Periglacial Landforms

Question 1

Ice Wedges

Answer 1

When temperatures drop low in winter, the ground contracts and cracks form in the permafrost (this is called frost contraction.)

When temperatures increase in spring, the active layer thaws and meltwater seeps into the cracks.

The permafrost layer is still frozen so the water freezes in the cracks (forming ice wedges.)

Frost contraction in following years can reopen cracks in the same place, splitting the ice wedge. More water seeps in and freezes, widening the ice wedge.

Question 2

Frost Heave

Answer 2

Water freezing in the ground can make jumps on the surface.

When the active layer freezes in winter, the ice forms a lens shape.

In fine grained soil, the ice heaves up the surface layers of soil (frost heave.)

Ice lenses also form underneath stones because they lose heat faster than the soil around them. As the ice lenses expand, they push the stones upwards, eventually they rise above the surface of the ground.

Question 3

Patterned Ground (circles/polygons/stripes)

Answer 3

Stones can get pushed to the surface by frost heave, once they reach the surface, they roll down to the edges of the mounds that have formed, forming circles around them (or polygons when the mounds are close together.) If the mounds are on a slope, the stones roll downhill and form lines.

Frost contraction causes the ground to crack in polygon shapes. The cracks get filled in with stones, creating polygon patterns on the surface.

Question 4

Nivation Hollows

Answer 4

Continual fluctuations in temperature cause freezing and thawing of ice. The freezing breaks debris off slopes via frost shattering and the melting carries the material away in meltwater.

Can be the beginning of a corrie.

Question 5

Lobe Formations

Answer 5

The waterlogged active layer of soil flows easily over the frozen impermeable layer beneath.

Solifluction produces lobe formations where one section of the soil is moving faster than the soil around it.

Question 6

Pingos

Answer 6

Conical hills with a core of ice.

80m high and 500m wide.

Open system- form in discontinuous permafrost when groundwater is forced up through gaps in between permafrost. The water collects together and freezes, forming a core of ice that pushes the ground above it upwards.

Closed system- form in continuous permafrost where there is a lake at the surface. The lake insulates the ground so the area beneath it remains unfrozen. When the lake dries up, the ground is no longer insulated and the permafrost advances around the area of unfrozen ground. The water eventually freezes and creates a core of ice that pushes the ground above it upwards.

If the ice core thaws, the pingo collapses, leaving behind a pond of meltwater surrounded by ramparts.