Norridgewock De Geer Moraine EarthCache
Norridgewock De Geer Moraine
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Driving along you can see out of the window of your vehicle farm fields that have an unusual appearance. What has caused the terrain to form in this manner?
What you are looking at is called a De Geer moraine. It was named after the Swedish geologist, Gerard De Geer. Who during fieldwork in 1878, noticed that the appearance of laminated sediments deposited in glacial lakes at the margin of the retreating Scandinavian ice sheet at the end of the last ice age, closely resembled tree-rings. While these observations were not new, De Geer was the first geologist to exploit its potential application. De Geer called these annual sedimentary layers varves. However, it was not until 1910, at the International Geological Congress, that De Geer's pioneering work reached the wider international scientific community.
The De Geer moraine or washboard moraine occur as a type of moraine landscape that consists of a series of separate, narrow ridges trending parallel to a former ice front, and which can form annually. The ridges may be up to 300 m apart and up to 15 m high. They consist typically of a till core, capped by a layer of partly rounded rocks. This landscape may have formed beneath the grounded part of an ice sheet that extended into a sea. These small ridges were formed between 13, 000 and 12, 500 years ago as the ice retreated. According to the current moraine genesis theory, the moraine ridges were formed beneath the ice in crevasses running parallel to the ice margin. Huge icebergs were released from the ice front and the De Geer moraines reflect the probable position of the retreating ice margin. They are referred to as a washboard moraine due to the annual glacial advances and recessions causing parallel ridges to form a few meters apart. Because the accumulation of debris is annual, the moraines do not get very large and stand only a few meters high. The name "washboard moraine" refers to the fact that, from the air, it resembles a washboard.
At the posting coordinates you will find yourself on the edge of the road looking across a field that is showing a De Geer moraine.
Remember this is an earthcache so there is no container just an earth science lesson at an amazing natural feature. To log this cache, email me through my profile:
1) The name of the Earthcache and the number of people in your group.
2) Looking at the field what would you guess the direction of the retreating ice flow to be at this location?
3) While not necessary a photo is always nice so others have some idea of what they will be seeing at this location.
If you enjoy this earthcache you may want to check the Maine Geological Survey located at (visit link)
They have developed a number of information sheets or field localities giving a great deal of information about geologic features. They also have a number of books and maps about Maine’s natural history/ geology that you might find interesting.
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