What is the name for a large block of ice that breaks off a glacier into water? The answer is an iceberg. The process that creates one is called calving: a fracture causes a piece of glacier ice or floating ice shelf to separate and drift away in a lake or ocean.
Icebergs can be small chunks or enormous tabular masses. Because ice is less dense than seawater, roughly 90 percent of an iceberg's volume remains below the surface. That hidden underwater portion is why icebergs are hazardous to ships and why their visible shape can give a misleading impression of their true size. Wind, waves, melting, and rolling can continually reshape them.
An ice floe is sea ice floating on water, not a piece calved from a glacier. An ice shelf is a broad floating platform fed by land ice, while an ice sheet is a continental-scale mass of grounded ice. Icebergs may calve from glaciers that reach water directly or from the seaward edge of an ice shelf.