That means that ice (like icebergs) also floats in sea water. What about the density of salt water? Because of the dissolved sediments and minerals, sea water is slightly denser than pure water. And because ice’s density is lower than that of water, ice floats in water. This means that the density of ice (0.92 g/mL) is less than that of liquid water (1.0 g/mL). But the amount of matter hasn’t changed – it is just spread out over a larger space. While most other substances contract, water expands as it becomes a solid.īecause water expands as it freezes, ice takes up more space (has a greater volume) than the liquid water does. You’ve observed this if you’ve ever noticed the bump on an ice cube or had a can of soda explode in the freezer. When water freezes, the water molecules spread out to align in a definite crystalline structure. Pure liquid water’s density is 1.0 g/mL, and a standard by which to compare other substances. For example, pure gold always has a density of 19.3 g/mL (grams per milliliter). Density is a defining property of a substance, and it is constant no matter how much of the substance there is. Substances with a high density have tightly packed atoms, while the atoms in a low-density substance are more spread out. Density essentially describes how tightly packed a substance’s atoms are. Density is calculated by dividing an object’s mass (amount of matter) by its volume (the space it occupies), or D=M/V. To understand why ice floats, it is necessary to understand the concept of density. That’s an amazing statistic to consider given the massive size of some icebergs, but the very fact that ice floats is pretty remarkable. You have probably heard the statistic that approximately 90 percent of an iceberg is found under water. Wind and water erode icebergs into amazing sculptural shapes. Tabular icebergs have steep sides and a flat top like a plateau, while non-tabular icebergs include irregular shapes such as rounded tops, spires, sloping sides, and blocks. Icebergs are also classified by their shape. Photo courtesy of Josh Landis, National Science Foundation. The northern edge of the giant iceberg B-15A, located close to Ross Island, Antarctica. The storm created ocean swells that traveled over 8,000 miles and caused B-15 to crash repeatedly against the coast. Why did this massive berg break apart? Seismic recordings showed that an Arctic storm six days prior to the event was to blame. B-15 subsequently broke into smaller pieces, named B-15A, B-15B, and so on. Iceberg B-15, which calved from the Ross Ice Shelf of Antarctica in 2000, was half a mile thick and covered an area of about 4,500 square miles (about the size of Connecticut). Since the bulk of an iceberg is below the water, the entire berg was estimated to be as tall as a 55-story building! The tallest known iceberg in the North Atlantic was 550 feet (168 m) above sea level. Small bergs (a little smaller than a car) are known as “growlers,” while slightly larger bergs (about the size of a house) are called”bergy bits.” Larger bergs are classified as small, medium, large, and very large. Icebergs float in salt water because they are formed by calving, or splitting, glaciers and are thus made of fresh water. Icebergs are found in the Arctic, North Atlantic, and Southern Oceans.
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