Chunks periodically break from the ice cliff, splash into the sea, and drift on as bobbing icebergs. Calving happens when a glacier's forward flow outpaces melting at its terminus, stressing the ice until cracks (crevasses) propagate and a section shears off — sometimes triggered by tidal flexing where the ice meets the ocean. Glacial ice is only about 90% as dense as seawater, so calved blocks float with roughly a tenth of their mass showing above the surface, in classic "tip of the iceberg" fashion. Large calving events at glaciers like Jakobshavn in Greenland or Antarctica's ice shelves can release chunks the size of city blocks in seconds, and the world's glaciers together lose several hundred billion tons of ice per year, a major contributor to sea-level rise. Drag to orbit, scroll to zoom.