L6/7: Patterned Ground Flashcards
What do we need in order for sorting to occur?
An undulating frost front.
This means that frost pulling of coarse clasts upwards.
As the freezing front penetrates (especially in cracks), it pushes forward fine soils.
If repeated any slight undulations will get exasperated.
Why do we get an undulating freezing front?
Contraction cracking- the cold temperatures can penetrate quicker, then the clasts are pushed up and concentrated within the cracks, where each year it will cool quicker and quicker.
if you have heterogeneous material (lots of sizes and shapes), where there is lots of clasts the freezing front will penetrate quicker, where there is frost susceptible material penetration will occur slower as there is air and latent heat release during ice lenses formation.
Why is there fixed dimensions of these patterns?
Less frost susceptible material overlying less susceptible material and slight inclination of freezing front.
As freezing front penetrates = vertical movement of clasts, material is pushed at an angle and in the thaw freezes vertically.
Eventually get a plug of frost susceptible material.
What are sorted circles?
Fine material surrounded by coarse material.
“Sorted” patterns essentially vegetation free- heave in winter disturbs roots of material.
If really tightly packed, the polygorms form instead.
What is the movement in sorted polygons?
Vertical movement is a matter of upfreezing.
Horizontal movement may be gravity or convection.
