Geosphere

Through spatial and temporal evolution of the earths surface

Spatial: location and height (space) - erosion, deposition, deformation

Temporal: evolution over time

Landscapes formed by running water. Water is delivered as rain or snow but this will melt. They dominate the earths surface

Fluvial landscapes

WM davia developed the cycle of erosion- landscape evolution (19th century). This is an evolutionary approach borrowed from Darwinism. Davis model had key concepts.

Potential energy

Base level

Peneplanation

The potential to do work through erosion. This is determined by the land surface height above a reference level. Newer landscapes with steep slopes have more surface for potential energy

The level to which the landscape erodes e.g. reference level. This is the equivalent to sea level

The decline in surface elevation, gradient and relief over time as the landscape erodes

That there should be some sort of uplift event. The concept expressed that there was a mechanism that would uplift land - high altitude. Uplift brings valleys and mountains together. Older, mature landscapes are typically quite flat

Renewed uplift

Climate

Geology

Leads to landscape rejuvenation and creation of a polycyclic landscape (mix of young and old landforms). Leads to further steepening

Landscape evolution depends on the intensity of geomorphic processes, which varies between humid, arid and glacial climates

Lithology and structure influence the evolution of drainage patterns. Resistant material leads to positive relief compared to sedimentary areas that are lower and more eroded

Uplift by horizontal compression and folding of the earth crust. E.g. Himalayas (rate of 5-10mmyr-1). Crushing together of crust leads to thickening of the crust that's then pushed up

Uplift by vertical elevation of large blocks of the earth crust e.g. Colorado plateau (rate of 0.1mmyr-1). Due to slower tectonic processes. Causes are likely to be cooling or heating of the underlying mantle. Mantle under Africa is quite hot so it floats up. Level beds as there's no cracking or distortion. Rates are slow

•80-85% height lost to erosion is regained by isostatic adjustment of the crust

•surface uplift = rock mass uplift - exhumation

•mountains are high because material has been crushed together but is light than the underlying mantle rock. Mantle rock is denser allowing the overlying rock to stay up

•oceans are low cos floor is made of heavier rock (basalt). It's denser than continental rock so it doesn't take as much to make the same weight

•when landscape erodes it's removing weight so mass floats up from underneath.

Continental - can approach 100s kilometres

Oceanic- 5-10kilometers

Unweighted the landscape so it started to rise. Material is very viscous so it's much denser. It responds but takes a while -readjustment

Physical (frost thawing alternation) - rapid in areas where ice is thawing

Chemical (dissolution of CaCo3) - physical and biological processes

Biological (roots)

All are temp and moisture dependent (plant growth, presence of ice vs water)

Water

Mass movement- failures of weaker rock and soil due to steep slope

Glaciers

Wind

The total amount of material transported by a river

Dissolved load (carried in solution 20%)

Suspended load (sand, silt, clay 70%)

Bedload (sand and gravel 10%)

1. Foot slope positions before reaching rivers (colluvium) - common in regions that were previously glaciated u shaped valleys

2. In river flood plain: alluvium

3. Intertidal zones building up estuaries or deltas e.g. Nile

4. Reach open sea, building up fans at sea/ocean basin floor - Bengal fan

•basin relief

•climate and vegetation- low erosion rates in areas of little rain. More vegetation in areas of high rainfall

•lithology, tectonics and storm frequency

•river incision rate - controls river relief. As mean local relief increases, erosion increases

•glaciers- deepen valleys and may promote uplift. Isostatic uplift response due to removal of mass

Sea water and ice volumes, thermal expansion of water

Due to surface loading and unloading

On ocean basin volume

Processes of uplift and denudation

Global topography, mountain height and net denudation

The processes that cause the wearing away of the earth surface by moving water, by ice, by wind and by wave, leading to a reduction in elevation and in relief of landforms and landscapes

General concept is that mass can't be created nor destroyed - only exception is radioactivity which doesn't apply to physical geography. Basic concept is that you have sediment coming in. Most change upwards in land surface if you have land upward and material being deposited. Balance between uplifting forces bringing land up and erosion forces bringing land down

Amount of uplift or subsidence + balance between sediment supply and removal

M3 = measurement of volume

M2 = measurement of area

Qs = discharge of sediment

Q= discharge of something

Equilibrium when they experience no net change in form. This occurs when sediment input - sediment output + uplift = 0

To identify an equilibrium, one must specify the time and space scale of interest - it is a scale dependent concept. It's important as we need to understand if landscapes as in a steady, static condition or in the middle of changing conditions.

