Icebergs are colossal pieces of freshwater ice floating in the ocean. They are formed from compacted snow on land and represent some of the largest free-floating objects on Earth. A typical iceberg can weigh hundreds of thousands of tons, yet it remains supported by the ocean’s surface. This ability to float is a consequence of physics involving the unique properties of water. The phenomenon is a dynamic balance between the ice’s immense weight and the upward force exerted by the displaced seawater.
The Science of Density and Buoyancy
The explanation for why icebergs float lies in the concept of density, a measure of mass per unit volume. For nearly all substances, the solid form is denser than the liquid form. Water is a rare exception because its solid state, ice, is less dense than its liquid state. When water freezes, hydrogen bonding causes molecules to form an open crystalline lattice structure, making the same mass occupy approximately nine percent more volume. Freshwater ice has a density of about 917 kilograms per cubic meter. Seawater, which contains dissolved salts, is denser still, averaging around 1,025 kilograms per cubic meter. An object floats when the upward buoyant force equals the object’s weight, a principle known as Archimedes’ principle. Since the iceberg’s density is less than the surrounding saltwater, it displaces a volume of water that weighs the same as the entire iceberg, allowing it to remain afloat.
The Submerged Mass: How Much is Hidden?
Density and buoyancy dictate the precise ratio of an iceberg that remains hidden from view. The fraction submerged is determined by the ratio of the ice’s density to the seawater’s density. Using the approximate densities (917 kg/m³ for ice and 1,025 kg/m³ for seawater), the ratio is around 0.89. This means roughly 89 percent of an iceberg’s total volume is submerged beneath the water line. This large hidden mass is the origin of the familiar phrase, “tip of the iceberg.” While the exact submerged fraction can vary slightly based on the iceberg’s density and the local salinity of the ocean, it consistently falls within the range of 85 percent to 90 percent.
How Icebergs Are Formed
Icebergs begin as compressed snow on land and are composed of freshwater, which is crucial to their lower density compared to the ocean. Over centuries, continuous snowfall accumulates on ice sheets and glaciers. The weight of the new snow compresses the layers below into dense glacial ice. Icebergs are born through “calving,” where large chunks of ice break off from the edge of a glacier or an ice shelf that extends over the ocean. Calving is a natural form of ice loss at the terminus of a glacier, often stimulated by tidal forces or the melting of ice at the waterline. The resulting ice mass is then carried away by ocean currents.