A flat-topped iceberg with steep vertical sides.
Environment and Climate Change - Canada https://www.ec.gc.ca/glaces-ice/default.asp?lang=En&n=2CE448E2%E2%80%931&offset=4&toc=hide

Photo: © Masterfile Corporation

https://www.ec.gc.ca/glaces-ice/default.asp?lang=En&n=2CE448E2%E2%80%931&offset=5&toc=hide