Feb 09-07

Past-E-Mail: Cam Notes - 2007: February: Feb 09-07
Snowy wall    ...scroll down to share comments
Photo by Karl Berg


By
Mary Drew at Pasty Central (Mdrew) on Friday, February 9, 2007 - 08:13 am:

The first thing everyone needs to know about this natural wonder, known to folks as the Natural Wall, is that it is located on PRIVATE PROPERTY, so if you want to see more than pictures of it, you'll need to get permission first. That being said, Karl Berg shares a winter shot of this local wonder that has connections to the Keweenaw Fault. I'm not going to even try to explain all the geological aspects of this wall, but I will supply you with a link to Kevin Musser's page about the
Natural Wall on his Copper Range Railroad website. Then of course if Capt. Paul and Dr. Nat would like to chime in, I'm sure they'll be able to give us the scoop on how
this came to be!


By Janie T. (Bobbysgirl) on Friday, February 9, 2007 - 08:19 am:

Cool pic!


By Cindy Pihlaja Russell (Gone2long) on Friday, February 9, 2007 - 08:20 am:

Morning!


By Gonna be a Yooper (Joanie) on Friday, February 9, 2007 - 08:21 am:

Wow, every rock is perfectly laid in place, how did this happen?
Thank you Karl for sharing this natural wonder!


By Margaret M. Edwards (Pedwards) on Friday, February 9, 2007 - 08:25 am:

Looks like an Indian chief to me....perhaps the model for the Indian head nickel.


By Smfwixom (Trollperson) on Friday, February 9, 2007 - 08:34 am:

Neat pic!


By Jeff Kalember (Jeffkal) on Friday, February 9, 2007 - 08:42 am:

cool, i've seen a lot of great UP pics but never this one !!


By Cindy Pihlaja Russell (Gone2long) on Friday, February 9, 2007 - 08:43 am:

I thought it looked like an Indian chief as well. OK, Capt Paul and Dr Nat...give us the details.


By Richard L. Barclay (Notroll) on Friday, February 9, 2007 - 09:29 am:

Looks like an exposed dike that has weathered and cracked to fool our eyes into thinking it's a man-made wall? I think dikes are formed when lava fills a crack with what will be harder stone (after it cools) than the matrix that forms its mold.


By Pete Wilberding (Peshtigopete) on Friday, February 9, 2007 - 09:41 am:

Mary I'm trying to recall exactly where this is and it seems it's accross the road from Koskela's is that right?


By Richard L. Barclay (Notroll) on Friday, February 9, 2007 - 10:02 am:

Here's a picture I took in 1985 from a boat on Crater Lake in Oregon looking at a dike they call the devil's backbone. Besides the triangular part in the foreground it continues up the crater wall to the right.
Devil's Backbone on the wall of Crater Lake


By Shelley Trowbridge (Shelleyt36) on Friday, February 9, 2007 - 10:15 am:

What an amazing formation! Too bad it's not in a location that everyone can readily admire it. Guess we'll have to settle for pictures!


By Brooke (Lovethekeweenaw) on Friday, February 9, 2007 - 10:28 am:

That is amazing, it looks like it was manmade.


By Mr. Bill (Mrbill) on Friday, February 9, 2007 - 10:50 am:

Reminds me of New Hampshire's Old Man of the Mountain, which finally slipped away on May 3, 2003.


By Capt. Paul (Eclogite) on Friday, February 9, 2007 - 11:03 am:

Hmmm, looks like weíve been called out!! ;-) Since Dr. Nat is in class all day, I can give the low-down on Natural Wall. I apologize if this gets a bit long and I use some scientific jargon, but you can always ask me laterÖ..

First and foremost, Natural Wall is not a dike. Dikes are tabular or sheet-like bodies of magma (i.e., igneous rock) that cut through and across the layering of adjacent rocks. They form when magma rises into an existing fracture, or creates a new crack by forcing its way through existing rock, and then solidifies. Once it solidifies, itís not necessarily harder than the country rock. Natural Wall is made completely of Jacobsville Sandstone, and while it stands very near the Keweenaw Fault, there are very few basalts incorporated into the sandstone and none in the Wall. The photo NoTroll shows is a mafic basalt dike associated with the Crater Lake/Mt. Mazama region of Oregon. That is not to say that there arenít any dikes in the UP. A dike swarm develops when the land is stretched to a point it thins and magma is allowed to come to the surface following fractures in the rock. One of these small swarms associated the Mid-continent Rift is south of LíAnse near Alberta, and other single dikes of this age can be seen along M-95 near Republic and in the Empire/Tilden Mine pits.

