Periglacial Landforms Flashcards
What is permafrost?
Soil or sediment that’s been frozen for at least two consecutive years
What are ice wedges?
Ice wedges develop in permafrost soil
- Ground contracts and cracks form in the permafrost. Temperature increases in spring so the active layer thaws and meltwater seeps into the cracks
- Permafrost layer is frozen so water freezes in the cracks
What is patterned ground?
Patterned ground can be formed by frost heave or frost contraction
What are blockfields?
Extensive frost-shattered bedrock including broken-up angular fragments of rock. They are formed in place by frost shattering of the bedrock due to freeze-thaw weathering.
What is a pingo?
A big mound of sediment reaching heights of 90m and 800m across.
They come in two types, open and closed.
Open pingos form where there’s discontinuous permafrost
Closed pingos form where there’s continuous permafrost where there’s a lake at the surface
How is a closed pingo formed?
Stage 1: the lake fills with sediment and liquid water is trapped in the talik between the lake sediment and permafrost
Stage 2: Water freezes as climate cools to form ice core. The ice expands due to increased pressure and the talik is squeezed up.
What is talik?
Unfrozen ground
How much of the earth’s ground is permafrost?
Roughly 25%
What is frost heave in context of patterned ground?
- When water underneath stones freezes and expands, forcing stones upwards.
- Once they reach the surface, they roll down to the edges of the mounds and form circles around them. If the mounds are on a slope, the stones roll downhill and form lines
What is frost contraction in the context of patterned ground?
Causes the ground to crack in a polygon shape. The cracks get filled in with stones forming the polygon patterns on the surface
What are Terracettes?
Terracettes form when vegetation interrupts soil moving down a slope due to a mass movement process such as frost creep
This causes a flatter area to build up behind the obstruction which leads to a series of step-like terraces.
What is a Thermokarst?
Occurs when ice in the ground melts causing the ground to collapse and holes to form
The holes become filled with water creating and uneven marshy landscape.
How is an open pingo formed?
Groundwater is forced up through the gaps between areas of permafrost.
The water collects together and freezes, forming a core of ice that pushes the ground above it upwards.
