Explaining Ring Patterns in a Frozen Puddle
January 28, 2014
Photographer: Douglas Stith; Doug's Web site
Summary Authors: Douglas Stith; Steven Arcone CRREL; Zachary Stith
My son, Zachary, found this curious frozen puddle in Concord, New Hampshire on the afternoon of February 1, 2013. January 31 had unseasonably warm temperatures (in the 50’s F, about 12 C) and heavy rain, but temperatures plummeted after sundown. The official morning temperature on February 1 was 16 F (-9 C), but the temperature was still well below freezing later in the day. The puddle’s diameter was approximately 6 ft (2 m). Upon closer inspection we found that the ice wasn't completely frozen to the puddle's shallow bottom. We easily picked up the thin frozen layers on the puddle that were no more than about a quarter inch (5 mm) thick. We also observed slight bulges below the rings of ice. The overall milky-white color resulted from the presence of minute air bubbles, but some clear bubbles were also present.
How various ice features form, change shape and melt is rarely straightforward and sometimes quite confounding. Factors such as water purity, the rate of cooling, the preferred growth of ice in crystalline planes, etc., all play a role.
The shallowness of this puddle suggests that it rapidly froze; only a thin water layer remained below the puddle. Then the fast-falling temperatures likely caused the ice to contract, which produced the cracking. Continued cooling widened the cracks. The ring pattern shows that the main direction of the stress force was radial, but the scalloped pattern along the rings shows that some stress varied with angle around the center. The small amount of water that didn't freeze rose into the cracks due to the hydrostatic pressure of the ice above and capillary action. Water in the rings then froze and expanded, and as it did it widened the rings and also directed the remaining small amount of liquid to the top of the ice. The slight bulges on the bottom of the rings were remnants of its last contact with the deepest water. In other words, the unfrozen water at the bottom of the puddle was, in essence, pushed and suctioned into the cracks.
Photo details: Camera Model: Canon PowerShot SX120 IS; Lens: 6.0-60.0 mm; Focal Length: 6mm; Aperture: f/2.8; Exposure Time: 0.033 s (1/30); ISO equiv: 250.