| What it is | A block or tower of glacial ice |
| Danger | Can collapse without warning |
| Hazard type | Objective (serac fall) |
| Found | On steep, broken glaciers |
A serac is a large block or pinnacle of glacial ice, formed where a glacier breaks up over steep or uneven ground. Seracs can topple without warning, making serac fall one of the deadliest objective hazards in mountaineering. Climbers minimize the time they spend beneath them.
Why they’re feared
Driven by the glacier’s movement, a serac can collapse at any moment — a classic uncontrollable objective hazard, often in chaotic icefalls alongside crevasses.
Managing the risk
You can’t predict serac fall — only avoid lingering beneath them during glacier travel.
Frequently asked questions
What is a serac?
A serac is a large block, column, or tower of ice on a glacier, formed where the ice fractures as it flows over a steepening or bend — often in chaotic zones called icefalls. Seracs can be the size of houses or larger.
Why are seracs dangerous?
Because they can collapse at any moment, with no reliable warning, driven by the glacier's constant movement rather than by weather or time of day. A falling serac is an 'objective hazard' you can't control — only avoid by limiting time spent below it.
What is an icefall?
An icefall is a steep, heavily crevassed and serac-strewn section of a glacier, like a frozen waterfall of broken ice. Icefalls — such as Everest's Khumbu Icefall — are notoriously dangerous because of unstable seracs and shifting crevasses.
Sources
- Objective hazards — American Alpine Club