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THE GEOSPHERE
Landform evolution
Landscape shaping processes
Drainage networks and source to sink
Coastal geomorphology
Vegetation and the topographic signature of life
Extreme events
Landscape responses to environmental change
LANDFORM EVOLUTION
Outline:
- Conceptual models of landscape evolution
- Uplift + denudation
- Controls on mountain height
- Global sediment yield
- Base level
How do landscapes change over time?
- Spatial and temporal evolution of earth’s surface
- Storms events
- Natural disasters (earthquakes, volcanic events etc.)
- Spatial: x, y, z. (location + height)
- Temporal: evolution over time
- Scale: mm, m, km; years, MA
Types of landscape?
-
Erosional landforms
Depositional landforms
Fluvial landscapes. - these dominate the land surface area - rainfall + slopes: soil erosion
Etc.
Understanding landscape evolution: how is this done? Models including…
- Experimental models
- Testing and studying, testing theorems
- Numerical models
- Data sets and presentation of data
- Conceptual models
- diagrams
Conceptual models of landscape evolution
WM Davis: - ‘Cycle of erosion’ = an evolutionary approach; the idea was borrowed from Darwin.
- Young —> mature —> old landscapes. Gradually eroded away into a flat land.
Key concepts:
Potential energy - potential to erode. This is determined by the land surface height above a reference
level.
,Base level - The level to which the landscape erodes (i.e. the reference level) this is equivalent to sea
level.
Peneplanation - the decline in surface elevation, gradient and relief over time as the landscape
erodes.
Davis’ model of landscape evolution
Modifications to this model
Renewed uplift - leads to landscape rejuvenation and creation of a polycyclic landscape (mix of young
and old landforms)
Climate - landscape evolution depends on the ‘intensity’ of geomorphic processes, which varies
between humid, arid & glacial climates
Geology - lithology and structure influence the evolution of drainage patterns
Alternative models of
landscape evolution
Mechanisms + rates of uplift
● Orogenic uplift
○ Uplift by horizontal compression and folding of the earth's crust
■ Peruvian Andes, Himalaya, New Zealand Alps
■ Typical rates (past few Ma) = 5-10 mm yr-1
● Epeirogenic uplift
○ Uplift by vertical elevation of large blocks of earth’s crust
■ Colorado Plateau, Deccan Plateau
■ Typical rates (past few Ma) 0.01-0.1 mm yr-1
Isostatic response to erosion
- 80-85% of the height lost due to erosion is regained by isostatic adjustment of crust
- Surface uplift = Rock mass uplift - exhumation
Isostatic responses to deglaciation
Short-term rates (for a few thousand years) immediately after deglaciation may approach up to
100mm yr-1.
Mechanisms of denudation: Weathering
Physical - frost-thawing alternation
Chemical - Karst: dissolution CaCo3
, Biological - roots, animals
Temperature and moisture dependant! - plant growth, ice versus water...etc.
Mechanisms of denudation: erosion + transport
Water, Mass movement, Wind, Glaciers
Estimating denudation rates from river ‘loads’
- The total amount of material transported by a river is called its load.
- This has three components:
- Dissolved load - carried in solution 20%
- Suspended load - carried within solution (sand, silt, clay) 70%
- Bedload - carried along by the solution (sand + gravel) 10%
Eroded sediments will be re-deposited
1. At footslope positions, i.e. before reaching (permanent) rivers: Colluvium
2. In river floodplains: Alluvium
3. Intertidal zones, building-up estuaries or deltas
4. In open sea, building-up fans at sea/ocean basin floor
Controls on denudation rates: Basin relief
What controls the rates?
- Steep (most incline) places have highest erosion rates
Controls on denudation rates: Climate + Vegetation
- Lower rates of vegetation leads to higher rates of erosion - less inception + infiltration, more
surface runoff (taking with it, sediment)
Controls on denudation rates: Lithology, tectonics & storm frequency
- 2% of suspended sediment to the global ocean
- 0.024% of the global land area
Controls on denudation rates: Glaciers
- Glaciers deepen valleys (may promote uplift)
- Can erosion build build mountains?
What controls the height of mountains?
Glacial erosion: ‘ signature of glacial buzzsaw’
- Mountain surface area is concentrated at the snowline…
- Climate + latitude control the height to which uplift can drive mountains
What controls tributary junctions?
