Blue Hills Felsenmeer
This is a relatively long hike into a beautiful gem! It is a State Natural Area located in Rusk County, WI.
The Blue Hills Felsenmeer (sea of rock in German) is actually ... not real felsenmeer! A felsenmeer is from rocks shattering in place from frost, while a talus deposit is associated with falling rocks. True felsenmeers form on slopes of 10` or less; If the slope is more than that, gravity will cause the rocks to fall. This location has slopes of at least 25`. There are some outcrops of quartzite most of the way up the slopes, and below these are indented below, showing that most of the boulders were placed where they are from gravity. On slopes that are gently sloping, there may be some true felsenmeer.
The valley has angular quartzite boulders that were originally beds of Precambrian Barron quartzite, a rock between 1.63 and 1.75 billion years old. The Blue Hills were covered by galcial ice during the Chippewa Phase of the Wisconsin Glaciation, which is when this valley was likely eroded. Later glaciations may not have had enough ice in this area to create this. It probably started out as a normal stream and then glacial meltwater quickly deepened the valley 15,000 to 20,000 years ago. This is the point where the rocks would have started shattering.
(These rocks likely shattered on the hillsides north and south of this valley and then the glacial runoff carved out the valley where we now see them fallen. Rocks on the hillside next to the canyon might be true felsenmeer.)
In order to log this cache, you must send the answers to these questions to the CO within 48 hours:
1. What is the elevation difference between the bottom of the 'felsenmeer' and the top of it? (please take side trail in the woods to the top, do not walk up the unstable rocks)
2. How long do you estimate this valley is?
3. Do you notice anything different about the north-facing slopes and the south facing slopes?
4. Do any rocks look out of place? How do they look different and what you do think happened to them?
5. Does the 'felsenmeer' go beyond this valley? (please look at an aerial map)
6. In your own words, please explain how this geological feature was formed.
7. Take a picture of you/your GPS at the 'felsenmeer'!
Sources: en.wikipedia.og/wiki/Blockfield
www.uwec.edu/geology/pdfs/felsenmeer.pdf
Permission has been granted by Thomas Meyer from the State Natural Area Program.