B15A - A Huge Tabular Iceberg
Huge tabular icebergs such as this one are only found in Antarctica, they were once part of a floating ice-shelf before they broke away from the edge. The ice-shelf would have been fed by glaciers from the land.
They can take many years to break up and melt once they are adrift. The larger ones are routinely tracked by satellite as they can be significant shipping hazards.
Photo; © Mike Usher - Pictures from an icebreaker cruise to Eastern Antarctica.