Ocean Ice eruptions

Can you figure out why the ice here has numerous "pock mark" eruptions? Living on the Atlantic Ocean in winter provides some interesting sights. We have the worlds largest tidal swings near here, with a 50 foot difference between high tide and low tide! This happens every 6 hours! That's a lot of water moving - good for electrical power generation.
In the area of this photo the tidal swing is only a few feet, and this inland cove has a mix of fresh water with the salt water which makes it freeze in the shallow areas. So it freezes at high tide, then the water filters out under the ice forcing the rocks beneath the ice to protrude up through the thin ice.

Near Peggys Cove Lighthouse, Halifax, Nova Scotia, Canada
Photos by Rob vanNostrand