NATURE NARRATIVES: An icy canvas


Interlocking arcs and circles are etched into a frozen pond.
Melissa Walker photo
By Melissa Walker

       The temperature plunged last night (Feb. 1), taking us from a winter thaw to an arctic freeze. Our backyard pond, free of ice yesterday afternoon, was frozen over this morning - a common event during a Colorado winter. But the frozen surface of our pond today looked completely different than I've ever seen it before. The ice was inscribed with a maze of concentric circles and arcs.
       The patterns in the ice were partially covered by a sprinkling of sugary snow, except where high winds had blown away the snow near the pond's edges. That's where the interlocking icy arcs transformed our pond into a mysterious work of art.
       What could have caused these curved lines on the pond ice? When I went outside to investigate, I discovered that all the arcs and circles were actually etched into the ice about one-third inch deep. Could they have been caused by last summer's flower stalks bending in the wind and sweeping across the pond as it froze, engraving the patterns? No, the patterns were too extensive and were out of reach of the stalks.
       Could the patterns have been caused by someone throwing pebbles? The circular patterns certainly looked like ripples that had frozen as they receded from pebbles tossed into the pond. But no one had been tossing pebbles last night as the cold front blew through with its zero-degree wind chill.
       Looking for a plausible explanation, I called my brother Winston in Steamboat Springs. As a biologist, he is a very thoughtful observer of Colorado's flora and fauna, and has spent more time ice fishing and fly fishing on Colorado's lakes and rivers than anyone else I know. After reviewing the photos I sent him, Winston deduced that gas bubbles rising to the pond's surface had created ripples that froze in the action of receding. I hadn't put our de-icer into the pond before the cold front, so maybe that's why I had never seen these patterns before. Without the de-icer, the ripples couldn't dissipate, and instead pushed up against other ripples that were in the process of freezing.
       The exchange of oxygen and other gases between our pond and the air is usually invisible to us. But last night's perfect conditions for flash freezing revealed wondrous shapes caused by this dynamic phenomenon. And because of the wondrous shapes, I now realize that our backyard pond is a canvas - a canvas where nature paints in shadows, reflections, leaves, tracks, wind and ice. The artwork is ephemeral, yet continual and ever changing.

A Westside naturalist, Walker posts regular entries in her online blog at naturenarratives.com. She has given her permission to reprint selected pieces in the Westside Pioneer.