Yesterday I placed clay sorbent granules on my steep, north facing driveway to add some friction so the car and visitors can negotiate the grade in the snow and ice. The clay granules are used for absorbing oil and are similar to cat litter. I used the granules because I did not have sand.
The granules were deposited on freshly shoveled concrete with just a thin layer of clear slush. I would estimate that, overnight, the temperature ranged between 25-32 F. In the morning, the 1-5 cm stalks of ice were observed only where the granules were deposited.
The slender stalks were capped with flat, irregular plates of ice. Many of the stalks had lifted granules off the ground. Most appear to have arisen from the granules. Obviously, the process forming the stalks lifted some of the granules and ice vertically. Curved ice stalks appear to have extruded gradually from the granule and, under the influence of gradually shifting cover of snow or other ices, have extended produced a curved shaft of ice.
The granules are manufactured with absorbency in mind. In this circumstance, I will hypothesize that capillary action pulling liquid water from the concrete surface is delivered to the upper surface of the granule where it freezes at the air/water interface by evaporative cooling. Why it doesn’t just stop is puzzling. Perhaps the action of freezing at the granule upper surface reduces the vapor pressure of water enough to induce a small pressure drop through the pores of the clay that draws liquid phase to the surface where is freezes continuously. The heat of fusion at the surface may be sufficient to prevent freezing of the water within the pores of the granule in the subfreezing range of the air and shutting the process down.
This is a very curious type of ice formation, one that I have observed on two separate occasions. This is another odd thing water can do.