Great Esker is maintained by the Town of Weymouth. It is highly accessible for walking, hiking, and bicycling as well as kyaking in the Weymouth Back River, which winds along side of the Great Esker. Picnic areas are available.
Graced by salt marshes and reversing falls, Great Esker features more than six miles of trails where visitors can enjoy beautiful views. Bird watching is a popular activity as osprey, great blue heron, snowey egrets, red-tailed hawks, owls and many other species of birds are abundant seasonally.
Twelve thousand years ago, the glacier that stood 1,000 feet above the Weymouth landscape began to melt, eventually leaving behind the tallest esker river bed in the United States.
Great Esker was formed by a river of rushing water underneath the glacier. Over time the river deposited layer upon layer of sediment, cutting upward through the glacier. When the glacier retreated, the remaining deposits of sand and gravel that had built up within the glacier remained creating a long winding hill where the river used to be.
It is believed that the sediment deposits from as far away as Canada make up Weymouth's Great Esker. It is 90 feet high and stretches for over two miles.
"An aerial picture of Great Esker Park. (Elevation is exaggerated.) From Google Earth. Approximate location of the original esker is outlined in red.".
Geology:
An esker is formed by a stream or river in a tunnel underneath a glacier. It is made up of the sediments dropped by that stream or river. When the glacier retreats, the deposits remain, exposing a long, winding hill where the stream or river used to be. Eskers are great sources of gravel and sand (used in construction), and consequently most eskers have been stripped away for these materials.
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
Eskers have been desirable places to mine gravel and sand because they contain very little clay and mud. This is because the streams that deposit the materials under the glacier move very rapidly, and carry the finer-grained sediments away.
Great Esker Park is one of the few remaining places in the Boston area where you can see a relatively intact esker.
Etymology:
The name Esker is derived from the Irish 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 material.
Requirements to Post:
Note: Please do not post answers in logs. Please Email answers and then log the EarthCache.
Observe the esker in the picture above:
1) Describe the shape of the esker.
2) Why do you think it has this shape?
Observations at the site:
3) Record the elevation from your GPS /Phone at the posted coordinates (GZ).
4) At GZ look towards the east side of the trail. You will see a small patch where the sediments are visible. Please describe in detail what you see. What is the composition of the sediment? Large rock, medium rock, small rock, or a mix? Is the sediment in the patch lightly scattered or densely gathered?
Just for fun: Enjoy the scenic view on the way back!
References:
http://en.wikipedia.org/wiki/Esker
http://www.bostongeology.com/geology/fieldtrips/trips/weymouth/esker.htm
Thanks to Mike Doyle and the Weymouth Parks and Recreation Dept. for their help with this EarthCache.
*Congratulations to foragess for FTF!*
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