Not so sure that I agree that lake ice and waterfall ice behave the same - a hanging icicle is under different load stress from gravity than a flat lake ice, and the direction of pull in the test in the PDF is 90 degrees different between the two cases. IE on lake ice, the pull is at 90 degrees to gravity stress whereas on vertical ice, the pull is in the same direction as gravity... on vertical ice, fractures prefer to spread horizontally while there should be no preferred direction on a flat lake.