serac

"The disaster took place after a huge serac broke and fell, sweeping away several climbers and stranding as many as a dozen mountaineers above a steep gully without ropes at a height of about 27,000 feet, not far from the summit."

The New York Times, Rescuers Wait to Reach K2 Survivor, by Salman Masood and Tom Rachman, August 6, 2008

The American Meteorological Society's glossary defines a serac as "A large block of ice, generally taller than broad, formed by the fracturing of ice. Most commonly found within an icefall, at the edge of an ice cliff, or at the margins of fast-moving ice."

Cares in reverse.