Frequency and magnitude of events that shape the landscape

Form is the shape. Water has to flow down channels - effects where sediment is transported, how quickly, how deeply and where it's left = erosional and depositional processes.

Water discharge x slope = power (sediment transport law determined empirically)

Power laws plot straight lines on graphs that have logarithmic axes. Graphs without logarithmic axes, the power laws appear as curves

Something moves in response to only a surface gradient (steeper location, the faster stuff moves like landslides and soil creep)

Includes slope term and discharge. Sediment movement by water- driven processes

Driven by relationships that had transferred into laws. Negative feedback e.g. deposition of sediment reduces slopes which = more deposition. Positive feedbacks amplify initial disturbances whereas negative feedbacks dampen initial disturbances. Topographic landscape evolution lead to strong negative feedbacks

Defines drainage direction of the river systems

An area of land that all drains in the same outlet

The flow rate measured in m3s-1 (cubic meters per second) and is the amount of water that passes by time unit through a section of the river

Width x height

The discharge that fills a stable alluvial channel up to the elevation of the active floodplain

A river formed by itself by it's own channel material and water flow

Width x height x velocity or area

Measured in meters per second (ms-1) and is dependent on slope (s), depth (h) and roughness coefficient (C)

Leads to changes in basin drainage area, river discharge and sediment load. Drainage basin splitting is driven by uplift and denudation.

Has a constant uplift rate and rainfall rate. Rivers are one of the more stable features on a continent

The interaction of fluvial processes of erosion and deposition. Geological processes also play out over deep geological time. Erosion rates are low in flat landscapes.

Production of runoff and the erosion, transport and deposition of sediment

Precipitation, interception, transpiration, overland flow, infiltration. Erosion of soils is usually due to surface runoff

The ability of water to erode and transport sediment particles depends on the competence of the flow and sediment size. Sand is around 2mm in diameter. It takes a higher velocity to move gravel. Finer material is harder to move because it's usually sticky- individual clay particles stick together.

The measure of the total amount of sediment it can carry. It's calculated as a function of shear stress exerted by the fluid and critical shear stress instead of velocity

The fraction of sediment eroded from slopes that reaches the drainage basin outlet. It tends to decline downstream because sediment storage potential increases as valleys become wider and less steep. It's the ratio between sediment output from the basin and sediment eroded from slope. Higher delivery ratio when there's less sediment sinks

Sediment output from basin / sediment eroded from slope

That sediment moves from source to sink along a jerky conveyor belt. More erosion in steeper upward regions. Water needs gravitational slope to erode

Environments that used to be glaciated. Aeolian systems represent stores of sand that's migrating

A tectonic down working crust. Subsidence has occurred so topographically, the bedrock is many kilometres down with a high storage rate

12.5million km3 (size of Amazon basin) - fans collect sedimentary material from systems

Space available to store sediment

The equilibrium long profile shape of the land surface/river that transports the sediment

Sea level rise and tectonic uplift. Sediments as deposited during relative sea level rise. Tectonic uplift changes the slopes in the system. Sediment is transported out of eroded headwaters. Rivers will adjust their profiles, so they can transport the material that's coming into them otherwise they build up

•represents the change in height of the riverbed moving downstream from the headwaters to the sea

•they adjust to transport the amount of water and sediment supplied from upstream

•discharge increases downstream as drainage basin area increases - profiles are concave

•adjust their transport of sediment to end up in a dynamic equilibrium

Discharge of sediment x diameter of sediment goes as (linear function of) discharge of water x slope of river

When more sediment is being eroded and transported out

•sediment load increases at a declining rate cos of increased sediment storage

•the size of the sediment being transported tends to decline due to abrasion and changes in sediment sources and river competence

•leads to changes in river gradient - if slope didn't decrease, all sediment would be flushed away. Rivers adjust so the lower regions tend to have lower slopes = long profiles

•straight rivers are engineered

•bedforms are pushing at the banks and trying to get the river to migrate

•most rivers are meandering - move laterally due to sediment deposits

•Rivers won't migrate if constrained between hard bedrock

•braided rivers are found where there is a high sediment flow and is a function of discharge and slope

Slope and discharge

Bank strength

Braided rivers tend to be steeper than meandering as this gives the flow more energy to carve banks. Helps us understand how a river moves from one form to another

Controls widening, limits lateral sediment supply and depends on bank material, sediment load and mechanism of floodplain construction. If banks are weak rivers can migrate into them easily. Aggradation of systems has to happen along a valley floor. When rivers flood they as slowly infilling their accommodation space

A way rivers infill their accommodation space

Base level, tectonics and equilibrium landform morphology

Include sea water and ice volumes, thermal expansion

Surface loading and unloading

Tectonic controls

Extent corresponds to limits associated with changes in sea level of the quaternary. Level of oceans is significant because the periphery of continents is low gradient - caused by sea level change.

