Ice cubes spawn frozen stalagmite-in-a-cup

Attention science geeks: Your assistance is requested in explaining a double-take-inducing natural phenomenon I recently experienced during an otherwise mundane morning at my place of employment.

Like most offices, mine is not especially renowned as a hotbed of double-take-inducing natural phenomena; however, its proprietors are thoughtful enough to provide a number of amenities that help make working there from day to day an eminently satisfactory experience, including an ice machine and a dispenser of chilled and filtered drinking water. It was while availing myself of these particular amenities that the aforementioned phenomenon occurred.

Here’s what happened: I filled a plastic cup with ice, placed it under the water dispenser, pressed the button, and what can only be described as a stalagmite of ice sprang from the top-most cube as the stream of water froze, rising up and instantly reaching almost to the mouth of the dispenser.

Photographic evidence is offered here. I’ll grant that the definition on the stalagmite image leaves something to be desired, so you’ll just have to take my word for it that what you see is the result of what I’ve described, and that the Photo has not been Shopped in any way. After taking it, I was eager to see whether I could replicate the event and capture it on video. No dice, and I discarded the stalagmite in the process, so I couldn’t get any better shots.

What I want to know is, what combination of conditions allowed this to happen? The process must be similar in some respects to the way that icicles form, but this literally took place in about three seconds, whereas my impression is that your typical icicle needs hours to materialize. Had the water likely been supercooled by sitting in the chiller all night? Did the unusual shape of the ice cubes (sort of like tiny frozen stovepipe hats, image also provided here) have anything to do with it?

Anybody have a theory, or do I need to submit my query to Professor Proton while he’s still around?

The water was supercooled; that is, the temperature of the water had dropped below its freezing temperature, but there was no place for a seed crystal to form. It happens in very smooth and very still containers.

Here’s a demonstration for everyone who wasn’t there.

Edit: As soon as the water hit the ice, it promptly began turning to ice, which resulted in the stalagmite form as the water froze upwards. It’s the lack of an ice crystal or a place for one to for that makes supercooling possible.