Esker
Encyclopedia
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Ridge
A ridge is a geological feature consisting of a chain of mountains or hills that form a continuous elevated crest for some distance. Ridges are usually termed hills or mountains as well, depending on size. There are several main types of ridges:...
of stratified
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
and gravel
Gravel
Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...
, examples of which occur in glaciated
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...
and formerly glaciated regions of Europe and North America. Eskers are frequently several kilometres long and, because of their peculiar uniform shape, are somewhat like railway embankment
Embankment (transportation)
To keep a road or railway line straight or flat, and where the comparative cost or practicality of alternate solutions is prohibitive, the land over which the road or rail line will travel is built up to form an embankment. An embankment is therefore in some sense the opposite of a cutting, and...
s.
Geology
Most eskers are argued to have formed within ice-walled tunnels by streamStream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
s which flowed within (englacial) and under (subglacial) glaciers. They tended to form around the time of the glacial maximum when the glacier was slow and sluggish. After the retaining ice walls melted away, stream deposits remained as long winding ridges. (Water can flow uphill if it is under pressure in an enclosed pipe, such as a natural tunnel in ice.)
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.
Tributary
A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...
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. They can reach hundreds of kilometers in length and are generally 20–30 metres in height.
The path of an esker is governed by its water pressure in relation to the overlying ice. Generally the pressure of the ice was at such a point that it would allow eskers to run in the direction of glacial flow, but force them into the lowest possible points such as valleys or river beds, which may deviate from the direct path of the glacier. This process is what produces the wide eskers upon which roads and highways can be built. Less pressure, occurring in areas closer to the glacial maximum, can cause ice to melt over the stream flow and create steep-walled, sharply-arched tunnels.
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
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
in an esker. The sediment generally consists of coarse-grained, water-laid sand and gravel, although gravelly loam may be found where the rock debris is rich in clay. 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
Cross-bedding
In geology, the sedimentary structures known as cross-bedding refer to horizontal units that are internally composed of inclined layers. This is a case in geology in which the original depositional layering is tilted, and the tilting is not a result of post-depositional deformation...
is common.
Etymology
The name Esker is derived from the IrishIrish language
Irish , also known as Irish Gaelic, is a Goidelic language of the Indo-European language family, originating in Ireland and historically spoken by the Irish people. Irish is now spoken as a first language by a minority of Irish people, as well as being a second language of a larger proportion of...
word eiscir (Old Irish: escir), which means: "a ridge or elevation, especially one separating two plains or depressed surfaces".
The term was used particularly to describe long sinuous ridges, which are now known to be deposits of fluvio-glacial
Fluvio-glacial
Fluvio-glacial is the water created by the melting of glaciers. It literally means "Water Glacier." It is also commonly called melt water.Fluvio-glacial can also mean sediments deposited by the glacier meltwater....
material. The best-known example of such an eiscir is the Eiscir Riada
Esker Riada
Esker Riada, , is a system of ridges that stretch across the middle of Ireland, between Dublin and Galway.-Geography:The Esker Riada is a collection of eskers, that passes through the counties of Dublin, Meath, Kildare, Westmeath, Offaly, Roscommon and Galway...
, which runs nearly the whole width of Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
from Dublin to Galway
Galway
Galway or City of Galway is a city in County Galway, Republic of Ireland. It is the sixth largest and the fastest-growing city in Ireland. It is also the third largest city within the Republic and the only city in the Province of Connacht. Located on the west coast of Ireland, it sits on the...
, a distance of 200 km, and is still closely followed by the main road from Dublin to Galway.
Examples of eskers
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
Uppsalaåsen stretches for 250 km (155.3 mi) and passes through Uppsala
Uppsala
- Economy :Today Uppsala is well established in medical research and recognized for its leading position in biotechnology.*Abbott Medical Optics *GE Healthcare*Pfizer *Phadia, an offshoot of Pharmacia*Fresenius*Q-Med...
city.
Great Esker Park
Great Esker Park
Great Esker Park is a geological formation along the Weymouth Back River in Weymouth, Massachusetts.This area was formed by a glacier 12,000 years ago...
runs along the Back River in Weymouth, Massachusetts
Weymouth, Massachusetts
The Town of Weymouth is a city in Norfolk County, Massachusetts, United States. As of the 2010 census, Weymouth had a total population of 53,743. Despite its city status, it is formally known as the Town of Weymouth...
and is home to the highest esker in North America (90 ft).
Pispala
Pispala
Pispala is a city district 2.5 km from the centre of Tampere, Finland. It is located on the northern slope of Pispalanharju, the highest esker in Finland....
in Tampere
Tampere
Tampere is a city in southern Finland. It is the most populous inland city in any of the Nordic countries. The city has a population of , growing to approximately 300,000 people in the conurbation and over 340,000 in the metropolitan area. Tampere is the third most-populous municipality in...
, Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
is on an esker between two lakes carved by 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...
s.
The village of Kemnay
Kemnay
Kemnay is a town west of Aberdeen in Scotland. It has a population of about 4,500 .- History :The villagename Kemnay is believed to originate from the Celtic words that mean bend and river due to...
in Aberdeenshire, Scotland has an excellent 5 km esker locally called the Kemb Hills.
