many vegetated islands. Floodplain is clearly distinct with typical regular or predictable flow regime with a low-moderate slope.
• Wandering
e) Transitional between braided and meandering with 1 main channel and 2 secondary channels having a gravel bed and an occasional, stable, vegetated islands.
- Depositional Zone
All rivers end somewhere and when they do… sediments are dropped (in oceans, lakes or larger rivers) that create these forms;
Alluvial fans
Sloping fan shaped deposits in larger valleys. Vary from gravity flowed (colluvial fans ~ poorly sorted with steep gradient) to fluvial flow (fluvial fans with braided stream sands or gravel and a relatively low gradient)
Deltas
when a river enters lake or ocean. They are flatter and finer grained then alluvial fans with their shape dependant on coastal processes (tides, waves
Channel Gradation
has an exact slope needed to move its sediment load given its discharge regime ~ Aggradation=excessive deposition of sediment or degradation=excessive erosion of the river bed
Fluvial Sediments (alluvium):
happen on bars and floodplain that have diverse properties that depend on the depositional situation… properties of channel sediments: well rounded, well sorted, clast-supported, non-compacted and rich in sedimentary structures(cross bedding) whereas the properties of a floodplain sediments are usually: silty and fine sands, organics with horizontal bedding.
• Implications for stream ecosystems could be: (Dam Building)
1) Habitat loss, fragmentation or degradation
2) Water quality changes (temp, O2, Nutrients)
3) Invasive species no colonizing
4) Riparian succession
Primary changes to a river (Dam building)
: Flow magnitude and timing, sediment supply or cut off by the reservoir whereas,
Secondary changes (Dam building)
above… becomes a lake and below the dam… degradation or aggradation, bedding material changes, and channel size +pattern changes
River regime
seasonal variability in the water balance with 4 main river regimes;
4 Main river regimes
1) Snow/ice melt
2) Temperate Oceanic environments
3) Tropical, non- equatorial river system
4) Equatorial
Highest erosion Conditions-
sparse vegetation or heavy rainfall, sediment yield/unit area is highest for small rivers and Calibre of sediments vary
Sediment affected by anthropogenic
poor agricultural practises, construction and deforestation
Dominant Discharge concept
rivers erode and receive sediment input during flood events, of which the flood with the most geomorphological work
Dominant Discharge concept a) Large floods
most potential to erode + transport
Dominant Discharge concept medium floods
occur more frequently (most influential)
Dominant Discharge concept small floods
cannot mobilize course fragments
Perturbation
caused by tributary inputs and bank collapse
- Channel bed morphology
Downstream fining of bed material particle size and rounding.
Erosion + depositional bedforms include
pool-riffle sequences, Dunes and anti-dunes, Bars(variability in grain size) etc…
- Littoral Zone:
interface between land and water body. It extends inland usually several km’s from the point of wave break to backshore
Coastal Landscapes
all coasts feature either a combination of erosional and depositional processes/landforms.
- Erosional features can be classed 3 ways;
a) Headlands + bays
b) Caves, arches and stacks
c) Cliffs +wave-cut platforms
- Depositional landforms
a) Beaches, spits, bay barriers, tombolos, lagoons, dunes, deltas
- Waves
• Friction of wind on water creates waves… energy source for most coastal geomorph processes
Wave energy
a) E depends on, wind strength + duration and fetch
b) Wave modification
refraction ~ conforms to bottom topography ad becomes almost parallel to shoreline
Wave refraction results in:
Energy is concentrated on headlands( Erosional), Diffused in bays ( depositional- beaches)
Promotes Coastal Straightening over time.
Wave induced currents Result
Sediment zigzags along coast in multiple jumps
Wave induced currents Shore-normal
Swash and back wash- Undertow, rip currents
Wave induced currents (longshore or littoral)
Direction depends on incoming waves
Swash zone Processes (longshore)
Uprush (swash) Water sinks and backwashes and lifts sediments back obliquely into swash zone= Net result= beach drift
Beaches are
depositional
Energy Dissipaters
Highly Transient
Components of t beach
Step bar berm beach face low tide terrace
Beach profile
Shape and steepness related to wave conditions
Steep vs gentle profiles
Steep is reflects, gentle dissipates
Swells vs Storm waves
(summer vs winter)
Storm beaches
Storm surge : high winds pile water up
Builds abnormally high beaches
beach sediment properties
Highly sorted: Fine particles washed away
Texture of beach sediments
is proportionate to wave energy
