by nathanroser » Apr 5, 2013 3:54 pm
The Cave Minerals of the World book has excellent descriptions of how many speleothem types form. When you see helictites check the walls and ceiling for an obvious solid calcite coating that they would grow out of. One of the better explanations I read is that a thin layer of pressurized water gets in between the bedrock wall and the calcite layer and then it seeps out to make the helictites. The same hypothesis has also been applied to popcorn growth.