* Periglacial processes and landforms

What do periglacial areas contain?

Permafrost - permanently frozen ground with a top layer that can melt in the summer (the active layer).

20-25% of Earth’s land surface is permafrost.

What 2 categories can permafrost fall into?

Can be continuous (all the ground is frozen) or discontinuous (only patches of ground are frozen).

What must the conditions be for discontinuous permafrost to form?

The mean annual temperature needs to be below 0’c for at least 2 years.

What must conditions be like for continuous permafrost to form?

Mean annual temperature needs to be below -5’c.

What can occur in areas of permafrost?

Mass movement can occur.

It can happen as the ground starts to thaw.

What is the layer of permafrost like?

It is impermeable (water can’t flow through it).

If the temperature gets above 0’c in summer the active layer melts but meltwater can’t drain away.

How does mass movement occur in areas of permafrost?

Because meltwater can’t drain away in warm temperatures, the active layer becomes waterlogged and heavy, and flows easily.

What is it called when the active layer becomes waterlogged and flows easily?

Is called solifluction and it can occur wherever there's a gradient.

What does solifluction produce?

Produces love formations - one section of soil moves faster than the soil around it, e.g. if it's on steeper ground, so it flows further and forms a tongue shape.

When else can mass movement occur?

On slopes due to regular freezing and thawing.

Why does freezing and thawing create mass movement?

• Water in soil expands when it freezes, causing soil particles to be forced upwards at right angles to the slope.

• When the grounds thaws, the soil particles move vertically downwards.

• As a result, they end up further down the slope - this is called frost creep.

What happens when temperatures drop very low in winter?

The ground contracts and cracks form in the permafrost. This is called frost contraction.

What happens when temperatures increase in spring?

The active layer thaws and meltwater seeps into the cracksmade in winter.

The permafrost layer is still frozen, so the water freezes in the cracks - the ice filled cracks formed in this way are called ice wedges.

What can frost contraction do in following years after ice wedges have formed?

Frost contraction in following years can re-open cracks in the same place, splitting the ice wedge.

More water seeps in and freezes, widening the ice wedge. The ice wedge gets bigger each time this happens.