- Major rivers set the base level of their smaller tributaries
What controls sea level? (Sets base level)
Eustatic controls
- sea water + ice volumes, thermal expansion of water)
Isostatic adjustments
- due to surface loading and unloading)
Tectonic controls on ocean basin volume
THE GEOSPHERE
Landform evolution
Landscape shaping processes
Drainage networks and source to sink
Coastal geomorphology
Vegetation and the topographic signature of life
Extreme events
Landscape responses to environmental change
LANDFORM EVOLUTION
Outline:
- Conceptual models of landscape evolution
- Uplift + denudation
- Controls on mountain height
- Global sediment yield
- Base level
How do landscapes change over time?
- Spatial and temporal evolution of earth’s surface
- Storms events
- Natural disasters (earthquakes, volcanic events etc.)
- Spatial: x, y, z. (location + height)
- Temporal: evolution over time
- Scale: mm, m, km; years, MA
Types of landscape?
-
Erosional landforms
Depositional landforms
Fluvial landscapes. - these dominate the land surface area - rainfall + slopes: soil erosion
Etc.
Understanding landscape evolution: how is this done? Models including…
- Experimental models
- Testing and studying, testing theorems
- Numerical models
- Data sets and presentation of data
- Conceptual models
- diagrams
Conceptual models of landscape evolution
WM Davis: - ‘Cycle of erosion’ = an evolutionary approach; the idea was borrowed from Darwin.
- Young —> mature —> old landscapes. Gradually eroded away into a flat land.
Key concepts:
Potential energy - potential to erode. This is determined by the land surface height above a reference
level.
,Base level - The level to which the landscape erodes (i.e. the reference level) this is equivalent to sea
level.
Peneplanation - the decline in surface elevation, gradient and relief over time as the landscape
erodes.
Davis’ model of landscape evolution
Modifications to this model
Renewed uplift - leads to landscape rejuvenation and creation of a polycyclic landscape (mix of young
and old landforms)
Climate - landscape evolution depends on the ‘intensity’ of geomorphic processes, which varies
between humid, arid & glacial climates
Geology - lithology and structure influence the evolution of drainage patterns
Alternative models of
landscape evolution
Mechanisms + rates of uplift
● Orogenic uplift
○ Uplift by horizontal compression and folding of the earth's crust
■ Peruvian Andes, Himalaya, New Zealand Alps
■ Typical rates (past few Ma) = 5-10 mm yr-1
● Epeirogenic uplift
○ Uplift by vertical elevation of large blocks of earth’s crust
■ Colorado Plateau, Deccan Plateau
■ Typical rates (past few Ma) 0.01-0.1 mm yr-1
Isostatic response to erosion
- 80-85% of the height lost due to erosion is regained by isostatic adjustment of crust
- Surface uplift = Rock mass uplift - exhumation
Isostatic responses to deglaciation
Short-term rates (for a few thousand years) immediately after deglaciation may approach up to
100mm yr-1.
Mechanisms of denudation: Weathering
Physical - frost-thawing alternation
Chemical - Karst: dissolution CaCo3
, Biological - roots, animals
Temperature and moisture dependant! - plant growth, ice versus water...etc.
Mechanisms of denudation: erosion + transport
Water, Mass movement, Wind, Glaciers
Estimating denudation rates from river ‘loads’
- The total amount of material transported by a river is called its load.
- This has three components:
- Dissolved load - carried in solution 20%
- Suspended load - carried within solution (sand, silt, clay) 70%
- Bedload - carried along by the solution (sand + gravel) 10%
Eroded sediments will be re-deposited
1. At footslope positions, i.e. before reaching (permanent) rivers: Colluvium
2. In river floodplains: Alluvium
3. Intertidal zones, building-up estuaries or deltas
4. In open sea, building-up fans at sea/ocean basin floor
Controls on denudation rates: Basin relief
What controls the rates?
- Steep (most incline) places have highest erosion rates
Controls on denudation rates: Climate + Vegetation
- Lower rates of vegetation leads to higher rates of erosion - less inception + infiltration, more
surface runoff (taking with it, sediment)
Controls on denudation rates: Lithology, tectonics & storm frequency
- 2% of suspended sediment to the global ocean
- 0.024% of the global land area
Controls on denudation rates: Glaciers
- Glaciers deepen valleys (may promote uplift)
- Can erosion build build mountains?
What controls the height of mountains?
Glacial erosion: ‘ signature of glacial buzzsaw’
- Mountain surface area is concentrated at the snowline…
- Climate + latitude control the height to which uplift can drive mountains
What controls tributary junctions?
- Major rivers set the base level of their smaller tributaries
What controls sea level? (Sets base level)
Eustatic controls
- sea water + ice volumes, thermal expansion of water)
Isostatic adjustments
- due to surface loading and unloading)
Tectonic controls on ocean basin volume