Continental slope

Continental shelf

Shoreface

Coastal plain

Usually 100-200m

Coastal environments have significant morphodynamic feedbacks. Processes give rise to sediment transport which feeds back into the morphology. Estuarine coasts have a minor sediment budget, deltaic coasts have a higher budget

•generated by wind and seismic activity

•deep water wave height is determined by wind speed and duration

•as waves approach the shore they are influenced by frictional drag of the sea bed

•waves steepen before breaking - some energy is dissipated, providing energy to drive sediment transport processes

•produced by the attraction of the sun and moon and are influenced by the shape and size of ocean basins and the coriolis force

•spring tides are when the moon is aligned

•neap tides happen at other times

•controlled by bathymetry, width of continental shelf, coastal configuration and distance from zero tide amphidromic point

•tidal range and coast gradient determine the extent of the intertidal zone

•variations is set by the interplay of the earth and moon gravity

•microtidal (2m or less), mesotidal (2-4m), macrotidal (4m +)

•microtidal is wave dominated, macrotidal is tide dominated

•Wave environment (height, storm, event frequency)

•coastal lithology (susceptibility to weathering and erosion, structure, availability of erosional tools)

•morphology (platform configuration, cliff height and angle, bathymetry)

•tidal action, climate, biological activity

•higher energy systems with low sediment inputs and high tidal flushing

Protect coastal areas due to stronger underlying bedrock

Sediment is moved and deposited in areas where it's not quickly flushed away. Shingle beaches are higher gradients than sand beaches. Beaches form on wave energy - higher flow velocities = bigger sediment size. Beaches adjust themselves in equilibriums

Deposits formed out of sand where waves are breaking

Linear and parallel to land and separated by a lagoon. Low gradient coasts with low tidal range. Dependent on river discharges. Susceptible to erosion and and storm surges due to low tidal range. Provide resilience to lagoons

Valleys and lowland areas drowned by postglacial sea level rise. Usually a zone of salt and freshwater mixing. Sediment derived from local, fluvial and coastal sources. Deposition controlled by sediment size, water energy and salinity

Occur on upper parts of intertidal zones. Dissected by tidal creeks that supply/remove water and sediment. Salt tolerant vegetation trap sediment. Sensitive to changes in sea level and sediment supply

Catchment characteristics (size, relief, lithology, tectonics)

Climate, soil, vegetation

Human activity and engineering in catchment

River flow characteristics - flood frequency

River sediment load - amount and size of sediment

Strength of estuarine tidal currents

Strength or absence of offshore currents

Buoyancy or river water - determined by density contrast

Wave environment at coast

Fluvial dominated

Tide dominated e.g. ganges-brahmaputra in Bangladesh

Wave dominated

Soil erosion and dam construction

Changing sediment input

Precipitation change

Sea level change

Land and shelf subsidence

Coastal erosion

Subsurface abstraction oil, water, gas

Increased population pressure (500 people per km2 on average)

Dam construction

Agriculture

Deforestation

Up to half a billion will be living in the coastal zone at risk from flooding due to sea level rise, coastal subsidence, declining sediment supply from rivers and climate change

Hydrology

Slope stability

Soil quality

Sediment trapping

Atmospheric composition

Surface roughness

•when water flows into landscapes

•into soil quality and helps the formation of clay and secondary minerals formed by the dissolution of bedrock

Sand movement is reduced with vegetation. It traps it resulting in an increased dune size. Input outweighs erosion due to coastal winds

25-50cm of precipitation per year

Atmospheric circulation

Continental isolation

Rain shadow effects

Ocean circulation

Large scale flow of air on earth that results in Hadley cells - sun energy hitting near the equator creating warm air that rises up. There is a mass of upwelling air near the equator. Once it reaches a higher zone in the atmosphere, it moves sideways to north and south - sinks 30 degrees. On average air is coming down making it more stable so less chance of convective precipitation and thunderstorms

Waters in the ocean and large lakes. The further from the ocean, the warmer things get

If air is forced over higher topography, it will rain. Greater moisture curing capacity, yet there is no moisture leading to less chance of rain in lower topography areas considered arid like death valley

