Information AboutEsker |
| CATEGORIES ABOUT ESKER | |
| glaciology | |
| mountain and glacial landforms | |
|
National Natural Landmark , Washington state. Note trees next to and the single lane road crossing the esker to the right of the photo which provide scale.]] An Esker is a long, winding ridge of Stratified Sand and Gravel , examples of which occur in Glaciated and formerly glaciated regions of Europe and North America. Eskers are frequently several miles in length and, because of their peculiar uniform shape, somewhat resemble Railroad Embankment s. Most eskers are believed to form in ice-walled tunnels by Stream s which flowed within and under glaciers. After the retaining ice walls melt away, stream deposits remain as long winding ridges. Eskers may also form above glaciers by accumulation of sediment in supraglacial channels, in crevasses, in linear zones between stagnant blocks, or in narrow embayments at glacier margins. Eskers form near the terminal zone of glaciers, where the ice is not moving as fast and is relatively thin (Easterbrook, 1999). The rate of plastic flow and melting of the basal ice determines the size and shape of the subglacial tunnel. This in turn determines the shape, composition and structure of an esker. Eskers may exist as a single channel, or may be part of a branching system with Tributary eskers. They are not often found as continuous ridges, but have gaps that separate the winding segments. The ridge crests of eskers are not usually level for very long, and are generally knobby. Eskers may be broad-crested or sharp-crested with steep sides (Easterbrook, 1999). They can reach hundreds of kilometers in length. The concentration of rock debris in the ice and the rate at which sediment is delivered to the tunnel by melting and from upstream transport determines the amount of Sediment in an esker. The sediment generally consists of coarse-grained, water-laid sand and gravel. This sediment is stratified and sorted, and usually consists of pebble/cobble-sized material with occasional boulders. Bedding may be irregular but is almost always present, and Cross-bedding is common (Easterbrook, 1999). The name '''esker'' is derived from the '', which runs virtually the entire width of the island of Ireland from Dublin to Galway , a distance of about 100 miles, and is still closely followed by the main road linking those two cities. The Mason Esker, at approximately 22 miles, is one of the longest eskers in the U.S.[http://www.cacvoices.org/main.asp?a=2&b=0&pageid=670&view=] It is located in Mason, Michigan . It stretches from DeWitt through Lansing and Holt, finally ending in Mason. Esker systems in the U.S. state of Maine can be traced for up to 100 miles[http://www.maine.gov/doc/nrimc/mgs/explore/surficial/facts/surficial.htm]. Eskers are sometimes used for construction of highways as an economic measure. This includes the Denali Highway in Alaska and the Trans-Taiga Road in Quebec . SEE ALSO Glacial Landforms Glacier Morphology REFERENCES |
|
|