Dynamic Landscapes Flashcards
Sediment flux is controlled by the what?
balance between existing and driving forces.
What is sheer stress
Stress component which measures ability to withstand sheering stress. Basically is about the critical velocity for movement of particles.
What do Wolman and Miller acknowledge about frequency and magnitude of events
50% are slow events
What % hydroelectirc power comes from Norwegian glaciers
15%. Glaciers hold 77% global freshwater
What are cirque glaciers and valley glacier
Cirque: High in mountains
Valley: Fills a valley and is larger
What are ice sheets vs ice shelf and ice streams.
Ice sheets made of ice caps. Ice shelf move over the sea and the ice streams are the parts that move, while the shelf acts as a buffer ti prevent quick movement
What control the amount of regression v advancing in glaciers
Levels of accumulation v ablation
What is a bergschrund
Glacier is against the mountainside and this creates a crevasse behind. As the glacier moves the crevasse enlarges
What is a secrac
A small chunk of glacier - cause by ice falls
What do Ogives show
The flow of glacier due to the colours
What are the 3 movements of glaciers
Creep: glacier moves over own weight as its semi-viscous (glens law)
Basal sliding: move due to layer of melt water
Subglacial deformation: 90% of all movement and due to sediment on an unconsolidated bed
Who came up with subglacial deformation
bOulton 1979
What is glacier thermal regime
Idea that pressure melting point varies depending on pressyure on water (more = freeze in warmer condition)
COld glaciers - dont move as much only creep
warm - move and geomorphologically active
What are the 3 terms for deposited sediment based on loctaion?
- Supra - on top
- Englacial - inside
- Subglacial - underneath
What i a median moraine
Medial moraine forms when 2 glacier meet and join - supraglacial
What are debris cones
These ate when the debris bands become exposed
What are stiration
When big rocks in glaciers cut into bedrock and create rock flour. Meltwater flushes this flour, but can cause bed separation - however, removal of flour is good as it can stop abrasion.
In what % of glaciers is debris rich basal ice found
10%
What is roche moutonee (small scale erosion)
glaciers pluck rock from the uneven land which causes uneven surfaces to continue
What are 3 large erosions caused by glaciers
Cirque - hollows in mountainside
Trough- creates fjords
Arete- glacial valleys leave behind the points of the mountains
What is glacial sediment till and what does it usually compromise of (3 things)
Material on surface is deposited = till. It is clats (stone) whcih rests in finer matrix. Often has oriental clats.
WHat does supraglacial till not have
fabric as it is deposited from above
What are the 3 types of subglacial till?
- Melt out till - melt of debris rich basal area and preserved in hard rock environment
- Lodgement till - friction retardation, rock gets stuck so till builds behind it
- Deformation till
What are the three types of proglacial landforms (moraines)?
- Lateral
- End
- Ice core
- Push up - push on the top of the glacier
What is an example of a subglacial landform?
Flute - small elongated features in the ice direction which have a proximal core (a stone) made of till. Till flows into low pressure areas in the lee side of the clast
What are the 4 ways by which glacial ice is melted?
- Suraface melt
- Internal deformation (creates own heat insdie)
- Basal friction
- Geothermal heating
How does water travel through a glacial supraglacially?
Surface melt through moulins (channels).
How are moulins formed
Moulins are formed by continuous streams flowing into crevasses
How does water travel through a glacial englacially? (2)
- Veins - slowly, through circular spheres of snow particles.
- Conduits - tunnels, fast, open by continuous flow
How does water travel through a glacial subglacially? (3)
- Sheet flow - base
- Conduits - cut through glacier
- Cavities - caused when glacier goes over obstacle and then leaves an area of ice
What are 2 types of subglacial conduits?
- Roethlisberger – doesn’t erode in the bedrock
- Nye channel – when the bedrock is eroded
How does glacier discharge vary? (2 variations)
- Diurnal variation - daily (peak insolation)
- Annual variation - yearly (winter conduits close)
What impacts the glacial fluvial sedimentation?
- Low energy - clay
- Medium - sand
- High - gravel
What is a kame terrace
formed between glacier and valley walls (sand and gravel)
What are outwash plains
Build by proglacial rivers. Proximal are course and distal are finer due to velocity
What is glaciolacustrine and glaciomarine sedimentation?
When they reach the water, glacier move faster as they melt and rush quicker, this causes huge crevasses and this causes icebergs – which carry debris. When it reaches the subaquatic margin it melts and retreats faster.
What is periglacial
Periglacial is the land which is not under ice but near the edge of the glacial environment
What % of land does permafrist make up?
10%
What is the active layer in regard to glacial environments
This is the area of permafrost which melts every year
What are the 4 main periglacial regimes
High arctic: dark all winter, short thaw season
Continental: extreme temp range, long thaw
Alpine: High altitude
Low temp: Mild
What are the 3 types of permafrost
Continuous
Discontinuous
Sporadic
What are areas called without permafrost (even thought theyre in a perma area)
Taliks
What are the 2 types of ground ice?
- Pore ice
- Segregation ice - causes frost heaving
What is frost heaving
30% increase in volume of water v ice, so land is elevated. Water is drawn to the freezing sediment which enhances the effect.
