Dr. James R. Carter, Professor
Illinois State University, Normal IL
In the process of Ice Segregation cold
water moves through a medium toward the presence of ice, freezes and adds to
the ice. When this occurs at the
surface of soil, it produces Needle
Ice . When it occurs on plant
stems it produces Ice Flowers
. When it occurs on pieces of dead
wood the resulting ice is called Hair
Ice . Recently it has been found to occur on small rocks and pieces
of brick and pottery, all the size of pebbles. (4 - 64 mm / 0.016 - 2.5 in.) Thus, I propose to call this form of ice
Ice Segregation is
known to occur in subsurface environments and can be a significant geologic
force in areas with permafrost.
Pebble Ice in Nature
Then I received photos from colleagues in
Alabama and Missouri.
colleagues in Alabama and Missouri sent me pebbles on which they had seen ice
grow. I put those pebbles in my yard where I had seen needle ice. Indeed, ice did
grow on some of those pebbles, but not as dramatic as shown in their photos.
But it demonstrated the process that produced needle ice also produces
growths of ice on small rocks.
found that there are two postings of images of ice on pebbles on the Story of Snow web
pages. On the first page the author tells of
seeing columns of ice standing apart from needle ice in a rice field. He noted the cap of ice easily and cleanly
separated from the pebble. This is
obviously Pebble Ice. On a second page written in 2013 the
author shows photos of ice growing from asphalt and offers an explanation of
the processes underlying such growths of ice and suggests the name Pebble
Caps for such ice formations.
Growing Pebble Ice in a Freezer
wait for cold mornings to produce such ice, I set out to replicate the
process in a refrigerator freezer. I
used a small ice chest that fits in the freezer. I put a small light bulb in a clear plastic
bucket in the bottom to generate heat.
I overlaid a sheet of aluminum to disperse the heat and then set
another plastic bucket with wet sand over my heat source - the light
bulb. I packed insulation between the
walls of the chest and the plastic buckets.
I then adjusted the amount of light with a rheostat to find the right
combination of temperatures that might grow ice on the pebbles placed on the
wet sand/soil. Sometimes it worked
on Growing Ice in a Freezer
in my refrigerator has permitted me to try many different pebbles under
different conditions. I have had ice grow on a few pebbles and pieces of clay
pots and brick. After many trials and thousands of photos, I show what I have
discovered in the selected images below.
You can do it 12 months of the year
You can experiment by varying only
one factor at a time
It is quite inexpensive but gives
Being inside gives access to
electricity, lighting, water and other equipment.
The height of the water in the bucket
of sand can fall below the base of a pebble and I have
found no way to add water during a growth session. When this
happens, growth stops for the lack of water. In nature soil moisture
is drawn from a larger area and may include some flowage.
top of the freezer limited the height to which the ice could grow, on
The setup does not permit setting
precise standards for temperature and humidity, so you work with what you
There appears to be no difference
between using tap water and distilled water
It seems to be impossible to replicate
the growths of ice on the same pebbles in the same position, suggesting some
randomness in the process.
On the nature of the
pebbles which grow ice
Because such growths are produced
by ice segregation the pebble must be permeable enough to permit water
to move through it but not so porous that water will drain from
pores. Such pebbles when dry will wick-up moisture displaying
To identify pebbles that might have such
capillarity I weighed dry pebbles, then wetted them on a sponge for 15
seconds and then weighed them again. If the pebble gained 0.02
mg or more then it was likely to produce ice through ice
segregation. Most pebbles tested gained no noticeable weight and did
not grow ice.
A petrologist noted that another test is to
place the pebble against your tongue. If it will wick-up water through
capillarity it will stick to your tongue. It works.
Good Examples of
Pebble Ice Grown in the Freezer
The pebble below from Jerry Green measures 5
X 3.5 X 1 cm (2 X 1.4 X 0.4 in)
When placed flat on the sand a thin sheet of
ice covered the entire surface (lower left).
In the lower right image, the ice formed part way up the pebble and
not at the sand surface. In this case
none of the other pebbles in the setup had any ice, indicating the freezing
plane was not at the sand surface but some 2 - 3 cm above the sand.
These four images show the water in the
pebble takes the shortest route to the freezing surface. Thus, in the upper left image the diagonal
route to the ice is shorter than going to the top of the rock. In most cases the ice grows from the sides
of the pebbles.
The Pebble Ice
This diagram shows the basic environment in
which pebble ice forms. The sand is
porous and contains water that will drain away under the influence of
gravity. The pebble contains water
that is held in place by capillary attraction. Once Ice Segregation starts, water moves
from within the pebble to the freezing front, which is on the surface of the
pebble. As new ice is formed on the
pebble surface it pushes out the existing ice. As water moves to the freezing front
additional water is wicked up through the pebble, lowering the level of water
in the sand.
