Periglacial Landscapes Flashcards
In which 2 areas are periglacial environments found in?
• High latitude: Arctic regions (e.g., Siberia).
• High altitude: Mountain ranges (e.g., Himalayan Plateau)
What is permafrost?
Permanently frozen ground that remains at or below 0°C for at least two years.
What are the three types of permafrost?
• Continuous permafrost
• Discontinuous permafrost
• Sporadic permafrost
What is the active layer in permafrost? (Give 2 facts)
• The upper layer of permafrost that thaws in summer and refreezes in winter.
• Can become waterlogged and unstable, leading to solifluction and thermokarst formation.
What are the 5 main periglacial processes?
• Nivation: Seasonal snow accumulation encourages frost weathering, deepening hollows.
• Frost heave: Ice lenses form beneath stones, pushing them upwards in the soil.
• Freeze-thaw weathering: Water in rock cracks expands when freezing, breaking the rock apart.
• Solifluction: Saturated soil flows downslope during summer thaw.
• Meltwater erosion: Rapid spring meltwater erodes river banks and transports sediment.
What are ice wedges and how do they form in 5 steps?
- In permafrost areas, the active layer freezes in winter and thaws in summer.
- In winter, cracks (fissures) form in the ground and fill with water, which freezes and expands, widening the cracks.
- Deeper ground (over 3 m down) stays frozen, helping keep the wedge shape.
- Each year, this process repeats, and ice wedges grow.
- Over time, they form polygonal patterns called ice-wedge polygons, typically 20–30 m across.
What is patterned ground and how are they formed in 5 steps?
- Frost heave causes stones to be pushed upwards as the soil freezes from the surface down.
- Frozen soil expands, lifting stones, while loose soil fills the gap underneath, stopping them from sinking back.
- Ice lenses also push stones upwards from below.
- In summer, stones warm up faster, melting ice beneath them and allowing wet soil to fill the gap — they stay raised.
- Over time, larger stones move to the edges, and finer material stays in the centre, forming polygonal shapes less than 10 m across.
What are pingos?
Domed mounds of layered sediments with a core of ice and are usually up to 100m in diameter and 2km wide.
What is a thermokarst?
The irregular hummocky terrain often studded with small water-filled depressions created by the melting of ground ice.
What are solifluction lobes and terracettes?
• Lobes: Tongue-shaped deposits formed by flowing saturated soil.
• Terracettes: Step-like features on valley slopes where soil slowly moves downhill.
What are blockfields (felsenmeer) and how they form in 4 steps?
A field or sea of isolated rocks
- Frost shattering (freeze-thaw weathering) breaks up rock on exposed hilltops or cliffs.
- This creates large, angular blocks of rock.
- Over time, these rocks accumulate and spread out across the surface.
- The result is a blockfield — a sea of angular rocks covering flat or gently sloping ground.
What is continuous permafrost?
- covers the largest areas with air temperatures below -5°C. The ground can be frozen to depths of several hundred metres.
What is discontinuous permafrost?
over smaller areas with mean air temperatures between -5°C and -1.5°C. Its depth is much shallower, up to 35m.
What is sporadic permafrost?
the smallest areas where mean air temperatures are between -1.5°C and 0°C. Permafrost occurs only in markedly cold spots.
What are the 2 types of pingos?
• Open-system pingos
• Closed-system pingos
Explain how open pingos are formed in 4 steps?
- Open pingos form in areas of discontinuous permafrost, often in clusters (e.g. Canada, Siberia).
- In winter, the active layer re-freezes, increasing hydraulic pressure in the talik (unfrozen ground).
- This pressure pushes groundwater upward, where it freezes near the surface.
- As the water freezes, it expands, causing the ground to dome upward into a pingo.
Explain how closed pingos are formed in 4 steps?
- Closed pingos form in continuous permafrost areas (e.g. Alaska, Greenland).
- When lakes freeze, water beneath the lake sediments is trapped and pushed down.
- This water accumulates, then freezes and expands, forcing the ground above to dome upward.
- Some closed pingos develop a small dip at the top due to localised melting.
Explain how thermokarsts form in 4 steps?
- Thermokarst forms when permafrost is disrupted, causing the active layer to deepen.
- This creates an uneven, sinking landscape with hollows, pits, and subsidence features.
- Climate change is likely to increase thermokarst formation, making the ground unstable.
- It can damage infrastructure like buildings, roads, bridges, and pipelines in periglacial regions.
Explain how solifluction lobes and terracettes form in 4 steps?
- In discontinuous permafrost areas, the subsoil stays frozen in summer, so meltwater can’t drain away.
- The soil becomes saturated and slowly flows downhill, even on slopes as gentle as 1°.
- Waterlogged soil, with reduced friction and no vegetation, slides down, forming tongue-shaped solifluction lobes.
- On steeper valley sides, the same process creates solifluction terracettes — step-like ridges on the slope.
What are the only landforms which are formed by continuous permafrost? (Hint: C.I.I.)
- Closed pingos
- Ice wedges
- Ice-wedge patterned ground
What are the only landforms which are formed by discontinuous permafrost? (Hint: B.O.S.S)
- Blockfields
- Open pingos
- Solifluction
- Stone Polygons
What is the only landforms which can occur in both continuous and discontinuous?
Thermokarst
