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 glaciersA slowly moving mass of ice formed by snow building up on mountains. . The ice inside them is made up of snow that has been layered and re-layered over millennia like sedimentary rockFormed when sand, mud and pebbles get laid down in layers.. 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 concreteConcrete with long steel bars inside it to make it stronger., 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 notoriousTo be famous - usually for something dangerous or illegal. shipping lanes in the world. Most icebergs drifting through Iceberg Alley come from the coast of GreenlandAn island country in North America that is part of the Kingdom of Denmark. It lies between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is the world's largest island., 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 treacherousDangerous..

How do they affect the environment? Icebergs support entire ecosystems. The freshwater trapped inside them melts out slowly. As it does, it releases vitalVery important. nutrients into the sea around it, which supports a network of photosyntheticPlants or organisms that use sunlight to create nutrients from carbon dioxide and water - therefore removing carbon from the atmosphere. organisms. Nutrients also feed planktonA general term for small organisms drifting in the sea or freshwater. Krill fall into the category, and are actually a kind of small shrimp. 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 sinkA forest, ocean or other natural environment able to absorb large amounts of carbon dioxide from the atmosphere. The Amazon rainforest, for example, absorbs two billion tons of carbon dioxide each year. 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.

Glaciers - A slowly moving mass of ice formed by snow building up on mountains.

Sedimentary rock - Formed when sand, mud and pebbles get laid down in layers.

Reinforced concrete - Concrete with long steel bars inside it to make it stronger.

Notorious - To be famous - usually for something dangerous or illegal.

Greenland - An island country in North America that is part of the Kingdom of Denmark. It lies between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is the world's largest island.

Treacherous - Dangerous.

Vital - Very important.

Photosynthetic - Plants or organisms that use sunlight to create nutrients from carbon dioxide and water - therefore removing carbon from the atmosphere.

Plankton - 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 forest, ocean or other natural environment able to absorb large amounts of carbon dioxide from the atmosphere. The Amazon rainforest, for example, absorbs two billion tons of carbon dioxide each year.