Icebergs float because, as large and heavy as they are, they are still less dense than water. When water freezes, it expands and takes up more space, which means its volume has increased. However, its mass hasn't changed, and this allows ice to float in liquid water.
Moreover, icebergs are full of air bubbles. These air bubbles also give the iceberg their white color. The ice that icebergs are made of is made of fresh water, and can be thousands of years old. This makes an iceberg even more buoyant, as saltwater is more dense than fresh water.
An iceberg is considered an iceberg if it's at least 16 feet long. Small, car-sized icebergs are called growlers, while those about the size of a house are called bergy bits. Even though some icebergs can be hundreds of feet tall, only about one-eighth of the iceberg is above water. The difference between the densities of ice and water aren't so great that a very large iceberg can float right on the water's surface.
Most icebergs last only a few years. They drift into warmer waters and begin to melt. The waves of the oceans also crash into and degrade them. But some icebergs that stay in colder climates can last for decades.