Periglacial landforms Flashcards
What is different about periglacial environments?
The landforms are as a result of repeated cycles of freezing and thawing in the active layer.
What are the 7 landforms created in periglacial environments?
Ice wedges
Patterned ground
Pingo
Blockfields
Solifluction lobes
Terracettes
Thermokarst
What is an ice wedge?
Gaps in the permafrost made from ice
* normally dound in multiple
* Can lead to patterned ground
Formation of ice wedges
- When temperature rises ice in crack will melt an turn into water
- Because ice occupies more space, more water from the thawed active layer fills the crack with mroe water
- Colder temoeratures - water will freeze
- due to hydrogen bonds un ice it occupies 9% - cracks get larger
- ground contracts and cracks develop - Forms a wedge as happens repeatedly
Formed by ground contraction
Patterned ground
What are the three processes that occur within its formation.
- Hydrostatic pressure
- Frost heaving
- Frost thrusting
Hydrostatic pressure
The pressure exerted by a fluid caused by the force of gravity. By the force of gravity.
Frost heaving
Frost heaving occurs when the freezing of moisture into ice crystals within the ground creates upward movement of soil.
Frost thrusting
Frost thrusting occurs when the freezing of moisture into ice crystals within the ground creates lateral movement.
Movement of rocks due to rock heaving
How is patterned ground formed?
- As hydrostatic pressure increases → the moisture in the ground begins to freeze and rise → forms an ice lens as they group together
- Capillary action - leads to more moisture joining together enlarging ice lens
- As ice lens grows - begins to push up stones (frost heave) that are above it → due to stones having lower heat capacity → ice lens forms around it
- Smaller sediment in the soil will filter into the gap left by the rising soil → preventing from falling back down
- Stones now poke out of ground
Larger one may fall due to gravity → roll down
Finer sediment is left as the highest part of the soil
Solifluction lobes
- Created when the saturated active layer has thawed
- The gradient of the ground - only form on slopes
- Winter freeze - thaw weathering loosens the material
- Summer → thaw melts the ice content flows down the hill
- When gradient changes again and flattens out, the material flow slows and is deposited in a tongue shape.
What are blockfields?
Periglacial landscapes - particularly in mountainous regions
→ characterised by extensive frost shattered bedrock ( angular / fragments of rocks)
→ are subjective to cycles of freezing and thawing
What are pingos
Rounded ice -cored hills that can be as ,ice as 90m in height and 800m in diameter
How is an open system pingo formed ?
- Groundwater is forced up through the gaps within the permafrost through artisean pressure
- As the groundwater rises the temperature cools so it freezes
- As it continuously rises up it forms an ice core that gets larger overtime
- As it increases it pushes the active layer upwards creating the dome shape
How is a closed system pingo formed?
- A lake insulates the ground below resulting in a talik surrounded by continuous permafrost
- As temperature increases the lake drains
- Permafrost advances as the ground is no longer insulated
- Hydrostatic pressure on water within the talik forms an ice core
- Overtime the continued hydrostatic pressure drives up the ice core
What is a thermokarst and how is it formed?
Thermokarst - landscapes to the process by which distinctive landforms result from thawing of ground ice.
- Permafrost thaw + degradation
- Increase in active layer depth
- Accumulation of water on soil surface
- Retreat of permafrost table
