The sound comes from the popping of compressed air bubbles which are in the ice. The bubbles form when air is trapped in the snow layers which are compressed to form glacial ice. Icebergs may make very loud booming and cracking sounds without any sign of movement or calving. The sounds probably result from the sudden formation of cracks due to thermal an buoyant stresses in an iceberg. When icebergs do calve loud noises are common.
Birds taking flight from an iceberg are a good sign that the berg is going to roll soon.
A possible explanation is that bird's keen sense of balance enables them to detect gradual movements in icebergs long before people can see them. Both products are available in Newfoundland at retail stores. More products are expected soon as more people are entering the iceberg ice business. The Hibernia platform is designed to withstand the impact of an iceberg in excess of 5 million tonnes. The massive reinforced concrete structure has vertical wedge shaped elements on the surface intended to reduce iceberg impact loads.