Imagine you are standing on the icecap of Greenland perhaps 10,000 years ago. Snow is falling. The cold is penetrating. In fact, over a full the year, it's so cold that the snow accumulates faster than it melts, hence the icefield grows.
A glacier meets the sea, northern Greenland
If you could live long enough, you would see the icefield thicken and spread. Where the outer edge of the icefield meets with lower ground, the ice creeps down-hill as a "glacier". This slow-moving ice river gradually slips down through a valley eventually meeting the sea where a thick overhang forms that becomes undercut by the sea - a "tide-water glacier". Some glaciers melt away before reaching the sea. They don't produce icebergs.
Pressure from the moving ice uphill, wave action from the sea and warm temperatures in the summer causes the ice to break off in an explosive event called "calving".
An iceberg begins its journery
Finally an iceberg is born about 10,000 years after the snow fell around your feet.
Once floating, its sea journey begins. The icebergs that calve into the waters off west Greenland first float north carried by the dominant current. As they reach the north end of Baffin Bay, they are swept westward into Canadian waters, picked up by the southward flowing current and gradually move down the coast of the arctic islands, Labrador and eventually reach Newfoundland. The full journey might take 2 or 3 years with the bergs freezing into the icepack each winter.
Iceberg and fishing boat off St. Anthony, Newfoundland
About nine out of ten icebergs that reach Newfoundland waters, in the area known as "iceberg alley", come from west Greenland, while one out of ten is from the Canadian arctic.
Grounded iceberg, St. Anthony, Newfoundland
Once in the warmer waters, the icebergs melt and eventually disappear, but this is not a quiet and gentle process like the melting of the ice-cube in your summer libation. With most of the iceberg (80-90%) underwater, the submerged part generally melts faster than that above the waterline. As the ice melts, the centre of gravity changes disrupting the forces holding the berg together. It can begin to shift its position in the water, first tipping, then rocking and sometimes rolling over entirely. Often an explosive breakup accompanies this event with great chunks of ice blown into the air and shards falling back into the sea as though the iceberg was just hit by the shell of a giant cannon. The whole process is called "foundering". You can be standing on land many kilometres from an iceberg, but, with the tell-tale, thunder-like boom, you know it has foundered.