Esker

Also termed as Escher, Eskers are sand and gravel ridges formed by glacial meltwater flowing through tunnels within and beneath glaciers or meltwater channels on top of glaciers. Sediments accumulate in the channel or tunnel over time. As the ice recedes, the sediments form a ridge in the landscape. It is a type of fluvioglacial landform.

Eskers are significant because they can provide information about how ice sheets and glaciers behaved in the past. They can tell us about meltwater and aid in the reconstruction of the glacier's former ice surface and snout orientation.

Physical Features of Escher

Eskers are typically a few metres to tens of metres high and tens to hundreds of metres wide, for example, 2,3. Cross-sectionally, they can be sharp-crested (triangular), round-crested (semi-circular), flat-topped (trapezoid), or multi-crested (having two or more crests).

The size and shape of the subglacial tunnel are determined by plastic flow and melting of the basal ice. This, in turn, determines an esker's shape, composition, and structure. Eskers can be a single channel or part of a branching system with tributary eskers. 

They are rarely found as continuous ridges, but rather with gaps between the winding segments. Esker ridge crests are typically knobby and do not remain level for long periods of time. Eskers can have broad or sharp crests and steep sides. 

Eskers can be hundreds of metres or hundreds of kilometres long. Individual esker ridges formed beneath the massive continental-scale ice sheet that covered North America, for example, can reach lengths of up to 100 km. Aligned ridge groups can form fragmented esker chains up to 300 km long. The Eurasian Ice Sheet created similarly long eskers in Scandinavia.

Significance of Esker

Eskers formed in subglacial tunnels are useful tools for learning about the nature and evolution of glaciers and ice sheets. They document the routes of basal meltwater drainage near the ice margin.

Because of the weight of the overlying ice, the subglacial meltwater is under high pressure. As a result, it can flow uphill! This means that eskers frequently go uphill and climb local topography on a local scale.

The path of pressurised meltwater in subglacial channels is primarily determined by the slope of the ice surface rather than the slope of the bed. As a result, eskers are typically oriented parallel to the ice flow and transverse to the ice terminus.

As a result, the path of an esker section can be used to reconstruct the ice surface slope and orientation at the time of formation.

The eskers produced by the last North American and Eurasian ice sheets most likely record the ice sheets' final retreat as climate warming increased the rate of meltwater production towards the end of the Pleistocene. As a result, by studying eskers, we can gain a better understanding of how glaciers and ice sheets respond to climate change.

These palaeo glaciological insights are critical for forecasting the contemporary Antarctic and Greenland Ice Sheets' responses to human-caused climate change, as well as their potential contribution.

Origin of Eskers

Eskers can be found all over the land that was once covered by the former North American (Laurentide) Ice Sheet, Eurasian Ice Sheet, and British-Irish Ice Sheet. 

The most common subglacial eskers preserved on palaeo-ice-sheet beds are those formed in subglacial meltwater channels (termed R-channels, which are incised upwards into the basal ice).

Breiamerkurjökull in Iceland and Hybyebreen in Svalbard are two excellent examples of recently formed eskers.

The zig-zagging eskers are mostly in the flow direction, whereas the moraines are parallel to the ice margin.

Eskers are more common on paleo-ice-sheet beds in areas of crystalline bedrock with thin surficial sediment coverings than in areas of thick deformable sediment. This is because meltwater flowing at the bed is more likely to incise upwards into the ice to form an R-channel where the bed is hard; meltwater is more likely to incise downwards where the bed is deformable.

Detailed Geology of Escher

The majority of eskers are thought to have formed within ice-walled tunnels by streams flowing within and beneath glaciers. They were most common during the glacial maximum when the glacier was slow and sluggish. Stream deposits remained as long winding ridges after the retaining ice walls melted. If water is under pressure in an enclosed pipe, such as a natural tunnel in ice, it can flow uphill.

Eskers can form above glaciers as a result of sediment accumulation in supraglacial channels, crevasses, linear zones between stagnant blocks, or narrow embayments at glacier margins. Eskers form near the terminal zone of glaciers, where the ice is slower moving and thinner.

Path:

The water pressure of an esker in relation to the overlying ice determines its path. In general, the ice pressure was high enough to 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 glacier's direct path. This process is responsible for the formation of wide eskers on which roads and highways can be built. Less pressure, which occurs closer to the glacial maximum, can cause ice to melt over the streamflow, resulting in steep-walled, sharply-arched tunnels.

Examples of Esker

Glacial landforms like Escher are found in the following regions-

1. Europe:

Uppsala Sen is a 250-kilometre-long (160-mile-long) river in Sweden that runs through the city of Uppsala. The Badelundasen esker stretches over 300 kilometres (190 miles) from Nyköping to Lake Siljan. Pispala is located on an esker between two glacier-carved lakes in Tampere, Finland. Punkaharju in Finnish Lakeland is a similar location.

The Kemba Hills are a 5 km esker in Aberdeenshire, Scotland, near the village of Kemnay. Bedshiel Kaims is a 3km long example in Berwickshire, southeast Scotland, that is up to 15m high and is the legacy of an ice-stream within the Tweed Valley.

2. North America:

In Michigan, there are over 1,000 eskers, mostly in the south-central Lower Peninsula. The Mason Esker, which stretches south-southeast from DeWitt through Lansing and Holt before ending near Mason, is Michigan's longest esker at 22 miles.

Esker systems can be traced for up to 100 miles in the U.S. state of Maine.

The Thelon Esker is an 800-kilometre (497-mile) river that runs through Canada's Northwest Territories and Nunavut.

Uvayuq, also known as Mount Pelly, is an esker in the Kitikmeot Region of Nunavut's Ovayok Territorial Park.