Sound waves are used to probe the oceans' depth, locate objects in the ocean, measure bottom sediment thickness and communicate underwater. The speed that sound travels underwater varies from about 4,750 - 5,150 feet per second. The sound velocity profile for a particular part of the ocean is often determined by lowering or towing an instrument called a sound velocimeter. Approximately 7,500 icebergs are formed by this process each year. Portions of an iceberg may have hues of blue or green depending upon the age of the ice.
Blue ice is old ice, while green ice usually contains algae.
Glaciers on the west coast of Greenland produce most of the icebergs found in the Northern Hemisphere. The icebergs vary in size, but are typically irregular with pinnacles. About seven-eighths of an iceberg is submerged. Thus iceberg drift is affected more by ocean currents than by wind. When they drift into shipping lanes, they become a serious hazard.