Landscape Evolution Flashcards
What is spatial evolution?
How a process or landform changes in its dimensions and shape
What are the three dimensions/axis used to measure spatial evolution?
X (Latitude), Y(Longitude), Z(Height)
What is the importance of the Z axis in spatial evolution?
It sets the amount of energy that goes in to a system. This is because height determines potential energy which affects relief, runoff rates etc.
What is temporal evolution?
Evolution over time usually using models for landforms that are difficult to monitor
What are many of the earth’s landscape shaped by?
Fluvial processes such as rainfall and erosion
What are the three types of model used to understand fluvial systems?
Numerical, experimental and conceptual
What type of model was WM Davis’ ‘cycle of erosion?
Conceptual
Who’s work did WM Davis’ ‘cycle of erosion’ closely follow?
Darwin’s evolutionary model
What did WM Davis’ ‘cycle of erosion’ model?
The changes in a fluvial landscape over time.
Outline the stages within WM Davis’ ‘cycle of erosion’ and the processes determining them
It begins solely with UPLIFT creating a starting platform, then this would be met with down cutting in YOUTH, over time these would both diminish and the landscape would MATURITY with the emergence of hills, finally it would transition in to OLD AGE where it would become very flat
What are the three key concepts within the ‘cycle of erosion’ model?
Potential Energy: Potential for erosion determined by land surface height above…
Reference/Base Level: This can be sea level or localised and is what erosion works toward to
Peneplanation: Reduction in the relief, altitudes and highest divides over time
What are three areas of simplification within the ‘cycle of erosion’ model?
Renewed Uplift: The model ignores the possibility for renewed uplift
Climate: It can vary between two extremes which can drastically alter things
Geology: Too complicated at the time but this can drastically alter process rates
What was Penck’s alternative to Davis’ model?
He devised a model that did account for renewed uplift unlike Davis
What was King’s alterative to Davis’ model?
He devised a model from South African fluvial systems consisting of irregular patterns. the model therefore acknowledged the variation in geology over a system
What followed on from the three conceptual models developed by Davis, Penck and King during the 19th Century?
More numerical and experimental models, deriving from the abilities of geography after the quantitative revolution
What are the most important landscape evolution mechanisms?
Uplift, Isostatic Response to erosion, denudation
What is orogenic uplift?
Horizontal compression generated by folding of the earth’s crust causes the landscape to rise
What is an example of orogenic uplift and the rate of uplift?
Himalayas 5-10mm yr^-1
What is epeirogenic uplift?
Vertical forcing generated by the elevation of wide areas of the earth’s crust due to large changes in the lithosphere
What is an example of epeirogenic uplift and the rate of uplift?
Colorado Plateau 0.1mmyr^-1 or a lot of Africa
What is the main difference between Orogenic and Epeirogenic uplift?
Orogenic is much faster and localised compared to Epeirogenic that is very slow but broad in geographical coverage
How do you need to think of mountains to understand their isostatic response to erosion and why?
Icebergs. This is because they are essentially floating as part of the lithosphere due to their lower relative density
What is the isostatic response to erosion of mountains?
By eroding part of the mountains above the earth’s crust this affects their density and because they are floating, part of the mountains below the crust will float back up to fill the space created by its erosion
How much of the eroded landscape is replenished by isostatic rebound to erosion?
80-85%
What is the rate of isostatic response in places such as Canada and Scotland?
~100mmyr^-1 but then slows down after a few thousands of years
What is a side effect of the exhumation generated through isostatic response to erosion?
If some areas rise then others surrounding them will subside
What is an area of subsidence caused by isostatic response to erosion?
Devon and Cornwall are amongst areas subsiding due to the rise of scotland
What is denudation?
the process wearing away and causing a reduction in the elevation of earth’s surface
What are the different stages of denudation?
Weathering, Transportation and Deposition
What is physical weathering?
Fracturing of rock through freeze-thaw variations as well as collisions of rock and sand
What is chemical weathering?
Dissolution of the rock. The rates are dependant upon the rock and solution type but eventually all disolve
What is biological weathering?
Roots contain acids that can dissolve rocks and minerals in the ground to access nutrients such as phosphorus and nitrogen
What are all weathering processes dependant upon?
temperature and moisture
What are the four mechanisms of transportation?
Water: Rivers and Oceans etc.
Glaciers: Melting, mass movements
Mass Movement: Can remove large sums of material from a landscape
Wind: Transports fine material
What is the term given to describe the material transported within rivers?
‘Load’
what is the estimated structure of a river’s transported load?
Bedload: 10%
Suspension: 70%
Dissolved: 20%
What are the four main sites of deposition?
Footslope
River Floodplains
Intertidal zones (Deltas or estuaries)
Open Sea
what sort of material is deposited at footslopes?
Coarser material before it reaches the main channel
What sort of material is deposited at floodplains?
Coarser sediments
What sort of material is deposited at intertidal zones and what does this enable to form?
Fine sediments that can form landforms such as deltas and estuaries
What sort of material is deposited in the open sea and what can form with an example?
suspended or dissolved load such as clay that can form continental shelves like the Bengal Fan
How does mean relief of the fluvial system affect denudation rates?
It increases potential energy that can therefore increase erosion rates
How does the time since uplift affect denudation rates?
With increased time since uplift the elevation of fluvial systems decreases
How does climate affect denudation?
Starting with a completely dry landscape that is exposed, increased rainfall causes more erosion, however at a point the rainfall improves soil quality that leads to vegetation which acts as a natural barrier against erosion. Eventually the rainfall becomes too powerful for the vegetation to handle so denudation increases
How doe lithology affect denudation?
Earthquakes can drastically increase the amount of erosion as found in Taiwan which has very responsive systems
Which study discovered the effect of earthquakes and typhoons on Taiwan fluvial systems?
Dadson et al. 2013
How does river incision rate affect denudation?
The speed at which river cuts down through the valley and channel affects relief which increases denudation
How do glaciers affect denudation rates?
Glaciers can retreat and subsequently erode a valley by scraping material from the landscape which increases denudation. However, the melting of glaciers will cause the land to isostatically rebound.
How can sea level affect denudation?
Sea level can respond to Eustatic and isostatic changes as well as tectonic controls. this can cause land to emerge and alter the base/reference level
How can typhoons/extreme weather events affect denudation?
They can drastically deprive/provide fluvial systems of water which can either drastically increase or decease denudation rates
