1. Introduction
When water freezes into ice, the expansion that occurs during the solidification process sometimes
causes the formation of “ice spikes” that rise out of the free ice surface. The phenomenon has been
observed sporadically out-of-doors in cold climates for many decades [1—6]. These rare sightings have
documented the appearance of rather large ice spikes, perhaps 100 mm in length, sometimes with
triangular cross-sections, usually forming overnight in containers of standing water. Much smaller
ice spikes (also known as ice spicules) have been observed coming out of sleet particles [7—10]. These
appear in droplets of order 1 mm in size or larger, and they have been successfully reproduced and
studied in the laboratory [9, 10].

4. References
[1] H. E. Dorsey, “Peculiar Ice Formations,” Phys. Rev. 18, 162 (1921).
[2] J. Hallet, “Crystal Growth and the Formation of Spikes in the Surface of Supercooled Water,”
J. Glaciology 3, 698 (1960).
[3] G. Abrusci, “What conditions determine crystal growth,” Am. J. Phys. 65, 941 (1997).
[4] C. A. Knight, “Answer to Question #65. What conditions determine crystal growth? The
triangular ice spike,” Am. J. Phys. 66, 1041 (1998) (follow-up to [3]).
[5] H. F. Perry, “Ice Spikes — Can You Explain Them,” Phys. Teacher 31, 112 (1993); correspondence
on the topic is at Phys. Teacher 31, 264 (1993).
[6] H. F. Perry, “A ‘Last Word’ on Ice Spikes,” Phys. Teacher 33, 148 (1995).

Why studies indicate that water needs to be quite pure (1% salt concentration eliminates the spike formation) while we saw these in many dirty locations in the soil is unclear.  Our spikes were also layered as if they had been laid down or grown over time in many cycles or water deposition and freezing.  Delving into the cited references is called for, perhaps in a senior undergraduate thesis.

All in all, a thoroughly enjoyable hike.  We had lots of laughs and were proud to have selected a nice route in the particularly unwinterlike conditions.  Here's to another fine Thanksgiving event!