When you picture an iceberg, you probably see a triangular shape skimming along the surface of the ocean. However, these masses of freshwater ice, which have broken from glaciers or polar ice sheets are much larger than they appear. Scientists classify a chunk of floating ice as an iceberg if its height is greater than 16 feet above sea level, it is 98 to 164 feet thick, and it covers an area of at least 5,382 square feet.
Iceberg Sizes Vary Widely
Generally only one-seventh to one-tenth of an iceberg's mass shows above the surface of the ocean. Icebergs form during warmer weather. Their separation from a glacier or ice sheet is referred to as calving. In the northern hemisphere, roughly 10,000 icebergs form each year. Arctic icebergs range from the size of a large piano to the size of a 10-story building.
Why Only Part of an Iceberg Is Visible Above Water
The visible part of an iceberg is composed of snow, which is less compact than the formation's core, which is composed of solid ice. The ice, being heavier, keeps most of the formation underwater. However, an iceberg that has rolled over loses its snow coating and therefore becomes comparatively heavier. The latter type of iceberg will generally only show one-tenth of its mass above the surface of the water.
Experiment Explains Icebergs' Appearance
A simple experiment using a plastic bag, rubber band, large bowl, water, a freezer and a ruler will show why icebergs only show a fraction of their mass above the waterline. To perform the experiment, partially fill the plastic bag with water, secure it with the rubber band and place it in the freezer overnight. The next day, measure the height of the frozen bag of water.
Next place the bag in a bowl filled with water. Using the ruler, measure the portion of ice that appears above the surface of the water and the portion that remains below the surface. Your results should indicate that about one-eighth, or 12.5 per cent, of the bag protrudes above the surface.
The Iceberg that Sank the Titanic
One of the more famous icebergs was the one that the RMS Titanic collided with on April 14, 1912 in the North Atlantic Ocean. While the precise size of that iceberg may never be known, newspaper accounts at the time indicated it was about 50 to 100 feet high and 200 to 400 feet long.