Dr. James R. Carter, Professor Emeritus
Illinois State University, Normal IL 61790-4400
Figure 1 - An example of needle ice observed in east Tennessee in December. The knife is 6 cm long (2.5 inches). Note the individual strands of ice, in many places fused together. On a few small rocks in this immediate area unique forms of ice grew atop the rocks forming what is called Pebble Ice. The occurrence of both forms of ice in the same place shows the close relationship between Needle Ice and Pebble Ice.
In a process called Ice Segregation cold water moves through a medium toward the presence of ice, freezes at the interface and adds to the ice. When this occurs at or near the surface of soil it produces Needle Ice, which takes the form of strands of ice rising vertical from the surface or near surface of the soil.
When this same process of Ice Segregation occurs on certain plant stems it produces Ice Flowers . When it occurs on pieces of dead wood the resulting ice is called Hair Ice. When it occurs on some small rocks it forms Pebble Ice. All of these forms of ice have similarities but are unique.
In all cases these growths of ice occur at the Earth’s surface when moisture in the medium is liquid, and the air temperature is below freezing. Normally such conditions occur over night in late fall, winter and early spring. As the water freezes latent heat of fusion is released helping keep everything from freezing solid. As long as there is a balance of energy flows keeping the water in the medium from freezing and keeping the temperature of the ice surface below freezing, ice will continue to grow at that interface. (Outcult, 1971)
Ice Segregation is known to occur in subsurface environments and can be a significant geologic force in areas with permafrost and in periglacial environments.
Nature of Needle Ice
Needle ice is quite common, and many people have encountered it when they walk across a grassy surface on a cold morning and the ground crunches underfoot. In some cases, it can be quite large or unique and attract attention. The process of moving soil particles with ice can disrupt the soil surface and in the process be a factor in shaping the landscape and eroding the land as well as doing road damage. On occasion it can produce attractive displays similar to ice flowers and hair ice, but generally needle ice is destructive and disruptive and not particularly attractive.
Considerable research has been conducted on needle ice. Lawler (1988) published a bibliography of Needle Ice listing 267 references dating back to 1824. The phenomenon occurs in many countries and is known as Kammeis or Stengeleis in German, Shimobashira in Japanese, Hielo acicular in Spanish and Piprakes in Swedish. Lawler provides a table listing the many terms people have given for this phenomenon.
For Ice Segregation to produce ice, the medium must have enough pore space to conduct water to the surface to supply the growth of ice, but the pore spacing must be small enough to hold the water in place against gravity. In general, this spacing exhibits capillarity which will wick water toward the surface. Meetenmeyer and Zippin (1982) discuss the texture of soils that produce needle ice, noting that a significant presence of clay and silt are required in such soils. They were able to ‘create’ soils that grew ice in a refrigerated environment.
If you ever had the soil crunch underfoot on a cold morning, then it is likely you were walking on needle ice. Such needle ice would not be as impressive as above, but still, it is needle ice.
Once I started looking for ice, I noticed that one area of bare soil had small ridges and pits on cold, frosty mornings. These ridges are needles of ice. This area of bare soil is under the leaves of a large lily during the summer and in the winter is barren.
In central Virginia I found needle ice that had pushed up a thin crust of soil by about 3 cm, below.
In my observations on ice, I found ice growing on pebbles and explored this process by conducting experiments in a freezer of a refrigerator. Most of the time I used sand as my base material but on occasion I used a fairly heavy soil with relatively large clay content as the base material. The results below show what I got one time in this setup.
Needle ice can vary in appearance but always shows the consistent growth of ice perpendicular to the land surface. In many cases the freezing plane is a little below the surface and thus some soil and particles on the surface will be lifted by the needle ice.
Needle ice is likely to occur throughout the world where there is freezing and thawing, and the soil contains sufficient proportions of fine particles to wick water toward the surface through capillarity.
Lawler, D. M., 1988. A Bibliography of Needle Ice. Cold Regions Science and Technology, 15, pp. 295-310.
Meentmeyer, V. and J. Zippen, 1981. Soil Moisture and Texture Controls of Selected Parameters of Needle Ice Growth. Earth Surfaces Processes and Landforms. Vol. 6, pp. 113-125.
Outcalt, S. I., 1971. An Algorithm for Needle Ice Growth. Water Resources Research, Vol. 7 pp. 394-400.
There is a Wikipedia page on needle ice: http://en.wikipedia.org/wiki/Needle_ice
Related web pages showing products of Ice Segregation
Hair Ice - ice growing on pieces of dead tree branches on the ground or suspended in the tree
Ice Flowers - ice growing on the stems of a few species of plants
Pebble Ice - ice growing on small rocks through ice segregation
Sub-surface ice formation in geologic environments
On a web site discussing frost heave a photo shows the presence of ice needles about a meter below the surface. Note that the ground had to be removed to expose these needles.
The presence of needle ice at the surface, a centimeter below the surface, and a meter below the surface are manifestations of the same processes. The Wikipedia page on Ice Segregation discusses even deeper occurrences of such ice.
Some of the ice formed by Ice Segregation can be quite attractive but in general needle ice does not take such forms. But it is quite common where freezing occurs and can be an important in shaping the land surface and contributing to surface erosion.
Thank goodness for the Internet and digital cameras for they let us exchange information about these small ice formations. Please look for interesting ice when the freeze/thaw processes are underway. With your help we might gain more insights about these products of ice segregation.
For more on my perspectives see my web pages at http://www.jrcarter.net/ice/
Feel free to contact me at email@example.com to share your photos of ice of this nature from your early morning outings.