In glaciology

Glaciology

Glaciology Glaciology Glaciology (from Middle French dialect (Franco-Provençal): glace, "ice"; or Latin: glacies, "frost, ice"; and Greek: λόγος, logos, "speech" lit...

, a roche moutonnée (or sheepback) is a rock formation

Rock formation

This is a list of rock formations that include isolated, scenic, or spectacular surface rock outcrops. These formations are usually the result of weathering and erosion sculpting the existing rock...

 created by the passing of 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...

. When a glacier erodes down to bedrock, it can form tear-drop shaped hills that taper in the up-ice direction.

Name

The 18th-century Alpine explorer Horace-Bénédict de Saussure

Horace-Bénédict de Saussure

200px|thumb|Portrait of Horace-Bénédict de Saussure Horace-Bénédict de Saussure was a Genevan aristocrat, physicist and Alpine traveller, often considered the founder of alpinism, and considered to be the first person to build a successful solar oven.-Life and work:Saussure was born in Conches,...

 coined the term 'roches moutonnées' in 1786. He saw in these rocks a resemblance to the wig

Wig

A wig is a head of hair made from horsehair, human hair, wool, feathers, yak hair, buffalo hair, or synthetic materials which is worn on the head for fashion or various other aesthetic and stylistic reasons, including cultural and religious observance. The word wig is short for periwig and first...

s that were fashionable amongst French gentry in his era and which were smoothed over with mutton fat (hence 'moutonnée') so as to keep the hair in place.

Nature

The appearance of the erosional stoss and lee feature is very defined on Roche moutonnée as all the sides and edges have been smoothed and eroded in the direction that the glacier that once passed over it. It is often marked with glacial striations

Glacial striations

Glacial striations or glacial grooves are scratches or gouges cut into bedrock by process of glacial abrasion. Glacial striations usually occur as multiple straight, parallel grooves representing the movement of the sediment-loaded base of the glacier...

.

The rough and craggy down-ice side is formed by "plucking", the erosional process in which ice melts slightly by pressure and seeps into cracks in the rock. When the water refreezes, the rock becomes attached to the glacier. But as the glacier continues its forward progress it subjects the stone to frost shattering ripping strips away from the rock formation.

Note that the side profile of a roche moutonnée is opposite to that of a drumlin

Drumlin

A drumlin, from the Irish word droimnín , first recorded in 1833, is an elongated whale-shaped hill formed by glacial ice acting on underlying unconsolidated till or ground moraine.-Drumlin formation:...

. In a drumlin, the steep side is facing the approaching glacier, rather than trailing it.

External links

• A roche moutonnée and perched boulders, northeastern Manitoba, image from Geological Survey of Canada Canadian Landscapes Photo Collection
• Roche moutonnée, northern Abitibi, Québec, image from Geological Survey of Canada Canadian Landscapes Photo Collection
• Roche Moutonnée, Melville Peninsula, Nunavut, image from Geological Survey of Canada Canadian Landscapes Photo Collection