* Periglacial processes and landforms

How are stones on the surface of the ground sometimes arranged?

Sometimes stones on the surface are arranged in circles, polygons or stripes- this is called patterned ground.

What 2 ways can patterned ground be formed?

• By frost heave

• By frost contraction.

When does frost heave happen?

When water underneath stones freezes and expands, forcing stones upwards.

Once they reach the surface, they roll down to the edges of the mounds that have formed, so they form circles around them (polygons form when the mounds are close together).

If the mounds are on a slope, the stones roll downhill and form lines.

What does frost contraction cause?

It causes the ground to crack in polygon shapes.

The cracks get filled in with stones, forming polygon patterns on the surface.