Sets where the water is coming from that could evaporate and cause rain. If water is sourced from the poles it will be cold. Cold water will not evaporate as readily as warm water, so it provides more water to the atmosphere meaning less chance of rain

Suspension

Saltation

Creep

Finest particles - clays

Carried by turbulent eddies and over large distances

Dominates water flow due to viscosity

Coarser particles - sand

Move in long, low hops - bouncing

Pass momentum by grain impacts and dominates air flow

Strong gradient between sand moving

•Larger particles slide along the surface

•Transported water- water is stronger and more viscous because rock weight is displaced by water buoyancy

•loose particles eroded from the surface

•sediment sorting is by selective entrainment which produces a pavement

•erosion is limited by surface coarsening

•dry, not densely vegetated, finer sediments blown by wind

•coarse material left behind, rest blown away

•no longer a sediment source if area is dominated by heavier sediment

•Produced by abrasion (sand blasting) by wind

•changing wind directions and ventifact orientation of multiple facets that meet at sharp ridges

•erosional features of rocks that's stuck up

•wind abraided ridges orientated with prevailing winds and separated by abraded chutes that conduct wind blown sand

•larger versions of rock left behind

•not much vegetation

Isolated mountains of resistant rock. Rounded slowly by abrasion over long periods. Found in central australia

•large regions of sand deposition, induced by changes in wind speed (due to barriers or transitions between climate zones)

•finer material moves in direction of prevailing wind

•regions where more sand is arriving than is blowing out

•transport rates and location induced by winds and velocity

•regional transitions between climate zones affect these areas

Sand supply

Wind regime

Vegetation

Barchans/crescentic dunes

Transverse dunes

Parabolic dunes

Longitudinal (seif)

Solitary, crescent shaped whose horns point downwind. Form where sand supply is limited, and wind is strong and constant. Dunes are isolated from each other

Form in sand rich environments with strong, steady prevailing winds. Barchans merge to form wavy perpendicular to the wind. More sand is needed. Barchans dunes competing so merge to form these ridges. There's a continuum, so more than 1 dune

Crescent shaped with tips pointing upwind. Common in coastal areas with moderated abundant sand and winds and some vegetation. Depending on wind strength and impacts, parts of vegetation become more mobile. Lower portions of dunes become armoured with vegetation. Higher part of dune will continue to move in direction. Vegetation causes shape of dune to invert

Long straight ridges that are fairly parallel to the wind. Moderate to low sand supply and strong prevailing wind with minor variations in direction. Wind angle adjusts on a regular basis, so they are constantly reforming in directions

Loss of vegetation

Increased runoff and erosion

Soil organic matter decline

Soil compaction

Downward spiral in soil quality and fertility

•steep fertile landscapes that high erosion

•solution to build terrace systems to slow erosion

•a lot of effort to maintain and will collapse quickly when not maintained

Soil erosion

Slope instability

Loss of soil productivity

Increased river sediment load

Destruction of coral reefs

Climate impacts - loss of carbon storage

•influences external (water and sediment supply)

•influences internal by forming feedbacks (bank strength, roughness, sediment transport, island development and floodplain formation) that control river form and functioning

•roughness to landscape that slows water = feedback between form of sediment transport and deposition leading to flood plains

•force water into single channel

Flashy regimes with high rates of sediment transport due to floods. Unarmoured riverbed. As shear stress increases, sediment transport increases. More flashy flow regimes, deviate from normal river regimes seeing more sediment moved at one time

Deep channels found in semi-arid environments where formation is driven by land use and climate change. Common occurrence of intense storms and positive feedbacks

1. Vegetation colonises bars that are dry at high flow

2. Vegetation prevents significant floodplain flow - sediment stays in floodplain

3. Vegetation slows bank erosion and prevents bend cut off

Reduce channel width and force thalweg regions (pools) to link up to form an overall channel. In an abiotic world, soils would be shallow or absent, hillslopes would be rocky, rivers would be steeper and barely meander - no forced channelization and formation of single channels rather than braided. Would be chemical weathering

Crescent dunes due to lack of wind and vegetation. Topographic signature of life is not yet detectable

Atmospheric and ocean circulation

Topography

Continentiality

That landforms were created through mega floods. They were unaware of uplift and didn't have an understanding of tectonics

Uniformitarianism and gradualism. He explained the features of the earths crust by means of natural processes over geologic time

Was at the centre of the development of geology and influenced Darwin. The notion of things happening slowly over time laid the foundation for Darwin's theory of evolution

