A large block or column of glacial ice formed by intersecting crevasses is called a serac. Crevasses split moving glacier ice into towering, irregular blocks, especially where the glacier steepens or passes over uneven terrain.
Seracs are common in icefalls and on the lower edges of hanging glaciers. Their size can range from relatively small pinnacles to blocks as large as houses. Because the ice is fractured and often poorly supported, a serac can collapse suddenly, creating a major hazard for climbers and routes beneath it.
A serac is not an iceberg, which is a piece of glacier or ice shelf that has broken off and is floating in water. An ogive is a curved band or wave-like feature often visible below an icefall, a kame is a mound of glacial sediment, and a nunatak is a mountain peak projecting through an ice sheet or glacier. The word serac comes from a type of Swiss cheese whose irregular appearance resembles broken glacier ice.