Upside Down Icicle

I recently saw this pretty cool picture that a friend took on an icicle which has grown upwards out of a small pool.  It is no trick, it really has grown upwards. The surface of the pool freezes first. As the rest of the water freezes and expands, the pressure increases within the remaining liquid. This pushes out the liquid up through the weakest point, which will generally be somewhere near the middle of the surface ice layer. As soon as some water gets pushed through that hole it flows out slightly building up a small circular wall. As the pool continues to freeze, more water gets pushed out, building up wall further and so on to finally produce an upsidedown icicle.

However, conditions (in terms of temperature, shape of pool etc) have to be correct for this process to work. I have only ever seen one picture of one of these before, and it was not quite as good as this example.