Geomorphological processes Flashcards
What are the two types of weathering processes?
- Frost Action
- Nivation
What is frost action?
- water enters cracks during day (as temperatures are warmer during the day) amd freezes at night (as temperatures are usually are colder at night).
- As it freezes it expands by approximately 10%, exerting pressure
- this process repeats itself
- When repeated the crack widens and causes rock fragments to break off
Typical mistake
The frequency of freeze thaw cycles is more effwvtive in frost action than in sub-zero temperatures.
What is nivation
A process of weathering
How does nivation occur?
- a series of processes that occur underneath patches of snow
- freezethaw and chemical weathering processes loosen rock and melt water removed debris
- the repetition of this process of meltomg amd freezing over seasons forms nivation hollows
What are the two zones of movement?
- upper zone
- lower zone
Characteristics of the upper zone?
- brittle
- breaking and forming crevasses
Characteristics of the lower zone?
- steady pressure
- meltwater from pressure melting and frictional heats leads to more rapid movement.
What are the types of movement?
- internal deformation
- rotational flow
- compressional flow
- extensional flow
- basal sliding
How many types of movement are there?
5
What is internal deformation
- ice crystals orientate themselves in the direction of movement of the glacier
- they slide past eachother
- main tupe of flow in cold glaciers in the absence of meltwater
How does rotational flow occur?
- occurs within corries (cirque)
- a depression on which the glaciers occur
- the ice pivots/rotates as it starts to move downhill
What is a gradient in geography?
an increase or decrease in the magnitude of a property (e.g. temperature, pressure, or concentration) observed in passing from one point or moment to another.
Pressure caused by the ice mass leads to ice …
Melt at temperatures well below freezing
What is compressional flow
- reduction in gradient
- leads to a thickening in ice mass and slowing of movement
What extensional flow?
This is where a steeper gradient leads to the thinning and acceleration of the ice
What is basal sliding?
- As ice moves over bedrock there is fiction
- causes pressure and subsequently heat
- heat leads to melting
- the resulting meltwater acts as a lubricant and the ice flows more rapidly
What are the two procwsses of erosion?
- Abrasion
- plucking
Describe the process of abrasion
- as material at the bottom of a glacier rubs away at the valley sides and floor.
- scratches may be left - stritations
- if debris is very fine it is called rock flour
What is plucking?
The glacier freezes onto and into rocks
- as the glacier moves the rocks are plucked out
- mainly occurs at the base of the glacier where jointed rocks have been weakened by freeze thaw action
What type of landscape does plucking leave?
A jagged landscape
What is transportation?
This is where glaciers carry large amounts of debris from weathering and erosion processes and rock falls from valley sides.
What are the three types of transportation?
- supraglacial
- englacial
- subglacial
What is supraglacial?
On the surface
What in englacial?
Within the ice
What is subglacial?
At the base of the glacier
What is deposition
When ice melts at the snout, material is deposited.
What is a snout?
The end point of the glacier
When does deposition occur?
When the glacuer changes between conpressing and extensional flow
What is meant by the term till?
Unsorted rocks, clay, and sand debris.
What does the composition of till show?
It reflects the geological conditions over which the ice has travelled.
Fluvioglacial processes
- Meltwater is formed when glaciers melt.
- large quantities are produced
- large quantities which are produced transport large amounts of debris.
Characteristics of meltwater channel (fluvioglacial)
- steep sided
- deep
- straight
Why do meltwater channels have significant levels of erosive power?
- high discharge
- turbulent flow
What are periglacial environments?
- not glaciated
- exposed to cold conditions
- intense frost and permanently frozen ground
Permafrost
- permanently frozen ground
- in areas where temperatures below ground surface remain below 0° continuously for more than 2 years
Whatvare the three categories of permafrost?
- continuous
- discontinuous
- sporadic
Continuous permafrost
- coldest regions of Siberia
- can be 1500 m thick
Discontinous permafrost
- slightly warmer regions
- 20-30 m thick
Sporadic permafrost
Isolated spots of permafrost occur in areas where there is summer thawing.
What are the three mass movement processes that occur in periglacial areas?
- solifluction
- frost creep
- rock fall
Solifluction
- in the summer, water in surface layer melts
- this is due to an impermeable frozen layer below it cannot drain away
- lack of evaporation = surface layer become very wet, soil particles become lubricated and will move down the most gentle slopes
Frost creep
The gradual downslope movement of individual soil particles due to freeze-thaw weathering.
