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 kilometres long and, because of their peculiar uniform shape, are somewhat like railway embankments.
Most eskers are argued to have formed within ice-walled tunnels by streams which flowed within and under 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.
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.
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. 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 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.
To get credit for this EarthCache email the cache owner with this information:
From the parking lot (see cords above) look up to the top of the ridge and guess the height.
Take a altitude reading in this area.
Now drive or walk to the highest point you can find near the children’s playground on top and take another reading.
1) What is the difference of these two readings?
2) What was your guess?
3) From the edge of the field does the bank go up steep like an Esker or slower like a moraine which is a deposit of glacial debris.
4) Is this a well defined long ridge like an esker or an irregular shaped deposit like a moraine.
5) Find the walking trail at the end of the playground parking area. What type of soil do you find exposed by the trail here? Loam, Clay, Sand, Gravel, or a mix?
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