Figure 1 – Frazil and pancake ice on the shores of Fresh Pond, Cambridge, MA, April 8, 2015. (c) DE Wolf 2015.

Yesterday was ridiculously cold and miserable.  So much so, that I left my camera behind and went out with the determination to finish my lunchtime walk as rapidly as possible but with enough distance to satisfy the Fitbit tyrant on my wrist.  Hmm! On the other hand conditions were perfect for all the glorious phenomena associated with melting ice.  More reassuring physics awe to sure.  So, to my delight yesterday there were ice pancakes on the pond, and I just couldn’t resist risking frozen fingers long enough to take a few IPhone images. Figure 1 is one of these images and I hope I may be excused the poetic license of a bit of over exaggerated color.  It was all so gloomy otherwise.

Pancake ice! Where does this come from? Well before I say anything more we have to realize that temperatures are such that the water world is ever on the edge of phase transition: ice to water and water to ice.  It is a precarious balance between entropy and enthalpy.  But most significantly, when you see physical structure, ice domains on the surface of a pond, like this you just know that somehow the root cause is going to be the interaction between water molecules on a scale way too small to see.  Therein, lies the reassuring awe that physics gives.

Ice crystals tend to form around particles in the water. It turns out that when things get really cold, but the water is in constant motion, these ice crystals are prevented from freezing into sheets and are pulled under the super-cooled water. Eventually they float to the surface and collect in round flat pancake like-blobs.  These blobs, called frazil, are prevented from further congealing by the currents, winds, and waves.  This is slush.  These pancakes will then cause further freezing where their edges are exposed to the water and as a result become raised.  The pancakes take on the appearance of great Victoria lilies.

Most interesting, perhaps, is that frazil and pancake ice are the start in Arctic regions of so-called sea ice.  Fresh Pond in the regard is a mini-North Pole, which is certainly what it felt like yesterday.