After a day of snow + sleet + ice, followed by overnight cooling, the bird feeder looked like this:
The ice generally doesn’t bond across the top, so the sheets slide off separately to the front and back. This time, they stayed together and began sliding off to the side.
The next two days were unusually cold and the glacier stopped sliding:
The temperature warmed enough during the day to let the glacier resume sliding, whereupon it fell and shattered on the patio.