Beautiful and dangerous, icebergs wander the ocean’s surface until they melt. These powerful mountains of ice have the ability to capsize huge vessels – and support entire ecosystems.
What is an iceberg?
Icebergs are huge lumps of floating freshwater ice that start life as part of glaciers. The ice inside them is made up of snow that has been layered and re-layered over millennia like sedimentary rock. Most icebergs contain ice that is estimated to be as old as 10,000 years. Once in the open ocean, they float along, carried by currents, until warmer air and water temperatures eventually melt them down.
The average iceberg is 1,982 cubic metres – enough ice for around 840,000 ice cubes. But they can grow much larger. The tallest known iceberg was spotted off the coast of Greenland in 1967 and measured 168 metres high.
Are there different types?
There are six – and all can come in a huge range of sizes.
Tabular icebergs are flat slabs of ice, much wider than they are tall. Blocky icebergs are angular and steep, while dome icebergs have a rounded top. Wedged icebergs have one steep side and one shallow slope. Pinnacles have several steep peaks that jut up out of the base of the iceberg, while dry rock icebergs are U-shaped.
Why are they so dangerous?
The most notorious iceberg in history is probably the one responsible for sinking the RMS Titanic in 1912. On this occasion, the accident occurred because those on board were unable to see the true size of the iceberg. Around seventh eights remains below the waterline, making their shape and size invisible.
They are also unpredictable. As they drift further south, they melt faster and become unstable. Icebergs can break apart and even flip over. And with a consistency similar to reinforced concrete, they have the power to destroy any boat that happens to be nearby when they do.
What is Iceberg Alley?
A stretch of the Atlantic Ocean that goes from the Arctic to Newfoundland in Canada, and one of the most notorious shipping lanes in the world. Most icebergs drifting through Iceberg Alley come from the coast of Greenland, where, in the spring and summer months, chunks of glaciers break off in a process called calving. Between 400 and 800 icebergs a year flow through it, colliding with shipping routes. And as hot and cold currents collide, deep fog descends, making the icebergs easy to miss and the waters extremely treacherous.
How do they affect the environment?
Icebergs support entire ecosystems. The freshwater trapped inside them melts out slowly. As it does, it releases vital nutrients into the sea around it, which supports a network of photosynthetic organisms. Nutrients also feed plankton including krill, which become food for fish and whales and attracting seals and polar bears.
As members of these communities die and produce waste, they settle on the ocean floor and act as a fertiliser. Recent estimates suggest that icebergs account for as much as 20% of carbon sink activity in the ocean.
So, they’re a good thing?
Yes and no. Icebergs support millions of creatures and ecosystems, but too many can disrupt much larger processes. As temperatures rise around the world, more icebergs form, reducing the amount of freshwater locked into ice sheets.
Not only are more icebergs forming, they are also melting faster, according to research at the University of Sydney. As well as adding to rising sea levels, the addition of freshwater can disrupt the salt balance, affecting global currents. As Eric Hester from the University of Sydney summarises, icebergs are “part of a global climate system”. The way they behave affects ecosystems, humans – even entire oceans.
- Are icebergs the most misunderstood objects in the ocean?
- Using the iceberger tool in the expert links, draw your own iceberg and then create a diagram. Decide what type it is – for example, tabular or pinnacle – and complete the diagram with three more interesting facts about icebergs.
- Huge masses of ice that “flow” like very slow rivers. They form over thousands of years and can grow as large as entire US states.
- Sedimentary rock
- Formed when sand, mud and pebbles get laid down in layers. Glaciers are formed in much the same way, with snow falling on top of snow and compressing it down into solid ice.
- Reinforced concrete
- Concrete with long steel bars inside it to make it stronger. Icebergs can easily rip holes in the metal hulls of boats, causing them to capsize and sink in minutes.
- To be famous – usually for something dangerous or illegal.
- Filled with hidden dangers or hazards. It also describes somebody who is likely to betray your trust.
- Necessary for survival. It comes from the Latin word “vita”, meaning life.
- Plants or organisms that use sunlight to create nutrients from carbon dioxide and water – therefore removing carbon from the atmosphere.
- A general term for small organisms drifting in the sea or freshwater. Krill fall into the category, and are actually a kind of small shrimp.
- Carbon sink
- A natural environment that has an ability to absorb carbon dioxide from the atmosphere.
- Around 60% of the world’s total freshwater is held in ice sheets which would be equal to 70m of sea level if all of it were to melt.