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Flying circus of physics

Pointy ice drops

Thursday, October 01, 2015


Video series

The fifth episode of my Flying Circus of Physics video series with Cleveland State has now been posted.

Pointy ice drops
Jearl Walker
October 2015   On rare occasions, water that is frozen in an ice-cube tray can develop an upward spike. That is, of course, in a container with rigid walls. What happens when a liquid drop is placed on a sub-freezing surface and then freezes from the bottom up? If the drop is small (say, a millimeter in diameter), it remains in the drop-like shape for most of the process:

But then as freezing reaches the top, the top forms a peak:

Shortly afterwards, fern-like dendritic growths sprout from the surface, starting on the peak, as you can see in this close up.

This behavior and these images were recently published by A. G. Marin of Bundeswehr Univiversity in Munich, O. R. Enriquez of Univesity of Twente, The Netherlands, and others. (Their several publications are listed below.) Here is a link to the video posted by Enriquez that gives a microscopic view of the freezing water drop that was placed on a metal plate kept at a temperature of about -20ºC by an underlying bath of liquid nitrogen.

As Enriquez explains in the video, the freeze line between solid and liquid water begins at the contact with the cold plate and then climbs upward. We can see the freeze line because ice refracts (redirects) light differently than liquid water and thus there is contrast in the illumination above and below the freeze line. The liquid portion of the drop remains roughly spherical as the freeze line ascends because of the water’s strong surface tension due to the mutual attraction of water molecules.

However, water is peculiar in that it expands when it freezes. So, as the freeze line reaches the top of the drop, the liquid portion is pushed upward by the expansion of freezing water below it in spite of the surface tension, and then that water immediately freezes, forming a peak. That peak is said to be a singularity because the surfaces on two sides are not smoothly curved over the top but instead makes a sudden transition from side to side (the slope suddenly changes at the peak).

After the singularity forms, water vapor begins to form ice on the peak and down along the sides. The concentration of water vapor is strongest at the peak, so the formation of ice begins there. However, the ice does not form in layers. Instead it forms fern-like structures, as if miniature ferns grow outward from the drop. If you live in cold winters, you can see similar dendritic structures in the ice flowers that form on a window on very cold days. Here is one of my photographs of ice flowers that formed during a polar vortex in Cleveland, Ohio:

Michael Nauenberg of the University of California at Santa Cruz made his own pointy ice-drops but with somewhat larger drops that he placed on a block of dry ice (frozen carbon dioxide). (Obtaining dry ice is a lot easier than cooling a plate with liquid nitrogen.) He described how the freeze line forms a crater as it nears the tope. He also saw shapes other than a peak. Here is his video:

If you want to see the FCP story about frost-flower formations, go to

and scroll down to item 4.111.

Dots · through ··· indicate level of difficulty
Journal reference style: author, journal, volume, pages (date)
··· Anderson, D. M., M. G. Worster, and S. H. Davis, “The case for a dynamics contact angle in containerless solidification,” Journal of Crystal Growth, 163, 329-338 (1996)
· Enriquez, O. R., A. G. Marin, K. G. Winkels, and J. H. Snoeijer, “Freezing singularities in water drops,” Physics of Fluids, 24, # 091102 (2012)
··· Snoeijer, J. H., and P. Brunet, “Pointy ice-drops: How water freezes into a singular shape,” American Journal of Physics, 80, No. 9, 764-771 (September 2012)
· Nauenberg, M., “Comment on ‘Pointy ice-drops: How water freezes into a singular shape’ [Am. J. Phys. 80, 764-771 (2012)],” American Journal of Physics, 81, No. 2, 150-151 (February 2013); Snoeijer, J. H., and P. Brunet, “Response,” American Journal of Physics, 81, No. 2, 151-152 (February 2013)
··· Marin, A. G., O. R. Enriquez, P. Brunet, P. Colinet, and J. H. Snoeijer, “Universality of tip singularity formation in freezing water drops,” Physical Review Letters, 113, # 054301 (2014)


Are you looking for the stories from last several months? They are in the archives:

Sloshing, 2.199
Coffee heated in hot sand, 4.115
Pinhole sites and selfies, 7.33
Pub trick -- balancing pins on glass rim, 1.239

Loop-the-loop with cars, bikes, skateboards, and simply running, 1.270
Pub  trick --- spoon into mug, 1.271
Transparent when wet, 6.86
Hula-hoop, 1.84

Lethal upward streamers in an electric storm, 5.1
Floaters in your eye, 7.5
Pub trick --- musical wineglass, 3.43
Standing and walking in a strong wind, 1.227

Pub trick --- beer bottle tapping prank, 2.76
Bull riding, 1.92
Mianus Bridge collapse, 1.71
Sliding stick across outstretched fingers, 1.172

Café wall illusion, 7.58
Tire explosions, 4.114
Pub trick --- using thermal stress to open a wine bottle, 4.113
Giant Leg towers, 1.272

Pouring tea in an airplane during a barrel roll  2.197
Pub trick --- water from nowhere  6.166
Survival strategies of emperor penguin huddles   1.197
Racing over a rail crossing  7.59

V1 flying bombs tipped by Spitfire airplanes  1.273
Smallest electric train  5.61
Whispering bench in New York City's Central park  3.63
Pub trick --- separating salt and pepper  5.60

Tesla coils  5.62
Royle's self-pouring teapot  2.198
Self-righting of overturned turtles and the toy known as gomboc  1.274
Pub trick --- the self-righting bottle  1.106

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