If the freezing plane is a little above the
sand, pebble ice may form higher up on the pebble. This process will continue until the water
level in the sand drops below the pebble, or the energy flows become unbalanced
and freezing extends into the pebble and sand and everything freezes, or the
freezing plane extends above the pebble and nothing freezes.
On the Process of
Trying to Grow Ice
The diagram above shows conditions at the
time the ice is growing on the pebble.
When the cooler is placed in the freezer the temperature of the sand,
pebbles and water are normally at about 20 degrees C (68 degrees F). The base of the sand may be warmer because
the light bulb has been generating heat while the unit has been out of the
freezer. Once the unit is placed back
in the freezer everything has to cool to reach an
equilibrium as shown in the diagram.
Normally, I leave the setup in the freezer for 18 or more hours, many
times for multiple days.
Before putting pebbles in the wet sand, I
soak them in water. I put the wet
pebbles in the sand and then remove any standing water from the top of the
sand. Normally I then put the setup
into the freezer.
To see how long the pebbles will retain any
internal water, I have let them sit in the sand at room temperature for up to
22 hours to air-dry. Even when the top
of the sand was dry, I sometimes got good ice on the more productive pebbles.
To initiate Ice Segregation there
must be an ice crystal on the surface.
The freezer has frost built up in it and normally there is some frost
deposited on the sides of the plastic bucket holding the sand. So, I assume frost provides the ice
crystals needed to start the process.
However, there are times when no ice forms on one productive pebble
while good ice forms on a productive pebble 2 cm away. Is that because a
crystal of ice did not deposit on the pebble in the right place?
I would like to know much more about this
process. It is a slow process to grow
ice, but I have been at it long enough to get many examples that tell me
about the basic process.
More Examples of Good
Below are photos of ice grown in the
freezer. The shapes of these ice
formations vary considerably. In the
diagram above the top of the pebble extends well above the freezing front,
explaining why most ice will form along the sides of the pebble near the
In many examples there are growth ridges
shown in the ice. To keep a relatively
constant temperature a refrigerator cycles on and
off. Measurements show the temperature
in the freezer varies by about 1.2 degrees C over a 40-minute cycle. Although this is a fairly
small temperature variation, in some cases it is reflected in the
pattern of ice.
The pebbles below show wings of ice growing
out of the side of larger pebbles.
I set up many different experiments over the
years. I stacked up pebbles to see if
ice would move through one pebble to lift another. Indeed, it did in some cases. Below are examples using Wave, one of the
pebbles provided by Jared Wilson. Size
4x3x2.5 cm (1.6x1.2x1 in)
The pebble I named Round-black from Alabama
has been a very productive in growing ice.
Below are three examples of the many that have been produced with this
rock 4.5x2x2 cm (1.8x0.8x0.8 in)
The pebble below is a broken rock I
found. 4x4x2 cm (1.6x1.6x0.8 in) This pebble was included because it
is so common looking, yet still produced ice.
As noted, I found a few pieces of brick and
pottery that produce ice.
In my experiments I sometimes used a mix of
soil with a large clay content as the base, rather than sand. The results below show what I got one
time. Many times, I got a mess and
nothing worth photographing.
After observing the results of hundreds of
attempts to growth ice through the media of pebbles in a freezer in a refrigerator
I have gained an understanding of the process. The physical process is Ice Segregation and is
consistent with the products of ice segregation as seen in Ice Flowers on plant stems, Hair Ice on dead wood, Needle Ice in soil and in
layers of rock and deposits in the subsurface.
The key here is to have pebbles and rocks
that have the appropriate texture and porosity to transmit water to the
surface to feed the growth of ice.
Then these pebbles must be positioned so that they are wetted from
below while being exposed to freezing temperatures on the surface.
Remember to look down on frosty morning, take
photos and share them with a larger public.
I give thanks to the Jerry Green and Jared Wilson for capturing such
photos and sharing them with us.
Reflections on a
World of Ice Formations
Fifteen years ago, I knew about icicles and
patches of ice on streets and walkways, and that was about it. Now when it is above freezing part of the
day and below freezing part of the day, I look for ice in many places, and
often find it. I have learned much by observing these many forms of
ice. I hope you will join me in the
search for ice in its many forms.
We know that
Pebble Ice is not a form of frost, which comes about when the air becomes
saturated and water vapor is deposited on a surface as an ice crystal.
If the air temperatures are above freezing, we get dew, but when below
freezing water vapor is deposited as frost. And, frost is required
to initiate Ice Segregation. For this reason, people may give the
name frost to any formation of ice on anything at the surface.
There is no authority or process to regulate names plus it is fun to let our
imagination run wild and assign names for what we see. But, do not get confused. There are at least three different
types of features in nature people that use ‘frost’ as the appellation in
goodness for the Internet and digital cameras for they let us exchange
information about these attractive ice formations. Please look for
interesting ice when the freeze/thaw processes are underway. For
additional perspectives on ice see http://www.jrcarter.net/ice/
Feel free to
contact me at [email protected] to
share your photos of ice of this nature from your outings or