A serac is a block or column of ice

Ice

Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

 formed by intersecting crevasse

Crevasse

A crevasse is a deep crack in an ice sheet rhys glacier . Crevasses form as a result of the movement and resulting stress associated with the sheer stress generated when two semi-rigid pieces above a plastic substrate have different rates of movement...

s on a glacier

Glacier

A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

. Often house-sized or larger, they are dangerous to mountaineer

Mountaineer

-Sports:*Mountaineering, the sport, hobby or profession of walking, hiking, trekking and climbing up mountains, also known as alpinism-University athletic teams and mascots:*Appalachian State Mountaineers, the athletic teams of Appalachian State University...

s since they may topple with little warning. Even when stabilized by persistent cold weather, they can be an impediment to glacier travel.

Seracs are found within an icefall

Icefall

An icefall is a portion of some glaciers characterized by rapid flow and a chaotic crevassed surface. Perhaps the most conspicuous consequence of glacier flow, icefalls occur where the glacier bed steepens and/or narrows...

, often in large numbers, or on ice faces on the lower edge of a hanging glacier. Examples of the latter in the Alps

Alps

The Alps is one of the great mountain range systems of Europe, stretching from Austria and Slovenia in the east through Italy, Switzerland, Liechtenstein and Germany to France in the west....

 are found on the north-east face of Piz Roseg

Piz Roseg

Piz Roseg is a mountain in the Bernina Range in Graubünden, Switzerland.There are two summits on its main ridge:*the south-east and higher summit *the north-west summit, known as the Schneekuppe ....

, the north face of the Dent d'Hérens

Dent d'Hérens

The Dent d'Hérens is a mountain in the Pennine Alps, lying on the border between Italy and Switzerland. The mountain lies a few kilometres west of the Matterhorn.The Aosta hut is used for the normal route.-Naming:...

 and the north face of Lyskamm

Lyskamm

Lyskamm is a mountain in the Pennine Alps lying on the border between Switzerland and Italy. It consists of a five-kilometre-long ridge with two distinct peaks...

.