Wisconsin Nature

The Art and Science of Ice Formations

Winter brings spectacular sights along with the transformations that take place at Schlitz Audubon. Take a slow hike on the boardwalk by Mystery Lake or Mystery Pond to see some of them. If you look down into the frozen water, you will notice a number of intricate formations at various depths in the ice. These miniature constellations are waiting to be explored.

There are spheres consisting of small and medium-sized bubbles caught and suspended in ice. They are grayish spherical shapes that can get quite large, or can be so small they look like a thin, hazy layer spread like little points throughout the frozen water.

You will also see crystalline shapes made of fallen leaves, twigs, and other items, which freeze underneath the surface. Look for rings, too. Sometimes rings surround a branch rising from the surface of the frozen water. You can also find them by the shore, where water froze by the edge of the land.

Encountering these sparkling geometric entities is a treat to the eyes. However, when the science behind these structures is understood, it makes viewing them even more interesting.

How Ice Bubbles are Formed

Water bubbles arise when anaerobic bacteria decompose leaves and other organic material. This process lets out methane gas, which rises to the surface. When the temperature is at or below 32 degrees Fahrenheit, and ice begins to form, the downward moving ice stops the methane bubbles from reaching the surface. The bubbles freeze. As the ice gets thicker, this process creates more bubbles, frozen and stacked one beneath the other, forming a column-like shape.

When the conditions are just right, these bubble columns may form a pyramidal shape. Ice thickens more slowly as it grows downward. When the thicker ice sheet traps methane trying to rise to the surface, the methane has more time to pool at one level of the ice’s thickness. This process creates larger bubbles. As the ice grows thicker and more methane is trapped, even bigger bubbles are formed at greater depths. This creates a pyramid shape.

Making Leaf and Twig Crystals

The bubble columns are a unique sight, but you might also notice another formation that’s just as impressive. When a leaf, twig, or other natural object freezes in ice, the object can appear crystalline, with facets surrounding it. The facets reflect the light directed at them, making the object take on a sheen. It’s like a shiny piece of ancient crystal emanating pockets of silver light. Oftentimes, the thick ice surrounding these structures doesn’t have any facets, causing the crystal-like shapes to stand out. The thick ice is a solid piece without air inside, called black ice, and it is see-through.

Creating Nature’s Ice Rings

Another visually appealing phenomenon consists of concentric circles and wavy lines that form within puddles. They also form in areas of frozen water that surround objects that jut through the surface. Some of them look like rings around a branch, or rings within the edge of the ice’s border with the land.

The science is interesting here, too. One theory suggests that, first, ice forms a thin, roughly circular sheet around the base of a tree. If rain occurs when there is freezing at night, a bright ring can form from the outer edge of the submerged older ice.  If this cycle repeats itself, you can get another ring outside of the first. This year we had an exceptionally large number of these rain and freezing cycles in a concentrated time period.

However you look at them, these little universes of pattern are a remarkable sight. They’re a good thing to search for on your next winter hike at the Center. Just remember to remain on the boardwalks near the pond and lake, but feel free to bend down close to see the formations in detail.