When the glacier slides into the water it becomes an iceberg. Only the tip of an iceberg (about 10%) can be seen above the water. Wind and the water currents can move icebergs. Icebergs can weigh as much as several tons. Since most of the iceberg is under water it can easily sink and hurt ships and boats that don't see them. For example, the reason the Titanic sank is because it hit an iceberg.
The shape of the iceberg is always changing. In the distance and mist icebergs can have weird shapes that can look like anything from a dog to a knight. When exposed to the sun and water, icebergs melt very fast. In Alaska icebergs live about 2 months. When an iceberg melts, it can become unbalanced and flip over unsuspectingly, making a huge splash and shock waves.
You might wonder, how old is the ice that calves off the glacier? Well it depends on how fast the glacier is moving and how far it travels. Lots of people think that the ice in Portage Lake (in Alaska) is over a thousand years old, but it is only about 50-100 years old. Portage Glacier is six miles long. The ice there moves about 400 ft. every year. It takes about 80 years for the glacier to reach the lake. Even though Portage Glacier has been resting in Portage Valley for over a thousand years, the ice on the outside is only about 100 or so years old. People tend to think that glacial ice is colder than ice in your freezer, but it's not.