Hair Ice – An Elusive Delight in Our Winter Woods

by Ron Kleinknecht

We all know what ice is, but do we all know about the many interesting forms that it can take? Some of these forms such as hair ice (haareis) are often difficult to see as they are ephemeral and are often not seen in plain sight as they blend in with the frost or snow. But, they are all found in our local environments — in the woods or even in our backyards.

Although not really rare, hair ice is not often seen. As shown in the photo below, it consists of hair-like filaments of ice that protrude from dead wood such as sticks, logs or branches. It occurs under fairly specific circumstances, such as temperature, moisture, the substrate on which it will grow, and the presence of a specific fungus. When I saw my first specimen, I thought it was a weird form of frost, or maybe a form of mycelium (fungal underpinnings of mushrooms) with which I was unfamiliar. I was partially right on both counts as I’ll illustrate shortly.

Although hair ice has been described and theorized about in the scientific literature for over 100 years, the research into the conditions and mechanisms under which it occurs has only been more fully described by scientists in the last decade or so. (1)

The first scientist in modern times (1918) to describe hair ice was Alfred Wegener, a German arctic meteorologist. In describing this new ice form that he found in the forest, Wegener also observed that it appeared to be associated with fungi which were present in the wood on which it grew. (Wegener, a keen observer, was also the first scientist to postulate the theory of continental drift that became the basis for tectonic plate theory).

So, What Is Hair Ice?

First, hair ice is indeed ice from frozen water, although it is not frost. Instead of growing sheets of crystals like we see on a puddle, the frozen water forms minute hair-like structures that curl and wave (about 0.01 mm diameter, about the width of a human hair). However, it does not occur just any time there is water and freezing temperatures. It is very picky as to how, when and where it freezes into this unique form.

The necessary conditions are as follows:

• Temperature is just below freezing,
• Moisture is present from water vapor or ground water with minimal or no breeze.
• It only grows on dead twigs and branches of broad-leaf trees (e.g. here, red alder, big leaf maples).
  • The branches must be devoid of bark, or, if bark is present, it is loose and flaking from the limb leaving the underlying wood surface exposed,
  • These branches must be infiltrated with mycelium of the winter-active fungus, Exidiopsis effusa (E. effusa).
• “Geographically located between 45 and 55 degrees latitude.” (We are right in the center of its northern zone).
• It is not found on bare ground, on leaves, or on living trees.

Hair Ice Is Elusive

I have now seen hair ice on several occasions since I became aware of what it was and when and where to look for it. I might well have seen it before but did not know what I was observing. It typically forms at night with lower temperatures and then melts as daylight temperatures rise. Next is a photo of a specimen beginning to melt.

If there is snow around or ground frost, the hair ice is not obvious. However, if there had been a light freeze without frost or snow, it might stick out like batch of white cotton candy on a mossy green blanket.

How Hair Ice Forms

Nearly 100 years after it was first described, several researchers from Germany and Switzerland have been able to clarify many of the conditions and processes responsible for producing hair ice. Interestingly, each of these scientists became intrigued by hair ice after encountering it while walking in their local woods. They then took it into their laboratories.

To verify Wegener’s fungal hypothesis, Gerhart Wagner from Switzerland demonstrated that fungi were indeed involved. He treated wood on which hair ice had grown with either a fungicide or by boiling it in water, both of which should have killed any fungus. Subsequently, the treated woods did serve as a platform to host normal ice crusts, but it no longer produced hair ice. No fungus, no hair ice. (2)

But, was just any fungus sufficient or was there a specific species involved? To examine this issue, Giesla Pruess, a German biologist, brought 78 samples of wood that produced hair ice into her lab and analyzed the species of fungi found in each. Although 11 different fungal species were found in many of the samples, only Excidiopsis effusa was found in all of them. So, without E. effusa, no hair ice. (3)

Lignin as Antifreeze

After it was determined that a specific fungus was involved, Diana Hofmann, a German chemist, further determined that the melted water from hair ice contained (among other molecular substances), decomposed lignin, a product of fungal metabolic activity in the wood. Lignin acts as the glue and skeleton, providing structural support and binding fibers together in plant cell walls. Lignin was subsequently found to serve as a sort of antifreeze that kept the water and the surface of the wood from freezing. This allowed the not-yet-frozen water to continue to provide hairs to grow longer.