'The present is the key to the past' - things happen slowly and momentarily. Processes that operated in the past were the same as those that operate today

'The earth has evolved slowly over a long period of time'. The landscape is a product of slow processes operating over a long time, as opposed to single, rapid catastrophic events

Many landforms are a product of extreme events

The most important events are those that do the most geomorphic work. A measure of geomorphic work is the total amount of sediment eroded or amount transported by a river during a year

Magnitude x frequency

Total sediment flux because the landslide sediment flux is magnitude x frequency

Look at distributions of landslides following events and work out how big they are and how frequently they occur in some areas

Discharge needed to transport sediments

No

Size of transport x frequency

Amount of water flowing x slope

Large boulders that rafted on glaciers and were deposited by the glacial outburst flooding - rocktype doesn't match lithology so it's been transported far

Based on dimensions of river channel and sediment characteristics

Based on roughness and diameter of largest particles

Continental drainage pattern

Many hillsides were stripped of forest and as a result erosion has increased. The north fork toutle river is laden with sediment

At the beginning, shear stress is high because slopes are steep. It decreases when channels relax their slopes. It selectively moves fine material, leaving behind coarse material

Shear stress needed go move sediment

Initial aggradation

Subsequent incision and widening

Bed armouring

Stable equilibrium is one where the river stays in one steady state. A perpetually disturbed is when the system is frequently affected by flood events

Those that have a long term impact on landscape form and functioning

When a river transports less sediments than supplied by landslides

When the river has a higher transport capacity. As the supply declines, fan entrenchment occurs as river transport capacity declines

Land surface temp + rainfall affects processes and rates

Sea level affects energy and for of rivers, deltas and shelves

Ice albedo, periglacial processes - higher reflectance f solar waves

Carbon cycle - warmer means more vegetation so more co2 captured by plants

Thermohaline circulation - transporting heath to polar regions

Sea level changes

Precipitation and temp changes

Vegetation changes - feedbacks

10m

•ice melts so the ice sheet gets lighter making the lithosphere bounce back - isostatic rebound

•bedrock is eroded away

•the asthenosphere is moving under the crust which is pushing Scotland up, making England fall

•large continents are coming up because the oceans are coming down

Changes in the hydro cycles

Rates of surface erosion

Global distribution of landforms

Short term deviations from progressive landscape lowering

During glacial periods and more active during interglacial. During glacial periods, less energy is transported so there are bigger temp differences

Schumm interpreted Davis' cycle of erosion

Indicates different periods of erosion, steady state and deposition

formed by alternating periods of erosion and deposition

Valley floor is filled with sediment

Incise of the river in these deposited sediments - sediments are removed. The second phase of degradation leads to a second terrace and so on

To increase sediment discharge or decrease water discharge leading to a steeper slope

Long profiles are concave.

•degradation increases, aggradation also increases as well but less fast than degradation

•when aggradation/degradation decreases, distance also decreases

• during glacial, upland glaciers supply abundant coarse material to periglacial braided rivers

•sediment enters storage in braid plain deposits and is remobilised during interglacial

•remobilisation involves the cutting of a trench - it's deposited downstream as a fan

•post glaciation sediment piles up at the bottom of the slope - this delglaciation involves the carving of the trencn

Braid plain with alluvial terraces

Drops in the cliff created by sudden short uplift periods

•locally increased erosion potential due to increased steam power (runoff), bedrock differences

•creating a difference in height - difference increases locally the slope

•more stream power and erosional potential

•difference in height is bigger

•backward erosion of knickpoint - positive feedback

Deposits provide a record of past environmental conditions. Must understand relationships between environmental change and landscape response to make use of deposits

1. Paraglacial decline in sediment supply - from aggrading to degrading

2. Product of difference between slope and river sediment transport regimes

3. Process - form feedbacks

When different processes or environmental conditions can produce the same landform

Mainly glacial and landslide debris occurring in fully deglaciated headwaters

Soil erosion due to runoff

Flooding risks

Riverbank erosion risks

Coastal erosion risks

•agriculturslly - in Japan people don't live in the mountains because of natural hazards and land is unproductive so they live on coastal plains

•the Mekong has 10m+ people living on it

•sediment is important and needed for a river to reconstruct itself

Discharge and shear stress

Increased flood risk

Change in timing of snowmelt floods

Enhanced soil erosion potential in northern and southern europe

Ice volume

Sea level

Isostatic response

Local precipitation and vegetation

Sea level

Coastline position

Coastal landforms