This animated GIF (900kb) shows
Ruth's Waterfall in the process of refreezing.
The waterfall was frozen for 4 weeks in January, 2003. We had a quick
thaw in early February and then the temperature dropped to single digits
again. Here is the waterfall in the process of refreezing. The "ice
pancakes" get stuck under the edge of the ice and the pool gradually
freezes over.