Question

The photo on the next page shows an iceberg floating in the ocean near the coast of Greenland. a. How do icebergs form? What term applies to this process? b. Using the knowledge you have gained about these features, explain the common phrase "It's only the tip of the iceberg." c. Is an iceberg the same as sea ice? Explain. d. If this iceberg were to melt, how would sea level be affected?

Short answer

Icebergs form through calving. "Tip of the iceberg" means a small visible part of something larger. Icebergs and sea ice are different; icebergs come from glaciers. Melting icebergs don't affect sea level.

Step-by-step solution

Formation of Icebergs

Icebergs form when chunks of ice break off from glaciers, a process known as "calving." Glaciers flow from ice sheets on land into the ocean, and as the glacier reaches the water, parts of it break off into large floating ice masses called icebergs.

Understanding the Phrase

The phrase "It's only the tip of the iceberg" is used to indicate that what is visible or apparent is just a small part of something much larger. This metaphor arises from the fact that only a small portion of an iceberg is visible above the waterline, typically about 10%, while the rest is submerged.

Distinguishing Icebergs from Sea Ice

Icebergs are different from sea ice. Icebergs originate from glaciers on land, whereas sea ice forms when ocean water freezes. Thus, icebergs are freshwater ice masses, while sea ice is composed of frozen saltwater.

Melting Icebergs and Sea Level

When an iceberg melts, it contributes no additional water to the ocean, since it was already floating in it. Thus, the melting of an iceberg has no effect on sea level as it displaces the same amount of water while floating as when it melts.

Key concepts

Calving

Icebergs are born from a fascinating process called calving. Calving occurs when large chunks of ice detach from the edges of a glacier and float into the sea. The glacier, which is a massive body of dense ice, moves slowly over land. As it reaches the coastline or an oceanic edge, sections of ice break off due to stress and gravity. This newly formed iceberg floats away into the ocean. The term 'calving' is directly inspired by the way this process resembles the birth of a calf from its mother — it's the separation of a new part from the main mass.

Glaciers

Glaciers are enormous, slow-moving rivers of ice that form over many years. They begin as snow that compresses into dense ice over time. Glaciers are significant as they store about 70% of the world's freshwater. These ice giants flow slowly from high-altitude regions to lower altitudes and can be found on every continent except Australia. When glaciers, often situated in polar regions, reach marine environments, the interaction with the sea can cause parts of them to break off, forming icebergs through the calving process. The dynamics of glaciers are crucial in understanding the formation and lifespan of icebergs.

Sea Ice

Sea ice is quite different from icebergs, despite both being integral parts of polar marine environments. Unlike icebergs, which are pieces of glaciers that move from land to sea, sea ice forms directly on the ocean when the surface layer of saltwater freezes. Because sea ice comes from ocean water, it is usually saltier and lighter than freshwater icebergs. This type of ice covers a large part of the Arctic and Southern Oceans depending on the season, significantly influencing global climate patterns. Sea ice impacts the Earth's albedo — the reflection of solar radiation — and, as such, plays a critical role in regulating our planet's temperature.

Sea Level

The relationship between floating ice and sea level is a common concern. Icebergs floating in the ocean have already displaced water equal to their mass. So, when an iceberg melts, it does not contribute additional water to the ocean, thus having no impact on sea level. This principle is often described using the idea that the melted water was already part of the ocean system, akin to ice cubes in a glass of water. In contrast, if land-based ice, like parts of a glacier, melts into the ocean, it does contribute to sea-level rise, because this mass was not previously part of the oceanic water volume.