Yesterday I went walking on the Lagorai mountain, in northern Italy. Passing near the Lake Erdemolo, I noticed a small part of frozen water from the lake, separated from the rest (the lake was not frozen at all). I found a quite strange ice formation, which I cannot fully comprehend. At the borders of the pool there was a very thin layer of ice with no water underneath, and progressively going towards the center, more layers added up. A picture explains it better:
The layer at the center of the pool was very thick (a 5 kg rock hardly managed to brake it) and was covered with a thin layer of non-frozen water. Under this thick layer there was water.
Breaking the ice in various points I noticed that the various layers were supported by a lot of small columns and walls.
In the image the column in upside down. Those formations were collocated between the layers and the rocky ground.
I thought that the layers might be formed by an alternate solidification-evaporation process during which, once the first ice layer was formed, the water lowered its level (evaporating through the escape routes of the rocky ground). Maybe this can be caused by a higher outside temperature with respect to the ground one. I'm absolutely not sure about this explanation and, even so, I cannot figure out the cause of the columns between the layers. I guess it can depends of the velocity of the freezing process. If this is not too off-topic, can someone explain the cause of such formations?