“The action of the fungus is to enable the ice to form thin hairs — with a diameter of about 0.01 mm — and to keep this shape over many hours at temperatures close to 0°C. Our hypothesis includes that the hairs are stabilised by a recrystallisation inhibitor that is provided by the fungus.” (3) [British spellings]

The team appeared to have identified some of the players that were involved, but not which physical processes directly formed the hair ice. To address this issue, Swiss physicist Christain Mätzler, explored processes at work during freezing that resulted in the production of the ice hairs themselves. He determined that a physical process called “ice segregation” at the point of freezing was the “driving mechanism” responsible for producing ice filaments at the wood surface. (2, 3)

Sandwiching of Water

Mätzler postulated that liquid water near the branch surface freezes in contact with the just freezing cold air creating an ice front. Below this ice is a thin film of water on the branch. Mätzler called this “sandwiching” of the water between the ice on top and bare wood and its pores below.

Suction resulting from repelling intermolecular forces acting at this “wood-water-ice sandwich” then pulls the water from inside the wood through the pores and moves it towards the ice front. Water reaching the ice front freezes and then projects from the wood outward in the form of hair-like strands, shaped by the round wood pores. (4)

In summary, there is an ice front or layer, with unfrozen water under it and all on top of a piece of E. effusa-infused bare wood — no bark. Through ice segregation, the water is extruded through the tiny pores and pushed up to the frozen layer to form ice filaments that go through the ice front as ice hairs that grow outward. The E. effusa acts on the water in the wood (not ice) and keeps it from freezing in the wood, allowing more to be sucked from the wood pores into the ice front and projected as hair ice. The E. effusa keeps the water from freezing and allows the process to continue to grow more and longer ice hair.

When and where to look for hair ice: in the late fall or winter if the temperature is just below 320F and if there is plenty of moisture, I can usually find some hair ice — if I am out early enough. I go to forested areas with plenty of broad leaf trees with broken branches on the ground. For example, just this fall, I found hair ice in Arroyo Park, on Lookout Mountain trails and along the Nooksack River. According to Dr. James R. Carter of Illinois State University, Washington state is one of the most common places to find hair ice. We have moisture, fungi, mildly freezing temperatures and plenty of dead trees and branches. (5)

Good luck in finding some of these attractive and intriguing forms of silky ice.

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Ron Kleinknecht is professor emeritus of psychology and dean emeritus of Western Washington University’s College of Humanities and Social Sciences. He serves as a volunteer land steward and volunteer ambassador with the Whatcom Land Trust.

References:

1. A. Wegener, “Haareis auf morschem Holz,” Die Naturwissenschaften, 6, jahrgang, 1918, Heft 41, s. 598-601.
2. Gerhart Wagner, Christian Mätzler: “Haareis – Ein seltenes biophysikalisches Phänomen im Winter.” Naturwissenschaftliche Rundschau 62(3), S. 117–123 (2009), ISSN 0028-1050.
3. Hofmann, D., Preuss, G., and Mätzler, C.: “Evidence for biological shaping of hair ice,” Biogeosciences, 12, 4261–4273, https://doi.org/10.5194/bg-12-4261-2015, 2015.
4. A video provided by American Scientist illustrates the formation of hair ice narrated by Dr. Mätzler. https://www.youtube.com/watch?v=uZ_RJ1z22Vw
5. Professor J. R. Carter’s (Illinois State University) Websites: https://www.jrcarter.net/ice/ and https://www.jrcarter.net/ice/hair/