Bob, it's when two sheets of ice shift around and create ridges as they butt up against each other. Sometimes there's a void under the ridge. You do not what to drive over one.
Pat, you actually eat them big ol' stinky things or is that 'yote chum?
(grin)
We used to catch a bunch of 'em on Lake Pend Oreille.
Baked a couple but my aunt would also can/smoke 'em up and they weren't bad that way.
