Ice Segregation Dr. James R. Carter, Professor
Emeritus Illinois State University, Normal IL
61790-4400 |
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The process of Ice Segregation takes place in
a porous medium when supercooled water moves to the presence of ice and adds
to the ice through freezing. In this
case the ice grows away from the ice/water interface. It is logical to assume the name derives
from the fact that where water starts off widely dispersed within the porous
medium it becomes segregated into discrete pieces of ice in the form of
lenses, ribbons, needles, layers or strands of ice. In nature Ice Segregation occurs at or near
the surface of the Earth in the form of Needle Ice in soil, Ice Flowers on plant stems, Hair Ice on dead wood, and Pebble Ice on small
rocks. Such ice segregation products
may be quite attractive, and people post photos of such ice formations. In some cases, needle ice disturbs the soil
surface which has been shown to accelerate soil erosion. My Ice Segregation Garden: The four examples
of ice segregation above occurred in late January 2018 in an area of less than
1 square meter in central Virginia, USA. The flower is on a Penta stem left
over from the previous summer, the needles are in loops about 5 cm across in
the resident soil, the hair ice is on a stick sent to me from a person in
Washington State where the fungus exists to produce Hair Ice. The pebble is one I had used
previously in my refrigerator experiments and was turned over to better show
the ice in a photo. The
stick and pebble had been soaked in distilled water before being placed on
the soil. In the subsurface in some soils ice
segregation forms distinct layers of ice that can cause frost heaving. Within the crust of the Earth ice
segregation forms wedges and layers of ice that are found in tundra and periglacial
environments. In subsurface
environments ice segregation may disturb soil structure and wedge apart rock
formations. The process leads to so
much upheaval in some places that it produces unique landforms. Ice segregation occurs where above freezing
and below freezing temperatures are juxtaposed. At the Earth’s surface this is most common
in fall at night as the air cools to below freezing while the land surface
stays relatively warm. However,
micro-meteorological events may produce these conditions at other times. And as freezing takes place heat is
liberated into the immediate environment through the latent heat of
fusion. The process continues as long as rate of cooling is balanced by the rate of
warming with the latent heat of fusion.
When these get out of balance everything freezes up or it becomes warm
enough to stop freezing. Ozawa and Kinosita,
1989, conducted controlled experiments on ice segregation where they were
able to monitor and test the formation and growth of ice with great
precision, away from the vagaries of nature.
In their paper they provide explanations for the processes involved in
ice segregation. They used a
microporous filter as the barrier between supercooled water below and ice on
top of the filter. A small piece of
ice was placed on the filter to start the process. When they had the right temperatures, water
was drawn up from below and froze to the base of the ice, causing it to grow
up and away from the filter. At that
freezing front they confirmed there was a thin film of water between the
filter and the ice. They recognize that ice segregation occurs at
the surface producing things like needle ice and at depth leading to things
like frost heave, but also noted ice segregation may produce ice on the
surface of thin biomembranes leading to dehydration
of constitutive cells in a process called extracellular freezing (113). Thus, ice segregation is a significant
force in the natural environment. Ozawa and Kinosita
recognize that it is known that ice segregation occurs in soils only when
particle sizes are less than 0.1 mm (silt and clay)
so they selected filters with micropores in the range of 0.015 0.2 um
diameters. Pores of this size permit
water to pass through the filter but ice cannot. They found that when cold enough the
supercooled water below froze showing that ice segregation takes place within
a critical range of temperatures. By
making many observations they got insights into the critical degree of
supercooling, that temperature below which ice formed in the supercooled
water. They found that this
temperature was slightly higher with increasing pore size showing that finer
textured media can experience ice segregation through a larger range of
temperatures (all within a fraction of 1 degree C). In this study they did not answer all
questions about ice segregation, but they demonstrated how the process occurs
with precise measurements that could not be taken in nature. Indeed, ice segregation is the process that
accounts for ice flowers on some plant stems, needle ice in fine textured
soils, pebble ice on a few small rocks, hair ice on some pieces of dead wood,
frost heaving in some soils and ice wedges and more in tundra and periglacial
environments. Ozawa, Hisashi and Seiiti
Kinosita, 1989, Segregated Ice Growth on a
Microporous Filter, Journal of Colloid
and Interface Science, Vol. 132, No. 1, pp. 113-124. Concluding Statement This page is one of a number I have on ice in
nature. Ten 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 and now realize that much of the time I am observing
products of ice segregation. What we do
know is that this ice from ice segregation is not a form of frost.
Frost 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 it is below freezing moisture
is deposited out of the air as frost. In most cases the conditions
that are appropriate to the growth of ice flowers, needle ice, hair ice
and pebble ice are also appropriate to the formation of frost. For
this reason, people may give the name frost to any formation of ice
on anything at the surface. But, such
ice is not related to frost although it make take a deposit of an ice
crystal to start the Ice Segregation process. Thank
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 jrcarter@ilstu.edu to
share your photos of ice of this nature from your outings or
freezer experiments. |
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