What types of frost heave are there and why does segregation ice grow?

Question 1

What is frost heave?

Answer 1

Frost heave is a form of frost action, a physical weathering process involving the cyclic freezing and thawing of water in soil or rock. It involves the uplift of deposits due to the expansion of groundwater on freezing (Manz, 2011)

Question 2

What does heave mean?

Answer 2

Heave in this context refers to the upward movement of the ground surface that occurs in response to the seasonal formation of ice in the underlying soil (Rowley et al., 2015)

Question 3

When water changes to ice its expands and freezes…but by how much?

Answer 3

Phase change is up to a 9% volume change.

Question 4

What does expansion release?

Answer 4

Pressure

This occurs in two directions…

• Vertically, as frost heave
• Laterally, as frost thrust

Question 5

How does frost heave happen?

Answer 5

Stones in the active layer cool down faster than their surroundings because they have a low specific heat capacity (Heat flux greatest through pebble – cools quickly).

Film of ice forms around cold pebbles, particularly at it’s base.

Leaves cavity full of ice crystals at base which can get bigger and bigger.

The expansion of the frozen water pushes the rock upwards.

This process repeats until the rock is pushed through the surface of the soil.

When it is pushed through the surface it also causes the ground to mound.

With summer thaw, the cavity partially fills with sediment and the stone cannot settle back.

(Flerchinger et al., 2013).

Question 6

What noticeable qualities does stone heave or “upfreezing of clasts have?

Answer 6

It acts differentially on stones –larger particles are heaved most.
Freezing thawing freezing thawing = patterns occuring
Elongated stones are tilted into the vertical (at an angle).

Question 7

What soils are susceptible to frost heave?

Answer 7

They tend to be fine-textured; with silts, loams, and very fine sands providing the optimum balance of moisture affinity (favored by high particle surface to volume ratios, i.e. small soil grains), pore size, permeability and hydraulic conductivity.

Question 8

The problem with the theory that frost heave is caused by the expansion of water when it freezes is what?

Answer 8

That it was based on an erroneous assumption, which was that soils behaved as closed systems (nothing in or out).

Question 9

Who dubunked the theory that frost heave is caused by the expansion of water when it freezes?

Answer 9

Taber (1929) demonstrated that it was not expansion, but rather the formation of ice lenses by segregation of water from the soil as the ground freezes that is the principal cause of frost heave.

Question 10

How did Taber (1929) show the formation of ice lenses by segregation of water that caused frost heave?

Answer 10

By experimenting with soils as open systems he was able to show that lens growth may be sustained by the addition of groundwater drawn from warmer zones below the freezing front, and also that liquids other than water (Taber used benzene and nitrobenzene) can induce frost heave

Question 11

Why did Taber’s (1929) experimentation show that the volumetric expansion of water as it turns to ice could not be the driving force behind the vertical displacement of frozen soil?

Answer 11

Because, like almost all liquids besides water, benzene and nitrobenzene contract as they solidify.

Question 12

What are ice lenses?

Answer 12

Ice lenses are lens-shaped masses of almost pure ice that form in frozen soil or rock.

Question 13

Where does lens formation take place?

Answer 13

Formation takes place at, or a short distance behind, the freezing front at any depth where conditions are favorable and will continue until those conditions change.

Question 14

In what direction do ice lenses tend to grow?

Answer 14

Because they form perpendicular to the direction of heat flow, ice lenses tend to grow with their long axes oriented parallel to the ground surface. Most lensing is periodic, giving rise to multiple lenses separated vertically from one another by a layer of frozen soil.

The crystals develop, and are thus oriented; parallel to the direction of heat flow and it is their growth, not the path of least resistance, that controls the direction of heave.

Question 15

Why is it single, thick lenses are rare in temperate climatic zones?

Answer 15

Because their formation depends on persistent, steady state conditions.

Question 16

How do ice lenses grow?

Answer 16

The ground freezes from the surface down, progressing along a front parallel to the surface and perpendicular to the direction of heat flow, thereby creating a thermal gradient as the ground loses heat to the cold air above it.

An ice lens also forms from the top down and grows by the addition of water to its lower, warmer surface from soil below the freezing front.

Question 17

Why is it the formation of ice lenses is a far-from-straightforward process?

Answer 17

Because it requires a set of conditions that will allow water to (i) defy gravity and flow upwards and (ii) co-exist with ice at temperatures below freezing.

Question 18

In a porous medium like soil, how is water made to flow upwards?

Answer 18

It will rise naturally by capillary action.

Question 19

How is water in freezing soils moved around?

Answer 19

Down a thermal gradient OR by cryogenic suction forces.

Question 20

Why are the microscopic interactions between soil grains, ice, and water so important?

Answer 20

They are responsible for cryogenic suction forces, the fundamental controlling influence on ice lens formation and growth, and thus they ultimately drive the whole process of frost heave.

They are also the reasons why water can sometimes remain in liquid form at sub-zero (0°C) temperatures.

Question 21

What is differential heave?

Answer 21

Non-uniform movement of material in some areas than other, and lateral variations in the conditions that control ice lens formation and other freezing behavior

Can initiate an undulating surface that then causes positive feedback processes and ever more differentiation with each freeze thaw cycle.

Ultimately leading to patterning

Question 22

The main influences for the lateral variations in the conditions that control ice lens formation and other freezing behavior in differential heave are what…?

Answer 22

Soil texture and the availability of water (i.e. the height of the water table).

Other factors such as the presence or absence of vegetation, fluctuations in the thermal regime, and overburden pressure are also important but of lesser significance.

Question 23

Why is differential frost heave more destructive in spring?

Answer 23

Not only because the freeze depth is at or near its maximum, but also because its effects are intensified by an influx of water from melting snow and ice.

Question 24

Differential heave is a key mechanism in the formation of…

Answer 24

Some types of patterned ground (Kessler and Werner, 2003; Peterson and Krantz, 2003), the reorganization of surface materials into regular arrangements of various geometric shapes, commonly circles (fig. 9), polygons and lines (stripes).

Question 25

What is frost pull?

Answer 25

Can alter the orientation of a large stone causing it to stand upright.

This occurs when ice creeps downwards from the surface.

The growth of ice crystals on the upper part and the drying of the soil around the lower part cause the stone to be pulled into a more vertical inclination.