The coastal glaciers in Greenland, Chile, Alaska and the Antarctic come to a spectacular end, in a process called "calving".
As the glaciers flow towards the ocean they push over uneven ground.
This can create cracks, and crevasses are formed. Reaching the sea, the ice breaks off at the crevasses.
If the glacier or ice stream is still intact when it reaches the sea it doesn't break up immediately.
The waves hollow it out from below. The higher parts loose their support and fall into the ocean. This is how icebergs are created.