Rock glacier

Rock glaciers are distinctive geomorphological landforms of angular rock debris frozen in interstitial ice which may extend outward and downslope from talus cones, glaciers or terminal moraines of glaciers. There are two types of rock glaciers: periglacial glaciers, or talus-derived glaciers, and glacial rock glaciers. Possible Martian rock glacier features have been identified by the Mars Orbiter spacecraft.

Formation

Little is known about rock glacier formation. The two known factors that must be present in order to to create rock glaciers are low ice velocity and permafrost. Most glacial rock glaciers are created by the recession of debris covered glaciers. Glacial rock glaciers are often found in cirque basins where rocky debris falls off the steep sides and accumulates on ice glaciers. As the glaciers shrink,their composition changes as they become increasingly covered with debris. Eventually, the glacial ice is replaced by ice cored rocks. With the exception of ice-cored rock glaciers, rock glaciers are a periglacial process. This means that they are a nonglacial landform associated with cold climates, particularly with various aspects of frozen ground. Periglacial rock glaciers require permafrost instead of glacial ice in order to form. Instead, they are caused by continuous freezing occurring within a talus lobe.

Rock glaciers may also have a mass wasting or landslide origin which, does not require the presence of ice and suggests a sudden catastrophic origin with little subsequent movement.

Movement

Rock glaciers move downslope by deformation of the ice contained within them, causing their surface to resemble those of glaciers. Some rock glaciers can reach lengths of 3 km and can have terminal embankments of 60 m high. Blocks on the surface can be up to 8 m in diameter. Flow features on the surface of rock glaciers may develop from:

* Deformation of the ice core.

* Movement of the debris cover along the debris-ice interface.

* Deformation from a period of glacial advance.

* Changes in the hydrologic balance.

Their growth and formation is subject to some debate, with three main theories:

* A permafrost origin, which implies that the features are related to permafrost action rather than glacial action;

* A mass wasting or landslide origin which does not require the presence of ice and suggests a sudden catastrophic origin with little subsequent movement.

Rock glaciers may move or creep at a very slow rate in part dependent on the amount of ice present.

Human Use

Rock Glaciers in the Chilean Andes help supply the water for much of Chile, including the capital of Santiago. Mining operations in the high mountains have led to the degradation and destruction of more than two rock glaciers. Several copper mines dump their waste rock onto rock glaciers, which results in faster melting and higher velocity movement of these glaciers. The dumping of waste rock also destabilizes the glaciers. In of 2004, protesting irrigation farmers and environmentalists changed rules so new mining projects can no longer damage or alter rock glaciers in Chile.

References

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External links

Earth Observatory image and explanation of a rock glacier on Sourdough Peak, Alaska

USGS Glossary of Glacier Terminology

AGU - Terrestrial Models of Rock Glacier and Protalus Lobe Formation

Category:Glaciology