Spikes in the icetray

[raccoon]

I've noticed the last few years that occasionally there are "spikes" in my ice trays. They happen occasionally. There'll be a spike of ice up to almost 2 inches high, and about the thickness of a matchstick or a toothpick.

Anybody know what causes this?

[mzteris]

1. explanations

technical explanation:

http://www.its.caltech.edu/~atomic/snowcrystals/icespikes/icespikes.pdf

User friendly version:
http://www.wonderquest.com/cousin-ice-cube-engine.htm

Q: Why do the ice cubes in my ice tray occasional have spikes on them? Why would they defy gravity and spike upwards? —Bert, Massachusetts

A: Water expands as it freezes. The ice-cube tray restrains the water from expanding in all directions except the top. So the ice pokes its way up like milk freezing in an old-fashioned milk bottle. But why do spikes form?

Rising bubbles cause spikes.

Water forms bubbles as it freezes—ice cubes, hailstones, or whatever. "As ice forms, it excludes the gases that were dissolved in the water," says Gabor Vali, ice-nucleation and atmospheric-ice-physics scientist and professor at the University of Wyoming. "Growing ice crystals incorporate the water molecules but not the other gases (carbon dioxide, nitrogen, etc.)." A single crystal is completely transparent and has no bubbles. Exceptions to this only occur when ice forms extremely fast.

Ice forms first at the walls, bottom, and top of the ice cube tray since the freezer cools the tray from the outside. The walls and tray bottom (in contact with the freezer) conduct the cold quickest; ice forms first along these surfaces and becomes thicker than at the ice-cube top.

The bubbles rise and press their way through water "crevices" in the slowly growing ice front, says Vali. The bubbles and their clinging, freezing water push the top-layer ice and fracture the thinner ice. Pressure from the water below squeezes the bubbles and their clinging water up into a spike. Eventually the spike freezes solid and stops the rising bubbles. The ice traps other bubbles inside the cube in layers or groups.

"The questioner made a good and important observation," says Vali. When the air bubbles rise and break the thin crystalline layer, they shatter crystals—creating more crystals.

Ice crystals multiply in a cloud much as in an ice-cube tray. Indeed, raindrops frequently form tiny spikes like ice cubes do. "One parent drop can produce up to 100 ‘babies’ within a few minutes or less in the ice multiplication process," says Russell Schnell, NOAA, Climate Monitoring & Diagnostics Laboratory.

Each of these babies can grow into a snowflake that falls as a snowflake if the air near the surface is below freezing. Otherwise they fall as raindrops. "Over continents, even on the hottest summer day, raindrops begin life as a snowflake," says Schnell.

Further Surfing:

Met Ed: Ice multiplication and related cloud physics terminology
http://meted.ucar.edu/nwp/pcu2/rucpcp2.htm


Even simplier: Wiki's version

http://en.wikipedia.org/wiki/Ice_spike

[raccoon]

2. Thank you! nt

[seriousstan]

3. Check this out

http://www.physics.utoronto.ca/~smorris/edl/icespikes/Lozowski_icespike.avi

[benburch]

4. Very cool.

Quicktime users... Paste that URL into Windows Media Player as Quicktime cannot play that one.