Local Knowledge: A Sticky situation

By Paul Swenson EBS COLUMNIST

It’s that time of the year when the snow on the ski hill or in the backcountry becomes “grabby” or “sticky.” I decided to write this column after I got the jerks skiing between sun and shade. You all know that feeling when your skis jump out from under you on the fast icy shady spots only to suddenly slow down in the sunny spots. Let’s take a look at water, snow, the reason snow is slippery, then how to remedy a herky-jerky day on the slopes.

To begin with, snow is just solid water and water is a simple molecule with really interesting behavior. You probably learned in chemistry that Dihydrogen Monoxide (DHMO), or Hydrogen Hydroxide, are the appropriate names for water. Scary sounding chemical name for H₂O, or HOH. Water is a bent molecule that has an electrical property called polarity. Even though in totality it is neutral, the hydrogen ends have a positive charge, and the oxygen sitting at the vertex of the angle has a negative charge. This polarity gives water many of its unique characteristics: A universal solvent, strong adhesion, and cohesion which lead to a very strong surface tension. It is this surface tension that wants to draw a drop of water into a spherical shape, and the adhesion that holds a drop of water on your fingertip.

It is also this adhesion, defined as the attraction between dissimilar materials, that can slow down your skis.

So why is snow or ice slippery in the first place? Many of us are under the common misconception that when we ski or ice-skate that we put enough pressure on the snow, or ice, that it melts and a thin layer of water forms and that’s what makes it slick. That would be such a cool and easy explanation, but to lower the melting temperature of snow down by 1 degree Fahrenheit it takes 900 pounds per square inch. Now I am a big person, but I would need to weigh in at 260,000 pounds to put that amount of pressure on the base of my skis! But the answer is called a premelt layer.

A premelt layer is a disorganized layer of water molecules that sits at the interface between ice crystals and the air that surrounds them. They are not part of the lattice structure of the ice, but not thick enough to form droplets. The layer is only a couple molecules thick, but that is enough to make ice slippery. These molecules at the surface transition from the ice surface into a vapor state, then return to the ice crystal. They are free to move, translate, or rotate under stress.

So as long as the snow is “dry” this premelt layer creates a slippery layer that skis can glide across, as long as the skis do not attract the water molecules. With the addition of humidity, or warming from the sun to the melting point of the snow’s surface, the premelt layer can become thick enough to create water droplets which coalesce under the stress created by a ski. This is when the snow gets sticky.

So how to combat this problem? Find a surface that repels water—a hydrophobic surface. Chemicals that are non-polar are hydrophobic. The first skis made in the Norse countries were made of wood. To keep them from soaking up water, pine tar, resin, or animal fats were applied to their surfaces. Luckily for those first skiers these materials are non-polar by nature, creating good gliding surfaces for them even hundreds of years ago.

Today skiers, ski racers, and ski shops use ski waxes. These waxes come in a variety of chemical formulations, but the majority are hydrocarbon based. Hydrocarbons are chemicals made of hydrogen and carbon. They come in short chains, like propane, butane, gasoline, as well as longer chains like oils and waxes. The longer the chains, the harder the waxes. Then with the addition of some other side chain chemicals, such as chlorine or fluorine, a more hydrophobic wax can be made.

Fluorinated waxes are still around, but they are extremely harmful to the people applying the waxes, the racers who scrape and brush their bases, and the environment itself in and around the ski hill. There is a proposed ban on these types of waxes by the International Ski Federation, International Biathlon Union, U.S. Ski & Snowboard, International Orienteering Federation, and the International Olympic Committee, but these bans keep getting postponed. In the application of these waxes, if one does not wear the appropriate filtering apparatus, PFOAs and PFAS and other PFCs are inhaled and incorporated into the person’s tissues. They are “forever” chemicals that are not biodegradable, found in the soil and runoff at ski hills, and are proven carcinogens. Even regular hydrocarbon waxes produce nasty byproducts.

So this spring, I would encourage all of you that wax your own skis, or work in a shop, to get a high quality respirator with an organic fumes filter. Save your lungs.

Paul Swenson has been living in and around the Big Sky area since 1966. He is a retired science teacher, fishing guide, Yellowstone guide and naturalist. Also an artist and photographer, Swenson focuses on the intricacies found in nature.