I found these curious frozen puddles in the parking lot of the Rocky Hill section of the Delaware & Raritan Canal towpath last weekend. Earlier last week we had some rain and warm temperatures but the temperatures rapidly plummeted over the next few days. This puddle’s diameter was just under a meter.
Even though some sections of the puddle appeared white, the ice wasn't completely frozen. I could see the middle section of the puddle.
According to Douglas Smith of the Universities Space Research Association:
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.
I didn’t know that at the time I saw the puddles but I was fascinated by the shapes.