Now on the Wall itself. During the Mid-continent Rift stage as the land was being pulled apart (a modern day analog would be the East African Rift), normal faulting occurred along the edges of the rift. One of these major faults was the Keweenaw Fault, which runs the length of the peninsula. Towards the end of the rifting stage, sediments from the east and south (Jacobsville Sandstone) began to deposit along the southern edge of the basin that formed as a result of rifting. Next, a large continent sized chunk of crust began slamming into the east side of North America. This collision is known as the Grenville Orogen. During this event, compression on the Rift and Keweenaw Fault began changing the characteristics and movement of the Fault from being a normal to a high angle reverse fault. This compression also had a profound effect on the sandstone near the fault, tilting the once flat-lying beds of sandstone into vertical and even slightly backward. If one has the chance to walk the creek that flows beside the Wall, by all means do it!!! In about 1 km of walking the creek bed, you will go from flat to east dipping beds to vertical at the Wall. Of course as Mary said, you should obtain proper permission to enter and take a knowledgeable geo-person with you (hint hint ;-)

This is, of course, the Cliff Notes version of how Natural Wall came to be. Iím always open for more questions and a more in-depth look at the Wall, or any other geologic questions that may arise. I could yak about Lake Superior geology for hours; as you can probably tell, itís one of the most fascinating areas on the planet, and thatís why I absolutely love studying it!!!


By Bob Williams (Wabbit) on Friday, February 9, 2007 - 11:21 am:

Capt. Paul- What actually caused the uniform block-like effect?. I have visited the wall twice in the past 25 years. It is amazing to see.


By Mr. Bill (Mrbill) on Friday, February 9, 2007 - 11:52 am:

Capt. Paul,

Have you ever seen the tessellated rocks in Tasmania? Were these also formed along the same lines, sorry, in the same manner?


By Capt. Paul (Eclogite) on Friday, February 9, 2007 - 12:39 pm:

I haven't been to Tasmania, yet!! But I have seen pictures of the tessellated rocks and it has been widely accepted that the same processes that formed these rocks also may have formed the blocky texture of Natural Wall before compression flipped the Wall vertical. It's quite common in nature to see rocks with a blocky pattern. Usually, the blocks forms 6 sided hexagons (columnar jointing of basalt on end, for example). However, in some rare cases and depending on the stresses present, you can have rocks that take on a rectangular pattern of fracturing.

To give everyone an idea of what I'm talking about, take a look at the photo below and Mary's Cam photo today, then imagine the Jacobsville Sandstone as it was solidifying almost a billion years ago......

tessellated


By Uncle Chuck @ Little Betsy (Unclechuck) on Friday, February 9, 2007 - 01:02 pm:

Looks like a grizzled ol copper miner to me!


By Dr. Nat (Drnat) on Friday, February 9, 2007 - 01:20 pm:

Different stresses exerted on the rocks can cause joints to form. A joint is simply a crack in the rock. In some places, paralell joints form over a large region, resulting in what's called a joint system. These joint systems can cause some very interesting geology. In Arches National Park (in Utah), for example, two intersecting joint systems are part of the reason so many arches form there.

An entire branch of geology called structural geology examines things like faults, joints, and folds. As you can imagine, the structural geology of some regions is quite complex.


By Marianne Y (Marianne) on Friday, February 9, 2007 - 02:48 pm:

I am fascinated with how regular the joints are--they look like pre-formed, molded bricks of some sort, in all of these pictures. Mother Nature is truly amazing!


By Gonna be a Yooper (Joanie) on Friday, February 9, 2007 - 03:16 pm:

Capt. Paul & Dr. Nat, I always look forward to a geology lesson from the both of you. It's nice to liven up the brain with some interesting facts. Geez, it almost makes me wish I were back in school. Well, on second thought, strike out that last sentence. I said "almost".


By Capt. Paul (Eclogite) on Friday, February 9, 2007 - 04:55 pm:

Well your welcome, but it's Dr. Nat and I who should be thanking all of you for giving us an open ear (or eye in this case) and the time to share our geologic knowledge of an area we both think is simply amazing with all the PastyCammers. :-)


By Gonna be a Yooper (Joanie) on Friday, February 9, 2007 - 05:51 pm:

All I want to know is, when is the guided tour?


By Helen (Heleninhubbel) on Friday, February 9, 2007 - 07:13 pm:

Gee I thought this looked like one of those Swedish/Finnish horses with the wind blowing from the back towards the face....?????

I see no comment from you ole Blue eyes....????

God Bless............


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