Big icebergs, which are also called “ice mountains,” are huge pieces of freshwater ice that are floating in  open water. They have formed after breaking off continental ice shelves or glaciers. To be classified as an iceberg, the ice extruding from the water must be at least 15 feet above sea level, be between 100 and 165 feet thick, and must cover an area of at least one-third of a mile, according to the Antarctic Report. Icebergs can have a direct effect on the sea bed, scouring the seafloor where it makes contact.