Periglacial Flashcards
What is solifluction?
When the active layer of permafrost melts and it cannot drain away because of impermeable ground and it cannot evaporate because it is too cold, the soil moves down slope.
What is frost creep?
The gradual down slope movement of soil due to alternating freeze-thaw cycles in the active layer.
What is frost heave?
When the active layer freezes, ice develops and the volume of the soil increases. This results in upwards expansion of the surface, resulting in patterned ground.
What are ice wedges?
Narrow cracks in the ground, in the summer, filled with meltwater, then freezes in winter (forming an ice vein), then continuous freeze thaw.
They start less than 5cm across but over hundreds of years they reach over 10m wide.
In periglacial landscapes these are formed by ground contraction.
How is circular patterned ground formed?
Forms on flat ground by seasonal frost heave.
How is net patterned ground formed?
(The intermediate between circles and polygons) Formed by seasonal frost heave and freezing causing domes to form.
How is polygonal patterned ground formed?
Only on flat ground - Freezing causes domes to form and seasonal frost heave causes stones to move to the surface. Then gravity acts on the larger stones, making them roll down slope to form the border.
How is step patterned ground formed?
(Either terraces with stones or vegetation forming a banked edge - usually derived from either circles, polygons or nets) created by frost-action of permafrost, different types result from the processes that formed the parent feature.
How is striped patterned ground formed?
(Lines of stones running down slope on gradients over 6 degrees, originally circles, polygons or nets). Formed from the process of frost heave - similar origin to steps.
What is a closed system pingo?
(process is hydrostatic)
- Unfrozen waterlogged ground is sandwiched between the lake and the underlying permafrost
- Lake drains - the lakebed is no longer insulated so the waterlogged ground freezes
- Frozen lakebed and permafrost gathers together to form an ice lens that expands and pushes the sediments upwards - continues to grow as long as there is still unfrozen ground
What is an open system pingo?
(process is hydraulic)
- Water can seep into upper layers of the ground
- Water accumulates in flat low-lying areas between upper layers of permafrost and frozen ground beneath the water, then freezes.
- The ice core expands and creates a dome - can continue to grow as long as pressurised water flows in from surroundings
What are solifluction (gelifluction) lobes and sheets?
Sheets have smooth surface on 1-20 degree slopes and can move over 100m across a slope.
When slopes are steeper at 10-20 degrees, solifluction lobes happen which have a tongue-like appearance and can extend down slope - up to 50m wide and 5m high.
What are terracettes?
Small narrow pathways running horizontall down the side of a slope. Generally parallel to the contours of the slope, they are bounded by a low steep border that is steeper than the slope it occupies.
Could be due to frost action/creep but only a theory.
What is thermokarst?
The depressions in the ground surface resulting from ice melting within the permafrost. Features occur where human activity warms the surface layers of permafrost.
