• Sunday-What'sUP January 25 - 04:41 pm

A few months ago we featured an old dusty book out of the Library of Congress Archives, "Souvenir of the Copper Country". One of our occasional Pasty Cam contributors JT-in-Chicago found a photo among its pages that reminded him of one he took back in the 60's:

I really liked the 1903 photo book that you provided a link to, even though I could not get the raw photo file from enlarging the photo. I did find the HTTPS link as was able to download a 'zip' file that gave me better quality photos than the PDF. The PDF seems to be grainy, here anyway.

...On Page 67 is a photo of "Profile Rock" which I think might be the "Natural Wall" today. If there is a "Profile Rock" somewhere else in the Copper Country would you please post where?

But 'Profile Rock' sure looks like the Natural Wall just outside of Laurium before the hill on the South side of Old Colony Road. Attached is the only wall shot that I have of the Natural Wall taken in 1969. I have four other shots but there are just too many trees.

Also note ...there are three people standing on Profile Rock. Two men and a woman in the background. My guess is that another woman may have been the photographer. Could there have been drinking involved back then?

Sincerely,
JTinChicago

Very interesting!! Hope someone has an answer!

Have a blessed Sunday everyone!

I like the Autumn colors (P.S. Only 11 more months 'till Christmas).

Definitely looks like the same wall, even the cracks look the same, including the one located at top-center of the first photo. I thought I saw a woman standing bottom-left in first photo, but may just be a piece of wood.

Amazing...I saw the first pic and said "the natural
wall"....and it is....but I don't know a thing about
it...and doubt I'd find it today...it's been a few
decades since we all checked it out.

Very cool!! Reminds me of my youth when we'd go
to the Douglas Houghton Falls and try climbing.
And, no, we were never stupid enough to try
climbing up the falls.

Yes; based on the photos, Profile Rock is the same structure as Natural Wall. If you search under "Natural Wall" in the Keweenaw Digital Archives, you will see many photos of Natural Wall to compare to what Charlie/JT posted.

It also has a very interesting method of formation that has helped researchers decipher how the Keweenaw Peninsula formed.

Capt?

What is the explanation for how this "natural
wall" is so geometrically near perfect from a
brick mason's perspective?

Nice pics!

ooh, I feel dizzy!:-/

Without going into too much boring detail, it's basically a bed of Jacobsville sandstone that got tilted near-vertical at a time when the Keweenaw Fault was still active.

I LOVE boring details. Just ask my friends when
I break out my 35mm film canister of
Greenstones.

My point is that the now horizontal fractures
are at such superbly even intervals as if they
were cut by man. The now vertical fractures are
almost all offset as if a brick mason chose the
location of the overlap for each course. There
has to be a geologic factoid or two in there
somewhere.

I'm thinking maybe there was an evenly applied
shear force as the solid plate moved past the
shear point. The statics in the shear strength
and the dynamics of the movement would all need
to come together like a "perfect storm".

That might explain the horizontal fractures but
what about the vertical ones?

May i take the liberty to re-port something the Capt shared back in '07:

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

Hmmm, looks like we’ve 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 later…..

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, it’s 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 aren’t 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 L’Anse 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. I’m 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, it’s one of the most fascinating areas on the planet, and that’s why I absolutely love studying it!!!

Thanks jbuck,

That explains the macro forces that were at play
but my curiosity revolves around the micro forces
that created the right angled fractures, both
horizontal and vertical, that resulted in a
structure that so expertly resembles a man made
one.

Happy 178th Birthday, Michigan.

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......


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.