What can frost heave cause
cryoturbation - differential heating causes irregular structure in soil by frost penetration. Also caused involutions.
What features can cryoturbation cause to form
patterned ground
1. sorted (see ground eg circles and nets
2. unsorted (see vegetation cover
What are circles and nets
fined grain sediment surrounded by coarse grained sediment
What can thermal contraction cracking create?
ice wedged Polygons
What is solifluction
Slow flow of sediment downhill due t active layer of permafrost. This can cause stripes (sorted) or hummocks. It may move as a lobe
What are pingo
Hills which contain a massive ice core and are oval/circular.
What are the 3 types of pingos
- Hydrostatic – Lakes will have a local talik behind it, and when the lake drains, the talik freezes from the base and size.
- Hydraulic- This is created when there is a constant supply of water which pushes up the sediment which causes the pingo.
- Rock – These are those that develop in rocks, and the smaller ones are called rock blisters.
What are palsas
Similar to pingos but found in peat bogs. They have segregated ice rather than pingos intrusion ice.
What can thermokast processes cause?
- Thaw lakes
- Retrogressive thaw slumps
- General melting
- Alas (only in Siberia)
HUmans can cause them too eg by buildings
What is the main movement if dune transport
Saltation - relies on critical wind velocity. Sand usually moves in streamers
What is repetition ejection and how does it relate to dune transport
Repetition ejection - less energy needed to move sand as it gains energy from hitting the ground. However can be impacted by the resistance of substrate (system limiting factors)
How do dunes move
The sand moves up the dune and over the lee slope which causes sediment to move via the avalanche zone.
What are the wind types that impact the individual dunes?
Barchan: unidirectional
Linear: bimodal
Star: wind from multiple
The rose method can measure the variability of the wind.
What are superimposed dunes
When one small dune is sat on a larger dune.
They can be compound (2 of the same) or complex (2 different varieties)
How do dunes grow
As the dunes get larger they tend to separate as they consume smaller dunes not larger ones
What do blowouts cause (4 dunes)
Parabolic, fore, linear and nebkha dune types.
1. Nebkha - dunes growing around shrubs
2. Parabolic - long tendrils after the nose as vegetation colonises the end
How can we predict movement if dunes
The mobility index/lancaster index
Can you give 2 dust-related facts
- 2million people live in dust-prone environments
- dust path 5x that of river sediment
What is the largest source of dust
Ephemeral lakes (dried-up lakes). They only make up 1% desert surfaces. The Sahara emits 6-18% annual dust
What are 2 transportation of dusts
- Dust devils - small, frequent
- Dust storms - large and rarer
How are the right conditions created to create dust?
Wind can be created by a low level jet to create devils/storms. This is aided by moist convection which carries dust. However, wind can compress which may reduce the sediment budget.
How does dust impact solar radiation, marine productivity and cloud formation?
RADIATION: light colour and weight increases solar reflection
PRODUCTIVITY: iron can fertilise the sea which causes algal blooms blah blah
CLOUDS: more condensation nuclei
How can we reduce dust impacts
- causing more salt crusts
- revegetation
- covering land with gravel to reduce small dust being carried
How did the Aral sea impact human health
Highest rate of child pneumonia in the USSR due to pesticides stored in the sediment then transported from the ephemeral lake
How do dust graphs impact human health
Often bacteria can be carried in dust storms. For example, dust graphs have been used to predict when the next meningitis outbreak is expected to take place.
Rivers are agents of what?
Denudation - key players in weathering, transport and erosion of rock. They transport 20bn tonnes of sediment into the ocean each year
What do riparian areas suggest about geomorphological variation?
riparian zones in rivers make up less than 1% of the land area in temperate zones but make up 80% of the species in the area.
What are 4 types of drainage basin
- Dendritic
- Radial
- Rectangular
- Trellis
What can channel forms be impacted by?
- driving variables
- boundary characteristics
What is Lane’s balance
We can budget based on sediment size and stream slope, and water availability. Shows how altering these impacted degradation v aggradation
What is sediment flux dynamic
It creates and maintains physical habitats and associated ecology.
How can too much sediment transport impact channels
make them hydrologically inefficient and casue extensive maintainance and impacted biota.
What does total load make up?
Bedload, suspended load, wash load.
What is grain entrainment
Movement of grain and gravel, made of 2 driving forces
1. lift (from flow)
2. shear (from pushing)
What are 4 sediment transport controls
- Sediment size and bed arrangement
- Force extended by river flowing over bed
- Upstream sediment supply
- Connectivity to upstream sediment supply
What are 4 river planforms
- Braided
- Meandering
- Anabranching
- Anastomosing
However, classification can be based on formation or processes
What did Flume’s experiments find about rivers
straight, meandering and braided planforms are associated with increased slope and sediment supply respectively.
How do rivers have socio-econoic importance
40% world population live in the floodplains of the 30 largest rivers.
