And Geology?

[timcrews]

Hello:

I know this forum is called "Physics and Astronomy", but now that I am using very high-resolution Earth textures, I'm starting to notice various geological things that would be fun to discuss. May I presume to ask a Geology question?

I live in the Phoenix, Arizona area. To the northeast of Phoenix is a man-made lake, Lake Roosevelt. It can be seen in the following image about 1/3 of the way from the right side of the image, about halfway between the top and the bottom of the image. (BTW, in the image, Phoenix is exactly in the middle.)



My question is, doesn't that lake seem to be the lower-left part of a circle? I.E. the lake seems to occupy the 6:00 to 7:30 positions on the outside of a clock.

Is this an old crater? There's a mountain range going across it, so I'm having trouble imagining how a crater would interact with a mountain range in that way.

Thanks,

Tim Crews

[Evil Dr Ganymede]

It does look a little like the arc of a circle... it could be following an arcuate fault line or rock layer boundary, perhaps? I can't find any mention of there being a crater there.

[timcrews]

Evil:

Do you see that the arc extends all the way around, so that maybe only 11:00 to 2:00 is obscured?

In fact, I can almost imagine another concentric circle around the first circle, with perhaps double the diameter of the original circle.

I just looked at the Earth Impact Database, and it isn't listed.

Tim

[Don. Edwards]

If it was a crater it was made before the mountain building process. I have a feeling it is just by chance that it looks like a crater. With the amount of uplifting and mountain building that went on here any signs of a real crater would almost completely be erased if it was that old. I think Evil Dr Ganymede is right on this. The dead center of your suspect is full of fold mountains. Certainly any crater would cease to exist in this kind of environment. That’s why it is so hard to find real good candidates for craters on Earth.

Now Tim why don't you pan a little further to the east and south and see if you can find Meteor Crater. I think you should be able to just make it out at this resolution. If you can capture Mt. St Helens crater, which you did with your Washington volcanoes shots. Mt. St Helens is the volcano below Mt. Rainier that is surrounded by all the grey and beige. Well anyway that crater isn't much bigger or smaller than Meteor Crater. Good luck finding it.

Don. Edwards

[Evil Dr Ganymede]

Yeah I see that... I think I can vaguely see bits of your outer circle too. Though of course, you could just be leading my brain on, humans have an uncanny knack for seeing patterns that might not be there .

Thing is, the lower-left quadrant of the circle is just where the river continues, isn't it? Or are you thinking it's following the edge of the crater floor, and the mountains around it are the rim?

It could be an impact... I guess the best people to ask about this would be the folks at the astrogeology centre at Flagstaff? (BTW, would you be able to see Barringer Crater on this scale?)

[maxim]

Sorry, but that's definitely not a crater.
Craters wouldn't survive a mountains folding process at all. What you see I mostly the rock coloring that forms those 'cycles'. To me it looks like a main folding along a SE-NW axis superimposed by some 'subwave' foldings along E-W.

maxim

[Paul]

It may be volcanic. The region has a modest history of volcanism. It kind of reminds me of those flat worn-away volcanic domes and craters found in Mauritania and Chad. You can see them reasonably clearly on the 32k Blue Marble texture.

The more pronounced version would be Brandberg Massif:

http://landsat7.usgs.gov/gallery/detail/190/

And here's a meterorite impact structure I certainly wouldn't have recognised:

http://landsat7.usgs.gov/gallery/detail/212/

Cheers,
Paul

[timcrews]

Several people asked about Barringer Crater, a.k.a. Meteor Crater. It is not southeast of the location I showed in the first post, but northwest, at latitude 35.2, longitude -111.1, east of Flagstaff and west of Winslow.

It is only visible as a one or two black dots in my 64K normal map, and does not seem to be visible at all in the Blue Marble surface texture.

Here is a link to a nice web page with information about all known impact craters in the world: (BTW, my original theorized crater does not appear in this list, of course.)

http://www.unb.ca/passc/ImpactDatabase/NAmerica.html

Click on the numbered dots to see photos and other detailed information.

Tim