NASA's ICE mission found, as part of IceBridge Operation, a giant tabular iceberg of the Larsen C Ice Shelf, which appears to have been trimmed squarely with a giant saw. However, it is a purely natural phenomenon.
Like conventional icebergs, only 10% of its size stands out from the water, although its underwater mass seems to have a similar shape to the surface.
The tabular icebergs are huge ice plates with a flat top and vertical sides that are formed by loosing from the big ice shelves that surround the poles. They can take more regular geometrical shapes, unlike hard, non-tabular icebergs.
According to the calculations of researchers of the University of Maryland (USA) these particular icebergs can be truly immense, measuring hundreds and sometimes thousands of square kilometers, like the B-15, formed in the year 2000, that with its 11000 square kilometers became the world's largest floating object ever recorded. (Taken from https://actualidad.rt.com)