Often known locally as a "horseback," an esker is a long and narrow, slightly raised stretch of sediment. You see, around 1.5 million years ago glaciers began melting, forming rivers underneath. As with all rivers, they carried sediment quite easily across the landscape. The glaciers then completely melted, leaving behind a range of twisting ridges in regions such as Manitoba, Canada and Maine in the U.S..
The name esker comes from the Irish word eiscir, which means: "a ridge or elevation, especially one separating two plains or depressed surfaces." The term was used to describe long, winding ridges, which we now know to be deposits of glacial flows. The best-known example of such an esker is the Eiscir Riada, which runs the entire width of the island of Ireland from Dublin to Galway.
At the time of the glacial melting, much of the sediment from these rivers was carried out to the ocean to become marine sediment. That which was not carried to sea was left behind in long ridges of mineral deposit which are used today as highways.
These ridges are snake-like casts of a prehistoric landscape composed of glaciers and the rivers running underneath. Besides the fact that these places provide a descent vantage point and in most cases keep your feet dry, we can actually imagine how these rivers once flowed. When an esker is comprised of finer sediments, one can tell that 1.5 million years ago this part of the region was a particularly slow going river. In some cases all that's left behind is silt, which indicates an extremely fast paced water flow once passed through.
Even our own Adirondacks are home to several eskers, with a pair near Star Lake in the Western region.
Brandon, good topic. You might have localized it more by discussing one or two of the large eskers in the Adirondacks. Your explanation of how eskers are created could have been clearer. Also, why would a slow river leave "finer sediments" and a fast river silt? Isn't silt a fine sediment? I would think coarse material, such as gravel, would be deposited in a slower river. Glaciers in the Adirondacks melted about 10,000 years ago, roughly. Where do you get 1.5M years?
ReplyDeleteWhat do you mean eskers are used as highways? Do you mean the gravel deposits are used in highway construction? If not, where are eskers used as highways? Not in the Adirondacks, as far as I know.