Ice and Snow Patterns
There is a wide range of patterns that can be found on ice that often relfect what happened during the early stages of the formaiton of an ice sheet.  The following are a bunch of pictures which are the basis of some speculation on what lead to the patterns
 A frozen Ice Star.  The dark center is a frozen upflow hole formed when a thin icesheet (1/4"?) got four inches of snow on top.