Plymouth Rock - Urban glacial debris
In Minnesota, United States
Size:  (not chosen)
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This earth cache is located in Plymouth, Minnesota.
A glacier is a large body of ice moving slowly across the land.
It forms when snow accumulates faster than it melts over a long period of time. Because of the weight of the ice in the glacier, ice melts at the bottom and lets the glacier move. As the glacier moves, it picks up pieces of rock and debris, and deposits them later as it melts.
Till is sediment that has been moved by glaciers, and it can range in size from clay to boulders. Usually, till is not moved very far during this process. Because of this, till contains rocks and debris from the original area. Till is a mix of anything and everything glaciers have moved including bedrock, older till, soil, plant fragments, and animal remains.
Single rocks that are deposited long distances from their source are called erratics. These stones or boulders that have been carried from their place of origin by a glacier and then strewn across the surface of the land as a glacier retreats have smooth, rounded surfaces due to jostling and scraping that occurs during their journey in the glacier.
By looking at the composition of an erratic, we can sometimes tell its point of origin and learn something about the direction of the glacier’s movement.
For many years, farmers have been forced to clear their fields of rock obstacles in order to cultivate their crops. Sometimes these rocks were used to build home foundations or fences. Often, the rocks were just piled in out of the way places on the edges of fields. Larger rocks were left in place, or blasted apart with dynamite so the pieces could be hauled away.
To log this cache, please do the following:
1. Go to the above listed coordinates. They will take you to the information sign at this site. You can’t miss it. Take a picture of you with your GPS in front of the sign or object and post it in your “found it” log. Please make sure the answers are not legible in your picture!
2. Answer the following questions:
a. What is the geological definition of a boulder? (This might require a little research.)
b. What does the size of this rock suggest?
c. Where might this rock have originated?
d. Why did this rock have to be re-located?
Send the answers by e-mail, to piglet&tigger&pooh.
If we find the answers insufficient we will remove the log.
(Of course we hope this won't be necessary).
Please be careful, and enjoy.
We hope that you learned something new today!
(No hints available.)
Last Updated: on 8/19/2014 11:20:05 AM Pacific Daylight Time (6:20 PM GMT)
Coordinates are in the WGS84 datum