Ice Sail in Pothole
June 05, 2013
Photographer: Jacques Leblond-Murphy
Summary Author: Ray Murphy
The sail-like ice protrusion shown above formed in a natural pothole that was filled with rainwater. It stands about 3 in (7.5 cm) tall. There were a number of small potholes in the area, and most of them had these ice sails or ice blades in them. Though the temperature was 39 F (4 C) when the photo was snapped in the early afternoon of November 17, 2012, in Sudbury, Ontario, it was quite cold in the morning (21 F or -6 C). The fast falling temperatures during the overnight hours perhaps supercooled the water to some extent, promoting a relatively fast freezing event. The orientation of the bubbles in the ice gives some idea of the direction in which freezing occurred.
Water expands when it freezes and as it typically freezes along the edges first in a confined space the tendency is for the volume of water in the center to be slightly raised as it freezes. Ice cubes made in a freezer usually have a somewhat convex surface. When factors such as water purity, the rate of freezing and the preferred growth of ice in crystalline planes are considered, expansion of freezing water can result in a variety of interesting structures, such as linear spikes with triangular cross-sections.
Photo details: Camera Model: Canon PowerShot A590 IS; Focal Length: 5.8mm; Aperture: f/4.0; Exposure Time: 0.0050 s (1/200); ISO equiv: 100.