GLACIAL GEOMORPHOLOGY LAB - FORMATION OF ICE LENSES
Introduction
These exercises are designed to take two laboratory periods but some additional time
may be required outside the regularly scheduled times. The objective is to collect and
evaluate data from a laboratory or field study concerning the formation of ice lenses in
frozen ground.
Experiment A - Growth of Ice Lenses in the Laboratory
Equipment
- Controlled environment room or walk-in freezer (-5°C)
- Insulated styrofoam box with thermostatically controlled internal heat source (Fig. 1A)
- Plastic tray (about the size of a kitty litter pan) filled with silt-sized glass beads or fine
silica sand
- Silt, clay, sand, and peat
- Transparent PVC or plexiglass tubes (Fig. 1B)
- Nylon cloth and elastic bands
- Waxed paper or acetate sheets
Procedure
Line the plexiglass tubes with waxed paper or acetate sheets by rolling up a piece of
acetate sheet and inserting into the rigid plastic tube. This allows the frozen soil core to
be removed for analysis at a later time. Pack a different type of sediment into each tube
and cover the bottom of each tube with a piece of nylon cloth held on by an elastic band
(Fig 1B). The sediment must be packed firmly into the tubes so that excess void space is
eliminated. Different layering of sediments may also be tried using more tubes.
Once the sediment cores are prepared, they need to be fully wetted. Place them upright
in a shallow pan of water so that capillary rise will wet them to the top. After the cores
have soaked up as much water as possible, place them into the saturated bed of glass
beads in the styrofoam chamber (Fig 1A). Silt sized glass beads are the preferred medium
because they are clean, uniform in size and have high hydraulic conductivity and matric
potential (capillary rise). If glass beads are unavailable, fine silica sand can be used.
Check the water level in the glass bead tray every 12 hours to make sure that there is a
constant supply of water for ice lens formation. If the water supply is cut off, the ice
lenses will be quickly destroyed.
The controlled environment room should be set at -5°C and the temperature within the
styrofoam box should be just warm enough so that the bed of glass beads doesn't freeze.
This temperature gradient ensures that the freezing front (point of ice lens formation) is
somewhere within the artificial soil core.
Make sure that the freezing front (horizon at which the temperature is 0°C) is indeed
somewhere within the core as soon as possible, since as long a period as possible for ice
lens formation is desirable. If the sediment at the top of the tube is frozen and the bed of
glass beads is not, then conditions for ice lens formation are in place. Normally it takes
about one week for significantly thick ice lenses to develop. When ice lenses have
formed, remove the sediment from the cores. At this point the lenses can be described by
indicating their size, shape and lateral extent (use diagrams or photographs). Also make
sure to note the type of sediment they best form in. The ice lenses should be examined in
the walk-in freezer since they will melt quickly at room temperature.
Figure 1. A. Experimental setup for generation of ice lenses in the laboratory; B. Clear
plastic sediment tubes suitable for ice lens formation.
Experiment B - Examination of Ice Lenses in Natural Sediments
Equipment
- Pleistocene geology maps
- Frozen ground sampler (Fig. 2)
- Shovel
- Plunger to remove soil cores
Method
During the first lab session, it is useful to travel to a few locations in the area to look
at ice lens formation in a variety of environments. Use of the portable, frozen soil coring
device (Fig. 2) can be demonstrated during the trip.
Figure 2. Portable frozen-soil core sampler. The left hand view shows two coring devices
and parts. The right hand picture shows the assembled corer with the heavy steel
hammering sleeve and handles for removing the corer attached.
The next step is to examine the Pleistocene geology map of the area and pick a series
of locations for sampling based on their sediment type. Sediment and ice lenses should be
collected from each site and both sediment and ice lens morphology should be described
in detail.
In addition, the roads of cold climate regions are good natural examples of what
freeze-thaw processes and heaving can do. Note the road conditions on the way to, and
around the sampling locations and try to explain the deterioration (or lack of) relative to
the glacial landforms, geomorphologic location, drainage conditions and substrate.
Make some predictions about where ice lenses are likely to form in other glaciated
landscapes.
References
Benedict, J.B., 1976. Frost creep and gelifluction features: a review. Quat. Res., 6, 5576.
Czeratzki, W. and Frese, H. 1958. Importance of Water in Formation of Soil Structures.
HRB Special Report 40, p. 200-211.
Harris, S.A., 1982. Distribution of zonal permafrost landforms with freezing and thawing
indices. Biul. Peryglacj., 29, 163-182.
Hillel, D. 1980. Applications of Soil Physics. p. 288-296.
Katasonov, E.M., 1973. Classification of frost-caused phenomena with references to the
genesis of the sediments in central Yakutia. Biul. Peryglacj., 23, 42-80.
Linell, K.A. and Tedrow, J.C.F., 1981. Soil and permafrost surveys in the Arctic.
Clarendon Press / Oxford University Press (Oxford): 279 pp.
Menzies, J., 1981. Freezing fronts and their possible influence upon processes of
subglacial erosion and deposition. In: Proc. Symp. 'Processes of Glacier Erosion and
Sedimentation'. Ann. Glaciol., 2, 52-56.
Reimnitz, E., Kempema, E.W. and Barnes, P.W., 1987. Anchor ice, seabed freezing, and
sediment dynamics in shallow Arctic seas. J. Geophys. Res., 92, 14671-14678.