The Mason Esker, about 22 miles long, is one of the longest eskers in the USA. http://www.cacvoices.org/main.asp?a=2&b=0&pageid=670&view= It is in Mason, Michigan
Mason, Michigan
Mason is a city in the U.S. state of Michigan. It is named after the state's first governor, Stevens T. Mason. As of the 2010 census, the city population was 8,252. It is the county seat of Ingham County. Mason is the only city in the U.S. that serves as a county seat ahead of a state capital,...
. It stretches from DeWitt
DeWitt, Michigan
DeWitt is a city in Clinton County in the U.S. state of Michigan. The population was 4,507 at the 2010 census.-History:DeWitt was named after DeWitt Clinton, Governor of New York during the 1830s. It was first settled by Captain David Scott, who moved there from Ann Arbor in 1833, and platted the...
through Lansing and Holt
Holt, Michigan
Holt is an unincorporated community within Delhi Charter Township, Ingham County in the U.S. state of Michigan. It is a census-designated place used for statistical purposes. The population was 11,315 at the 2000 census....
, 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
The Thelon Esker runs for 800 kilometers and straddles the border between Northwest Territories
Northwest Territories
The Northwest Territories is a federal territory of Canada.Located in northern Canada, the territory borders Canada's two other territories, Yukon to the west and Nunavut to the east, and three provinces: British Columbia to the southwest, and Alberta and Saskatchewan to the south...
and Nunavut
Nunavut
Nunavut is the largest and newest federal territory of Canada; it was separated officially from the Northwest Territories on April 1, 1999, via the Nunavut Act and the Nunavut Land Claims Agreement Act, though the actual boundaries had been established in 1993...
in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
.
Ovayok or Mount Pelly in Ovayok Territorial Park, Kitikmeot, Nunavut
Nunavut
Nunavut is the largest and newest federal territory of Canada; it was separated officially from the Northwest Territories on April 1, 1999, via the Nunavut Act and the Nunavut Land Claims Agreement Act, though the actual boundaries had been established in 1993...
in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
.
Roads are sometimes built along eskers to save expense. Examples include the Denali Highway
Denali Highway
Denali Highway is a lightly traveled, mostly gravel highway in the U.S. state of Alaska. It leads from Paxson on the Richardson Highway to Cantwell on the Parks Highway. Opened in 1957, it was the first road access to Denali National Park...
in Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, the Trans-Taiga Road
Route Transtaïga
The Trans-Taiga Road is an extremely remote wilderness road in northern Quebec, Canada. It is long to Centrale Brisay and another along the Caniapiscau Reservoir, all of it unpaved....
in Quebec
Quebec
Quebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....
, and the "Airline" segment of Maine State Route 9
Maine State Route 9
State Route 9 is a numbered state highway in Maine, running from the New Hampshire border at Berwick in the west to the Canadian border with New Brunswick at Calais in the east. State Route 9 runs a total of .-Route description:...
between Bangor
Bangor, Maine
Bangor is a city in and the county seat of Penobscot County, Maine, United States, and the major commercial and cultural center for eastern and northern Maine...
and Calais
Calais, Maine
Calais is a city in Washington County, Maine, United States. The city has three United States border crossings or also known as a Port of entry with the busiest being on the St. Croix River bordering St. Stephen, New Brunswick, Canada...
. http://www.downeastregion.com/way_downeast.php There are numerous long eskers in the Adirondack State Park
Adirondack State Park
The Adirondack Park is a publicly protected area in northeast New York. It is the largest park and the largest state-level protected area in the contiguous United States, and the largest National Historic Landmark....
in upstate New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
.
See also
- Tunnel valleyTunnel valleyA tunnel valley is a large, long, U-shaped valley originally cut under the glacial ice near the margin of continental ice sheets such as that now covering Antarctica and formerly covering portions of all continents during past glacial ages....
- Glacial landformsGlacial landformsGlacial landforms are those created by the action of glaciers. Most of today's glacial landforms were created by the movement of large ice sheets during the Quaternary glaciations...
- Glacier morphologyGlacier morphologyGlacier morphology, or the form a glacier takes, is influenced by temperature, precipitation, topography, and other factors. Types of glaciers range from massive ice sheets, such as the Greenland ice sheet or those in Antarctica, to small cirque glaciers perched on a mountain...
- Eskers Provincial ParkEskers Provincial ParkEskers Provincial Park is a provincial park in British Columbia, Canada. The park comprises roughly and was created in 1987. Located west of Nukko Lake, which lies northwest of the city of Prince George, it protects an area of the Stuart River Eskers Complex. Eskers are winding ridges of gravel...
(British Columbia, Canada)
External links
- Oblique aerial photo of an esker in Waterford, Maine
- Esker Riada Webpage
- Diagram illustrating (i) tunnel in glacier before retreat of ice, forming (ii) meandering esker in The Ice Melts: Deposition on page 6 of "Pennsylvania and the Ice Age" published 1999 by PA DCNR Bureau of Topographic and Geologic Survey
- The Bridgenorth Esker: geomorphology and sedimentology