Is ground ice active or passive? Flashcards
Introducing frost heave
Primary versus secondary heave
General heave or ground heave involves the whole ground.
Primary heave- phase-change from water to ice expansion follows the 9% volume change
Secondary heave from water migration (30% volume change)
Expansion pressures are released in “two” directions …
Vertically in frost heave
Laterally in frost thrust
Stone heave or “upfreezing of clasts
Acts differentially on stones –larger particles are heaved most
Coarse particles collect at the surface – affecting patterning
- Freezing thawing freezing thawing = patterns
Elongated stones are tilted into the vertical
Describe the process of frost push
Is it active or passive?
Heat flux greatest through pebble – cools quickly
Film of ice forms around cold pebbles, particularly at it’s base
Ice pushes stone up by ice at base, leaving cavity full of ice crystals which can get bigger and bigger
With summer thaw, the cavity partially fills with sediment and the stone cannot settle back
ACTIVE
Who came up with the idea of frost push?
Hogbom, 1914 and Nansen, 1922
and draw a diagram by Ballantyne 2018
Whats the problem with frost push?
Ice crystals are certainly found in cavity beneath stone, but were they responsible for pushing the stone? Tiny ice crystals are supposed to push the pebble up through an overlying zone that has already frozen!
Or are the crystals just forming passively in a cavity that has already been produced by a different process?
…active vs passive ice
Describe the process of frost pull
Autumn
- Preferential freezing occurring stone starts to cool quicker as the frost front is penetrated- ice lenses forming = ground surface is rising.
- Clast gets pulled up with the heaving ground (start freezing quicker than the matrix around me) but the whole ground surface is rising
- Still leaves a cavity beneath where ice crystals grow beneath (not formed by ice pushing up the stone)
Spring
- Forefront penetrating stones warm up quicker
- Ice melt material falls into cavity
- Stone doesn’t fall back down- mound on top
Who came up with the idea of frost pull?
(Beskow, 1930)
and draw a diagram by Ballantyne 2018
Describe the process of cryostatic pressure
Is it active or passive?
Moving coarser material through finer material
Not a perfect horizontal freezing front (some relief) and so as it goes down through frozen material it’s exerting cryostatic pressure ahead of the frost table
Where the frost table bends, convergent pressure may lift pebble (would have to have warm/unfrozen bit above clast)
(Vanderberghe)
What is differential frost heave?
Non-uniform movement of material in some areas than other (building segregation ice in some areas and not others). Some material is moved based on texture due to frost susceptibility.
Can initiate an undulating surface that then causes positive feedback processes and ever more differentiation with each freeze thaw cycle.
Positive- frost susceptibility increases towards to surface (gravel to coarse sand to fine sand…)
Negative- frost susceptibility decreases towards to surface
(Ballantyne, 2018)
Who came up with the idea of differential frost heave?
Van Vliet-Lanoe
Contraction cracking hypothesis in ice wedge polygons…
Active or passive?
Lachenbruch, 1962
Ice fulled contraction crack provides line of weakness
In subsequent winters the crack reopens and further water enters and freezes.
Widens ice wedge.
Movement of material occurs in summer, not due to ice pushing, but because of summer expansion.
PASSIVE!!
Frost shattering
Active or passive ice
Frost shattering breaks rocks off the back and side walls of the valley.
Caused when melt water seeps into cracks in rocks, freezes and expands, so exerts pressure on the rock and bits of the rock break off.