They have distinctive management challenges
What are the usual features of large rivers
Have a low gradient with a high valley floor width
What are the 4 characteristic hydraulic systems in large rivers
- Floodplain prominent - stable, ponded water
- Single channel dominance
- Plural sedimentation systems - equi-style, contra-style and tributary
- Bedrock dominated - confined not self-formed
What is bifurcation stability
This is the discovery of how water flows and curves. The passage of water and sediment through large anabranches is critical in controlling the shape of the planform. The measure of its stability varies on the distribution of sediment through the two channels.
How has sand damaged banks and rivers (2 ways)
Illegal dredging for construction has caused 6m lowering (on average), 20% banks unstable. Dredging is now 7x the natural supply of sand.
How are anti-biotic fears impacted rivers
People argue the release of antibiotics into rivers may be impacting the levels of anti-biotic resistance negatively.
What is the Bruun rule
The Bruun rule enables analysis of shoreline change using shoreline change and sediment transport.
What is closure depth
Closure depth is the initial point at which you can feel waves passing over a selected area
Why do people dispute the Bruun rule?
People argue it ignores sediment supply and ignores gradient change by using invariable cross shore profile.
What is along-shore and cross-shore
Alongshore is along the width, cross-shore involves moving up into the beach.
What does the steep gradient in alongshore movement mean for beaches
They can erode more easily
how is energy impacted when waves come ashore
there isnt any impact, the energy is conserved. however this can create changes in the shape of the wave eg height
what is key when studying wave transport
net transport - ass waves may change direction throughout the day. This is known as the wave climate.
What determines wave breaking height and angle?
refraction. different sea depths can impact the bending of the wave
What is wave shadowing
when waves bend around a headland which causes the waves to reduce in height. This causes a reduction in wave energy and therefore causes a wave shadow. The era in the ‘shadow’ zone erodes due to no sediment feeding as the waves reduce power.
how are the usa littoral cells set?
theyre set by submarine canyons - which tap the nearshore zone via the pathway of alongshore sedimen = termini
How do headlands w/ fluvial systems, tectonics and basin shapes impact coastal processes?
headlands: estuaries due to catchment feeding
tectonics: wave cut platforms, isostatic rebound
basin shape: no tides in some basins (amphidromes)
What is resonance
Resonance is the idea that every basin sloshes with specific frequency. when this and the natural basin resonance are additive = amplitude of motion increases
How are humans agents of geomorphic change?`
They move 100GT of sediment annually, natural movements account for 75GT a year
What does Nordstom 1994 argue about humans and coastlines
He argues that we need to submerge human change into research and prediction surrounding coastal change as we now have geomorphological significance
What does Haff 2003 argue about humans, historical records and geomorphic change
human alterations have no geological record which prevents accurate predictions. It is argued that we see the present as a key to the future, but this change has minimal relationship to the natural past.
What is Mc Namara and Werner 2008 study on divergent trajectories showing
Following this research, McNamara and Werner argue that coastal protection measures created enhanced levels of damage – both environmentally and environmentally.
Why is the replacement of identical sand, during beach nourishment, very important in relation to the biodiversity of sea turtle?
This is because the eggs are sensitive to temperature – so if the sand is darker it will absorb more heat which can alter the breed of the animal.
Other animals can also be impacted by the increased turbidity of water during beach nourishment
What is masked erosion and how does it link to anthrome
masked erosion - changing of erosion to accretion (eg Atlantic coast) via human activity.
It is known as anthrome – which is the idea that there is now an anthropogenic biome with human systems embedded in a natural environment.
Why is delta subordination occurring
Delta elevation is determined by: local sea level, aggregation rate (deposition), eustatic sea level (global) change, natural compaction (wet sand compressed) as well as accelerated compaction.
Impacted by humans, abstraction, climate change etc.
What do Temmerman and Kirwan 2015 argue about natural restoration
working with the environment can reduce these impacts - eg reforestation
Mangroves can currently work to survive in our environment - as they engineer ways to work. Can you give an example?
- Above ground
- In water: Plant shoots influence material deposition by slowing water velocities, and add organic matter to the surface.
- Below ground: Balance of plant root growth and deposition adds organic matter to the soil profile which raises elevation by sub surface expansion. This mass grows faster which slows water, lowers wave height, reduced erosion too.
- These processes also occur in the root zone.
What was an example of managed realignment in the UK
Medmerry, Sussex which was completed in 2013 at a cost of £28 million. It was the largest open-coast project in Europe and heralded as a big win by Environmental Agency.
Why do cliffs occur on some coasts?
Shoreface slope is set by wave environment – such as typical wave heights or periods.
Landscape slope - geological setting
If landscape slope is greater than shoreface slope = cliff. This is because erosion will create an uppercut and erode
How are barrier beaches created?
The top of the shoreface sits above the background landscape, so wave action builds that missing land which creates a barrier (shoreface + beach + crest + back-barrier). Therefore, a barrier is creates when the landscape slope is smaller than the shoreface slope.
What is over-wash morphology?
This occurs when elevated water level (due to storm surge waves, and swash during storms) exceeds the height of a barrier which causes sediment to be transported in a shallow overland flow from the barrier face to the barrier top or back barrier environment
What is morphometry?
the geometric traits of the landscape morphology (length, width, height etc). Scaling relationships are designed to compare these different characteristics and how they change in relation to one another
